Expression of genes encoding bone morphogenetic proteins and sonic hedgehog in talpid (ta³) limb buds: Their relationships in the signalling cascade involved in limb patterning

Abstract

The chicken mutant talpid3 (tu3) has polydactylous limbs with up to 7-8 morphologically similar digits. This lack of antero-posterior polarity in digit pattern is correlated with symmetrical expression of genes of the HoxD complex. We determined the distribution of polarizing activity in limb buds of the chick mutant tu3 by assessing the ability of mesenchyme from various positions along the antero-posterior axis to induce digit duplications when grafted anteriorly into a normal limb. Cells with highest polarizing activity were found at the posterior margin of the wing as in the polarizing region of normal limb buds. However, in contrast to normal limb buds, tu3 anterior mesenchyme also had low polarizing activity. Application of retinoic acid or a polarizing region graft to the anterior of tu3 limb buds changed digit morphology but did not induce digit duplications or digits with any characteristic a-p pattern. To determine which genes are associated with polarizing activity and which are associated with patterning of the digits, we examined expression of the genes Sonic hedgehog (shh), Bmp-2, and Bmp-7, whose expression is normally confined to the posterior margin of the early wing bud and is associated with the polarizing region. In addition, we determined the distribution of Fgf-4 transcripts which in normal limb buds are restricted to the posterior part of the apical ectoderma1 ridge. In tu3 limb buds, shh expression is restricted to the posterior limb mesenchyme, which has high polarizing activity, but is not expressed in regions which have low polarizing activity. In contrast, Bmp-2 and Bmp-7 are expressed uniformly along the a-p axis. Fgf4 transcripts are present throughout the apical ectodermal ridge in tu3 limb buds. In the tu3 mutant, there is both an abnormal distribution of signalling activity and response to polarizing signals. In addition, the dissociation between the expression of shh and Bmps suggests distinct roles for the encoded molecules in signalling and response in a-p patterning of limb buds. o 1995 Wiley-Liss, Inc.

Generation of mice with functional inactivation oftalpid3, a gene first identified in chicken

“…Formation of digit condensations and intervening interdigital spaces is delayed and irregular in talpid3 CKO mouse limbs, whereas in talpid 3 chicken mutant limbs no interdigital spaces expressing Raldh2 are seen at a stage when this process is complete in wild type, correlating with extensive digital fusion. Interestingly, we showed sometime ago that implanting a bead soaked in retinoic acid or grafting a polarising region to wing buds of talpid 3 chicken mutant embryos could, to some extent, rescue syndactyly and result in digit separation (Francis-West et al, 1995).…”

Pitx2promotes development of splanchnic mesoderm-derived branchiomeric muscle

“…The myogenin, MyoD, Tbx1 and MyoR probes have been previously described (Kelly et al, 2004). In situ hybridization to whole chick embryos was carried out as described by Francis-West et al (Francis-West et al, 1995).…”

Wnt signalling regulates myogenic differentiation in the developing avian wing

“…In situ hybridization to whole embryos was carried out as described by Francis-West et al (Francis-West et al, 1995). cDNA and ribroprobes were made as described previously: MyoD (Lin et al, 1989), cWnt5a (Kawakami et al, 1999) and cWnt11 (Tanda et al, 1995).…”