1: Mol Biol Cell. 2005 Nov;16(11):5283-93. Epub 2005 Aug 31. 

Dynamic Alterations in Gene Expression after Wnt-mediated Induction of Avian
Neural Crest.

Taneyhill LA, Bronner-Fraser M.

Division of Biology, California Institute of Technology, Pasadena, CA 91125.

The Wnt signaling pathway is important in the formation of neural crest cells in
many vertebrates, but the downstream targets of neural crest induction by Wnt
are largely unknown. Here, we examined quantitative changes in gene expression
regulated by Wnt-mediated neural crest induction using quantitative PCR (QPCR).
Induction was recapitulated in vitro by adding soluble Wnt to intermediate
neural plate tissue cultured in collagen, and induced versus control tissue were
assayed using gene-specific primers at times corresponding to premigratory (18
and 24 h) or early (36 h) stages of crest migration. The results show that Wnt
signaling up-regulates in a distinct temporal pattern the expression of several
genes normally expressed in the dorsal neural tube (slug, Pax3, Msx1, FoxD3,
cadherin 6B) at "premigratory" stages. While slug is maintained in early
migrating crest cells, Pax3, FoxD3, Msx1 and cadherin 6B all are down-regulated
by the start of migration. These results differ from the temporal profile of
these genes in response to the addition of recombinant BMP4, where gene
expression seems to be maintained. Interestingly, expression of rhoB is
unchanged or even decreased in response to Wnt-mediated induction at all times
examined, though it is up-regulated by BMP signals. The temporal QPCR profiles
in our culture paradigm approximate in vivo expression patterns of these genes
before neural crest migration, and are consistent with Wnt being an initial
neural crest inducer with additional signals like BMP and other factors
maintaining expression of these genes in vivo. Our results are the first to
quantitatively describe changes in gene expression in response to a Wnt or BMP
signal during transformation of a neural tube cell into a migratory neural crest
cell.

PMID: 16135532 [PubMed - in process]


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2: Dev Cell. 2005 Feb;8(2):167-78. 

Msx1 and Pax3 cooperate to mediate FGF8 and WNT signals during Xenopus neural
crest induction.

Monsoro-Burq AH, Wang E, Harland R.

Department of Molecular and Cell Biology, University of California, Berkeley,
Berkeley, California 94720, USA. anne-helene.monsoro-burq@curie.u-psud.fr

FGF, WNT, and BMP signaling promote neural crest formation at the neural plate
boundary in vertebrate embryos. To understand how these signals are integrated,
we have analyzed the role of the transcription factors Msx1 and Pax3. Using a
combination of overexpression and morpholino-mediated knockdown strategies in
Xenopus, we show that Msx1 and Pax3 are both required for neural crest
formation, display overlapping but nonidentical activities, and that Pax3 acts
downstream of Msx1. In neuralized ectoderm, Msx1 is sufficient to induce
multiple early neural crest genes. Msx1 induces Pax3 and ZicR1 cell
autonomously, in turn, Pax3 combined with ZicR1 activates Slug in a
WNT-dependent manner. Upstream of this, WNTs initiate Slug induction through
Pax3 activity, whereas FGF8 induces neural crest through both Msx1 and Pax3
activities. Thus, WNT and FGF8 signals act in parallel at the neural border and
converge on Pax3 activity during neural crest induction.

PMID: 15691759 [PubMed - indexed for MEDLINE]


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3: Development. 2004 Nov;131(21):5327-39. Epub 2004 Sep 29. 

Canonical Wnt activity regulates trunk neural crest delamination linking
BMP/noggin signaling with G1/S transition.

Burstyn-Cohen T, Stanleigh J, Sela-Donenfeld D, Kalcheim C.

Department of Anatomy and Cell Biology, Hebrew University-Hadassah Medical
School, PO Box 12272, Jerusalem 91120, Israel.

Delamination of premigratory neural crest cells depends on a balance between
BMP/noggin and on successful G1/S transition. Here, we report that BMP regulates
G1/S transition and consequent crest delamination through canonical Wnt
signaling. Noggin overexpression inhibits G1/S transition and blocking G1/S
abrogates BMP-induced delamination; moreover, transcription of Wnt1 is
stimulated by BMP and by the developing somites, which concomitantly inhibit
noggin production. Interfering with beta-catenin and LEF/TCF inhibits G1/S
transition, neural crest delamination and transcription of various BMP-dependent
genes, which include Cad6B, Pax3 and Msx1, but not that of Slug, Sox9 or FoxD3.
Hence, we propose that developing somites inhibit noggin transcription in the
dorsal tube, resulting in activation of BMP and consequent Wnt1 production.
Canonical Wnt signaling in turn stimulates G1/S transition and generation of
neural crest cell motility independently of its proposed role in earlier neural
crest specification.

PMID: 15456730 [PubMed - indexed for MEDLINE]


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4: Dev Biol. 2004 Jul 15;271(2):439-66. 

Molecular anatomy of placode development in Xenopus laevis.

Schlosser G, Ahrens K.

Brain Research Institute, University of Bremen, 28334 Bremen, Germany.
gschloss@uni-bremen.de

We analyzed the spatiotemporal pattern of expression of 15 transcription factors
(Six1, Six4, Eya1, Sox3, Sox2, Pax6, Pax3, Pax2, Pax8, Dlx3, Msx1, FoxI1c, Tbx2,
Tbx3, Xiro1) during placode development in Xenopus laevis from neural plate to
late tail bud stages. Out of all genes investigated, only the expression of
Eya1, Six1, and Six4 is maintained in all types of placode (except the lens)
throughout embryonic development, suggesting that they may promote generic
placodal properties and that their crescent-shaped expression domain surrounding
the neural plate defines a panplacodal primordium from which all types of
placode originate. Double-labeling procedures were employed to reveal the
precise position of this panplacodal primordium relative to neural plate, neural
crest, and other placodal markers. Already at neural plate stages, the
panplacodal primordium is subdivided into several subregions defined by
particular combinations of transcription factors allowing us to identify the
approximate regions of origin of various types of placode. Whereas some types of
placode were already prefigured by molecularly distinct areas at neural plate
stages, the epibranchial, otic, and lateral line placodes arise from a common
posterior placodal area (characterized by Pax8 and Pax2 expression) and acquire
differential molecular signatures only after neural tube closure. Our findings
argue for a multistep mechanism of placode induction, support a combinatorial
model of placode specification, and suggest that different placodes evolved from
a common placodal primordium by successive recruitment of new inducers and
target genes.

PMID: 15223346 [PubMed - indexed for MEDLINE]


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5: Development. 2000 May;127(10):2155-64. 

The expression of the homeobox gene Msx1 reveals two populations of dermal
progenitor cells originating from the somites.

Houzelstein D, Cheraud Y, Auda-Boucher G, Fontaine-Perus J, Robert B.

Laboratoire de Genetique Moleculaire de la Morphogenese, CNRS URA 1947, Institut
Pasteur, 75 724 Paris Cedex 15, France.

Experimental manipulation in birds has shown that trunk dermis has a double
origin: dorsally, it derives from the somite dermomyotome, while ventrally, it
is formed by the somatopleure. Taking advantage of an nlacZ reporter gene
integrated into the mouse Msx1 locus (Msx1(nlacZ) allele), we detected segmental
expression of the Msx1 gene in cells of the dorsal mesenchyme of the trunk
between embryonic days 11 and 14. Replacing somites from a chick host embryo by
murine Msx1(nlacZ )somites allowed us to demonstrate that these
Msx1-(beta)-galactosidase positive cells are of somitic origin. We propose that
these cells are dermal progenitor cells that migrate from the somites and
subsequently contribute to the dorsalmost dermis. By analysing Msx1(nlacZ)
expression in a Splotch mutant, we observed that migration of these cells does
not depend on Pax3, in contrast to other migratory populations such as limb
muscle progenitor cells and neural crest cells. Msx1 expression was never
detected in cells overlying the dermomyotome, although these cells are also of
somitic origin. Therefore, we propose that two somite-derived populations of
dermis progenitor cells can be distinguished. Cells expressing the Msx1 gene
would migrate from the somite and contribute to the dermis of the dorsalmost
trunk region. A second population of cells would disaggregate from the somite
and contribute to the dermis overlying the dermomyotome. This population never
expresses Msx1. Msx1 expression was investigated in the context of the onset of
dermis formation monitored by the Dermo1 gene expression. The gene is
downregulated prior to the onset of dermis differentiation, suggesting a role
for Msx1 in the control of this process.

PMID: 10769239 [PubMed - indexed for MEDLINE]


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6: Development. 1999 Nov;126(22):4965-76. 

Msx1 antagonizes the myogenic activity of Pax3 in migrating limb muscle
precursors.

Bendall AJ, Ding J, Hu G, Shen MM, Abate-Shen C.

Center for Advanced Biotechnology and Medicine, Department of Neuroscience and
Cell Biology and Department of Pediatrics, UMDNJ-Robert Wood Johnson Medical
School, Piscataway, NJ 08854, USA.

The migration of myogenic precursors to the vertebrate limb exemplifies a common
problem in development - namely, how migratory cells that are committed to a
specific lineage postpone terminal differentiation until they reach their
destination. Here we show that in chicken embryos, expression of the Msx1
homeobox gene overlaps with Pax3 in migrating limb muscle precursors, which are
committed myoblasts that do not express myogenic differentiation genes such as
MyoD. We find that ectopic expression of Msx1 in the forelimb and somites of
chicken embryos inhibits MyoD expression as well as muscle differentiation.
Conversely, ectopic expression of Pax3 activates MyoD expression, while
co-ectopic expression of Msx1 and Pax3 neutralizes their effects on MyoD.
Moreover, we find that Msx1 represses and Pax3 activates MyoD regulatory
elements in cell culture, while in combination, Msx1 and Pax3 oppose each
other's trancriptional actions on MyoD. Finally, we show that the Msx1 protein
interacts with Pax3 in vitro, thereby inhibiting DNA binding by Pax3. Thus, we
propose that Msx1 antagonizes the myogenic activity of Pax3 in migrating limb
muscle precursors via direct protein-protein interaction. Our results implicate
functional antagonism through competitive protein-protein interactions as a
mechanism for regulating the differentiation state of migrating cells.

PMID: 10529415 [PubMed - indexed for MEDLINE]


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7: Development. 1999 Jun;126(12):2689-701. 

The homeobox gene Msx1 is expressed in a subset of somites, and in muscle
progenitor cells migrating into the forelimb.

Houzelstein D, Auda-Boucher G, Cheraud Y, Rouaud T, Blanc I, Tajbakhsh S,
Buckingham ME, Fontaine-Perus J, Robert B.

Laboratoire de Genetique Moleculaire de la Morphogenese, CNRS URA 1947,
Departement de Biologie Moleculaire, Institut Pasteur, 75724 Paris Cedex 15,
France.

In myoblast cell cultures, the Msx1 protein is able to repress myogenesis and
maintain cells in an undifferentiated and proliferative state. However, there
has been no evidence that Msx1 is expressed in muscle or its precursors in vivo.
Using mice with the nlacZ gene integrated into the Msx1 locus, we show that the
reporter gene is expressed in the lateral dermomyotome of brachial and thoracic
somites. Cells from this region will subsequently contribute to forelimb and
intercostal muscles. Using Pax3 gene transcripts as a marker of limb muscle
progenitor cells as they migrate from the somites, we have defined precisely the
somitic origin and timing of cell migration from somites to limb buds in the
mouse. Differences in the timing of migration between chick and mouse are
discussed. Somites that label for Msx1(nlacZ )transgene expression in the
forelimb region partially overlap with those that contribute Pax3-expressing
cells to the forelimb. In order to see whether Msx1 is expressed in this
migrating population, we have grafted somites from the forelimb level of
Msx1(nlacZ )mouse embryos into a chick host embryo. We show that most cells
migrating into the wing field express the Msx1(nlacZ )transgene, together with
Pax3. In these experiments, Msx1 expression in the somite depends on the axial
position of the graft. Wing mesenchyme is capable of inducing Msx1 transcription
in somites that normally would not express the gene; chick hindlimb mesenchyme,
while permissive for this expression, does not induce it. In the mouse limb bud,
the Msx1(nlacZ )transgene is downregulated prior to the activation of the Myf5
gene, an early marker of myogenic differentiation. These observations are
consistent with the proposal that Msx1 is involved in the repression of muscle
differentiation in the lateral half of the somite and in limb muscle progenitor
cells during their migration.

PMID: 10331980 [PubMed - indexed for MEDLINE]


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8: Development. 1996 Nov;122(11):3607-16. 

The role of bone morphogenetic proteins in vertebral development.

Monsoro-Burq AH, Duprez D, Watanabe Y, Bontoux M, Vincent C, Brickell P, Le
Douarin N.

Institut d'Embryologie Cellulaire et Moleculaire du CNRS et du College de
France, Nogent-sur-Marne. monsoro@infobiogen.fr

This study first shows a striking parallel between the expression patterns of
the Bmp4, Msx1 and Msx2 genes in the lateral ridges of the neural plate before
neural tube closure and later on, in the dorsal neural tube and superficial
midline ectoderm. We have previously shown that the spinous process of the
vertebra is formed from Msx1- and 2-expressing mesenchyme and that the dorsal
neural tube can induce the differentiation of subcutaneous cartilage from the
somitic mesenchyme. We show here that mouse BMP4- or human BMP2-producing cells
grafted dorsally to the neural tube at E2 or E3 increase considerably the amount
of Msx-expressing mesenchymal cells which are normally recruited from the somite
to form the spinous process of the vertebra. Later on, the dorsal part of the
vertebra is enlarged, resulting in vertebral fusion and, in some cases (e.g.
grafts made at E3), in the formation of a 'giant' spinous process-like structure
dorsally. In strong contrast, BMP-producing cells grafted laterally to the
neural tube at E2 exerted a negative effect on the expression of Pax1 and Pax3
genes in the somitic mesenchyme, which then turned on Msx genes. Moreover,
sclerotomal cell growth and differentiation into cartilage were then inhibited.
Dorsalization of the neural tube, manifested by expression of Msx and Pax3 genes
in the basal plate contacting the BMP-producing cells, was also observed. In
conclusion, this study demonstrates that differentiation of the ventrolateral
and dorsal parts of the vertebral cartilage is controlled by different molecular
mechanisms. The former develops under the influence of signals arising from the
floor plate-notochord complex. These signals inhibit the development of dorsal
subcutaneous cartilage forming the spinous process, which requires the influence
of BMP4 to differentiate.

PMID: 8951076 [PubMed - indexed for MEDLINE]


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