Characterization of the receptors for secretory signaling proteins involved in inductive interaction during embryogenesis

点击翻译按钮获取中文摘要

We have characterized the receptors for BMP,Sonic hedgehog (Shh), and Wnt family involved in organogenesis during vertebrate development. We identified three BMP receptors, called BRK-1 (ALK-3), BRK-2 (ALK-6), and BRK-3 (BMPRII), from the chick embryo. BRK-2 abd BRK-3 constitute high affinity receptor system for BMP-4 homodimer, and are expressed in the precartilagenous mesenchyme of the limb bud, whereas BRK-1 is poorly expressed in the limb bud. Kinase domain-deficient forms of BRK-2 and BRK-3 inhibited chondrogenic differentiation of limb mesenchymal cells, eventually leading to defects in the digital bones, when the defective receptors were co-expressed in the limb bud with retrovirus vector.Shh could induce expression of the BMP-2 gene and also the BRK-2 receptor gene, when Shh was applied to the anterior limb bud by using either retrovirus or recombinant protein. The Patched gene encoding the Shh receptor was also upregulated in the limb mesenchyme by Shh shortly after applicatio … More n. The time course of the Shh-induced expression pattern of the HoxD genes and other marker genes suggests BMP signaling is implicated in determination of positional identity in the limb bud at early stages.Several Wnt family members are expressed in the limb bud with speciffic pattern, and Wnt-5a reveals distal expression domain at stages 19-26. Over-expressing the Wnt-5a gene resulted in the truncation of zeugopod, but did not affect HoxD and HoxA expression. We isolated several Frizzled (Fz) cDNAs encoding the transmembrane receptors for Wnt family, and their expression patterns indicate involvement of Wnt signaling in specifying regional identity in the limb bud. The Fz-4 is expressed in the apical ectodermal ridge and distal mesenchyme of the limb bud, whereas the novel Fz-10 gene is expressed in the posterior-distal region of the dorsal mesenchyme. Fz-6 is expressed in the somite, and Fz-3 and Fz-10 are expressed in the neural tube, suggesting their roles in Wnt-3a and Wnt-7a signaling. Less