Fig. 5. Cell lineage defects in hlh-14 mutants. (A) In wild-type embryos, the ABpl/rappp cell divides to generate the PVQ/HSN/PHB neuroblast and the hyp7/T blast cell. The PVQ/HSN/PHB neuroblast subsequently undergoes a series of divisions, ultimately generating the PVQ, HSN and PHB neurons. The hyp7/T blast cell divides only once during embryogenesis, generating a hyp7 cell and the T blast cell, a seam cell that divides postembryonically. (B) In hlh-14 mutants, the ABpl/rappp cell divides at the appropriate time. However, the presumptive PVQ/HSN/PHB neuroblast does not undergo a series of divisions to generate the PVQ, HSN and PHB neurons. Instead, it divides just once, like its sister cell, the hyp7/T blast cell. In hlh-14 mutants, it is possible that the PVQ/HSN/PHB neuroblast is transformed into a hyp7/T blast-like cell, a model shown in this lineage. (C) A wild-type L1 larva containing a C50B6.8::gfp reporter construct, which expresses GFP in the ten hypodermal seam cells, H0-H2, V1-V6 and T (Mounsey et al., 2002). (D) An hlh-14 mutant L1 larva expressing the C50B6.8::gfp reporter. In addition to expressing GFP in the ten hypodermal seam cells, this larva expresses GFP in an extra cell in the tail, presumably a T-like cell (arrow). In 38% of the of hlh-14 mutants, we observed this ectopic GFP expression (n=60 sides scored). We never observed this extra cell in wild-type animals bearing C50B6.8::gfp.