Together with tsp-14, regulates cell fate specification in the postembryonic mesodermal M lineage, body size and male development, probably by positively modulating BMP-like Sma/Mab signaling (PubMed:25978409, PubMed:28068334). May regulate BMP-like Sma/Mab signaling by mediating protease sup-17 trafficking to the cell surface (PubMed:28068334). Together with tsp-14, probably acts by modulating the activation of glp-1, a Notch-like receptor, to regulate germline maturation (PubMed:20220101). Probably acts by modulating the activation of lin-12, a Notch-like receptor, to regulate cell fate specification such as the anchor cell/ventral uterine precursor cell decision (PubMed:20220101). May interact with protease sup-17; the interaction promotes sup-17 cell membrane localization. Expressed in the germline. Expressed in embryos, larvae and in adults. Expressed in the developing vulva at the L4 larval stage and in the hypodermis at the L3 larval stage. Viable and fertile (PubMed:28068334). In embryos, loss of protease sup-17 cell membrane localization (PubMed:28068334). In a tsp-14 mutant background, exhibits vulva morphogenesis defects, impaired egg-laying, smaller body size and reduced RAD-SMAD reporter expression, a reporter system for the sma-6/daf-4 BMP-like pathway (PubMed:28068334). Males have severe tail defects including crumpled spicules, fused and shortened sensory rays and smaller fans (PubMed:28068334). F1 progeny die at the late embryonic stage with defects in ventral enclosure (PubMed:28068334). In a sma-9 (cc604) and tsp-14 mutant background, restores the production of the 2 M lineage-derived coelomocytes (PubMed:28068334). In a glp-1 (ar202) mutant background, partially restores normal fertility (PubMed:20220101). In a glp-1 (e2142) mutant background, enhances embryonic lethality (PubMed:20220101). In a sup-17 (n1258) or adm-4 (ok265) mutant background, causes lethality at various developmental stages (PubMed:20220101). In a lin-12 (n302) mutant background, restores egg-laying function (PubMed:20220101). Belongs to the tetraspanin (TM4SF) family.