Transcriptional activator that induces gene expression by binding to the NGFI-B response element (NBRE) 5'-AAAGGTCA-3' (PubMed:20506374). Required for proper morphogenesis of the spermatheca and the spermatheca-uterine valve formation (PubMed:18096150, PubMed:25529479). Promotes cell proliferation and differentiation of the spermatheca precursor cells during spermatheca development in larval stage L4 (PubMed:18096150, PubMed:25529479). Might play a role in promoting G1/S phase progression in the spermatheca precursor cell lineage (PubMed:25529479). Also required for the differentiation of the spermatheca-uterine junction core (sujc) cells which are generating the spermatheca-uterine valve (PubMed:18096150). In hermaphrodites, expressed in the developing spermatheca and dorsal uterus (PubMed:18096150, PubMed:20506374). Expression includes the 8 cells of the dorsal somatic gonad primordium and the sujc cells that form the core of the spermatheca-uterine valve (PubMed:18096150). Expressed in the precursor cells of the spermatheca-sheath lineages (SS cells) and in the precursors and descendents of the dorsal-uterine lineage (DU cells) (PubMed:20506374). In both hermaphroditic and male animals, expressed in a pair of head chemosensory neurons (PubMed:18096150). Most abundant in larval stage L3 (PubMed:7816808). Expressed in larval stages L3 and L4 (PubMed:18096150, PubMed:20506374). Weakly expressed in adult animals (PubMed:18096150). The NR LBD domain and the nuclear receptor DNA binding domain are sufficient for binding to the NGFI-B response element (NBRE) 5'-AAAGGTCA-3'. Reduced brood size, abnormal egg morphology and arrested egg development. Defects in ovulation with fragmentation of the proximal oocyte and endomitosis. Misplacement of ovulated oocytes into the gonad arms due to a lack of spermatheca-uterine valve formation. Degeneration of gonad tissue. Decreased spermatheca organ size due to decreased spermatheca cell number. Disorganized actin microfilaments in the spermatheca, lack of distal constriction and defects in spermathecal cell differentiation. Misexpression of let-502 in all cells of the spermatheca instead of restricted expression to the distal and proximal regions of the spermatheca. Abnormal differentiation and morphology of the sujc cells that form the core of the spermatheca-uterine valve (PubMed:18096150). Lack of cell divisions of the proximal spermatheca precursor daughter cells due to a failure of progressing to S phase during larval stage L4 (PubMed:25529479). In a fzr-1(ku298) mutant background, increase in spermatheca nuclei number as compared to the nhr-6 single mutant (PubMed:25529479). In a fog-2(q71) mutant background, a large mass of fragmented oocytes in the spermatheca and uterus (PubMed:18096150). RNAi-mediated knockdown leads to reduced brood size and abnormal egg morphology (PubMed:20506374). In a vab-1(e2), vab-1(e699), vab-2(ju1) or vab-2(e96) mutant background, enhanced reduction in brood size (PubMed:25529479). In a vab-2(ju1) mutant background, reduced spermatheca cell number and abnormal spermatheca morphology (PubMed:25529479). In a RNAi-sensitive rrf-3(pk1426) mutant background, defects in spermatheca morphology, including decreased organ size, decreased spermatheca cell number and misplaced spermatheca nuclei. In a RNAi-sensitive eri-1(mg366) mutant background, reduced brood size, abnormal egg morphology and arrested eggs (PubMed:18096150). Belongs to the nuclear hormone receptor family. NR4 subfamily.