Lineage-specific regulators couple cell lineage asymmetry to the transcription of the Caenorhabditis elegans POU gene unc-86 during neurogenesis

The POU homeo box gene unc-86 specifies neuroblast and neural identities in the developing Caenorhabditis elegans nervous system. After an asymmetric neuroblast division, unc-86 is expressed in one of two daughter cells in 27 lineage classes that are not obviously related by function or position. We show here that unc-86 transcriptional regulatory regions detect cell lineage asymmetry to activate unc-86 expression in one of two neuroblast daughter cells. Distinct regulatory regions activate unc-86 expression in particular sets of sublineages. Therefore the unc-86 regulatory region integrates distinct cell lineage asymmetry cues to activate unc-86 expression in the many classes of neuroblast cell lineages. In agreement with such lineage-specific regulation of unc-86 asymmetric activation, mutations in lin-11 (LIM homeo box), ham-1, and lin-17 affect the asymmetry of unc-86 expression in particular cell lineages, and mutations in lin-32 (achaete/scute family), vab-3 (Pax-G homolog) and egl-5 (Abd-B homolog) affect the establishment of unc-86 expression in other cell lineages. Homologs of unc-86 and many of these unc-86 regulators have been implicated in control of neurogenesis in vertebrates and invertebrates. These data suggest that unc-86 acts in a phylogenetically conserved pathway that couples neuroblast cell lineage asymmetry to the generation of diverse neural types.