Fig. 2. egl-15(5A) mutations result in posteriorly displaced SMs. (A) Distributions of SMs in egl-15(Egl) mutants are represented as box-and-whisker plots (see Materials and Methods). Asterisks indicate dorsally positioned SMs. All four egl-15(Egl) alleles display a similar distribution of posteriorly displaced SMs. The distribution of SMs in the egl-15(Soc) mutant, n1783, is shown for comparison. (B) An extracellular alternate splicing event gives rise to two distinct receptor isoforms. Three out of four egl-15(Egl) alleles contain point mutations that specifically affect the 5A exon. (C) Alternate splicing of exon 5 encoding the EGL-15-specific insert results in two distinct isoforms that specifically differ in this domain. A simple, modular hypothesis for normal signaling specificity is suggested by the phenotypic similarities of mutations affecting the ligands and receptor isoforms. Misexpression of the ligands can allow them to stimulate the heterologous function via the heterologous receptor isoform.