MURINE FGF-4 GENE-EXPRESSION IS SPATIALLY RESTRICTED WITHIN EMBRYONIC SKELETAL-MUSCLE AND OTHER TISSUES

Fibroblast growth factors are believed to play many distinct roles in vertebrate development, owing to their ability to stimulate cell growth, prevent cell death, determine cell fate, and inhibit terminal differentiation in a variety of in vitro culture systems. We have used in situ hybridization to localize fibroblast growth factor-4 (FGF-4, also termed HST and K-FGF) gene expression in 7.5 to 16.5 day gestation mouse embryos. Seven discrete sites of gene expression were detected: (1) primitive streak (E7.5-8.5); (2) paraxial presomitic mesoderm in the trunk (E7.5-11.5); (3) primitive neuroectoderm (E8.0-8.5); (4) pharyngeal pouch endoderm (E8.5-9.5); (5) branchial arch ectoderm (E8.5-9.5); (6) limb apical ectoderm (E10.5-12.5), and (7) skeletal myoblast groups (E9.5-13.5). FGF-4 gene expression is spatially restricted within many of these sites. The profile of FGF-4 gene expression among skeletal muscle groups is overlapping, but distinct, from that of FGF-5, thereby revealing myoblast heterogeneity at the molecular level and suggesting distinct roles for multiple FGFs in muscle development.