Fig. 7. Expression pattern of gene products that are upstream and downstream of BMPR-IA signaling during early hindlimb development. (A-C) Expression of BMPR-IA ligands, Bmp4 and Bmp7, and their relationship to the domain of Msx2 expression in normal 9.75 dpc hindlimbs, which is just before limb bud formation. (A) High levels of Bmp4 expression are detected in tissues of the ventral part of the embryo, including the lateral mesoderm from which the limb mesenchyme develops. (B) Bmp7 expression is highest in the most ventral region of the embryo in the outermost cell layers. Bmp7 expression demonstrates a diminishing gradient of expression from ventral to dorsal, and its expression domain ends at the junction of lateral and intermediate mesoderm (indicated by an arrow in C). (C) The Msx2 expression pattern is similar to that of Bmp7, except the dorsal border of expression (arrowhead) does not extend as far dorsomedially (difference between arrow and arrowhead). (D-G) Expression of BMPR-IA ligands, Bmp4 (D) and Bmp7 (F), and their relationship to the domain of Fgf8 (E) and Msx2 (G) expression in normal 10.0 dpc hindlimb buds. (D,F) The expression of both Bmp7 and Bmp4 have been significantly downregulated when compared with their 9.75 dpc expression domain. Furthermore, the Bmp4 expression domain has been restricted to the pre-AER region as indicated by the expression of pre-AER marker, Fgf8, in a serial section (E).