Fig. 4. EGL-15 splice variants mediate different responses. (A) The wild-type egl-15 genomic rescuing fragment [EGL-15(5A⁺B⁺)] rescues defects associated with the egl-15 (null) allele, including defects in both the essential role and SM chemoattraction. The essential role is also restored by expression of EGL-15(5A^-B⁺); however, these lines exhibit aberrant SM migration. The EGL-15(5A⁺B^-) transgene failed to restore the essential function in this null mutant, but rescued the chemoattraction defect of the egl-15(Egl) mutant, egl-15(n1458), based on final SM positions. (B) SM distributions for two transgenic lines for each of the constructs shown in A. As these transgenic animals bear extrachromosomal arrays that are mitotically lost at a significant frequency, some of these SMs may have lost the transgene. Complete loss of EGL-15 in the SMs results in centrally dispersed SMs (C.S.B., S.J.G. and M.J.S., unpublished), probably accounting for the outlying SMs.