fgfr-1 is required for embryonic growth and mesodermal patterning during mouse gastrulation.

Experiments in amphibians have implicated fibroblast growth factors (FGFs) in the generation and patterning of mesoderm during embryogenesis. We have mutated the gene for fibroblast growth factor receptor 1 (fgfr-1) in the mouse to genetically dissect the role of FGF signaling during development. In the absence of fgfr-1 signaling, embryos displayed early growth defects; however, they remained capable of gastrulating and generating mesoderm. The nascent mesoderm of fgfr-1 homozygous mutant embryos differentiated into diverse mesodermal subtypes, but mesodermal patterning was aberrant. Somites were never generated and axial mesoderm was greatly expanded at the expense of paraxial mesoderm. These results suggest that FGFR-1 transduces signals that specify mesodermal cell fates and regional patterning of the mesoderm during gastrulation.