Inhibitory action of BMPs on Pax1 expression and on shoulder girdle formation during limb development.

in Developmental Dynamics : An Official Publication of the American Association of Anatomists (1998), 213(2), 199-206

Pax1 expression in vertebrate limb buds is confined to cells in a discrete anterior proximal domain (Timmons et al. [1994] Development 120:2773-2785; Ebensperger et al. [1995] Anat. Embryol. 191:297-310 ... [more ▼]

Pax1 expression in vertebrate limb buds is confined to cells in a discrete anterior proximal domain (Timmons et al. [1994] Development 120:2773-2785; Ebensperger et al. [1995] Anat. Embryol. 191:297-310). In dorsoventral patterning of Drosophila, expression of pox meso, an insect gene with high sequence similarity to Pax1, is repressed by decapentaplegic (dpp) in dorsal mesoderm and, thus, is restricted to a discrete ventral domain (Staehling-Hampton et al. [1994] Nature 372:783-786). In the chick wing, cells expressing a vertebrate homolog of dpp, bone morphogenetic protein 4 (Bmp4), abut the Pax1 domain, suggesting a similar relationship between homologous genes in both vertebrates and invertebrates. Here, we show that two BMPs (BMP4, and BMP2, also highly related to dpp) can repress Pax1 in the developing chick wing. Chick wing bud cells expressing Pax1 give rise to the shoulder girdle. Cells in an equivalent position in the mouse forelimb also express Pax1, and Pax1 mutant mice display shoulder girdle defects. Similarly in chick embryos, girdle defects are produced by treatments with signalling molecules that lead to expression of BMPs, which subsequently reduce Pax1 expression in the limb bud. Recently, BMP4 has been shown to inhibit Pax1 expression in the developing trunk (Monsoro-Burq et al. [1996] Development 122:3607-3616) and Pax9 expression in developing teeth (Neubuser et al. [1997] Cell 90:247-255). Thus, a property of BMPs appears to be to regulate pox meso homologs negatively and, thus, limit their expression domains. [less ▲]

Pax9-deficient mice lack pharyngeal pouch derivatives and teeth and exhibit craniofacial and limb abnormalities.

in Genes and Development (1998), 12(17), 2735-47

Pax genes have been shown to play important roles in mammalian development and organogenesis. Pax9, a member of this transcription factor family, is expressed in somites, pharyngeal pouches, mesenchyme ... [more ▼]

Pax genes have been shown to play important roles in mammalian development and organogenesis. Pax9, a member of this transcription factor family, is expressed in somites, pharyngeal pouches, mesenchyme involved in craniofacial, tooth, and limb development, as well as other sites during mouse embryogenesis. To analyze its function in vivo, we generated Pax9 deficient mice and show that Pax9 is essential for the development of a variety of organs and skeletal elements. Homozygous Pax9-mutant mice die shortly after birth, most likely as a consequence of a cleft secondary palate. They lack a thymus, parathyroid glands, and ultimobranchial bodies, organs which are derived from the pharyngeal pouches. In all limbs, a supernumerary preaxial digit is formed, but the flexor of the hindlimb toes is missing. Furthermore, craniofacial and visceral skeletogenesis is disturbed, and all teeth are absent. In Pax9-deficient embryos tooth development is arrested at the bud stage. At this stage, Pax9 is required for the mesenchymal expression of Bmp4, Msx1, and Lef1, suggesting a role for Pax9 in the establishment of the inductive capacity of the tooth mesenchyme. In summary, our analysis shows that Pax9 is a key regulator during the development of a wide range of organ primordia. [less ▲]

Pax genes and organogenesis: Pax9 meets tooth development.

in European Journal of Oral Sciences (1998), 106 Suppl 1

Pax genes encode a family of transcription factors that play key roles during embryogenesis. They are required for the development of a variety of organs including the nervous and muscular system ... [more ▼]

Pax genes encode a family of transcription factors that play key roles during embryogenesis. They are required for the development of a variety of organs including the nervous and muscular system, skeleton, eye, ear, kidney, thymus, and pancreas. Whereas the developmental roles of many of the nine known Pax genes have been analyzed in great detail, a functional analysis of Pax9 has just begun. During mouse embryogenesis, Pax9 exhibits a highly specific expression pattern in derivatives of the foregut endoderm, somites, limb mesenchyme, midbrain, and the cephalic neural crest. In the mandibular arch mesenchyme, the expression of Pax9 marks the prospective sites of tooth development prior to any morphological signs of odontogenesis and is maintained in the developing tooth mesenchyme thereafter. To understand the function of Pax9 during mouse embryogenesis, we recently have created a null allele by gene targeting. Preliminary analyses show that Pax9 is essential for the formation of teeth, and we conclude that Pax9 is required for tooth development to proceed beyond the bud stage. Here, we briefly summarize our current knowledge about Pax genes and introduce Pax9 to the growing family of factors which are involved in tooth development. [less ▲]

Pax genes and organogenesis.

in BioEssays (1997), 19(9), 755-65

Pax genes are a family of developmental control genes that encode nuclear transcription factors. They are characterized by the presence of the paired domain, a conserved amino acid motif with DNA-binding ... [more ▼]

Pax genes are a family of developmental control genes that encode nuclear transcription factors. They are characterized by the presence of the paired domain, a conserved amino acid motif with DNA-binding activity. Originally, paired-box-containing genes were detected in Drosophila melanogaster, where they exert multiple functions during embryogenesis. In vertebrates, Pax genes are also involved in embryogenesis. Mutations in four out of nine characterized Pax genes have been associated with either congenital human diseases such as Waardenburg syndrome (PAX3), Aniridia (PAX6), Peter's anomaly (PAX6), renal coloboma syndrome (PAX2) or spontaneous mouse mutants (undulated (Pax1), Splotch (Pax3), Small eye (Pax6), Pax2(1)Neu), which all show defects in development. Recently, analysis of spontaneous and transgenic mouse mutants has revealed that vertebrate pax genes are key regulators during organogenesis of kidney, eye, ear, nose, limb muscles, vertebral column and brain. Like their Drosophila counterparts, vertebrate Pax genes are involved in pattern formation during embryogenesis, possibly by determining the time and place of organ initiation or morphogenesis. For most tissues, however, the nature of the primary developmental action of Pax transcription factors remains to be elucidated. One predominant theme is signal transduction during tissue interactions, which may lead to a position-specific regulation of cell proliferation. [less ▲]

Transgenic technology as a tool

in P. Thorogood (edt.) Embryos, Genes and Birth (1997)

Antagonistic interactions between FGF and BMP signaling pathways: a mechanism for positioning the sites of tooth formation.

in Cell (1997), 90(2), 247-55

Vertebrate organogenesis is initiated at sites that are often morphologically indistinguishable from the surrounding region. Here we have identified Pax9 as a marker for prospective tooth mesenchyme prior ... [more ▼]

Vertebrate organogenesis is initiated at sites that are often morphologically indistinguishable from the surrounding region. Here we have identified Pax9 as a marker for prospective tooth mesenchyme prior to the first morphological manifestation of odontogenesis. We provide evidence that the sites of Pax9 expression in the mandibular arch are positioned by the combined activity of two signals, one (FGF8) that induces Pax9 expression and the other (BMP2 and BMP4) that prevents this induction. Thus it appears that the position of the teeth is determined by a combination of two different types of signaling molecules produced in wide but overlapping domains rather than by a single localized inducer. We suggest that a similar mechanism may be used for specifying the sites of development of other organs. [less ▲]

Von Knick- und Ringelschwänzen - Mäuse als Modellorganismus

in Forschung-Mitteilungen der DFG (1996), (2), 13-14

Rbt (Rabo torcido), a new mouse skeletal mutation involved in anteroposterior patterning of the axial skeleton, maps close to the Ts (tail-short) locus and distal to the Sox9 locus on chromosome 11.

in Mammalian Genome (1996), 7(12), 881-5

Rbt (Rabo torcido) is a new semidominant mouse mutant with a variety of skeletal abnormalities. Heterozygous Rbt mutants display homeotic anteroposterior patterning problems along the axial skeleton that ... [more ▼]

Rbt (Rabo torcido) is a new semidominant mouse mutant with a variety of skeletal abnormalities. Heterozygous Rbt mutants display homeotic anteroposterior patterning problems along the axial skeleton that resemble Polycomb group and trithorax gene mutations. In addition, the Rbt mutant displays strong similarities to the phenotype observed in Ts (Tail-short), indicating also a homeotically transformed phenotype in these mice. We have mapped the Rbt locus to an interval of approximately 6 cM on mouse Chromosome (Chr) 11 between microsatellite markers D11Mit128 and D11Mit103. The Ts locus was mapped within a shorter interval of approximately 3 cM between D11Mit128 and D11Mit203. This indicates that Rbt and Ts may be allelic mutations. Sox9, the human homolog of which is responsible for the skeletal malformation syndrome campomelic dysplasia, was mapped proximal to D11Mit128. It is, therefore, unlikely that Ts and Rbt are mouse models for this human skeletal disorder. [less ▲]

Expression of avian Pax1 and Pax9 is intrinsically regulated in the pharyngeal endoderm, but depends on environmental influences in the paraxial mesoderm.

in Developmental Biology (1996), 178(2), 403-17

Pax1 and Pax9 represent a subfamily of paired-box-containing genes. In vertebrates, Pax1 and Pax9 transcripts have been found specifically in mesodermal tissues and the pharyngeal endoderm. Pax1 ... [more ▼]

Pax1 and Pax9 represent a subfamily of paired-box-containing genes. In vertebrates, Pax1 and Pax9 transcripts have been found specifically in mesodermal tissues and the pharyngeal endoderm. Pax1 expression in the sclerotomes has been shown to be indispensable for proper formation of the axial skeleton, but expression of Pax1 in the endoderm has not been studied in detail. We have cloned the chick homologue of the murine Pax9 gene. Our results show that transcripts of Pax1 and Pax9 are first detectable in the prospective foregut endoderm of headfold-stage avian embryos. Endodermal expression correlates with the highly proliferative zones of the folding foregut and evaginating pharyngeal pouches. In later stages, Pax1 and Pax9 are expressed in overlapping but distinct patterns within the developing sclerotomes and limb buds. From grafting experiments we conclude that activation of pharyngeal Pax1 and Pax9 expression is an intrinsic property of the endoderm, not requiring midline structures or head mesoderm. In contrast, notochord is required to induce Pax1 in competent sclerotomes. Here we show that in vitro there is a cranio-caudal gradient of inductive capacity in the notochord. This coincides with the graded expression of Pax1 and Pax9 along the cranio-caudal axis in 2- to 3-day-old embryos. Furthermore, paraxial head mesoderm shows no competence to express Pax1. Finally, in vitro we find counteracting influences on notochord signaling by lateral tissues (lateral plate, intermediate mesoderm), leading to an inhibition of Sonic hedgehog (Shh) expression in notochord and floor plate, as well as Pax1 and Pax9 expression in sclerotomes. Taken together, our results demonstrate that different mechanisms regulate expression of Pax1 and Pax9 in foregut and sclerotome, but suggest a common function for both genes in the two tissues that is promoting proliferation and preventing fusion of neighboring blastemas. [less ▲]

Analysis of limb patterning in BMP-7-deficient mice.

in Developmental Genetics (1996), 19(1), 43-50

Bone morphogenetic proteins (BMPs) are polypeptide signaling molecules, belonging to the TGF-beta superfamily. They were originally identified by their ability to induce ectopic bone formation, but their ... [more ▼]

Bone morphogenetic proteins (BMPs) are polypeptide signaling molecules, belonging to the TGF-beta superfamily. They were originally identified by their ability to induce ectopic bone formation, but their expression patterns in embryos suggest multiple functions. BMP-7-deficient mice show among other mesodermal and skeletal patterning defects, polydactyly in the hindlimbs [Luo G, Hofmann C, Bronckers ALJJ, Sohocki M, Bradley A, Karsenty G (1995): Genes Dev 9:2808-2820; Dudley AT, Lyons KM, Robertson EJ (1995): Genes Dev 9:2795-2807]. Here we report a more detailed analysis of the limb phenotype in BMP-7-deficient mice using in situ hybridization to monitor expression of molecules implicated in patterning processes of the developing vertebrate limb. In previous studies we showed that Sonic hedgehog (Shh) was expressed normally, but Hoxd-13 expression in limb mesenchyme was lower in BMP-7 mutant limbs. Here we show that Hoxd-11 expression domains are also contracted and decreased in intensity in mutant limbs, suggesting that 5' genes of the Hoxd cluster are coordinately downregulated, while another Bmp, Bmp-2, which can be activated by Shh, is similarly expressed. The mutant limb buds are broader than normal buds, and fibroblast growth factor Fgf-8 is expressed throughout the extended ridge. However, expression of the homeobox gene Msx-1, which has been shown to be involved in epithelial-mesenchymal interactions during limb development, was decreased in the mesenchyme of BMP-7 mutant limbs. Taken together, our data suggest that BMP-7 is involved in regulating proliferation and/or epithelial-mesenchymal interactions in the developing limb. [less ▲]