1 Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY
10461, USA
2 Department of Neurology, Northwestern University, Feinberg Medical School,
Chicago, IL 60611, USA
3 Department of Neuroscience, Albany Medical College, Albany, NY 12208,
USA
* Author for correspondence (e-mail: jakessler{at}northwestern.edu)
Accepted 18 November 2003
![]() |
SUMMARY |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: BMP, Neurotrophin, Dorsal root ganglion, Trigeminal ganglion, Innervation, Noggin
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Although the mechanisms by which neurons become dependent upon
neurotrophins are uncertain, several lines of evidence suggest that members of
the bone morphogenetic protein (BMP) family of the TGFß superfamily are
involved. Embryonic ganglia throughout the PNS express BMP receptors
(Zhang et al., 1998),
indicating their potential for BMP sensitivity, and members of the BMP family
of ligands including BMP2, BMP4 and BMP7 are expressed in the developing skin
during the time that this target organ is innervated
(Jones et al., 1991
;
Lyons et al., 1989
;
Lyons et al., 1990
;
Winnier et al., 1995
). BMPs
limit population size of a number of embryonic cell types, including
neocortical ventricular zone cells both by promoting exit from cell cycle and
by inducing apoptosis (Furuta et al.,
1997
; Mabie et al.,
1999
). Moreover, BMP treatment of MAH cells, a sympathoadrenal
cell line (Birren and Anderson,
1990
) promotes exit from cell cycle and induces apoptosis and
neurotrophin dependence (Song et al.,
1998
). BMPs also promote apoptotic cell death of postmigratory
enteric and sympathetic neural precursors unless rescued by gut-derived
factors (Pisano et al., 2000
;
Chalazonitis et al., 2003
).
Finally, treatment of cultured embryonic sympathetic neuroblasts with BMP4
induces premature dependence of the neurons on neurotrophins for survival
(Gomes and Kessler, 2001
),
suggesting that the BMPs might be the crucial factors that induce neurotrophin
dependence during development.
As homozygous deletion of Bmp2 or Bmp4 or their receptors
causes lethality in early development
(Winnier et al., 1995;
Zhang and Bradley, 1996
;
Beppu et al., 2000
;
Mishina et al., 1995
), we
chose a strategy of overexpressing an inhibitor of BMP signaling, noggin
(Zimmerman et al., 1996
) in
skin to define the role of BMP signaling on the development of peripheral
sensory neurons in vivo. We also generated mice that overexpress BMP4 in skin
under the same keratin14 (K14) promoter to look for complementary findings.
Our observations indicate that BMPs may regulate both the final neuron number
in sensory ganglia and the extent of innervation of targets. Coupled with
prior observations, this suggests that BMP signaling may regulate the
acquisition of neuronal dependence upon neurotrophins for survival, as well as
their dependence on target-derived neurotrophins for determining the density
of innervation of the target.
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
In-situ hybridization and western blot analysis
Whole-mount in situ hybridization analysis was performed on E12.5 mouse
embryos with riboprobes prepared against the full length noggin or
Bmp4 cDNA using a Digoxigenin labeling kit (Roche). Western Blot
analysis was carried out on lysates from 1-month-old mouse back skin from both
the transgenic and corresponding wild-type littermates. noggin protein was
identified by rat monoclonal antibody against mouse noggin, clone RT57-16, a
kind gift from Regeneron pharmaceuticals. BMP4 protein was identified using a
BMP4-specific monoclonal antibody
(Masuhara et al., 1995).
Processing of adult mouse tissues
Anesthetized animals were perfused with 4% paraformaldehyde (4% PF) in 0.1M
phosphate-buffered saline (PBS) pH 7.4 at 4°C and the mystacial pads and
the trigeminal ganglia were postfixed by immersion for 4 hours in 4% PF at pH
7.4 at 4°C. Following fixation, specimens were rinsed and stored in PBS at
4°C. Mystacial pads were cryoprotected by overnight filtration in 30%
sucrose in PBS and frozen sectioned (14 µm) by cryostat in a plane
perpendicular to the skin surface and parallel to the central rows of vibrissa
follicles. The sections were directly thawed in an alternating series onto
5-10 slides coated with chrome-alum gelatin and air dried overnight.
Immunofluorescence
Immunofluorescence analyses and controls were performed as described
previously (Rice et al., 1997;
Paré et al., 2001
) with
polyclonal primary antibodies against pan-neuronal protein gene product 9.5
(PGP) (rabbit polyclonal, 1:1000, UltraClone); calcitonin gene-related peptide
(CGRP) (rabbit polyclonal, 1:800, Chemicon; sheep polyclonal, 1:800,
Infiniti); neurofilament 200 (NF) (rabbit polyclonal, 1:800; Chemicon).
Quantitation of neurons and innervation
Quantitative microscopic analyses of ganglion cells and their cutaneous
innervation were assessed with NeuroLucida software (MicroBrightField,
Colchester, VT). 4% PF fixed trigeminal ganglia were dehydrated in graded
series of alcohol, cleared with histoclear and embedded in paraffin. Entire
ganglia were serial sectioned at 8 µm and stained with Cresyl Violet. Cell
counts were obtained using a modified Abercrombie method as described
previously (Albers and Davis,
2001; Davis et al.,
1996
).
For total neuronal counts in embryonic stages, E12.5 embryos were fixed in 4% PF for 18-24 hours. Embryos were dehydrated in graded series of alcohol, cleared in histoclear and embedded in paraffin wax to cut 5 µm transverse sections upwards from neck. Every tenth section of the serially sectioned trigeminal ganglion was counted and the total number of neurons [cells immunoreactive for ß-III tubulin (Chemicon, Temecula, CA)] in 10 sections was multiplied by the interval.
To quantify the cutaneous innervation, the following data were obtained from five sections of whisker pads in three transgenic and three wild-type littermates: (1) epidermal thickness at 20 equally spaced intervals, (2) the length of the epidermal surface, (3) the location of each sensory ending in the underlying epidermis, and (4) the location, outer contour and length of each piece of the nerves in the underlying dermis. Data 1-3 were used to calculate average epidermal thickness and epidermal innervation density. Because the nerves are cylindrical and the plane of sectioning was parallel to their long axis, the average diameter of each nerve profile was determined from the fourth set of data by dividing the area of each profile by the length of its long axis. The average diameter of each nerve was used to calculate the average cross-sectional area.
BrdU immunohistochemistry
Pregnant females at E12.5 gestational day were injected with
5-bromodeoxyuridine (BrdU, Sigma Chemicals, St Louis, MO) at 100 µg/g body
weight and sacrificed 1 hour later, embryos collected and immersion fixed
for12 hours in 4% PF in 0.1M PBS, pH 7.4. Embryos were washed in PBS,
dehydrated in a graded series of alcohol, paraffin wax embedded and 5 µm
thick serial sections cut transversely through the head. Sections containing
the trigeminal ganglia were stained for BrdU immunohistochemistry with the
BrdU in-situ detection kit (BD Pharmingen, San Diego, CA).
Trigeminal ganglion cell culture
E10 trigeminal ganglia were cultured on poly-D-lysine/laminin coated
culture dishes in defined medium containing BDNF (10 ng/ml) following the
protocol of Davies et al. (Davies et al.,
1993). Six-hundred cells were plated per each 35 mm culture dish.
At 6 hours, the number of attached cells in each plate was counted twice in
10x10 mm grids and the number of cells for the whole area of the dish
was calculated and used as the initial number of cells for the experiment.
Additional growth factors [BMP4 (30 ng/ml), NGF (10 ng/ml), or BDNF (10
ng/ml)] were added at this time. After 72 hours, the number of surviving cells
was counted twice in 10x10 mm grids and the overall number of surviving
cells for the whole area of the dish was calculated.
Neurotrophin protein quantitation
NGF, BDNF and NT3 protein quantitation was determined by ELISA on lysates
prepared from the mystacial pads of 3-day-old mice using the corresponding
Emax Immunoassay System (Promega Corporation, Madison, WI).
Quantitative real time PCR (QRT-PCR) to estimate levels of neurotrophin transcripts
QRT-PCR was performed using Perkin-Elmer's ABI mPrism 7700 Sequence
Detector System. Total RNA was extracted from the mystacial pads of E14.5 and
P2 wild-type and K14-noggin transgenic littermates using Trizol reagent
(Invitrogen, Carlsbad, CA). cDNA was prepared using the thermoscript RT-PCR
kit (Invitrogen). QRTPCR was performed with an initial denaturation of 10
minutes at 95°C followed by 40 cycles of 15 seconds denaturation at
95°C and 1 minute annealing and elongation at 60°C. SYBR green 1 dye
was used to produce the fluorescent signal, which was detected at the
annealing phase. As SYBR green 1 binds to double stranded DNA nonspecifically,
the specificity of the reaction was confirmed by running the PCR products on
2% agarose gel and detecting a single specific band of the right size. Two
replicates were run for each cDNA sample and five animals of each genotype
were used.
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
|
|
|
|
In K14-noggin overexpressing mice, the thickness of the nerves in the third
and fourth tiers is 9 and 12 times greater than in wild-type animals, and the
density of FNEs in the epidermis is at least twice as great
(Fig. 2B). This increase
obviously involves the nonpeptidergic and especially the peptidergic
innervation. CGRP-IR is far more extensive in the transgenic dermal plexus,
especially in the fourth tier where CGRP-IR is rarely detectable in wild-type
specimens. Double labeling with anti-CGRP and anti-NF revealed that most of
the third tier and virtually all of the increased fourth tier peptidergic
innervation had little or no detectable NF200. These results suggest that the
noggin overexpression preferentially increased the nonpeptidergic and
NF-negative peptidergic innervation to the epidermis. The increases in the
epidermal innervation were as evident in 1-month-old noggin transgenics as in
mature adults. However, there was no detectable change in the density of
innervation of the skin at E15. Thus, the changes in innervation occurred
after the major period of naturally occurring cell death in the trigeminal
ganglion (Enokido et al.,
1999; Davies,
2003
).
In contrast to the results in the noggin-overexpressing mice, the innervation of the epidermis is reduced in the BMP4 transgenic animals, especially related to the fourth tier. Interestingly, the epidermis is somewhat innervated in the 1-month-old BMP transgenics but the innervation is severely depleted in the mature adult. However, at both stages, virtually all of the epidermal innervation appears to be supplied by individual axons ascending directly from the third tier of the dermal plexus. Bundles of axons were rare against the deep surface of the basement membrane where the fourth tier is normally located. Compared with wild-type specimens, a relatively high proportion of the third tier epidermal innervation expresses CGRP-IR, especially in the mature adult. Double labeling with anti-CGRP and anti-NF revealed that most of this third tier CGRP innervation was NF positive. Importantly, the epidermis of BMP4 overexpressers also contained endings that co-express CGRP-IR and NF-IR, which are lacking in wild-type epidermis (Fig. 3). In wild-type epidermis, only CGRP-IR is expressed in the epidermal endings of axons that co-express CGRP-IR and NF-IR. These results suggest that the overexpression of BMP4 has a detrimental effect on the fourth tier nonpeptidergic and NF-negative peptidergic innervation, especially over time, but may favor the presence of NF-positive peptidergic innervation.
The Merkel innervation at the mouth of whisker follicles and occasional guard hair follicles is supplied from the second tier of the dermal plexus, and consists of Aß fibers that co-label with anti-PGP and anti-NF200. The Merkel endings penetrate the basement membrane of the epidermis at the mouth of the follicle to terminate on anti-PGP immunoreactive Merkel cells in lamina basalis. As seen in Fig. 4A-D, the mouths of comparable whisker follicles have far more Merkel cells and Merkel endings in noggin overexpressers than wild-type mice. By contrast, BMP4 overexpressing mice have fewer Merkel endings seen in the whisker pads (Fig. 4E,F). These results indicate that the overexpression of noggin promotes the development of Merkel cells and their endings whereas BMP4 is detrimental. (See Fig. 5 for a summary of the data presented in Figs 2, 3, 4.)
Increased neuron number in adult K14-noggin transgenic trigeminal ganglia
To determine whether BMP signaling also influences neuron numbers in the
peripheral nervous system, we quantified the total number of neurons in adult
trigeminal ganglia. As shown in Fig.
6A, there was a 35% increase in total number of neurons in the
trigeminal ganglia of K14-noggin mice compared with the wild type. There were
42194±1684 neurons (±s.e.m.; n=7) in the noggin
transgenic trigeminal ganglia compared with 31209±2888 (±s.e.m.;
n=9) neurons in control ganglia. Moreover, the increase was
specifically in the smaller size neuronal population as shown by size
distribution of the neurons in adult trigeminal ganglia
(Fig. 6B). This is consistent
with the increase in the peptidergic and the nonpeptidergic free nerve endings
in the epidermis that are normally derived from the smaller neuronal
population in the ganglion. There was also a 40% increase in the number of
neurons in the C6 DRG of the K14-noggin animals
(Fig. 6A). By contrast, there
was a 33% reduction in neuron numbers in the K14-BMP4 transgenic animals
(Fig. 6A).
|
Total numbers of neurons and proliferating neuroblasts are unchanged in E12.5 transgenic ganglia
The increased neuronal number in the K14-noggin mice could have resulted
from either increased proliferation or increased survival of the developing
sensory neurons in the ganglia. Proliferation of neuroblasts in the mouse
trigeminal ganglia occurs between E9 and E13. We therefore counted the total
number of ß-tubulin positive neurons in the trigeminal ganglion at E12.5
day of gestation and found no significant difference in the total number of
neurons between the transgenic and wild type littermates
(Fig. 7A). There were
39,107±2522 neurons in the noggin transgenic ganglia compared with
37210±3097 neurons in control ganglia. Thus, at this time period, there
was not an increase in the number of neurons generated in the K14-noggin
animal. Analysis of cell proliferation in the trigeminal ganglia at E12.5
using bromodeoxyuridine (BrdU) labeling also revealed no significant changes.
There were 15131±1092 BrdU-positive cells in the noggin transgenic
ganglia compared with 13172±716 in the control ganglia
(Fig. 7B) indicating that
proliferation was not altered. There were also no significant differences in
TUNEL labeling, although there was a trend towards a decrease in the
K14-noggin animals (Fig. 7C).
Comparison of neuron numbers at E12.5 with numbers in the adult ganglion
(Fig. 7D) demonstrates that
there is the expected loss of about a third of the neurons in the wild-type
animals but no loss in the K14-noggin trigeminal ganglia. Hence, the increased
neuronal number seen in the adult in the K14-noggin transgenic animals appears
to reflect increased survival of neurons that would normally have been
destined to die.
|
|
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
BMPs including BMP2, BMP4 and BMP7 are expressed in the developing
epidermis (Bitgood and McMahon,
1995; Jones et al.,
1991
; Lyons et al.,
1989
; Lyons et al.,
1990
; Takahashi and Ikeda,
1996
; Winnier et al.,
1995
). Moreover, embryonic ganglia throughout the PNS including
the trigeminal ganglion express both type I and type II BMP receptors
(Zhang et al., 1998
),
indicating their potential for BMP sensitivity. The responsiveness of sensory
neurons to BMPs is further evidenced by prior studies indicating that BMP
signaling regulates neuropeptide expression by developing peripheral sensory
neurons (Ai et al., 1999
;
Hall et al., 2001
).
Furthermore, treatment of E10 trigeminal neurons with BMP4 in vitro promoted
cell death (Fig. 6), indicating
responsiveness of the neurons to BMP4. Hence, the various components of the
BMP pathway are present in embryonic neurons for target-derived BMPs to have a
direct effect on neuron survival and on the innervation of the skin. However
the BMP receptors, BMPR-IA and BMPR-IB are also expressed in the basal layer
of the epidermis and the keratinocytes of the suprabasal layer, respectively,
at E16.5 (Botchkarev et al.,
1999
), and the signal transducers of the BMP pathway, Smad1 and
Smad5 are also expressed in the developing murine epidermis
(Dick et al., 1998
;
Flanders et al., 2001
).
Furthermore, substantial evidence indicates that BMP signaling plays a crucial
role in the development of both skin and hair follicles (for a review, see
Botchkarev, 2003
). It is
therefore possible that some of the changes in the sensory innervation occur
indirectly because of BMP-mediated changes in the target tissue.
Irrespective of whether the changes observed in the transgenic animals
reflect direct or indirect effects of the BMPs on the sensory innervation,
these studies indicate that the number of neurons surviving in the innervating
ganglion is not coupled exclusively to the level of neurotrophins produced by
the target tissue. Levels of NGF and BDNF were unchanged in the transgenic
mystacial pads at E14.5 and PN3, and NT3 protein abundance was actually
significantly lower in the hyperinnervated skin of the noggin transgenic
animals, possibly reflecting increased competition by the larger number of
nerve fibers for a limited supply of NT3. It is interesting that NGF
transcripts were increased fourfold in the transgenic skin at PN2. However,
more importantly there was no change in transcript expression of NGF at E14.5
mystacial pads, the time period when apoptosis in the trigeminal ganglion is
at its peak. BDNF transcript expression is also increased twofold at E14.5
mystacial pads in the transgenic mice. However, most neurons in the trigeminal
ganglion have switched their dependence from BDNF to NGF by this time period.
The mechanisms by which target-derived BMPs alter the requirements for
neurotrophins are unclear. BMP treatment of MAH cells, a sympathoadrenal cell
line, promotes exit from cell cycle and induces apoptosis and neurotrophin
dependence (Song et al.,
1998). Furthermore, treatment of cultured embryonic sympathetic
neuroblasts with BMP4 induces premature dependence of the neurons on
neurotrophins for survival (Gomes and
Kessler, 2001
), suggesting that the BMPs might be crucial factors
that induce neurotrophin dependence during development. The findings in this
study are consistent with this hypothesis. In control mice there was a
decrease in neuron number of about 30% between E12.5 and the adult. By
contrast, there was no decrease in neuron number in the noggin transgenic
animals during this period of time, indicating that the normal amount of
programmed cell death did not occur in the absence of BMP signaling in the
target. There was no significant difference in TUNEL-positive apoptotic cells
at E15.5 though the mean number of those cells was less in the transgenic. It
is possible that there is a small decrease of apoptotic cells in the
transgenic ganglia over a prolonged period of embryonic development when
normal cell death occurs. A role of increased proliferation of neuroblasts in
the transgenic ganglia followed by reduced neurotrophin dependence is
possible. However, at E12.5, both the total neuron number and BrdU-positive
proliferating cells in the trigeminal ganglia are unchanged in the
noggin-transgenic mice. Interestingly, once sensory neurons have become
dependent upon neurotrophins for survival, BMPs have been shown to augment
neuronal survival when neurotrophins are present
(Farkas et al., 1999
). This is
also consistent with the hypothesis that the pro-apoptotic effects of the BMPs
on embryonic neuroblasts reflect induction of neurotrophin dependence rather
than a direct toxic/pro-apoptotic effect of the BMPs on sensory neurons. This
conclusion is also supported by evidence that overexpression of noggin in
embryonic gut dramatically increases the density of the neural crest-derived
enteric neurons in both myenteric and submucosal plexuses in the gut of
4-week-old animals (Chalazonitis et al.,
2003
). Furthermore, treatment of E10 trigeminal neurons with BMP4
in vitro resulted in neuronal death that could be rescued by NGF but not BDNF
(Fig. 6). Trigeminal ganglion
neurons normally switch their dependence from BDNF to NGF between E10 and E13
through unknown mechanisms (Enokido et
al., 1999
). However dissociated E10 neurons do not develop NGF
dependence in vitro and survive well in the presence of BDNF
(Enokido et al., 1999
). By
contrast, exposure of E10 trigeminal neurons to BMP4 resulted in dependence
upon NGF for their survival, i.e. they died unless NGF (and not BDNF) was
added to the medium. This suggests that BMP signaling participates in the
acquisition of NGF dependence by trigeminal neurons.
At E15 there was no increase in the density of innervation of the skin in
the K14-noggin transgenic animals (Fig.
2). Because this corresponds to the normal period of maximal
neuronal death in the trigeminal ganglion, enhanced sprouting of nerve fibers
in the target did not mediate the enhanced neuronal survival. However, the
increase in the density of innervation could conversely reflect, in part, the
increase in the number of trigeminal neurons that survived. Nevertheless the
magnitude of the increase in innervation was much greater than the 40%
increase in neuron numbers in the K14-transgenic animals, suggesting that
other mechanisms were also involved. Treatment of cultured sympathetic or
cortical neurons with BMP7 promotes dendritic rather than axonal outgrowth
(Lein et al., 1996;
Le Roux et al., 1999
), and BMP
signaling exerts repulsive effects on axonal outgrowth by roof-plate
commissural neurons (Augsburger et al.,
1999
; Butler and Dodd,
2003
). These observations raise the possibility that BMP signaling
directly represses trigeminal innervation of the skin. However, treatment of
cultured trigeminal neurons with BMP4 did not alter process outgrowth, and
treatment with BMP7 and other BMPs also did not alter trigeminal outgrowth in
culture (Le Roux et al.,
1999
). This suggests that the changes in the density of
innervation do not solely reflect direct effects of BMP signaling. NGF
signaling regulates the density and pattern of innervation of target tissues
independent of effects on sensory neuron survival
(Patel et al., 2000
). Although
there was no change in the level of neurotrophins in the skin at the ages
examined, it is possible that there were changes in other elements of the
neurotrophin signal transduction pathway
(Kobayashi et al., 1998
;
Zhang et al., 1998
) or changes
in neurotrophins at other ages. In addition to an increase in the density of
innervation in the skin of the noggin transgenic animals, there was a marked
change in the pattern of innervation by different types of fibers. The most
striking observations in the K14-noggin transgenic mice are the increase in
the epidermal free nerve endings, the nonpeptidergic penicillate endings in
the epidermis, along with a hypertrophic fourth tier of innervation that abuts
the basement membrane of the epidermis. There is also some increase in the
peptidergic innervation labeled with CGRP in the third and fourth tier as well
as the unmyelinated CGRP FNEs in the epidermis. Interestingly, this excess
innervation and number of sensory endings increases with age in the noggin
transgenic animals. By contrast, in the K14-BMP4 transgenic mice, the fourth
tier of innervation is significantly reduced even in one-month-old mice and
there is deterioration of the fourth tier and epidermal free nerve endings
with increasing age. However, there is a marked increase in
CGRP-immunoreactive processes in the epidermis, consistent with known effects
of BMP signaling on expression of CGRP (Ai
et al., 1999
; Hall et al.,
2001
). The complementary findings in the K14-noggin and K14-BMP4
animals suggest that endogenous BMPs in the skin regulate the maintenance of
epidermal and upper dermal innervation apart from a possible effect on sensory
neuron number.
Another component of epidermal innervation, the Merkel innervation and the
Merkel cells at the mouth of the whisker follicle are also increased in
K14-noggin mice. Recently, it has been shown that the Merkel innervation has
two components, one dependant on trkA and the other on trkC. In mice mutant
for both these receptors, the Merkel innervation is completely lost
(Cronk et al., 2002). However,
levels of NT3 are reduced in the skin of the K14-noggin animals, and levels of
NT3 transcripts are unchanged. Further levels of NGF are also unchanged in the
skin, and levels of NGF transcripts are unchanged at E14.5, the time during
which the Merkel cells are specified. Hence, it is unlikely that the effects
on Merkel innervation and the Merkel cells occur indirectly because of changes
in neurotrophin expression.
In summary, these findings indicate that target-derived BMPs limit the final number of neurons in sensory ganglia as well as the extent and pattern of innervation of targets. Coupled with prior observations, these findings suggest that BMP signaling may regulate the acquisition of dependence of neurons on neurotrophins for survival, as well as their dependence on target-derived neurotrophins for determining the density of innervation of the target.
![]() |
ACKNOWLEDGMENTS |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Ai, X., Cappuzzello, J. and Hall, A. K. (1999). Activin and bone morphogenetic proteins induce calcitonin gene-related peptide in embryonic sensory neurons in vitro. Mol. Cell. Neurosci. 14,506 -518.[CrossRef][Medline]
Albers, K. M. and Davis, B. M. (2001). Construction and analysis of transgenic animals overexpressing neurotrophins. Methods Mol. Biol. 169,149 -166.[Medline]
Albers, K. M., Wright, D. E. and Davis, B. M. (1994). Overexpression of nerve growth factor in epidermis of transgenic mice causes hypertrophy of the peripheral nervous system. J. Neurosci. 14,1422 -1432.[Abstract]
Albers, K. M., Perrone, T. N., Goodness, T. P., Jones, M. E., Green, M. A. and Davis, B. M. (1996). Cutaneous overexpression of NT-3 increases sensory and sympathetic neuron number and enhances touch dome and hair follicle innervation. J. Cell Biol. 134,487 -497.[Abstract]
Augsburger, A., Schuchardt, A., Hoskins, S., Dodd, J. and Butler, S. (1999). BMPs as mediators of roof plate repulsion of commissural neurons. Neuron. 24,127 -141.[Medline]
Beppu, H., Kawabata, M., Hamamoto, T., Chytil, A., Minowa, O., Noda, T. and Miyazono, K. (2000). BMP type II receptor is required for gastrulation and early development of mouse embryos. Dev. Biol. 221,249 -258.[CrossRef][Medline]
Birren, S. J. and Anderson, D. J. (1990). A v-myc-immortalized sympathoadrenal progenitor cell line in which neuronal differentiation is initiated by FGF but not NGF. Neuron 4,189 -201.[Medline]
Bitgood, M. J. and McMahon, A. P. (1995). Hedgehog and Bmp genes are coexpressed at many diverse sites of cell-cell interaction in the mouse embryo. Dev. Biol. 172,126 -138.[CrossRef][Medline]
Botchkarev V. A. (2003). Bone morphogenetic
proteins and their antagonists in skin and hair follicle biology.
J. Invest. Dermatol.
120, 36-47.
Botchkarev, V. A., Botchkareva, N. V., Roth, W., Nakamura, M., Chen, L. H., Herzog, W., Lindner, G., McMahon, J. A., Peters, C., Lauster, R. et al. (1999). Noggin is a mesenchymally derived stimulator of hair-follicle induction. Nat. Cell Biol. 1, 158-164.[CrossRef][Medline]
Butler, S. J. and Dodd, J. (2003). A role for BMP heterodimers in roof plate-mediated repulsion of commissural axons. Neuron 38,389 -401.[Medline]
Chalazonitis, A., D'autreaux, F., Guha, U., Pham, T., Faure, C., Chen, J., Rothman, T., Kessler, J. A. and Gershon, M. (2003). Regulation of enteric neuronal development and specification of NT-3 dependence by bone morphogenetic proteins (BMPs)-2 and -4. Neurogastroenterol. Motil. 15, 196.
Cheng, J., Turksen, K., Yu, Q. C., Schreiber, H., Teng, M. and Fuchs, E. (1992). Cachexia and graft-vs.-host-disease-type skin changes in keratin promoter-driven TNF alpha transgenic mice. Genes Dev. 6,1444 -1456.[Abstract]
Conover, J. C., Erickson, J. T., Katz, D. M., Bianchi, L. M., Poueymirou, W. T., McClain, J., Pan, L., Helgren, M., Ip, N. Y., Boland, P. et al. (1995). Neuronal deficits, not involving motor neurons, in mice lacking BDNF and/or NT4. Nature 375,235 -238.[CrossRef][Medline]
Cronk, K. M., Wilkinson, G. A., Grimes, R., Wheeler, E. F.,
Jhaveri, S., Fundin, B. T., Silos-Santiago, I., Tessarollo, L., Reichardt, L.
F. and Rice, F. L. (2002). Diverse dependencies of developing
Merkel innervation on the trkA and both full-length and truncated isoforms of
trkC. Development 129,3739
-3750.
Crowley, C. S. S., Nishimura, M. C., Chen, K. S., Pitts-Meek, S., Armanini, M. P., Ling, L. H., MacMahon, S. B., Shelton, D. L., Levinson, A. D. et al. (1994). Mice lacking nerve growth factor display perinatal loss of sensory and sympathetic neurons yet develop basal forebrain cholinergic neurons. Cell 76,1001 -1011.[Medline]
Davies, A. M. (2003). Regulation of neuronal
survival and death by extracellular signals during development.
EMBO J. 22,2537
-2545.
Davies, A. M., Lee, K. F. and Jaenisch, R. (1993). p75-deficient trigeminal sensory neurons have an altered response to NGF but not to other neurotrophins. Neuron. 11,565 -574.[Medline]
Davis, B. M., Fundin, B. T., Albers, K. M., Goodness, T. P., Cronk, K. M. and Rice, F. L. (1997). Overexpression of nerve growth factor in skin causes preferential increases among innervation to specific sensory targets. J. Comp. Neurol. 387,489 -506.[CrossRef][Medline]
Davis, B. M., Wang, H. S., Albers, K. M., Carlson, S. L., Goodness, T. P. and McKinnon, D. (1996). Effects of NGF overexpression on anatomical and physiological properties of sympathetic postganglionic neurons. Brain Res. 724, 47-54.[CrossRef][Medline]
Dick, A., Risau, W. and Drexler, H. G. (1998). Expression of Smad1 and Smad2 during embryogenesis suggests a role in organ development. Dev. Dyn. 211,293 -305.[CrossRef][Medline]
Enokido. Y., Wyatt, S. and Davies, A. M.
(1999). Developmental changes in the response of trigeminal
neurons to neurotrophins: influence of birthdate and the ganglion environment.
Development 126,4365
-4373.
Ernfors, P., Lee, K. F. and Jaenisch, R. (1994a). Mice lacking brain-derived neurotrophic factor develop with sensory deficits. Nature 368,147 -150.[CrossRef][Medline]
Ernfors, P., Lee, K. F., Kucera, J. and Jaenisch, R. (1994b). Lack of neurotrophin-3 leads to deficiencies in the peripheral nervous system and loss of limb proprioceptive afferents. Cell 77,503 -512.[Medline]
Farinas, I., Jones, K. R., Backus, C., Wang, X. Y. and Reichardt, L. F. (1994). Severe sensory and sympathetic deficits in mice lacking neurotrophin-3. Nature 369,658 -661.[CrossRef][Medline]
Farkas, L. M., Jaszai, J., Unsicker, K. and Krieglstein, K. (1999). Characterization of bone morphogenetic protein family members as neurotrophic factors for cultured sensory neurons. Neuroscience 92,227 -235.[CrossRef][Medline]
Flanders, K. C., Kim, E. S. and Roberts, A. B. (2001). Immunohistochemical expression of Smads 1-6 in the 15-day gestation mouse embryo: signaling by BMPs and TGF-betas. Dev. Dyn. 220,141 -154.[CrossRef][Medline]
Fundin, B. T., Arvidsson, J., Aldskogius, H., Johansson, O., Rice, S. N. and Rice, F. L. (1997a). Comprehensive immunofluorescence and lectin binding analysis of intervibrissal fur innervation in the mystacial pad of the rat. J. Comp. Neurol. 385,185 -206.[CrossRef][Medline]
Fundin, B. T., Silos-Santiago, I., Ernfors, P., Fagan, A. M., Aldskogius, H., DeChiara, T. M., Phillips, H. S., Barbacid, M., Yancopoulos, G. D. and Rice, F. L. (1997b). Differential dependency of cutaneous mechanoreceptors on neurotrophins, trk receptors, and P75 LNGFR. Dev. Biol. 190,94 -116.[CrossRef][Medline]
Furuta, Y., Piston, D. W. and Hogan, B. L.
(1997). Bone morphogenetic proteins (BMPs) as regulators of
dorsal forebrain development. Development
124,2203
-2212.
Gomes, W. A. and Kessler, J. A. (2001). Msx-2 and p21 mediate the proapoptotic but not the anti-proliferative effects of BMP4 on cultured sympathetic neuroblasts. Dev. Biol. 237,212 -221.[CrossRef][Medline]
Guha, U., Gomes, W. A., Kobayashi, T., Pestell, R. G. and Kessler, J. A. (2002). In vivo evidence that BMP signaling is necessary for apoptosis in the mouse limb. Dev. Biol. 249,108 -120.[CrossRef][Medline]
Hall, A. K., Dinsio, K. J. and Cappuzzello, J. (2001). Skin cell induction of calcitonin gene-related peptide in embryonic sensory neurons in vitro involves activin. Dev. Biol. 229,263 -270.[CrossRef][Medline]
Hohn, A., Leibrock, J., Bailey, K. and Barde, Y. A. (1990). Identification and characterization of a novel member of the nerve growth factor/brain-derived neurotrophic factor family. Nature 344,339 -341.[CrossRef][Medline]
Huang, E. J. and Reichardt, L. F. (2001). Neurotrophins: roles in neuronal development and function. Annu. Rev. Neurosci. 24,677 -736.[CrossRef][Medline]
Ip, N. Y., Ibanez, C. F., Nye, S. H., McClain, J., Jones, P. F., Gies, D. R., Belluscio, L., le Beau, M. M., Espinosa, R., 3rd, Squinto, S. P. et al. (1992). Mammalian neurotrophin-4: structure, chromosomal localization, tissue distribution, and receptor specificity. Proc. Natl. Acad. Sci. USA 89,3060 -3064.[Abstract]
Jones, C. M., Lyons, K. M. and Hogan, B. L. (1991). Involvement of bone morphogenetic protein-4 (BMP-4) and Vgr-1 in morphogenesis and neurogenesis in the mouse. Development 111,531 -542.[Abstract]
Jones, K. R., Farinas, I., Backus, C. and Reichardt, L. F. (1994). Targeted disruption of the BDNF gene perturbs brain and sensory neuron development but not motor neuron development. Cell 76,989 -999.[Medline]
Kirstein, M. and Farinas, I. (2002). Sensing life: regulation of sensory neuron survival by neurotrophins. Cell Mol. Life Sci. 59,1787 -1802.[Medline]
Klein, R., Smeyne, R. J., Wurst, W., Long, L. K., Auerbach, B. A., Joyner, A. L. and Barbacid, M. (1993). Targeted disruption of the trkB neurotrophin receptor gene results in nervous system lesions and neonatal death. Cell 75,113 -122.[Medline]
Kobayashi, M., Fujii, M., Kurihara, K. and Matsuoka, I. (1998). Bone morphogenetic protein-2 and retinoic acid induce neurotrophin-3 responsiveness in developing rat sympathetic neurons. Mol. Brain Res. 53,206 -217.[Medline]
Leibrock, J. L. F., Hohn, A., Hofer, M., Hengerer, B., Masiakowski, P., Thoenen, H. and Barde, Y. A. (1989). Molecular cloning and expression of brain-derived neurotrophic factor. Nature 341,149 -152.[CrossRef][Medline]
Lein, P., Guo, X., Hedges, A. M., Rueger, D., Johnson, M. and Higgins, D. (1996). The effects of extracellular matrix and osteogenic protein-1 on the morphological differentiation of rat sympathetic neurons. Int. J. Dev. Neurosci. 14,203 -215.[CrossRef][Medline]
LeMaster, A. M., Krimm, R. F., Davis, B. M., Noel, T., Forbes,
M. E., Johnson, J. E. and Albers, K. M. (1999).
Overexpression of brain-derived neurotrophic factor enhances sensory
innervation and selectively increases neuron number. J.
Neurosci. 19,5919
-5931.
Le Roux, P., Behar, S., Higgins, D. and Charette, M. (1999) OP-1 enhances dendritic growth from cerebral cortical neurons in vitro. Exp. Neurol. 1, 151-163.[CrossRef]
Lyons, K. M., Pelton, R. W. and Hogan, B. L. (1989). Patterns of expression of murine Vgr-1and BMP-2a RNA suggest that transforming growth factor-beta-like genes coordinately regulate aspects of embryonic development. Genes Dev. 3,1657 -1668.[Abstract]
Lyons, K. M., Pelton, R. W. and Hogan, B. L. (1990). Organogenesis and pattern formation in the mouse: RNA distribution patterns suggest a role for bone morphogenetic protein-2A (BMP-2A). Development 109,833 -844.[Abstract]
Mabie, P. C., Mehler, M. F. and Kessler, J. A.
(1999). Multiple roles of bone morphogenetic protein signaling in
the regulation of cortical cell number and phenotype. J.
Neurosci. 19,7077
-7088.
Maisonpierre, P. C., Belluscio, L., Squinto, S., Ip, N. Y., Furth, M. E., Lindsay, R. M. and Yancopoulos, G. D. (1990). Neurotrophin-3: a neurotrophic factor related to NGF and BDNF. Science 247,1446 -1451.[Medline]
Masuhara, K., Nakase, T., Suzuki, S., Takaoka, K., Matsui, M. and Anderson, H. C. (1995). Use of monoclonal antibody to detect bone morphogenetic protein-4 (BMP-4). Bone 16, 91-96.[CrossRef][Medline]
Mishina, Y., Suzuki, A., Ueno, N., and Behringer, R. R. (1995). Bmpr encodes a type I bone morphogenetic protein receptor that is essential for gastrulation during mouse embryogenesis. Genes Dev. 9,3027 -3037.[Abstract]
Paré, M., Elde, R., Mazurkiewicz, J. E., Smith, A. M. and
Rice, F. L. (2001). The Meissner corpuscle revised: a
multiafferented mechanoreceptor with nociceptor immunochemical properties.
J. Neurosci. 21,7236
-7246.
Patel, T. D., Jackman, A., Rice, F. L., Kucera, J. and Snider, W. D. (2000). Development of sensory neurons in the absence of NGF/TrkA signaling in vivo. Neuron 25,345 -357.[Medline]
Pisano, J. M., Colon-Hastings, F. and Birren, S. J. (2000). Postmigratory enteric and sympathetic neural precursors share common, developmentally regulated, responses to BMP2. Dev. Biol. 227,1 -11.[CrossRef][Medline]
Rice, F. L., Kinnman, E., Aldskogius, H., Johansson, O. and Arvidsson, J. (1993). The innervation of the mystacial pad of the rat as revealed by PGP 9.5 immunofluorescence. J. Comp. Neurol. 337,366 -385.[Medline]
Rice, F. L., Fundin, B. T., Arvidsson, J., Aldskogius, H. and Johansson, O. (1997). Comprehensive immunofluorescence and lectin binding analysis of vibrissal follicle sinus complex innervation in the mystacial pad of the rat. J. Comp. Neurol. 385,149 -184.[CrossRef][Medline]
Rice, F. L., Albers, K. M., Davis, B. M., Silos-Santiago, I., Wilkinson, G. A., LeMaster, A. M., Ernfors, P., Smeyne, R. J., Aldskogius, H., Phillips, H. S. et al. (1998). Differential dependency of unmyelinated and A delta epidermal and upper dermal innervation on neurotrophins, trk receptors, and p75LNGFR. Dev. Biol. 198, 57-81.[CrossRef][Medline]
Rosenthal, A., Goeddel, D. V., Nguyen, T., Lewis, M., Shih, A., Laramee, G. R., Nikolics, K. and Winslow, J. W. (1990). Primary structure and biological activity of a novel human neurotrophic factor. Neuron 4,767 -773.[Medline]
Smeyne, R. J., Klein, R., Schnapp, A., Long, L. K., Bryant, S., Lewin, A., Lira, S. A. and Barbacid, M. (1994). Severe sensory and sympathetic neuropathies in mice carrying a disrupted Trk/NGF receptor gene. Nature 368,246 -249.[CrossRef][Medline]
Song, Q., Mehler, M. F. and Kessler, J. A. (1998). Bone morphogenetic proteins induce apoptosis and growth factor dependence of cultured sympathoadrenal progenitor cells. Dev. Biol. 196,119 -127.[CrossRef][Medline]
Takahashi, H. and Ikeda, T. (1996). Transcripts for two members of the transforming growth factor-beta superfamily BMP-3 and BMP-7 are expressed in developing rat embryos. Dev. Dyn. 207,439 -449.[CrossRef][Medline]
Tessarollo, L., Tsoulfas, P., Donovan, M. J., Palko, M. E.,
Blair-Flynn, J., Hempstead, B. L. and Parada, L. F. (1997).
Targeted deletion of all isoforms of the trkC gene suggests the use of
alternate receptors by its ligand neurotrophin-3 in neuronal development and
implicates trkC in normal cardiogenesis. Proc. Natl. Acad. Sci.
USA 94,14776
-14781.
Winnier, G., Blessing, M., Labosky, P. A. and Hogan, B. L. (1995). Bone morphogenetic protein-4 is required for mesoderm formation and patterning in the mouse. Genes Dev. 9,2105 -2116.[Abstract]
Zhang, D., Mehler, M. F., Song, Q. and Kessler, J. A.
(1998). Development of bone morphogenetic protein receptors in
the nervous system and possible roles in regulating trkC expression.
J. Neurosci. 18,3314
-3326.
Zhang, H. and Bradley, A. (1996). Mice
deficient for BMP2 are nonviable and have defects in amnion/chorion and
cardiac development. Development
122,2977
-2986.
Zimmerman, L. B., de Jesus-Escobar, J. M. and Harland, R. M. (1996). The Spemann organizer signal noggin binds and inactivates bone morphogenetic protein 4. Cell 86,599 -606.[Medline]