Probable ligand for lin-12/Notch and glp-1/Notch receptors and involved in the mediation of Notch signaling (PubMed:14960273, PubMed:7568229, PubMed:8575327). Involved in the lin-12/Notch pathway signaling of cell fate in vulval precursor cells (VPCs), acting redundantly with dsl-1 and lag-2 (PubMed:14960273, PubMed:7568229). Contributes to the establishment of the dorsal-ventral axis in early embryos (PubMed:8156602, PubMed:18036582). Involved in the specification of the blastomere cell ABp fate, probably acting as a signal from the P2 blastomere to the glp-1/Notch receptor on ABp and ABa (PubMed:8156602, PubMed:7925031, PubMed:8674418). Probably acts as a signal, from the secondary vulval epithelial cells and the vulval muscle type 1 (vm1) cells, to activate the lin-12/Notch pathway in type 2 vulval muscle (vm2) cells, contributing to formation of the postsynaptic muscle plasma membrane extensions, known as muscle arms (PubMed:23539368). Required for oocyte growth control, acting redundantly with lag-2, perhaps signaling via the glp-1/Notch pathway (PubMed:19502484). Plays a somatic role in ovulation during adulthood, perhaps via lin-12/Notch signaling (PubMed:29371032). Involved in establishing left-right asymmetry during intestinal organogenesis (PubMed:10903169). Nuclear localization of transcripts at 36-cell stage in embryos. First expressed in late 2-cell stage embryos at the anterior periphery of the P1 blastomere, where P1 contacts the AB blastomere (at protein level) (PubMed:8674418). Maternally expressed in newly fertilised eggs, and present in all blastomeres between 1-cell and 8-cell stages (PubMed:8674418). After the 8-cell stage, rapidly disappears from all somatic blastomeres, and then expressed in P3 blastomere at the 12 cell stage (PubMed:8674418). In 36-cell stage and later embryos, can be detected in one to five unidentified cells (PubMed:8674418). Expressed in the P6.p vulval precursor cell (VPC) during larval L3 stage, coinciding with extension and reflexing of the gonad (PubMed:14960273). Expressed in cells immediately adjacent to ventral mesodermal lineage (M lineage) cells, but not next to dorsal M lineage cells, beginning at the 4-M stage (PubMed:18036582). Expressed in the distal tip cell (DTC) starting in the larval L3 stage (PubMed:19502484). Expressed in the secondary vulval epithelial cells and the non-target vm1 cells at the larval L4 stage (PubMed:23539368). RNAi-mediated knockdown in the L1 larval stage causes an endomitotic oocyte phenotype; effect not seen if knockdown is targeted to germline, rather than somatic cells (PubMed:29371032). RNAi-mediated knockdown alters ovulation (PubMed:29371032). Spermatheca calcium flux is altered by RNAi-mediated knockdown (PubMed:29371032). RNAi-mediated knockdown, on a lag-2 mutant background, induces the presence of 1-2 extra mesodermal lineage (M lineage)-derived coelomocytes (PubMed:18036582). RNAi-mediated knockdown on a lin-15 mutant background, causes adjacent vulval precursor cells (VPCs) to adopt altered cell fate (PubMed:14960273). On a lag-2 mutant background, RNAi-mediated knockdown causes germ cells to display nuclear morphology consistent with meiotic prophase or gametogenesis in adult hermaphrodites (PubMed:19502484). RNAi-mediated knockdown, when combined with RNAi-mediated knockdown of lag-2, on a dsl-1 mutant background, causes adjacent vulval precursor cells (VPCs) to adopt altered cell fate; phenotype exacerbated on double mutant lin-15;dsl-1 background (PubMed:14960273).