Department of Biology, MSC03 2020, 1 University Avenue, University of New Mexico, Albuquerque, NM 87131-0001, USA
* Author for correspondence (e-mail: sstr{at}unm.edu)
Accepted 24 March 2003
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SUMMARY |
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Key words: Fertilization, GVBD, Maturation, Eggs, U0126, ERK, JNK, p38, DiI, Calcium Green, Roscovitine, Colchicine, Ca2+ oscillations, Cerebratulus, Micrura, Nemerteans
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INTRODUCTION |
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Fertilization can also cause ooplasmic ER to undergo dramatic
reorganizations, the timing of which depends on the species examined
(Kline et al., 1999;
Kline, 2000
). In animals that
produce a single Ca2+ wave at fertilization (e.g. sea urchins,
starfish and frogs), the ER is rapidly restructured following fertilization
(Jaffe and Terasaki, 1993
;
Jaffe and Terasaki, 1994
;
Terasaki et al., 2001
).
Alternatively, ER clusters remain intact for a comparatively longer time in
mammals and other species that generate multiple Ca2+ waves at
fertilization (Stricker et al.,
1998
; FitzHarris et al.,
2003
). Collectively, such findings suggest that the particular
configuration of the ER may help to modulate the type of Ca2+
response that is produced (Kline et al.,
1999
; Kline,
2000
). However, in spite of intensive analyses of
fertilization-induced Ca2+ signals (reviewed by
Sardet et al., 1998
;
Stricker, 1999
;
Tarin and Cano, 2000
;
Carroll, 2001
;
Runft et al., 2002
), the
underlying regulatory mechanisms and possible functions of ER reorganizations
have yet to be fully defined, particularly in the case of non-mammalian
species.
Marine worms in the phylum Nemertea are protostome invertebrates and thus
belong to the mollusc/annelid/arthropod lineage, rather than the deuterostome
grouping that includes chordates and echinoderms. Fully grown nemertean
oocytes characteristically lack follicle cells and spontaneously mature after
being placed in seawater (Stricker,
1987a; Stricker et al.,
2001
). In the nemertean Cerebratulus lacteus, oocytes
begin GVBD
40 minutes after contacting seawater and by 2 hours reach a
metaphase I arrest at which they remain until fertilization occurs
(Stricker and Smythe, 2000
).
In previous studies analyzing Ca2+ signaling and ER structure
during fertilization of C. lacteus oocytes, marked differences were
described both in the Ca2+ responses and the organization of the ER
displayed by immature prophase-arrested oocytes versus mature specimens at
metaphase I (Stricker et al.,
1998
).
In order to expand on those studies, the potential roles of MAPKs and MPF in regulating ER structure and Ca2+ dynamics in C. lacteus are assessed. For such investigations, pharmacological modulators and kinase activity assays are combined with in vivo confocal imaging of ER reorganizations and Ca2+ signals. In addition, oocytes of two other nemertean species Cerebratulus sp. and Micrura alaskensis are also analyzed and compared with those of C. lacteus.
Collectively, such investigations indicate for the first time that MAPKs
belonging to the ERK1/2 type (extracellular signal regulated kinases 1/2) are
not required for either ER reorganizations or repetitive Ca2+
oscillations at fertilization. Conversely, MPF levels appear to play an
essential role in shaping the normal patterns of ER structure and
Ca2+ signals in nemerteans. The findings presented here are also
compared with results obtained from recent investigations of deuterostome
oocytes, in which functional interactions between MPF levels, Ca2+
signaling, and/or ER organization have been described
(Kline et al., 1999;
Deng and Shen, 2000
;
Levasseur and McDougall, 2000
;
Terasaki et al., 2001
;
Gordo et al., 2002
;
FitzHarris et al., 2003
).
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MATERIALS AND METHODS |
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To block spontaneous maturation, oocytes stripped from ripe ovaries were
treated with Ca2+-free seawater (CaFSW)
(Schroeder and Stricker, 1983)
and/or inhibitors of MAPK signaling
(Stricker and Smythe, 2000
;
Stricker and Smythe, 2001
).
Unless stated otherwise, all assays, confocal runs and blots were repeated at
least three times using oocytes from two or more females. Statistical analyses
involved Student's t-tests and Mann-Whitney-U tests
(Stricker and Smythe,
2000
).
Morphology and Ca2+ imaging
For assessments of ER morphology, dejellied oocytes were attached to
protamine-sulfate-coated specimen dishes and microinjected with the
ER-specific probe DiI (Terasaki and Jaffe,
1993) before examination with a BioRad MRC-600 confocal microscope
(Stricker et al.,1998
). For
these studies, serial z-sections taken at 10 µm intervals with a
20x, 0.7 NA objective were routinely stacked together by means of a
maximum projection algorithm to produce a compressed image of the entire
oocyte (Stricker et al.,
1998
).
Confocal imaging was also used to monitor fertilization-induced
Ca2+ signaling in specimens injected with Calcium-Green- and
Rhodamine-B dextrans (Stricker and
Whitaker, 1999; Stricker,
2000
). Graphs were expressed as uncalibrated changes in
fluorescence intensity relative to either the pre-stimulus CG/RB ratio
(Ro) or the initial non-ratioed CG fluorescence (Fo). In
nearly all cases (see exception in Fig.
7), Ca2+ imaging was carried out on separate batches of
oocytes from those used to observe ER dynamics, as double injections of
DiI-saturated oil droplets and aqueous solutions of Ca2+-sensitive
probes led to reduced viability.
|
In addition, MPF activity was monitored by a phosphorylation assay that
used the retinoblastoma (Rb) protein as a substrate specifically targeted by
active MPF (Lees et al.,
1991), as attempts to use the more conventional substrate histone
H1 produced only a weak signal. For such assays, LN-frozen samples were thawed
and assayed for protein content. Based on such determinations, 10 µg of
total protein in lysis buffer from each timepoint was incubated in kinase
buffer (Cell Signaling) to comprise a total of 18 µl. To each tube with 18
µl of sample in kinase buffer, 2 µl was added of the following
constituents: 0.5 µl of a 10 mM ATP solution (Cell Signaling), 0.25 µl
of a C-terminal retinoblastoma fusion protein (Cell Signaling) and 1.25 µl
kinase buffer. After incubation at 30°C for 30 minutes, the samples were
boiled in sample buffer and processed for western blotting using an antibody
against phospho-Rb (Cell Signaling). In addition, because ELK-1
phosphorylation can be used to monitor ERK1/2 activity in marine invertebrate
eggs (Carroll et al., 2000
),
some Rb samples were co-incubated with 0.25 µl of ELK-1 fusion protein
(Cell Signaling) plus 0.75 µl kinase buffer for subsequent detection with a
phospho-ELK-1 antibody (Cell Signaling). Further descriptions of both the Rb
and ELK-1 phosphorylation assays are currently being prepared (T.L.S. and
S.A.S., unpublished)
Materials
All inhibitors of MAPK signaling, except for curcumin, were purchased from
Tocris (Ballwin, MO), whereas curcumin, roscovitine and 5-HT were from
Sigma-Aldrich (St Louis, MO). Primary and secondary antibodies were from Cell
Signaling Technology (Beverly, MA) and Accurate Chemical and Scientific
(Westbury, NY), respectively. Buffers for electrophoresis and blotting were
purchased from BioRad (Hercules, CA), whereas DiI and the fluorescent dextrans
were from Molecular Probes (Eugene, OR).
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RESULTS |
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By controlling the maturation state of nemertean oocytes via such
protocols, a broader sampling of oocytes could be checked for ER structure
prior to hormone-induced GVBD, and in all 58 C. lacteus oocytes
examined before GVBD, a conspicuous clustering of the ER was lacking.
Similarly, GV-containing oocytes of both Cerebratulus sp. and
Micrura alaskensis failed to display marked ER clusters, although
such structures typically formed after GVBD
(Stricker et al., 2001)
(S.A.S., unpublished).
To confirm that the lack of ER substructuring was not simply a sign of cell
death caused by the treatments used to block GVBD, prophase-arrested oocytes
of C. lacteus were injected with DiI in low-Ca2+ (75 nM)
ASW and subsequently incubated in a 1 µM solution of 5-HT in ASW. Based on
time-lapse confocal microscopy, controls that were not treated with 5-HT
typically did not mature or form ER clusters (data not shown). Conversely,
hormone addition routinely triggered GVBD, and 86% of these maturing oocytes
developed distinct ER clusters (n=28)
(Table 1). Such clusters were
typically 3-6 µm in size (Stricker et
al., 1998) and associated with normal development, as oocytes with
these ER aggregates cleaved properly when fertilized
(Stricker et al., 1998
).
|
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Reorganization of the ER after fertilizations or roscovitine
treatments
In the absence of fertilization, mature C. lacteus oocytes
retained their ER clusters for at least a day
(Stricker et al., 1998), but
fertilization caused the clusters to disassemble as the oocytes resumed
meiosis and formed polar body 1 and 2 at
45 and 90 minutes
post-insemination, respectively (Stricker,
1996b
; Stricker et al.,
1998
). In C. lacteus, such reorganizations of the ER
typically began
40 minutes after sperm addition and were completed by
about an hour post-fertilization in 80-90% of the oocytes examined
(Stricker et al., 1998
)
(S.A.S., unpublished).
Fertilization also caused the ER clusters of metaphase-I-arrested oocytes
to disassemble both in the case of Micrura alaskensis
(Stricker et al., 2001)
(S.A.S., unpublished) and in Cerebratulus sp., where 88% of the
oocytes possessing ER clusters prior to insemination underwent cluster
disassembly after fertilization (n=17). In Cerebratulus sp.
where the precise timing of ER disassembly was tracked, the ER clusters began
to be disassembled as early as 15-20 minutes post-fertilization, which in turn
was similar to the
20 minutes post-fertilization timepoint of first polar
body formation in this species. Unlike the
60 minute timeframe observed
for C. lacteus, the clusters of Cerebratulus sp. usually
disappeared by 30 minutes after sperm addition
(Fig. 4A;
Table 2). This in turn
corresponded to between first polar formation and the production of the second
polar body, which was usually achieved by
45 minutes
post-fertilization.
|
|
As post-GVBD oocytes of various animals have high MPF activity before
insemination and diminished MPF after fertilization
(Murray and Hunt, 1993;
Kishimoto, 1999
;
Maller et al., 2001
), the
effects of roscovitine, a relatively specific inhibitor of MPF
(Meijer et al., 1997
), were
assessed in DiI-loaded, mature specimens to determine if roscovitine-treated
oocytes also disassemble their ER clusters in a manner resembling
fertilization. In 21/24 C. lacteus specimens, a marked restructuring
of the clusters routinely occurred in such unfertilized specimens by 1 hour
after the addition of 50 µM roscovitine
(Fig. 5A,B). ER clusters were
also disassembled in all 12 unfertilized oocytes of Cerebratulus sp.
that had been treated with roscovitine. In addition, immature oocytes of
C. lacteus that had been arrested at prophase I by roscovitine
continued to retain their GV and failed to form ER clusters after being
treated with 5-HT (data not shown), suggesting that roscovitine can also block
maturation and ER cluster formation by keeping MPF levels low in
prophase-arrested specimens.
|
To verify that MPF activity decreases after fertilization, Rb
phosphorylation assays were performed on fertilized C. lacteus
oocytes. Such assays indicated a substantial drop in MPF activity occurred
after fertilization, as opposed to the lack of a marked decline in
metaphase-I-arrested specimens that were not inseminated
(Fig. 6A,B). As noted for the
Rb signal, fertilization also caused an apparent decrease in ERK1/2 activity,
based on phospho-MAPK western blots and phospho-ELK-1 phosphorylation assays
(Fig. 6C). However, in both
cases, MAPK activity diminished at a much slower rate than that observed for
MPF, with apparent t1/2 declines in activity registering
105-115 minutes for MAPK versus
45 minutes for MPF.
|
Fertilization-induced Ca2+ dynamics in oocytes with or
without altered MAPK or MPF levels
Previous analyses of fertilization in C. lacteus revealed that
metaphase-I-arrested oocytes normally undergo oscillations that typically last
60-80 minutes and thus end at a time that coincides with the
post-fertilization disassembly of ER clusters
(Stricker, 1996b
;
Stricker et al., 1998
).
Alternatively, it has been shown that insemination of prophase-arrested
specimens, which lacked ER clusters to begin with, triggered only one or a few
irregularly arranged, non-wavelike Ca2+ transients that typically
subsided by 25 minutes post-insemination
(Stricker et al., 1998
).
Similarly, in this study, multiple Ca2+ elevations could be observed in only 6/34 (18%) of the prophase-arrested C. lacteus oocytes that were inseminated prior to GVBD, and even in these six, the transients were more irregular and ephemeral than normal oscillations (Fig. 8; Table 3). Mature oocytes of Cerebratulus sp. exhibited multiple Ca2+ oscillations at fertilization, although the spiking was of higher frequency and typically less protracted than in C. lacteus (Fig. 9). Such Ca2+ oscillations were nevertheless characteristic of normal development, as specimens displaying these Ca2+ responses underwent proper cleavage (Fig. 9, inset). Moreover, the relatively short duration of the fertilization-induced Ca2+ oscillations in Cerebratulus sp. matched the comparatively rapid post-insemination disassembly of ER clusters displayed by this species (Table 2).
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DISCUSSION |
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To analyze possible regulatory mechanisms related to ER cluster formation and disassembly, immature oocytes were incubated in MAPK inhibitors and assayed for ER clusters after 5-HT-induced GVBD. In all species, inhibitors of ERK1/2 signaling failed to prevent the formation of ER clusters even at inhibitor concentrations that significantly reduced MAPK activity. Accordingly, oocytes that were fertilized in the presence of MAPK inhibitors continued to display normal Ca2+ dynamics and ER restructurings. Collectively, such findings indicate that active ERK1/2 MAPKs are not required for either ER reorganizations or fertilization-induced Ca2+ signaling. To our knowledge, this is the first report of the effects of the MAPK signaling pathway on ER structure in maturing or fertilized oocytes.
A comparable lack of effect was also observed in oocytes treated with
either the p38 inhibitor SB-202190, or curcumin, which supposedly targets JNK
MAPKs. Even though such inhibitors could block spontaneous GVBD, thereby
demonstrating their ability to cross the oolemma, they did not routinely alter
ER structure relative to controls. However, in tests employing another JNK
inhibitor, SP600125, oocytes of Cerebratulus sp. completed
5-HT-induced GVBD but failed to display ER clusters. Exactly why SP600125
blocked cluster formation, while another putative JNK antagonist, curcumin,
did not, remains unknown. Perhaps, either curcumin or SP600125 targeted other
substrates in addition to JNK that the other putative JNK inhibitor did not
affect, based on the findings that supposedly specific kinase inhibitors often
show some nonspecificity when tested against a broad spectrum of substrates
(Davies et al., 2000).
The loss of ER clusters in response to SP600125 may also pertain to the
results of a previous study in which inhibition of the proteasome by MG-132
stabilized ER clusters following fertilization of mouse oocytes
(FitzHarris et al., 2003).
Such results were attributed to the ability of MG-132 to block the
post-fertilization decrease in MPF activity, given that either MG-132 or
cyclin B overexpression maintained elevated MPF levels and ER clusters in
experimentally treated zygotes, whereas a roscovitine-triggered inactivation
of MPF caused cluster disassembly
(FitzHarris et al., 2003
).
However, MG-132 is also known to activate JNK in various somatic cells
(Meriin et al., 1998
;
Nakayama et al., 2001
). Hence,
the regulation of ER structure by activated JNK, either as part of the MPF
signaling pathway or as a redundant modulator in parallel to MPF activity,
remains a possibility.
MPF levels apparently modulate repetitive Ca2+ signaling
and cell-cycle-dependent reorganizations in ER structure
Based on the apparently non-essential nature of ERK1/2 MAPK signaling in ER
reorganizations, the possible effects of MPF were assessed both in normally
maturing specimens and in aberrant cases of development. By monitoring ER and
Ca2+ dynamics in Cerebratulus sp. where the first cell
cycle is accelerated compared that of C. lacteus, it could be shown
that ER cluster disassembly and the cessation of fertilization-induced
Ca2+ oscillations coincided with each other. However, instead of
the 60 minute timing that was displayed by C. lacteus, ER
disassembly and oscillation cessation in Cerebratulus sp. were
completed by
30 minutes post-insemination, indicating that ER cluster
disassembly occurs relative to progression in the first cell cycle, rather
than absolute time after fertilization.
In particular, ER disassembly appeared to track the drop in MPF levels that
drives oocytes from metaphase arrest to polar body formation
(Sagata, 1996;
Sagata, 1997
). Accordingly, in
idiopathic cases where nemertean oocytes failed to stop at metaphase I and for
some undetermined reason continued to make polar bodies, such spontaneously
progressing specimens lacked prominent ER clusters after polar body production
and thus mimicked the events normally triggered by fertilization. In addition,
whether MPF activity actually increases in maturing C. lacteus
oocytes that form ER clusters and drops in fertilized specimens that undergo
ER cluster disassembly was monitored using an Rb fusion protein as a substrate
for active MPF. Such activity assays demonstrated an apparent pre-GVBD rise in
MPF as well as a post-fertilization drop, and similar results were also
obtained by using phospho-specific antibodies against cdc2 epitopes
(anti-phospho-Y15 and anti-phospho-T161) to track phosphorylation states
indicative of inactive and active MPF (data not shown).
Exactly why no clear increase in MPF activity was observed before the
second meiotic division remains to be determined. In any case, an overall
trend of MPF activity rising before GVBD and falling after fertilization was
nevertheless evident. Moreover, P-MAPK and ELK-1 assays showed that compared
with the MPF drop, a much slower decrease in MAPK activity occurred during the
completion of meiosis. Such a continued elevation in MAPK activity while MPF
levels fall has been noted for other species
(Verlhac et al., 1994;
McDougall and Levasseur,
1998
), and presumably functions to prevent an intervening S phase
from occurring between meiosis I and II
(Tachibana et al., 2000
).
In order to assess whether MPF levels can affect ER structure and
Ca2+ signaling, mature specimens were treated with roscovitine and
were found to disassemble their ER clusters in a manner similar to that
demonstrated for mouse oocytes (FitzHarris
et al., 2003). Moreover, as noted in other species
(Deng and Shen, 2000
;
Levasseur and McDougall, 2000
;
Gordo et al., 2002
), nemertean
oocytes failed to produce normal Ca2+ oscillations if pre-treated
with roscovitine, and applications of roscovitine after fertilization-induced
Ca2+ oscillations had already started prematurely terminated the
oscillatory response as shown for mice
(Deng and Shen, 2000
). This
suggests that ER structure and Ca2+ signaling were altered by a
roscovitine-induced inhibition of MPF, but whether MPF was indeed the target
of the action of the drug, or the only target affected, remains to be
determined.
Conversely, in an attempt to maintain elevated MPF levels for a protracted
period, oocytes were inseminated in colchicine. Colchicine is not as specific
a blocker of the fertilization-induced drop in MPF, as other treatments that
have been used (Levasseur and McDougall,
2000; FitzHarris et al.,
2003
). Nevertheless, microtubule-depolymerizing agents such as
colchicine delay cleavage and/or prolong Ca2+ signaling in various
animals (Hunt et al., 1992
;
Keating et al., 1994
;
Jones et al., 1995
;
Stricker, 1995
;
Gordo et al., 2002
), and this
effect may result from a maintenance of MPF activity owing to reduced cyclin B
degradation (Whitfield et al.,
1990
; Hunt et al.,
1992
). Accordingly, during fertilization of nemertean oocytes,
colchicine-treated specimens typically generated Ca2+ oscillations
for 1 hour longer than did controls, and the ER clusters remained evident
during such prolonged oscillations. This in turn suggests MPF levels affect
both ER reorganizations and fertilization-induced Ca2+ signals, but
exactly how MPF might exert its putative effect on the ER remains unknown.
What are the relationships between ER structure, MPF levels and
Ca2+ signaling patterns?
Given the apparent linkage between ER clusters, MPF levels and
fertilization-induced Ca2+ oscillations, the clusters could be
strictly required to produce a normal Ca2+ response at
fertilization, or they may be dispensable for repetitive Ca2+
spiking in at least some mature oocytes. Preliminary results from
fertilizations of Cerebratulus sp. oocytes in SP600125 tend to
support the latter conclusion, because in some cases repetitive
Ca2+ spiking could still be observed in the presence of SP600125
a drug that, in parallel studies, proved to be highly effective in
preventing the formation of ER clusters. Such findings suggest either that the
clusters are not involved at all in producing a repetitive Ca2+
response at fertilization, or that they indeed facilitate normal
Ca2+ signaling, but their absence can be compensated for by
redundant mechanisms that do not rely on ER aggregates. It should be noted,
however, that of the seven specimens that were treated with SP600125 prior to
fertilization, only two displayed what could be classified as fully normal
Ca2+ oscillations. Thus, it remains possible that ER clusters are
indeed generally required for producing a completely normal Ca2+
response at fertilization. Accordingly, this unresolved question is to be
investigated further in subsequent analyses that aim to identify the exact
targets of SP600125, while clearly defining the patterns of ER reorganizations
and Ca2+ dynamics in oocytes that retain their viability after
being doubly injected with DiI and Calcium Green.
Should ER clusters turn out to be involved in mounting a normal
Ca2+ response at fertilization, two logical questions to address
are by what means are ER clusters formed, and how might such structures
facilitate the production and transmission of repetitive Ca2+ waves
at fertilization. As for how clusters form, microtubules do not appear to be
essential for ER cluster maintenance, based on the continued presence of these
aggregates in mature oocytes that had been treated with colchicine.
Accordingly, recent analyses of Xenopus oocyte extracts reveal that
an F-actin/myosin-V network is capable of rapidly repositioning ER components
(Wollert et al., 2002),
indicating that such a non-microtubular-based system could also play a role in
reorganizing the ER of nemertean oocytes.
As to how ER clusters might facilitate Ca2+ signaling, similar
appearing structures in the ER of vertebrate oocytes possess numerous
Ins(1,4,5)P3 receptors that regulate Ca2+
release from cisternal stores (Shiraishi
et al., 1995; Mehlmann et al., 1996;
Kume et al., 1997
;
Fissore et al., 1999
;
Terasaki et al., 2001
). In
vertebrate oocytes, the predominant isoform is a type 1
Ins(1,4,5)P3 receptor
(Miyazaki et al., 1993
;
Parys and Bezprozvanny, 1995
;
Fissore et al., 1999
;
Kline et al., 1999
;
Oda et al., 1999
;
Goud et al., 2002
), although
the ER clusters of mice may also possess type 2
Ins(1,4,5)P3 receptors
(Fissore et al., 1999
). Thus,
the ER clusters of nemertean oocytes may facilitate Ca2+ release,
owing to the increased density and/or specific types of
Ins(1,4,5)P3 receptors that are present in such
aggregates.
ER clusters of nemerteans could also aid in the global propagation of
Ca2+ waves by helping to integrate isolated 'elementary
Ca2+ signals' (Bootman and
Berridge, 1995; Berridge,
1997
). Such signals are elicited as localized 'puffs'
(Bootman et al., 2001
) that
spread
6-7 µm, based on measurements of Xenopus oocytes
(Marchant and Parker, 2001
).
This value in turn corresponds well to the inter-cluster distance observed in
nemertean oocytes (Stricker et al.,
1998
), suggesting that ER clusters may be positioned in a manner
to aid global wave propagation.
Comparative biology of ER dynamics and Ca2+ signaling:
patterns displayed by these protostome worms have parallels in other animal
groups
Based on classical embryological studies and more recent molecular data
(Winnepenninckx et al., 1995;
Turbeville, 2002
), nemerteans
clearly constitute a phylum of protostome worms. As such, nemerteans represent
the only non-deuterostome group of animals that has been investigated for both
ER structure and Ca2+ signaling patterns during oocyte maturation
and fertilization. However, in spite of the fact that nemerteans are
evolutionarily far removed from mammals and other deuterostome animals, it is
clear that the patterns observed here are not simply unique attributes of a
highly aberrant group of invertebrates. ER aggregates also form during oocyte
maturation in deuterostomes such as ascidians and mammals that undergo
Ca2+ oscillations at fertilization
(Speksnijder et al., 1993
;
Mehlmann et al., 1995
;
Kline et al., 1999
). To our
knowledge, neither the relationship between ER clusters and MPF activities nor
the fate of the individual ER clusters after fertilization has been reported
for ascidians, although the overall intracellular localizations of ER-rich
cytoplasm are well known (Speksnijder et
al., 1993
; Dumollard and
Sardet, 2001
; Dumollard et
al., 2002
). In mouse oocytes, however, the cortical ER clusters of
mature oocytes disassemble at
1.5-3.5 hours post-insemination, and this
disassembly is apparently caused by a drop in MPF levels
(FitzHarris et al., 2003
).
Similarly, in Xenopus, which produces a single Ca2+ wave
at fertilization (Fontanilla and
Nuccitelli, 1998
), ER clusters that are about 3-5 µm in
diameter develop transiently at metaphase I and then again in MII-arrested
specimens (Terasaki et al.,
2001
). Such clusters subsequently dissipate within a few minutes
after MII-arrested oocytes generate a Ca2+ wave in response to
prick activation (Terasaki et al.,
2001
). Accordingly, the high levels of MPF that occur at metaphase
II arrest are dramatically reduced within
10 min after prick activation
of these oocytes (Watanabe et al.,
1991
).
Such findings generally fit the cell cycle-related changes in ER structure
presented here and coincide well with recent demonstrations that elevated MPF
levels sustain fertilization-induced Ca2+ oscillations in ascidian
and mammalian oocytes (Deng and Shen,
2000; Levasseur and McDougall,
2000
; Nixon et al.,
2000
; Gordo et al.,
2002
). However, unlike in nemerteans where the ER clusters
disappear at about the time that fertilization-induced oscillations cease, the
ER clusters of mouse zygotes disassemble a full 2 hours before the
Ca2+ oscillations are terminated
(FitzHarris et al., 2003
).
Although the reasons for this discrepancy remain unknown, a differential
timing of the downregulation of Ins(1,4,5)P3 receptor
functioning may play a role (Parrington et
al., 1998; He et al.,
1999
; Brind et al.,
2000
; Jellerette et al.,
2000
). In mammals that possess a relatively protracted first cell
cycle, the fertilization-induced downregulation of
Ins(1,4,5)P3 receptors may take longer to achieve than
does the post-fertilization disassembly of ER clusters. Conversely, ER cluster
disassembly and Ins(1,4,5)P3 receptor downregulation may
simply be more synchronized during the comparatively short first cell cycle of
nemerteans. Alternatively, fertilization-induced Ca2+ oscillations
cease in mammals at the time of pronuclear formation, presumably owing to the
sequestration of either a soluble oscillogenic factor produced by the sperm or
a critical downstream target required for Ca2+ oscillations
(Jones et al., 1995
;
Kono et al., 1995
;
Day et al., 2000
). However,
the termination of Ca2+ signaling by nemertean pronuclei seems less
likely, as fertilization-induced oscillations tend to cease before the second
polar body is formed.
In any case, a model (Fig. 13) can be proposed for nemerteans. According to this model, prophase-arrested oocytes with low MPF levels lack ER clusters, whereas mature metaphase-I-arrested oocytes with high MPF levels assemble ER clusters that may facilitate the production of a normal fertilization-induced Ca2+ response. After fertilization, MPF activity is reduced, and the ER clusters are eventually disassembled between first and second polar body formation.
|
Aside from being spawned externally into the sea prior to fertilization, as opposed to undergoing internal fertilization in the female reproductive tract, the oocytes of nemerteans and mammals differ in the arrest point that is attained prior to fertilization (metaphase I versus typically, metaphase II), the length of the first cell cycle (a few hours versus up to about a day), and the absence versus presence of follicle cells, respectively. Nevertheless, in spite of such marked differences in the oocytes of these two distantly related groups of animals, a general concordance can be seen in the relationship between MPF levels on the one hand and both ER structure and Ca2+ signaling patterns on the other. Moreover, based on currently available data, an overall trend of MPF levels affecting Ca2+ signals and/or ER structure may also exist for ascidians and frogs. Such findings, in turn, suggest that further investigations of other animal groups are warranted in order determine what roles MPF activities and ER structure might play in shaping fertilization-induced Ca2+ signals in general.
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ACKNOWLEDGMENTS |
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REFERENCES |
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Abrieu, A., Doree, M. and Fisher, D. (2001).
The interplay between cyclin-B-Cdc2 kinase (MPF) and MAP kinase during
maturation of oocytes. J. Cell Sci.
114,257
-267.
Bennett, B. L., Sasaki, D. T., Murray, B. W., O'Leary, E. C.,
Sakata, S. T., Xu, W. M., Leisten, J. C., Motiwala, A., Pierce, S., Satoh, Y.
et al. (2001). SP-600125, and anthrapyrazolone inhibitor of
Jun N-terminal kinase. Proc. Natl. Acad. Sci. USA
98,13681
-13686.
Berridge, M. J. (1997). Elementary and global aspects of calcium signalling. J. Physiol. 499,291 -306.[Medline]
Bootman, M. D. and Berridge, M. J. (1995). The elemental principles of calcium signaling. Cell 83,675 -678.[Medline]
Bootman, M. D., Lipp, P. and Berridge, M. J. (2001). The organisation and functions of local Ca2+ signals. J. Cell Sci. 114,2213 -2222.[Medline]
Brind, S., Swann, K. and Carroll, J. (2000). Inositol 1,4,5-trisphosphate receptors are downregulated in mouse oocytes in response to sperm or adenophostin A but not to increases in intracellular Ca2+ or egg activation. Dev. Biol. 223,251 -265.[CrossRef][Medline]
Carroll, D. J., Albay, D. T., Hoang, K. M., O'Neill, F. J., Kumano, M. and Foltz, K. R. (2000). The relationship between calcium, MAP kinase, and DNA synthesis in the sea urchin egg at fertilization. Dev. Biol. 217,179 -191.[CrossRef][Medline]
Carroll, J. (2001). The initiation and regulation of Ca2+ signalling at fertilization in mammals. Semin. Cell Dev. Biol. 12, 37-43.[CrossRef][Medline]
Chen, Y. R. and Tan, T. H. (1998). Inhibition of the c-Jun N-terminal kinase (JNK) signaling pathway by curcumin. Oncogene 17,173 -178.[CrossRef][Medline]
Chen, Z., Gibson, T. B., Robinson, F., Silvestro, L., Pearson, G., Xu, B. E., Wright, A., Vanderbilt, C. and Cobb, M. H. (2001). MAP kinases. Chem. Rev. 101,2449 -2476.[CrossRef][Medline]
Chiba, K., Kado, R. T. and Jaffe, L. A. (1990). Development of calcium release mechanisms during starfish oocyte maturation. Dev. Biol. 140,300 -306.[Medline]
Davies, S. P., Reddy, H., Caivano, M. and Cohen, P. (2000). Specificity and mechanism of action of some commonly used protein kinase inhibitors. Biochem. J. 351,95 -105.[CrossRef][Medline]
Day, M. L., McGuinness, O. M., Berridge, M. J. and Johnson, M. H. (2000). Regulation of fertilization-induced Ca2+ spiking in the mouse zygote. Cell Calcium 28,47 -54.[CrossRef][Medline]
Deng, M. Q. and Shen, S. S. (2000). A specific
inhibitor of p34(cdc2)/cyclin B suppresses fertilization-induced calcium
oscillations in mouse eggs. Biol. Reprod.
62,873
-878.
Dudley, D. T., Pang, L., Decker, S. J., Bridges, A. J. and Saltiel, A. R. (1995). A synthetic inhibitor of the mitogen-activated protein kinase cascade. Proc. Natl. Acad. Sci. USA 92,7686 -7689.[Abstract]
Dumollard, R. and Sardet, C. (2001). Three
different calcium wave pacemakers in ascidian eggs. J. Cell
Sci. 114,2471
-2481.
Dumollard, R., Carroll, J., Dupont, G. and Sardet, C.
(2002). Calcium wave pacemakers in eggs. J Cell
Sci. 115,3557
-3564.
Eisen, A. and Reynolds, G. A. (1985). Sources and sinks for the calcium released during fertilization of single sea urchin eggs. J. Cell Biol. 147,1522 -1527.
Favata, M. F., Horiuchi, K. Y., Manos, E. J., Daulerio, A. J.,
Stradley, D. A., Feeser, W. S., VanDyk, D. E., Pitts, W. J., Earl, R. A.,
Hobbs, F. et al. (1998). Identification of a novel inhibitor
of mitogen-activated protein kinase kinase. J. Biol.
Chem. 273,18623
-18632.
Fissore, R. A., Longo, F. J., Anderson, E., Parys, J. B. and
Ducibella, T. (1999). Differential distribution of inositol
trisphosphate receptor isoforms in mouse oocytes. Biol.
Reprod. 60,49
-57.
FitzHarris, G., Marangos, P. and Carroll, J.
(2003). Cell cycle-dependent regulation of structure of
endoplasmic reticulum and inositol 1,4,5-trisphosphate-induced Ca2+
release in mouse oocytes and embryos. Mol. Biol. Cell
14,288
-301.
Fontanilla, R. A. and Nuccitelli, R. (1998).
Characterization of the sperm-induced calcium wave in Xenopus eggs
using confocal microscopy. Biophys. J.
75,2079
-2087.
Frantz, B., Klatt, T., Pang, M., Parsons, J., Rolando, A., Williams, H., Tocci, M. J., O'Keefe, S. J. and O'Neill, E. A. (1998). The activation state of p38 mitogen-activated protein kinase determines the efficiency of ATP competition for pyridinylimidazole inhibitor binding. Biochemistry 37,13846 -13853.[CrossRef][Medline]
Fujiwara, T., Nakada, K., Shirakawa, H. and Miyazaki, S. (1993). Development of inositol trisphosphate-induced calcium release mechanism during maturation of hamster oocytes. Dev. Biol. 156,69 -79.[CrossRef][Medline]
Gordo, A. C., Kurokawa, M., Wu, H. and Fissore, R. A.
(2002). Modifications of the Ca2+ release mechanisms
of mouse oocytes by fertilization and by sperm factor. Mol. Hum.
Reprod. 8,619
-629.
Goud, P. T., Goud, A. P., Leybaert, L., van Oostveldt, P.,
Mikoshiba, K., Diamond, M. P. and Dhont, M. (2002). Inositol
1,4,5-trisphosphate receptor function in human oocytes: calcium responses and
oocyte activation related phenomena induced by photolytic release of
InsP3 are blocked by a specific antibody to the type I receptor.
Mol. Hum. Reprod. 8,912
-918.
Han, J. and Nuccitelli, R. (1990). Inositol 1,4,5-trisphosphate-induced calcium release in the organelle layers of the stratified, intact egg of Xenopus laevis. J. Cell Biol. 110,1103 -1110.[Abstract]
He, C. L., Damiani, P., Ducibella, T., Takahashi, M., Tanzawa,
K., Parys, J. B. and Fissore, R. A. (1999). Isoforms of the
inositol 1,4,5-trisphosphate receptor are expressed in bovine oocytes and
ovaries: The type-1 isoform is downregulated by fertilization and by injection
of adenophostin A. Biol. Reprod.
61,935
-943.
Hunt, T., Luca, F. C. and Ruderman, J. V. (1992). The requirements for protein synthesis and degradation, and the control of destruction of cyclins A and B in the meiotic and mitotic cycles of the clam embryo. J. Cell Biol. 116,707 -724.[Abstract]
Jaffe, L. A. and Terasaki, M. (1993). Structural changes of the endoplasmic reticulum of sea urchin eggs during fertilization. Dev. Biol. 156,566 -573.[CrossRef][Medline]
Jaffe, L. A. and Terasaki, M. (1994). Structural changes of the endoplasmic reticulum of starfish oocyte during meiotic maturation and fertilization. Dev. Biol. 164,579 -587.[CrossRef][Medline]
Jellerette, T., He, C. L., Wu, H., Parys, J. B. and Fissore, R. A. (2000). Down-regulation of the inositol 1,4,5-trisphosphate receptor in mouse eggs following fertilization or parthenogenetic activation. Dev. Biol. 223,238 -250.[CrossRef][Medline]
Jones, K. T., Carroll, J., Merriman, J. A., Whittingham, D. G. and Kono, T. (1995). Repetitive sperm-induced Ca2+ transients in mouse oocytes are cell cycle dependent. Development 121,6671 -6677.
Keating, T. J., Cork, R. J. and Robinson, K. R.
(1994). Intracellular free calcium oscillations in normal and
cleavage-blocked embryos and artificially activated eggs of Xenopus
laevis. J. Cell Sci. 107,2229
-2237.
Kishimoto, T. (1998). Cell cycle arrest and release in starfish oocytes and eggs. Semin. Cell Dev. Biol. 9,549 -557.[CrossRef][Medline]
Kishimoto, T. (1999). Activation of MPF at meiosis reinitiation in starfish oocytes. Dev. Biol. 214, 1-8.[CrossRef][Medline]
Kline, D. (2000). Attributes and dynamics of the endoplasmic reticulum in mammalian eggs. Curr. Top. Dev. Biol. 50,125 -154.[Medline]
Kline, D., Mehlmann, L., Fox, C. and Terasaki, M. (1999). The cortical ER of the mouse egg: localization of ER clusters in relation to the generation of repetitive calcium waves. Dev. Biol. 215,431 -442.[CrossRef][Medline]
Kono, T., Carroll, J., Swann, K. and Whittingham, D. G.
(1995). Nuclei from fertilized mouse embryos have
calcium-releasing activity. Development
121,1123
-1128.
Kume, S., Yamamoto, A., Inoue, T., Muto, A., Okano, H. and Mikoshiba, K. (1997). Developmental expression of the inositol 1,4,5-trisphosphate receptor and structural changes in the endoplasmic reticulum during oogenesis and meiotic maturation of Xenopus laevis. Dev. Biol. 182,228 -239.[CrossRef][Medline]
Lees, J. A., Buchkovich, K. J., Marshak, D. R., Anderson, C. W. and Harlow, E. (1991). The retinoblastoma protein is phosphorylated on multiple sites by human cdc2. EMBO J. 10,4279 -4290.[Abstract]
Levasseur, M. and McDougall, A. (2000).
Sperm-induced calcium oscillations at fertilisation in ascidians are
controlled by cyclin B1-dependent kinase activity.
Development 127,631
-641.
Machaty, Z., Funahashi, H., Day, B. N. and Prather, R. S. (1997). Developmental changes in the intracellular Ca2+ release mechanisms in porcine oocytes. Biol. Reprod. 56,921 -930.[Abstract]
Maller, J. L. (1990). MPF and cell-cycle control. Adv. Sec. Messeng. 24,323 -328.
Maller, J. L. (1998). Recurring themes in oocyte maturation. Biol. Cell 90,453 -460.[CrossRef][Medline]
Maller, J. L., Gross, S. D., Schwab, M. S., Finkielstein, C. V., Taieb, F. E. and Qian, Y. W. (2001). Cell cycle transitions in early Xenopus development. In The Cell Cycle and Development, pp. 58-78. Chichester: Wiley.
Marchant, J. S. and Parker, I. (2001). Role of
elementary Ca2+ puffs in generating repetitive Ca2+
oscillations. EMBO J.
20, 65-76.
McDougall, A. and Levasseur, M. (1998).
Sperm-triggered calcium oscillations during meiosis in ascidian oocytes first
pause, restart, then stop: correlations with the cell cycle.
Development 125,4451
-4459
Mehlmann, L. M., Terasaki, M., Jaffe, L. A. and Kline, D. (1995). Reorganization of the endoplasmic reticulum during meiotic maturation of the mouse oocyte. Dev. Biol. 170,607 -615.[CrossRef][Medline]
Meijer, L., Borgne, A., Mulner, O., Chong, J. P. J., Blow, J. J., Inagaki, N., Inagaki, M., Delcros, J. G. and Moulinoux, J. P. (1997). Biochemical and cellular effects of roscovitine, a potent and selective inhibitor of the cyclin-dependent kinases cdc2, cdk2 and cdk5. Eur. J. Biochem. 243,527 -536.[Abstract]
Meriin, A. B., Gabai, V. L., Yaglom, J., Shifrin, V. I. and
Sherman, M. Y. (1998). Proteasome inhibitors activate stress
kinases and induce Hsp72: diverse effects on apoptosis. J. Biol.
Chem. 273,6373
-6379.
Miyazaki, S., Shirakawa, H., Nakada, K. and Honda, Y. (1993). Essential role of the inositol 1,4,5-trisphosphate receptor/Ca2+ release channel in Ca2+ waves and Ca2+ oscillations at fertilization of mammalian eggs. Dev. Biol. 158,62 -78.[CrossRef][Medline]
Murray, A. and Hunt, T. (1993). The Cell Cycle. An Introduction. New York: Oxford University Press.
Nakayama, K., Furusu, A., Xu, Q. H., Konta, T. and Kitamura,
M. (2001). Unexpected transcriptional induction of monocyte
chemoattractant protein 1 by proteasome inhibition: involvement of the c-jun
N-terminal kinase activator protein 1 pathway. J.
Immunol. 167,1145
-1150.
Nemoto, S., Jiang, J. L., Huang, S. and Lin, A. N.
(1998). Induction of apoptosis by SB-202190 through inhbition of
p38 beta mitogen-activated protein kinase. J. Biol.
Chem. 273,16415
-16420.
Nixon, V. L., McDougall, A. and Jones, K. T. (2000). Ca2+ oscillations and the cell cycle at fertilisation of mammalian and ascidian eggs. Biol. Cell 92,187 -196.[CrossRef][Medline]
Oda, S., Deguchi, R., Mohri, T., Shikano, T., Nakanishi, S. and Miyazaki, S. (1999). Spatiotemporal dynamics of the [Ca2+]i rise induced by microinjection of sperm extract into mouse eggs: preferential induction of a Ca2+ wave from the cortex mediated by the inositol 1,4,5-triphosphate receptor. Dev. Biol. 209,451 -461.
Parrington, J., Brind, S., de Smedt, H., Gangewara, R., Lai, F. A., Wojcikiewicz, R. and Carroll, J. (1998). Expression of inositol 1,4,5-trisphosphate receptors in mouse oocytes and early embryos: The type I isoform is upregulated in oocytes and downregulated after fertilization. Dev. Biol. 203,451 -461.[CrossRef][Medline]
Parys, J. B. and Bezprozvanny, I. (1995). The inositol trisphosphate receptor of Xenopus oocytes. Cell Calcium 18,751 -754.
Palmer, A. and Nebreda, A. R. (2000). The activation of MAP kinase and p34cdc2/cyclin B during the meiotic maturation of Xenopus oocytes. In Progress in Cell Cycle Research.Vol. 4 (ed. L. Meijer A. Jezequel and B. Ducommun), pp. 131-143. New York: Kluwer.[Medline]
Runft, L. L., Jaffe, L. A. and Mehlmann, L. M. (2002). Egg activation at fertilization: where it all begins. Dev. Biol. 245,237 -245.[CrossRef][Medline]
Sagata, N. (1996). Meiotic metaphase arrest in animal oocytes: its mechanisms and biological significance. Trends Cell Biol. 6,22 -28.[CrossRef]
Sagata, N. (1997). What does Mos do in oocytes and somatic cells? BioEssays 19, 13-21.[Medline]
Sardet, C., Roegiers, F., Dumollard, R., Rouviere, C. and McDougall, A. (1998). Calcium waves and oscillations in eggs. Biophys. Chem. 72,131 -140.[CrossRef]
Sardet, C., Prodon, F., Dumollard, R., Chang, P. and Chenevert, J. (2002). Structure and function of the egg cortex from oogenesis through fertilization. Dev. Biol. 241, 1-23.[CrossRef][Medline]
Schroeder, T. E. and Stricker, S. A. (1983). Morphological changes during maturation of starfish oocytes: surface ultrastructure and cortical actin. Dev. Biol. 98,373 -384.[Medline]
Shiraishi, K., Okada, A., Shirakawa, H., Nakanishi, S., Mikoshiba, K. and Miyazaki, S. (1995). Developmental changes in the distribution of the endoplasmic reticulum and inositol 1,4,5-trisphosphate receptors and the spatial patterns of Ca2+ release during maturation of hamster oocytes. Dev. Biol. 170,594 -606.[CrossRef][Medline]
Speksnijder, J. E., Terasaki, M., Hage, W. J., Jaffe, L. F. and Sardet, C. (1993). Polarity and organization of the endoplasmic reticulum during fertilization and ooplasmic segregation in the ascidian egg. J. Cell Biol. 120,1337 -1346.[Abstract]
Stricker, S. A. (1987a). Phylum Nemertea. In Reproduction and Development of Marine Invertebrates of the Northern Pacific Coast (ed. M. F. Strathmann), pp.129 -137. Seattle: University of Washington Press.
Stricker, S. A. (1987b). Phylum Nemertea. In Marine Invertebrates of the Pacific Northwest. (ed. E. N. Kozloff), pp. 94-101. Seattle: University of Washington Press.
Stricker, S. A. (1994). Confocal microscopy of living eggs and embryos. In Three Dimensional Confocal Microscopy (ed. J. K. Stevens, L. R. Mills and J. E. Tragodis), pp. 281-300. San Diego: Academic Press.
Stricker, S. A. (1995). Time-lapse confocal imaging of calcium dynamics in starfish embryos. Dev. Biol. 170,496 -518.[CrossRef][Medline]
Stricker, S. A. (1996a). Changes in the spatiotemporal patterns of intracellular calcium transients during starfish early development. Inv. Reprod. Dev. 30,135 -152.
Stricker, S. A. (1996b). Repetitive calcium waves induced by fertilization in the nemertean worm Cerebratulus lacteus.Dev. Biol. 176,243 -263.[CrossRef][Medline]
Stricker, S. A. (1999). Comparative biology of calcium signaling during fertilization and egg activation in animals. Dev. Biol. 211,157 -176.[CrossRef][Medline]
Stricker, S. A. (2000). Confocal microscopy of intracellular calcium dynamics during fertilization. Biotechniques 29,492 -498.[Medline]
Stricker, S. A. and Folsom, M. W. (1998). A comparative ultrastructural analysis of spermatogenesis in nemertean worms. Hydrobiologia 365,55 -72.
Stricker, S. A. and Whitaker, M. (1999). Confocal laser scanning microscopy of calcium dynamics in living cells. Microsc. Res. Tech. 46,356 -369.[CrossRef][Medline]
Stricker, S. A. and Smythe, T. L. (2000). Multiple triggers of oocyte maturation in nemertean worms: the roles of calcium and serotonin. J. Exp. Zool. 287,243 -261.[CrossRef][Medline]
Stricker, S. A. and Smythe, T. L. (2001). 5-HT
causes an increase in cAMP that stimulates, rather than inhibits, oocyte
maturation in marine nemertean worms. Development
128,1415
-1427.
Stricker, S. A., Centonze, V. E. and Melendez, R. F. (1994). Calcium dynamics during starfish oocyte maturation and fertilization. Dev. Biol. 166, 34-58.[CrossRef][Medline]
Stricker, S. A., Silva, R. and Smythe, T. (1998). Calcium and endoplasmic reticulum dynamics during oocyte maturation and fertilization in the marine worm Cerebratulus lacteus.Dev. Biol. 203,305 -322.[CrossRef][Medline]
Stricker, S. A., Smythe, T. L., Miller, L. and Norenburg, J. L. (2001). Comparative biology of oogenesis in nemertean worms. Acta Zool. 82,213 -230.[CrossRef]
Sun, Q. Y., Breitbart, H. and Schatten, H. (1999). Role of the MAPK cascade in mammalian germ cells. Reprod. Fertil. Dev. 11,443 -450.[Medline]
Tachibana, K., Tanaka, D., Isobe, T. and Kishimoto, T.
(2000). C-mos forces the cell cycle to undergo meiosis II to
produce haploid gametes. Proc. Natl. Acad. Sci. USA
97,14301
-14306.
Tarin, J. J. and Cano, A., eds (2000). Fertilization in Protozoa and Metazoan Animals. Cellular and Molecular Aspects. Berlin: Springer.
Terasaki, M. and Jaffe, L. A. (1993). Imaging endoplasmic reticulum in living sea urchin eggs. In Cell Biological Applications of Confocal Microscopy (ed. B. Matsumoto), pp.211 -220. San Diego: Academic Press.
Terasaki, M. and Sardet, C. (1991). Demonstration of calcium uptake and release by sea urchin egg cortical endoplasmic reticulum. J. Cell Biol. 115,1030 -1037.
Terasaki, M., Runft, L. L. and Hand, A. R.
(2001). Changes in organization of the endoplasmic reticulum
during Xenopus oocyte maturation and activation. Mol.
Biol. Cell 12,1103
-1116.
Turbeville, J. M. (2002). Progress in nemertean biology: development and phylogeny. Int. Comp. Biol. 42,692 -703.
Verlhac, M.-H., Kubiak, J. Z., Clarke, H. J. and Maro, B.
(1994). Microtubule and chromatin behavior follow MAP kinase
activity but not MPF activity during meiosis in mouse oocytes.
Development 120,1017
-1025.
Watanabe, N., Hunt, T., Ikawa, Y. and Sagata, N. (1991). Independent inactivation of MPF and cytostatic factor (Mos) upon fertilization of Xenopus eggs. Nature 352,247 -248.[CrossRef][Medline]
Whitfield, W. G. F., Gonzalez, C., Maldonado-Codina, G., Glover, G. M. (1990). The A-type and B-type cyclins of Drosophila are accumulated and destroyed in temporally distinct events that define separable phases of the G2-M transition. EMBO J. 9,2563 -2572.[Abstract]
Winnepenninckx, B., Backeljau, T. and de Wachter, R. (1995). Phylogeny of protostome worms derived from 18S rRNA sequences. Mol. Biol. Evol. 12,641 -649.[Abstract]
Wollert, T., Weiss, D. G., Gerdes, H.-H., Kuznetsov, S. A.
(2002). Activation of myosin V-based motility and
F-actin-dependent network formation of endoplasmic reticulum during mitosis.
J. Cell Biol. 159,571
-577.