Division of Developmental Neuroscience, Tohoku University Graduate School of Medicine, 2-1, Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan
* Author for correspondence (e-mail: osumi{at}mail.cc.tohoku.ac.jp)
Accepted 5 November 2003
![]() |
SUMMARY |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: Pax6, Olfactory bulb, Cell migration, Telencephalon, Whole embryo culture, Brain organ culture, Electroporation, Rats
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Numerous lines of evidence demonstrate that establishment of regional
identity and specification of cell types in the telencephalon is regulated by
several transcription factors (Shimamura
et al., 1995; Rubenstein et
al., 1998
; Campbell,
2003
). Pax6, a member of the Pax family of transcription
factors, has crucial roles in various developmental processes of the
telencephalon including dorsal-ventral and anterior-posterior patterning,
specification of neuronal subtypes, neuronal migration and axonal projection
(Engelkamp et al., 1999
;
Kawano et al., 1999
;
Stoykova et al., 2000
;
Bishop et al., 2000
;
Bishop et al., 2002
;
Yamasaki et al., 2001
;
Yun et al., 2001
;
Pratt et al., 2002
).
Pax6 homozygous-mutant mice (Sey/Sey) lack OB protrusion
but still have olfactory bulb-like structures (OBLSs) at the lateral side of
the telencephalon (Lopez-Mascaraque et
al., 1998; Jimenez et al.,
2000
; Hirata et al.,
2002
). This may indicate that Pax6 function is required
to determine the position where the OBs should form within the telencephalon.
However, the mechanisms by which Pax6 determines OB position in the
developing telencephalon and the primary cause of ectopic formation of the
OBLS in the Pax6 mutant are unknown.
In this study, we investigated how the OBLS develops ectopically in Pax6-mutant rats (rSey2/rSey2) using long-term culture systems of whole embryos and brain explants. Cell-tracing analyses revealed that misposition of the OBLS was not caused by ectopic generation of mitral cells, but by abnormal migration of mitral cell progenitors in the telencephalon of Pax6 mutants. Transplantation of mitral cell progenitors showed clearly that abnormal cell migration was caused by non-cell autonomous defects of the mitral cell precursors. Removal of olfactory innervation did not affect the migration pattern of the mitral cell progenitors, indicating that the mutant phenotype is not caused by the impairment of olfactory nerve innervation. Furthermore, transfection of exogenous Pax6 into the mutant telencephalon restored abnormal cell migration, implying that Pax6 function is required within the telencephalon. These results demonstrate that loss of Pax6 function in the telencephalon disrupts a positional cue that is required to direct the mitral cell progenitors to the rostral end.
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Immunohistochemistry
Embryos were fixed with 4% paraformaldehyde and sectioned with a Cryostat
(CM3050, LEICA). The sections were immersed in 5% skimmed milk in TBST
(tris-buffered saline plus 0.01% tween20) for 30 minutes, and incubated with
anti-Neuropilin 1 (rabbit polyclonal, a gift from Dr Hirata), anti-calretinin
(mouse monoclonal, CHEMICON), anti-GAD67 (rabbit polyclonal, CHEMICON),
anti-bromodeoxyuridine (BrdU, mouse monoclonal, Beckton-Dickinson) antibodies
at 4°C overnight. Cy3-conjugated anti-rabbit or anti-mouse IgG antibody
(Jackson) was used as the secondary antibody. After washing with TBST, the
sections were examined under the fluorescent microscope (Axioplan-2, Zeiss)
equipped with a cooled CCD camera (Roper). Confocal images of GFP/Cy3
double-positive cells were acquired using a Leica TCS NT confocal microscope
and 3D images constructed with Leica confocal software. Whole-mount
immunostaining of the telencephalon was performed according to previous
procedures (Nomura et al.,
1998). For detection of BrdU, sections were treated with 2M HCl at
37°C for 30 minutes before immunohistochemistry.
In situ hybridization
Digoxigenin (DIG)-labeled RNA probes were transcribed from neuropilin 1
(Kawakami et al., 1996),
Pax6 (Osumi et al.,
1997
), netrin G1 (Nakashiba et
al., 2000
) cDNAs that had been subcloned in pBluescript using the
DIG RNA labeling kit (Roche). The hybridization procedures have been described
previously (Osumi et al.,
1997
; Takahashi and Osumi,
2002
). Hybridization signals were detected with AP-conjugated
anti-DIG antibody (Roche) and nitroblue tetrazolium,
5-bromo-4-chloro-3-indol-phosphate (Roche).
Cell labeling and cell transplantation in cultured embryos
The experimental procedures of whole embryo culture (WEC) and cell labeling
have been described previously (Ishii et
al., 2000; Takahashi and
Osumi, 2002
; Takahashi et al.,
2002
). To label the progenitors of the olfactory bulb neurons, DiI
(D-282, Molecular probe) solution dissolved in dimethylfomamide was
microinjected with a fine-tipped glass needle (Shutter Instrument Co) into the
rostral end of the telencephalon. To analyze the birthdate of the labeled
cells, embryos were cultured in medium containing 40 µM BrdU (Boehringer
Mannheim) for 30 minutes. In whole brain culture (WBC), brain tubes including
the forebrain, midbrain and hindbrain regions were isolated by removing
mesenchymal tissues and cultured for 24 hours in rotating bottles filled with
culture medium for WEC (100% rat serum containing 2 mg ml-1 glucose
and 0.025% antibiotics) in 60% O2. Telencephalic organ culture
(TOC) was performed as described previously
(Sugisaki et al., 1996
).
Briefly, after 48 hours in WEC or WBC, the telencephalic hemispheres were
dissected out, treated with 0.2% collagenase IV to remove the pia matter, and
cultured on a collagen-coated membrane filter (transwell-COL 3492, Coaster)
for 2-3 days at 37°C, in 0.25% CO2. To transplant OB neuronal
progenitors, small fragments of the rostral telencephalon of Pax6
homozygote embryos and their littermates on GFP-transgenic background were
dissected out, and treated with 0.2% collagenase to remove the mesenchyme. The
fragments were further dissociated into single cells with 0.25% trypsin, and
50-100 cells microinjected into the rostral telencephalic wall of host
embryos.
Gene transfer by electroporation
Details of electroporation in cultured embryos were described previously
(Takahashi et al., 2002).
After 2 hours of preculture in WEC, embryos were transferred into tyrode's
solution, of 0.1 µl plasmid vector solution (either pCAX-GFP or pCAX-Pax6)
(Takahashi et al., 2002
) and
microinjected into the telencephalic vesicle. Square pulses (70V, 5 Hz) were
delivered into the embryos using an electroporator (CUY21, NEPPA GENE) and
tweezer-type electrodes (CUY-650).
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
Cell tracing of mitral cell progenitors in wild-type and Pax6-mutant rats
Because the OBLS developed at an ectopic position in the Pax6
mutant telencephalon, we hypothesized two possibilities to account for the
defect in OB formation. One is that the origin of the mitral cells may be
altered in the mutant. A previous study suggested that the mitral cells are
derived from the dorsal part of the telencephalon
(Bulfone et al., 1998;
Puelles et al., 2000
). Thus,
the mitral cells of the Pax6-mutant OBLS differentiate in an ectopic
position of the telencephalon compared to wild type. The other possibility is
that the mitral cells of the mutant embryo migrate abnormally and colonize in
an ectopic position to form the OBLS. To test these possibilities, we
performed cell-tracing analyses in embryos in culture and compared the origin
and migration patterns of the mitral cells in wild-type and
rSey2/rSey2 embryos
(Fig. 2A). Because mitral cells
are born at
E12-E13 in rat embryos
(Bayer, 1983
), we labeled a
part of the telencephalon at E12.5 and cultured the labeled embryos for 48
hours.
|
Differentiation of the mitral cells did not occur in embryos just after WEC
(data not shown). To examine whether the labeled cells contribute to the OB or
the OBLS and differentiate into mitral cells, we isolated telencephalons and
cultured them as explants. After 48 hours of WEC followed by 3 days of
telencephalic organ culture (TOC), a protruding OB, marked by calretinin,
developed at the rostral end of the telencephalon of wild-type embryos
(Fig. 3E''). Nrp and
netrin G1 were also detected in this OB
(Fig. 3F'' and data not
shown). Therefore, this long-term culture system seemed to be suitable for
examining the development of mitral cells from their origin to initial
differentiation. Next, instead of DiI injection, we electroporated a
GFP-expression vector to focally label the rostral telencephalon
because GFP-fluorescence is stable after the immunostaining using detergents.
When the GFP gene was introduced into the rostral part of the dorsal
telencephalon (i.e. the Pax6-positive area) of wild-type embryos,
GFP-positive cells stayed in the rostral part of the telencephalon, even 48
hours after electroporation (Fig.
3A-D). After 3 days of TOC, most GFP-positive cells contributed to
the OB evaginated from the rostral tip of the telencephalic explants
(Fig. 3E-E''). GFP-labeled
cells within the protruding OB expressed Nrp, indicating that they
differentiated into mitral cells (Fig.
3F-F'',G-G''). Of the GFP-positive cells,
69.8±6.2% were Nrp-positive in the OB (n=4). To further
confirm that cells that express GFP were mitral cells, we examined their
birthdate by labeling with BrdU. GFP-transfected embryos were cultured in
BrdU-containing medium for 30 minutes, 6 hours after electroporation
(n=3). This corresponds to E12.75. After a further 3 days of TOC,
50% of GFP-positive cells in the OB were labeled with BrdU
(Fig. 3H-H''). Because the
peak of mitral cell neurogenesis occurs at
E12-E13 in rat embryos
(Bayer, 1983
), these
BrdU/GFP-positive cells are considered to be mitral cells. Taken together, we
conclude that the mitral cells originate from the rostral-dorsal telencephalon
in normal development.
|
|
|
Impaired migration of the mitral cell progenitors is not caused by lack of olfactory nerve innervation
We next examined whether penetration of the olfactory nerve into the brain
affects mitral cell movement because development of the olfactory epithelium
is also impaired in Pax6 mutants
(Hogan et al., 1986;
Hill et al., 1991
;
Fujiwara et al., 1994
;
Grindley et al., 1995
). To
address this, we isolated brain tubes, by removing surrounding tissues
containing the olfactory epithelium and nerve, and cultured them to access the
localization of the mitral cells. Primary innervation of the olfactory nerve
commences at E13 in rat embryos (Gong and
Shipley, 1995
). Thus, we isolated brain tubes from E12.5, and
cultured them for 24 hours in rotating bottles (WBC) and, subsequently, as a
TOC for 2 days (Fig. 6A). After
a total 3 days of culture, specimens were stained for netrin G1.
|
Introduction of exogenous Pax6 into the mutant telencephalon restores the normal migration of mitral cell progenitors
To further confirm that Pax6 function is required to control
migration of mitral cell progenitors in the telencephalon, we examined whether
the mismigration of the mitral cell progenitors is rescued by transfection of
an exogenous Pax6-expression vector into the mutant
telencephalon.
Either GFP alone or GFP plus Pax6 expression vectors were introduced into the E12.5 mutant telencephalon by electroporation. After WEC followed by TOC, we examined the localization of netrin G1-positive cells in the mutant telencephalon. GFP fluorescence showed that exogenous genes were expressed throughout the rostral-half of the telencephalic neuroepithelium, including the origin and the migratory pathway of the mitral cell progenitors (Fig. 7A). As expected, when we introduced the GFP gene alone into the mutant telencephalon, accumulation of netrin G1-positive cells was observed at the lateral surface of the telencephalon (8/8 cases) (Fig. 7B, Fig. 1D, arrowheads). However, when the Pax6-expression vector was electroporated into the mutant hemisphere, netrin G1-positive cells accumulated at the rostral-most telencephalon (4/10 cases; Fig. 7C, arrowhead). Nrp was also expressed in the area containing netrin G1-positive cells (Fig. 7E). Nrp-positive cells were sorted from those expressing exogenous Pax6 as is seen in wild-type embryos (Fig. 7E,F, and data not shown). In 3/10 cases, clusters of netrin G1-positive cells were observed in the rostral-most part of the cortex, but there were also some cells at the lateral side of the cortex (Fig. 7G). However, the localization of netrin G1-positive cells was unchanged (Fig. 7G) in three other cases, probably because of limited expression of the Pax6 gene. These results demonstrate that transfection of exogenous Pax6 restored normal migration to mitral cell precursors in the mutant telencephalon. Taken together, Pax6 function in the telencephalon is necessary to retain mitral cells in the rostral-most part of the telencephalon.
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Pax6 controls the positioning of mitral cell progenitors in the telencephalon
The most striking result in the present study is the abnormal migration
pattern of mitral cell progenitors in the Pax6 mutant. In these
mutants, the mitral cell progenitors derived from the rostral region migrated
caudally and clustered at the lateral surface of the telencephalon. This
indicates that the ectopic formation of the OBLS in the mutants is not caused
by an alteration of the mitral cell origin, but by the abnormal migration of
mitral cell progenitors. It has been reported that Pax6 regulates
migration of cerebellar granule cells, which strongly express Pax6,
in a cell-autonomous manner (Engelkamp et
al., 1999; Yamasaki et al.,
2001
). By contrast, mitral cells originate from a
Pax6-positive, dorsal part of the telencephalon, but the migrating
precursors and differentiated mitral cells do not express Pax6
(Fig. 2 and data not shown). It
is, thus, unexpected that Pax6 is required for the mitral cell
progenitors to autonomously control their migration patterns, an effect that
was proved by cell transplantation experiments. Such a cell non-autonomous
function for Pax6 in the control of neuronal migration has also been
observed for the migration of neural crest cells from the midbrain towards the
frontonasal region (Osumi-Yamashita et
al., 1997
; Nagase et al.,
2001
). Therefore, Pax6 functions controls the migration
of neuronal cells in both cell-autonomous and non-autonomous ways, depending
on the developmental context.
It has long been believed that projection of the primary olfactory nerve to
the rostral telencephalon affects development of the OB. In frog and chick
embryos, removal of the olfactory epithelium abolishes OB development
(Graziadei and Monti-Graziadei,
1991; Wang et al.,
2001
). In our study, however, ablation of olfactory innervation
did not alter the location of the mitral cells within the telencephalon of
wild-type rat embryos. This excludes the possibility that penetration of the
olfactory nerve directs the migration of the mitral cell progenitors. However,
the OB in the wild-type cultured brain and the OBLS in the Pax6
mutant do not evaginate from the telencephalon. It may, thus, be possible that
olfactory innervation controls further protrusion of the OB in later
development. It has been reported that the frontonasal region may play an
essential role for OB morphogenesis
(LaMantia et al., 1993
).
Several types of secreted molecules such as retinoic acid (RA), FGF8 and BMP4
are expressed at the frontonasal region
(LaMantia et al., 1993
;
LaMantia et al., 2000
), and
disruption of RA- and FGF signaling leads to severely compromised OBs
(LaMantia et al., 1993
;
Anchan et al., 1997
;
Hebert et al., 2003
;
Garel et al., 2003
).
Therefore, interaction between the frontonasal region and the rostral part of
the telencephalon, through the activities of these molecules, could be
essential for OB protrusion.
Abnormal migration of mitral cell progenitors in Pax6 mutants was
rescued by transfection of exogenous Pax6 into the mutant
telencephalon. This indicates that mislocation of the OBLS in Pax6
mutants is caused by loss of Pax6 function in the mutant
telencephalon. Recent studies have reported that Pax6 regulates rostral-caudal
patterning of the telencephalon (Bishop et
al., 2000; Bishop et al.,
2002
; Muzio et al.,
2002
). Because the rostral-lateral area of the telencephalon,
which expresses Pax6 strongly, is reduced in Sey/Sey
embryos, Pax6 is thought to coordinate the rostral-lateral identity
of the telencephalon (Bishop et al.,
2002
; Toresson et al.,
2000
; Yun et al.,
2001
). It has also been demonstrated that the rostral-caudal
patterning of the telencephalon is influenced by FGF signaling
(Fukuchi-Shimogori and Grove,
2001
; Storm et al.,
2003
; Garel et al.,
2003
). We also identified that expression of fgfrs is
reduced severely in the telencephalon of Pax6 mutants, especially in
the rostral area (T.N. and N.O., unpublished). FGF signaling is, thus, likely
to be disturbed in the telencephalon of Pax6 mutants. These data
support the idea that transfection of exogenous Pax6 restores an
impairment in regional identity in the rostral area of the mutant
telencephalon and re-establishes the positional information that regulates the
migration patterns of mitral cell progenitors. However, we cannot rule out the
possibility that restoration of the cell migratory pattern in
Pax6-transfected embryos is unrelated to the initial defect in
Pax6 mutants, but is caused by a secondary event that is induced by
transfection of exogenous Pax6. To solve this problem, it will be
necessary to identify molecules downstream of Pax6 that directly
control the migration pattern of mitral cell precursors.
Mechanisms controlling migration patterns of mitral cell progenitors
What mechanisms could be responsible for controlling cell migration
patterns of mitral cell precursors? Because mitral cell precursors migrate
caudally towards the lateral part of the mutant telencephalon, it might be
possible that migratory cue(s) that inhibit or attract migration of mitral
cell precursors are absent and/or appear ectopically in the lateral region of
the telencephalon of Pax6 mutants. Pax6 regulates the
expression of cell adhesion molecules including R-cadherin, which is
responsible for maintaining the compartment boundary between the dorsal and
ventral parts of the telencephalon
(Stoykova et al., 1997;
Inoue et al., 2001
;
Tyas et al., 2003
). Thus, it
might be possible that contact-dependent, cell-cell interaction between mitral
cell precursors and cortical neuroepithelial cells is important for
positioning the olfactory bulb in the telencephalon. However, we could not
restore the position of the OBLS using an expression vector to overexpress
R-cadherin in the mutant telencephalon (data not shown). Also, we could not
identify altered expression of neuronal guidance molecules, such as netrin 1,
slit 2 and semaphorin 3A (T.N. and N.O., unpublished), implying that other
molecules are responsible for controlling mitral cell migration.
The mitral cells originate from the rostral-dorsal telencephalon
Many researchers have investigated the developmental origin of the OB, but
it is still ambiguous whether the OB is derived from the dorsal or ventral
telencephalon. Several morphological analyses have classified the OB as a
ventral telencephalon-derived structure
(Källen, 1962;
Nieuwenhuys, 1998
). By
contrast, molecular analyses and genetic approaches indicate that mitral cells
originate from the dorsal telencephalon
(Bulfone et al., 1998
;
Puelles et al., 2000
). In the
present study we performed cell tracing in WEC and TOC, which revealed
directly that the mitral cells are derived from the rostral part of the dorsal
telencephalon. However, several cell tracing and genetic analyses indicate
that interneurons of the OB are derived from the ventral telencephalon
(Anderson et al., 1999
;
Wichterle et al., 2001
;
Nery et al., 2002
). Thus, it
is likely that the OB is a mosaic structure consisting of several types of
neurons that have different origins within the telencephalon, as in the case
of the neocortex (Wilson and Rubenstein,
2000
) and the olfactory cortex
(Hirata et al., 2002
). In
Pax6 mutants, the OBLS consists of the projection neurons and
different types of interneurons probably corresponding to the perigromerular
cells and the granule cells (Fig.
1). The question of whether the origins and migratory pathways of
these interneurons are impaired in the mutants remains to be clarified.
Precise fate mapping of the OBLS interneurons in Pax6 mutants is
required to further understand the roles of Pax6 in positioning the
different types of OB neurons in the telencephalon.
![]() |
ACKNOWLEDGMENTS |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Anchan, R. M., Drake, D. P., Haines, C. F., Gerwe, E. A. and LaMantia, A. S. (1997). Disruption of local retinoid-mediated gene expression accompanies abnormal development in the mammalian olfactory pathway. J. Comp. Neurol. 10,171 -184.[CrossRef]
Anderson, S., Mione, M., Yun, K. and Rubenstein, J. L.
(1999). Differential origins of neocortical projection and local
circuit neurons: role of Dlx genes in neocortical interneuronogenesis.
Cereb. Cortex 9,646
-654.
Bayer, S. A. (1983). 3H-thymidine-radiographic studies of neurogenesis in the rat olfactory bulb. Exp. Brain Res. 50,329 -340.[Medline]
Bishop, K. M., Goudreau, G. and O'Leary, D. D.
(2000). Regulation of area identity in the mammalian neocortex by
Emx2 and Pax6. Science
288,344
-349.
Bishop, K. M., Rubenstein, J. L. and O'Leary, D. D.
(2002). Distinct actions of Emx1, Emx2, and Pax6 in regulating
the specification of areas in the developing neocortex. J.
Neurosci. 22,7627
-7638.
Bulfone, A., Wang, F., Hevner, R., Anderson, S., Cutforth, T., Chen, S., Meneses, J., Pedersen, R., Axel, R. and Rubenstein, J. L. (1998). An olfactory sensory map develops in the absence of normal projection neurons or GABAergic interneurons. Neuron 21,1273 -1282.[Medline]
Campbell, K. (2003). Dorsal-ventral patterning in the mammalian telencephalon. Cur. Opin. Neurobiol. 13, 50-56.[CrossRef][Medline]
Esclapez, M., Tillakaratne, N. J. K., Kaufman, D. L., Tobin, A. J. and Houser, C. R. (1994). Comparative localization of two forms of glutamic acid decarboxylase, and their mRNAs in rat brain supports the concept of functional differences between the forms. J. Neurosci. 14,1834 -1855.[Abstract]
Engelkamp, D., Rashbass, P., Seawright, A. and van Heyningen,
V. (1999). Role of Pax6 in development of the cerebellar
system. Development 126,3585
-3596.
Fujiwara, M., Uchida, T., Osumi-Yamashita, N. and Eto, K. (1994). Uchida rat (rSey): a new mutant rat with craniofacial abnormalities resembling those of the mouse Sey mutant. Differentiation 57,31 -38.[CrossRef][Medline]
Fukuchi-Shimogori, T. and Grove, E. A. (2001).
Neocortex patterning by the secreted signaling molecule FGF8.
Science 294,1071
-1074.
Garel, S., Huffman, K. J. and Rubenstein, J. L.
(2003). Molecular regionalization of the neocortex is disrupted
in Fgf8 hypomorphic mutants. Development
130,1903
-1914.
Gong, Q. and Shipley, M. T. (1995). Evidence that pioneer olfactory axons regulate telencephalon cell cycle kinetics to induce the formation of the olfactory bulb. Neuron 14, 91-101.[Medline]
Graziadei, P. P. C. and Monti-Graziadei, A. G. (1991). The influence of the olfactory placode on the development of the telencephalon in xenopus laevis. Neuroscience 46,617 -629.[CrossRef]
Grindley, J. C., Davidson, D. R. and Hill, R. E.
(1995). The role of Pax-6 in eye and nasal development.
Development 121,1433
-1442.
Hebert, J. M., Lin, M., Partanen, J., Rossant, J. and McConnell,
S. K. (2003). FGF signaling through FGFR1 is required for
olfactory bulb morphogenesis. Development
130,1101
-1111.
Hill, R. E., Favor, J., Hogan, B. L., Ton, C. C., Saunders, G. F., Hanson, I. M., Prosser, J., Jordan, T., Hastie, N. D. and van Heyningen, V. (1991). Mouse small eye results from mutations in a paired-like homeobox-containing gene. Nature 354,522 -525.[CrossRef][Medline]
Hinds, J. W. (1968). Study of histogenesis in the mouse olfactory bulb. I. Time of origin of neurons and neuroglia. J. Comp. Neurol. 134,287 -304.[Medline]
Hinds, J. W. and Ruffett, T. L. (1973). Mitral cell development in the mouse olfactory bulb: reorientation of the perikaryon and maturation of the axon initial segment. J. Comp. Neurol. 151,281 -306.[Medline]
Hirata, T. and Fujisawa, H. (1997). Cortex-specific distribution of membrane-bound factors that promote neurite outgrowth of mitral cells in culture. J. Neurobiol. 32,415 -425.[CrossRef][Medline]
Hirata, T., Nomura, T., Takagi, Y., Sato, Y., Tomioka, N., Fujisawa, H. and Osumi, N. (2002). Mosaic development of the olfactory cortex with Pax6-dependent and -independent components. Brain Res. Dev. Brain Res. 136, 17-26.[Medline]
Hogan, B. L., Horsburgh, G., Cohen, J., Hetherington, C. M., Fisher, G. and Lyon, M. F. (1986). Small eyes (Sey): a homozygous lethal mutation on chromosome 2 which affects the differentiation of both lens and nasal placodes in the mouse. J. Embryol. Exp. Morphol. 97,95 -110.[Medline]
Inoue, T., Tanaka, T., Takeichi, M., Chisaka, O., Nakamura, S.
and Osumi, N. (2001). Role of cadherins in maintaining
the compartment boundary between the cortex and striatum during development.
Development 128,561
-569.
Ishii, Y., Nakamura, S. and Osumi, N. (2000). Demarcation of early mammalian cortical development by differential expression of fringe genes. Brain Res. Dev. Brain Res. 119,307 -320.[Medline]
Ito, T., Suzuki, A., Imai, E., Okabe, M. and Hori, M.
(2001). Bone marrow is a reservoir of repopulating mesangial
cells during glomerular remodeling. J. Am. Soc.
Nephrol. 12,2625
-2635.
Jimenez, D., Garcia, C., de Castro, F., Chedotal, A., Sotelo, C., de Carlos, J. A., Valverde, F. and Lopez-Mascaraque, L. (2000). Evidence for intrinsic development of olfactory structures in Pax-6 mutant mice. J. Comp. Neurol. 428,511 -526.[CrossRef][Medline]
Kallen, B. (1962). Embryogenesis of brain nuclei in the chick telencephalon. Ergerb. Anat. Entwhickel-Gesch 36,62 -82.
Kawakami, A., Kitsukawa, T., Takagi, S. and Fujisawa, H. (1996). Developmentally regulated expression of a cell surface protein, neuropilin, in the mouse nervous system. J. Neurobiol. 29,1 -17.[CrossRef][Medline]
Kawano, H., Fukuda, T., Kubo, K., Horie, M., Uyemura, K., Takeuchi, K., Osumi, N., Eto, K. and Kawamura, K. (1999). Pax-6 is required for thalamocortical pathway formation in fetal rats. J. Comp. Neurol. 408,147 -160.[CrossRef][Medline]
Kosaka, K., Aika, Y., Toida, K., Heizmann, C. W., Hunziker, W., Jacobowitz, D. M., Nagatsu, I., Streit, P., Visser, T. J. and Kosaka, T. (1995). Chemically defined neuron groups and their subpopulations in the glomerular layer of the rat main olfactory bulb. Neurosci. Res. 23,73 -88.[CrossRef][Medline]
LaMantia, A. S., Colbert, M. C. and Linney, E. (1993). Retinoic acid induction and regional differentiation prefigure olfactory pathway formation in the mammalian forebrain. Neuron 10,1035 -1048.[Medline]
LaMantia, A. S., Bhasin, N., Rhodes, K. and Heemskert, J. (2000). Mesenchymal/epithelial induction mediates olfactory pathway formation. Neuron 28,411 -425.[Medline]
Long, J. E., Garel, S., Depew, M. J., Tobet, S. and Rubenstein, J. L. (2003). DLX5 regulates development of peripheral and central components of the olfactory system. J. Neurosci. 15,568 -578.
Lopez-Mascaraque, L., Garcia, C., Valverde, F. and de Carlos, J.
A. (1998). Central olfactory structures in Pax-6 mutant mice.
Ann. N. Y. Acad. Sci.
855, 83-94.
Muzio, L., DiBenedetto, B., Stoykova, A., Boncinelli, E., Gruss,
P. and Mallamaci, A. (2002). Emx2 and Pax6 control
regionalization of the preneuronogenic cortical primordium. Cereb.
Cortex 12,129
-139.
Nagase, T., Nakamura, S., Harii, K. and Osumi, N. (2001). Ectopically localized HNK-1 epitope perturbs migration of the midbrain neural crest cells in Pax6 mutant rat. Dev. Growth Differ. 43,683 -692.[CrossRef][Medline]
Nakashiba, T., Ikeda, T., Nishimura, S., Tashiro, K., Honjo, T.,
Culotti, J. G. and Itohara, S. (2000). Netrin-G1: a
novel glycosyl phosphatidylinositol-linked mammalian netrin that is
functionally divergent from classical netrins. J.
Neurosci. 20,6540
-6550.
Nery, S., Fishell, G. and Corbin, J. G. (2002). The caudal ganglionic eminence is a source of distinct cortical and subcortical cell populations. Nat. Neurosci. 5,1279 -1287.[CrossRef][Medline]
Nieuwenhuys, R. (1998). Plan and basic subdivision of the vertebrate brain. In The Central Nervous System of Vertebrates, Vol. 1 (ed. R. Nieuwenhuys, H. J. Ten Donklaar and C. Nicholson), pp.159 -228. Berlin: Springer.
Nomura, T., Kawakami, A. and Fujisawa, H. (1998). Correlation between tectum formation and expression of two PAX family genes, PAX7 and PAX6, in avian brains. Dev. Growth Differ. 40,485 -495.[Medline]
Osumi, N., Hirota, A., Ohuchi, H., Nakafuku, M., Iimura, T.,
Kuratani, S., Fujiwara, M., Noji, S. and Eto, K.
(1997). Pax-6 is involved in the specification of hindbrain motor
neuron subtype. Development
124,2961
-2972.
Osumi-Yamashita, N., Kuratani, S., Ninomiya, Y., Aoki, K., Iseki, S., Chareonvit, S., Doi, H., Fujiwara, M., Watanabe, T. and Eto, K. (1997). Cranial anomaly of homozygous rSey rat is associated with a defect in the migration pathway of midbrain crest cells. Dev. Growth Differ. 39,53 -67.[Medline]
Pinching, A. J. and Powell, T. P. S. (1971). The neurons types of the glomerular layer of the olfactory bulb. J. Cell Sci. 9,305 -345.[Medline]
Pratt, T., Quinn, J. C., Simpson, T. I., West, J. D., Mason, J.
O. and Price, D. J. (2002). Disruption of early events
in thalamocortical tract formation in mice lacking the transcription factors
Pax6 or Foxg1. J. Neurosci.
22,8523
-8531.
Puelles, L., Kuwana, E., Puelles, E., Bulfone, A., Shimamura, K., Keleher, J., Smiga, S. and Rubenstein, J. L. (2000). Pallial and subpallial derivatives in the embryonic chick and mouse telencephalon, traced by the expression of the genes Dlx-2, Emx-1, Nkx-2.1, Pax-6, and Tbr-1. J. Comp. Neurol. 424,409 -438.[CrossRef][Medline]
Rubenstein, J. L., Shimamura, K., Martinez, S. and Puelles, L. (1998). Regionalization of the prosencephalic neural plate. Annu. Rev. Neurosci. 21,445 -477.[CrossRef][Medline]
Shimamura, K., Hartigan, D. J., Martinez, S., Puelles, L. and
Rubenstein, J. L. (1995). Longitudinal organization of
the anterior neural plate and neural tube. Development
121,3923
-3933.
Storm, E. E., Rubenstein, J. L. and Martin, G. (2003). Dosage of Fgf8 determines whether cell survival is positively or negatively regulated in the developing forebrain. Proc. Natl. Acad. Sci. USA 18,1757 -1762.[CrossRef]
Stoykova, A. and Grüss, P. (1994). Roles of Pax-genes in developing and adult brain as suggested by expression patterns. J. Neurosci. 14,1395 -1412.[Abstract]
Stoykova, A., Götz, M., Grüss, P. and Price, D.
(1997). Pax6-dependent regulation of adhesive patterning,
R-Cadherin expression and boundary formation in the developing forebrain.
Development 124,3765
-3777.
Stoykova, A., Treichel, D., Hallonet, M. and Grüss, P.
(2000). Pax6 modulates the dorsoventral patterning of the
mammalian telencephalon. J. Neurosci.
20,8042
-8050.
Sugisaki, N., Hirata, T., Naruse, I., Kawakami, A., Kitsukawa, T. and Fujisawa, H. (1996). Positional cues that are strictly localized in the telencephalon induce preferential growth of mitral cell axons. J. Neurobiol. 29,127 -137.[CrossRef][Medline]
Takahashi, M. and Osumi, N. (2002). Pax6 regulates specification of ventral neurone subtypes in the hindbrain by establishing progenitor domains. Development 129,1327 -1338.[Medline]
Takahashi, M., Sato, K., Nomura, T. and Osumi, N. (2002). Manipulating gene expressions by electroporation in the developing brain of mammalian embryos. Differentiation 70,155 -162.[CrossRef][Medline]
Toresson, H., Potter, S. S. and Campbell, K.
(2000). Genetic control of dorsal-ventral identity in the
telencephalon: opposing roles for Pax6 and Gsh2.
Development 127,4361
-4371.
Tyas, D. A., Pearson, H., Rashbass, P. and Price, D. J.
(2003). Pax6 regulates cell adhesion during cortical development.
Cereb. Cortex 13,612
-619.
Wang, X., Gao, C. and Norgren, R. B., Jr (2001). Cellular interactions in the development of the olfactory system: an ablation and homotypic transplantation analysis. J. Neurobiol. 49,29 -39.[CrossRef][Medline]
Wichterle, H., Turnbull, D. H., Nery, S., Fishell, G. and
Alvarez-Buylla, A. (2001). In utero fate mapping
reveals distinct migratory pathways and fates of neurons born in the mammalian
basal forebrain. Development
128,3759
-3771.
Wilson, S. W. and Rubenstein, J. L. (2000). Induction and dorsoventral patterning of the telencephalon. Neuron 28,641 -651.[Medline]
Yamasaki, T., Kawaji, K., Ono, K., Bito, H., Hirano, T., Osumi, N. and Kengaku, M. (2001). Pax6 regulates granule cell polarization during parallel fiber formation in the developing cerebellum. Development 128,3133 -3144.[Medline]
Yun, K., Potter, S. and Rubenstein, J. L.
(2001). Gsh2 and Pax6 play complementary roles in dorsoventral
patterning of the mammalian telencephalon. Development128
, 193-205.