IGSF1 is a highly glycolylated immunoglobulin domain-containing protein. IGSF1 has been shown to act as a coreceptor in inhibin signaling, however, it does not appear to be a high-affinity inhibin receptor by itself. May reduce or inhibit activin A signaling and is believed to be necessary in the mediation of specific effects of inhibin B on activin-stimulated transcription. IGSF1 has been found to interact with several members of the ACVR family and possibly some members of the BMPR group. There are 3 known isoforms of IGSF1, with 1 and 2 likely being multi-pass membrane proteins. Isoform 3 is believed to be expressed as a secreted form. Expression is high in pancreas, testis and fetal liver, while heart, prostate and small intestine show only moderate expression. IGSF1 may be found at very low levels in brain, muscle, thymus, ovary, colon, fetal lung and fetal kidney. Isoform 3 has been detected in pituitary gland.