Worm Breeder's Gazette 14(3): 28 (June 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||Department of Cell Biology, Yale University School of Medicine, New Haven, CT. 06520|
|2||Department of Genetics, Yale University School of Medicine, New Haven, CT. 06520|
The sex myoblasts (SMs) undergo an anterior migration in hermaphrodite larvae to final positions that flank the precise center of the developing gonad. There they divide to give rise to the sex muscles necessary for egg laying. Mutations in egl-15 or egl-17 interfere with proper SM migration and confer posteriorly displaced SMs and an egg laying defective phenotype (Egl). egl-15 has been cloned previously and shown to encode a fibroblast growth factor receptor (FGF-R) homologue (1). We have characterized and cloned egl-17 in order to understand its role in SM migration. The genomic region of egl-17 was identified and subsequently narrowed to 7kb based on germline transformation rescue of the Egl defect of egl-17 mutants. We were unable to detect a transcript by Northern analysis or identify a corresponding cDNA in a number of cDNA libraries suggesting that the egl-17 mRNA is a rare transcript. In the absence of a cDNA we used transformation rescue to identify potential coding regions in the egl-17 genomic fragment. Four-basepair insertions were introduced at various sites in the rescuing fragment. Insertions in the egl-17 open reading frame would cause a frameshift mutation that might abrogate rescuing activity. Primers to two regions shown to be important for egl-17 rescue activity were used to obtain the cDNA by RT-PCR. The egl-17 cDNA has the potential to encode a 216 amino acid product with significant homology to the fibroblast growth factor (FGF) family of proteins and represents one of the first functional invertebrate FGFs known. Genetic and molecular evidence demonstrate that the SM migration defect seen in egl-17 mutant animals represents complete loss of egl-17 function. All ten known mutant alleles of egl-17 are viable as homozygotes and have similar distributions of displaced SMs. Analysis of the molecular lesions associated with egl-17 in the ten alleles has shown that all have the potential to eliminate egl-17 function: two alleles are deletions that remove all or part of the exon encoding the initiating methionine; six alleles are nonsense mutations; one allele alters an absolutely conserved residue in the splice donor site of an exon; and one allele is a missense mutation that alters the codon encoding the initiating methionine. We propose that EGL-17 may act as a ligand for EGL-15 (FGF-R). Besides affecting SM migration, mutations in egl-15 can result in larval arrest, scrawny body morphology, and the ability to suppress the effects of mutations in clr-1 (1). Since elimination of egl-17 function only results in SM migration defects, EGL-17 is likely to be an SM migration-specific ligand and additional ligands presumably play a role in the other function of EGL-15. We are currently constructing and analyzing expression constructs and conducting mosaic analysis to determine where egl-17 is expressed and where egl-17 expression is necessary for proper SM migration. 1. DeVore, D.L., Horvitz, H.R. and Stern, M.J. Cell 83, 611-620 (1995)