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.

EGL-17 is an FGF-like protein required specifically for sex myoblast migration.

Rebecca D. Burdine1, Michael J. Stern2

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)