LET-756/FGF is Implicated in the Control of C. elegans Body Size

LET-756 is one of the two fibroblast growth factors (FGF) of Caenorhabditis elegans. We have previously shown that worms homozygote for the let-756 null allele (s2887) die at larval stage and that homozygotes for the partial loss-of-function allele (s2613) are viable but shorter than wild-type animals. We now show that expression of let-756 in any region of the s2887 worm can rescue the lethal phenotype but with variations in body size depending on the site of expression, harmonious growth being achieved by let-756 expression in body wall muscles. Local action of let-756 was also observed in mosaic animals homozygotes for the s2613 allele. Our results support a paracrine activity for LET-756 exerting its effect locally on body size whether by acting as an actual growth factor or by acting on EGL-15/FGFR expressing hypodermal cells thereby regulating fluid balance.