Forty-two genes encoding nuclear hormone receptors (NHR) have been identified in C.elegans but, for the majority, knowledge of their biological functions is scant. For most of these NHRs, we have only gene sequences that identify them as members of this superfamily of transcription factors. Two genes,
nhr-2 and
nhr-20, have been shown previously to be expressed embryonically and in all stages respectively. We are surveying the temporal expression profiles for additional genes in order to obtain clues to their functions. Of specific interest for further study will be genes exhibiting temporally restricted expression patterns that may indicate regulation of individual developmental events. We plan also to focus on NHRs that are conserved in parasitic nematodes, as nematode-specific hormone receptors could provide effective targets for novel antihelminthic drugs. Profiles for
nhr-4,
nhr-6, and
nhr-18 were obtained using reverse transcriptase-polymerase chain reaction (RT-PCR). Northern blot analysis is underway to confirm the RT-PCR results. Of particular interest, our RT-PCR data for
nhr-4 indicates a peak of expression during the late larval stages, a time when many crucial events occur in preparation for the larva-to-adult molt. In concert, we are also conducting mutant screens using Tc1 transposon and chemical mutageneses. These efforts focus currently on
nhr-4, due to its limited temporal expression, and
nhr-6, for which a homolog has been identified in the filarial parasite dog heartworm (C. Maina, pers. comm.). Future work will include examination of the spatial expression patterns of these genes.