[
International C. elegans Meeting,
1999]
The availability of the complete C. elegans genomic sequence has allowed the identification of a family with new putative tyrosine kinase receptor (RTK) genes (see Popovici et al. in the abstract book) and our aim is to describe functionally the four members which compose this family. The main structural feature of this family, which includes F59F3.1, F59F3.5, T17A3.1 and T17A3.8, is the presence of seven immunoglobulin-like domains in the putative extracellular region of each of these molecules. This conservation of domain architecture resembles the mammalian VEGFRs. F59F3.1 and F59F3.5 are situated on chromosome X and although in tandem do not appear to belong to the same operon. T17A3.1 and 8 are in an opposite orientation on chromosome III and separated by what appears to be a pseudogene in which only part of the immunoglobulin-like domains containing extracellular region persists. Only F59F3.1 has the corresponding cDNAs in the Y. Kohara cDNA library collection. We examined the RNA expression of these RTK genes by RT-PCR. We detected the presence of F59F3.5 and T17A3.8 transcripts in embryo and L1 enriched populations, whereas the F59F3.1 and T17A3.1 transcripts were evidenced in the mixed stage populations. Transcriptional silencing of the F59F3.1 gene by RNAi led to a drastic phenotype combining early larval arrest with clear and scrawny larvae. Thus at least some of these genes appear to be important for the worm development. The existence of VEGFR like in the worm is intringuing and we hope getting and discussing more data during the poster session.
[
International C. elegans Meeting,
1999]
The availability of the complete genomic sequence of the C. elegans allowed the identification of new putative RTK genes . We describe here the genomic organization of two gene families that encode putative RTKs. One family encodes two already characterized proteins, KIN-15 and KIN-16, and 9 new proteins. The other nine proteins (encoded by the cosmids C08H9, M01B2, R09D1, T01G5, ZK938 and W04G5) have not yet been characterized. The putative extracellular region of proteins of this family is very short. A second family (F59F3.1, F59F3.5, T17A3.1 and T17A3.8) has a large extracellular region containing Ig domains (Popovici et al. , abstract book). It has not been described as functional in C. elegans . Analysis of the phylogenic tree built on the alignment of the tyrosine kinase shows that the two novel RTK families constitute a monophyletic group that does not branch clearly with one of mammalian RTK families. In addition, it seems that the two RTK families described here have evolved from a common ancestor containing a large extracellular region. The loss of exons encoding the majority of the extracellular region followed by cis or trans duplications may be the mechanism of apparition of the family with short extracellular region. RTKs with short extracellular region, in association with chitinase-like genes , are mostly found on chromosome II in two clusters. Among the 33 chitinase and chitinase-like genes, 24 are located in the two clusters. These clusters are separated by a 0.5 Mb region containing 2.5 kb of repetitive sequences that may enhance the unequal crossing-over and thus the high number of RTK copies and chitinase genes. The phylogenic analysis of the chitinases showed that all those located on chromosome II branched together and distinctly from the chitinases of genes located on the other chromosomes and from chitinases from other species. In this branch, two families are again recognized corresponding to the two clusters of RTKs-chitinases identified on the chromosome II. The mechanisms and driving forces conducting to an independent and specific evolution of these various families of genes in C. elegans will be discussed.