Fig. 5. Regulation of the interdigital expression of MSX2 in chick and duck limbs by FGFs and BMPs. (A) Control chick at stage 30. (B) Upregulation of MSX2 24 hours after the implantation of a FGF-bead (*). (C) Control duck at day 9.5 of incubation. Note that MSX2 expression in the duck is restricted to the most distal region of the interdigital webs. (D) Upregulation of MSX2 in the duck 14 hours after interdigital implantation of a FGF-bead (*). (E) Down-regulation of MSX2 in the chick 30 hours after implantation of a bead incubated in SU5402. (F) Down-regulation of MSX2 in the chick 14 hours after implantation of a Noggin-bead (*). (G) Expression of MSX2 in the chick 14 hours after implantation of a FGF-bead (white asterisk) and a Noggin-bead (black asterisk). Note the up-regulation by FGFs is inhibited in the zone of influence of the Noggin-bead. (H) Expression of MSX2 in the chick 8 hours after implantation of a BMP-bead (white asterisk) 24 hours after implantation of a SU5402-bead (black asterisk). Note that in these conditions BMPs fail to upregulate MSX2.
