Worm Breeder's Gazette 14(4): 55 (October 1, 1996)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
|1||Inserm U119, 27 Bld Lei Roure, 13009 Marseille, France|
|2||Simon Fraser Univ., Burnaby, British Columbia, Canada|
|3||CRBM, CNRS, Montpellier, France|
In the January issue of the WBG (14.2, page 85), we reported on the existence of an FGF on chromosome III (cosmid C05D11.4) in C. elegans which shares 30% identity with mammalian homologs and on our wish to fully characterize it at the molecular and functional levels. Transgenic animals containing a piece of genomic DNA including the gene (a 7.8kb piece with 4.3kb of 5'DNA and 1kb of 3' or a 4.6kb piece with 2kb of 5') were used to rescue candidate mutants, such as dig-1 or four lethals from the Baillie collection known to be rescued by the entire C05D11 cosmid. One mutant, let-756, was rescued in at least ten different FGF transgenic strains, indicating that let-756(FGF) is an essential gene in the worm. Sequence analysis of one allele of let-756 revealed the presence of a stop codon at the beginning of the last exon, indicating that the 3' end of the FGF gene, incorrectly spliced in genefinder, is crucial for functional activity. let-756(FGF) mutants arrest at the L2 stage. At first glance, this could be due to feeding defects: wouldn't it be ironical if FGF was a trophic factor in the worm? In line with the stage of arrest of let-756(FGF), developmental Northern analysis revealed a peak of expression at the L2 larval stage. We attempted to determine the cellular distribution by using GFP fusions (thanks to Andy Fire). Preliminary results were obtained with one strain and a few transients containing a promoter construct. Animals from that strain exhibited GFP expression as early as the comma stage embryo. GFP expression appeared restricted to a set of mesodermal cells. At the larval (especially L2) and adult stages, expression was very strong in the pharynx, especially in some muscle cells and pharyngeal gland cells, and weaker in the head and body muscles and a few yet unidentified cells. We plan to define the focus of the lethality, and started a mosaic analysis of let-756(FGF) using a new allele induced on a ncl-1 chromosome and transformation with new constructs encoding GFP-tagged FGFs. We are also in the process of analysing the interactions of both let-756(FGF) and the transgenic strains overexpressing FGF with other genes possibly involved in the FGF signaling pathway, such as egl-15 (FGF receptor gene), egl-17 (another FGF-like, see the abstract by Burdine and Stern, WBG 14.3 p.28), clr-1 or unc-52. We also plan a direct suppressor screen, molecular characterization of a second allele and the generation of possibly leaky mutations following in vitro mutagenesis, that would allow us to describe the effects of FGF at the L3, L4 or adult stages.