Fig. 1. The GMC-1 in sli and sim mutants symmetrically divide to generate two RP2s. Embryos are stained for Eve. Anterior is up, vertical lines indicate the midline. RP2, larger arrow; sib, smaller arrow; GMC-1, arrowhead. Scale bars, 15 µm. (A-C) Wild-type embryos. (D-F) sli mutant embryos, the symmetric division of GMC-1 to generate two RP2s is shown. (G-I) Symmetric division of GMC-1 in sim mutant embryos. The midline in sim mutants become fused by approx. 8.5 hours of development. Note that RP2, aCC, pCC and other neurons are somewhat misplaced within a hemisegment in the CNS of 13-hour or older mutant embryos, however, in younger embryos (approx. 10 hours or less) these cells are not misplaced and do not cross the midline or segmental boundary.