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 identiti es in the developing Caenorhabditis elegans nervous system. After an a symmetric neuroblast division, unc-86 is expressed in one of two daugh ter cells in 27 lineage classes that are not obviously related by func tion 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 act ivate unc-86 expression in particular sets of sublineages. Therefore t he 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 u nc-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 u nc-86 expression in other cell lineages. Homologs of unc-86 and many o f these unc-86 regulators have been implicated in control of neurogene sis in vertebrates and invertebrates. These data suggest that unc-86 a cts in a phylogenetically conserved pathway that couples neuroblast ce ll lineage asymmetry to the generation of diverse neural types.