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.

FGF is essential to the worm.

Regine Roubin1, Marie-Claude Voinier1, Daniel Birnbaum1, Greg Vatcher2, David Baillie2, Danielle Thierry-Mieg3

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.