Met signaling mutants as tools for developmental studies.

The Met receptor is widely expressed in embryonic and adult epithelial tissues; its ligand (hepatocyte growth factor/scatter factor, HGF/SF) is expressed in the mesenchymal component of various organs. The generation of hgf and met null mice has revealed an essential role for this ligand-receptor pair in the development of the placenta, liver, and limb muscles. However the early lethality of the null mutants has precluded analysis of Met function in late development. To extend the possible observation period, we generated mutant metalleles of different severity. This was done by impairing the ability of the receptor to transduce the HGF/SF signal, via mutation of consensus sequences in the multifunctional docking site present in the C-terminal tail of the receptor. Mice expressing a Met mutant still active as a kinase, but unable to recruit its effectors, died in mid-gestation with the same phenotype as the metknockout, proving the importance of phosphotyrosine-SH2 interactions in vivo. Mice expressing a Met receptor with partial loss of signaling function survived until birth and revealed novel aspects of HGF/SF-Met function during muscle development.