The family of Caenorhabditis elegans tyrosine kinase receptors: similarities and differences with mammalian receptors.

Transmembrane receptors with tyrosine kinase activity (RTK) constitute a superfamily of proteins present in all metazoans that is associated with the control and regulation of cellular processes. They have been the focus of numerous studies and are a good subject for comparative analyses of multigene families in different species aimed at understanding metazoan evolution. The sequence of the genome of the nematode worm Caenorhabditis elegans is available. This offers a good opportunity to study the superfamily of nematode RTKs in its entirety and to compare it with its mammalian counterpart. We show that the C. elegans RTKs constitute various groups with different phylogenetic relationships with mammalian RTKs. A group of four RTKs show structural similarity with the three mammalian receptors for the vascular endothelial growth factors. Another group comprises RTKs with a short extracellular region, a feature not known in mammals; the genes encoding these RTKs are clustered on chromosome II with other gene families, including genes encoding chitinase-like proteins. Most of the C. elegans RTKs have no direct orthologous relationship with any mammalian RTK, providing an illustration of the importance of the separate evolution of the different phyla.