The nuclear receptors constitute a class of conserved transcription factors that function in regulating animal development. The NR2E subclass nuclear receptor fax-1 of C. elegans is expressed in hermaphrodite somatic gonad cells and is required for normal brood size, in addition to roles already described in neuron differentiation.
The C. elegans fax-1 gene is the ortholog of PNR in vertebrates. We have found that fax-1 is expressed in the migrating distal-tip cells (DTCs) of the hermaphrodite gonad from L2 through L4 stages. Loss of fax-1 results in a low-penetrance DTC migration defect and a high penetrance brood size defect. The reduction in offspring appears to result from a defect in sperm production rather than oogenesis.
The vab-3 transcription factor plays a key role in regulating the migrations of the DTCs. In vab-3 mutants, the DTCs continue to migrate into adulthood and also fail to turn off fax-1, suggesting that expression of fax-1 is a property of a migrating DTC. A mutation in fax-1 does not suppress the vab-3 migration defect, indicating that fax-1 is not an essential downstream mediator of vab-3 function. We propose that fax-1 function in DTC migration is a robustness phenomenon, in contrast to the more demanding requirement for hermaphrodite spermatogenesis.
Supported by NIGMS..