Seems to be a coreceptor in inhibin signaling, but seems not to be a high-affinity inhibin receptor. Antagonizes activin A signaling in the presence or absence of inhibin B (By similarity). Necessary to mediate a specific antagonistic effect of inhibin B on activin-stimulated transcription. Interacts with INHA (By similarity). In PubMed:12385827 does not interact with INHA; standard receptor binding assay. Interacts with ACVR1B; the interaction appears to be ligand-dependent as it is diminished by inhibin B and activin A. Interacts with ACVR2A, ACVR2B, ACVRL1 and BMPR1B. Interacts with HECTD1. Additional isoforms seem to exist. Highly expressed in pancreas, testis and fetal liver. Moderately expressed in heart, prostate and small intestine. Expressed at very low levels in brain, thymus, ovary, colon, fetal lung and fetal kidney. Expressed in muscle. Isoform 3 is expressed in pituitary gland. Expressed in embryo Carnegie stage 18 in Rathke's pouch progenitors. The disease is caused by variants affecting the gene represented in this entry. It is uncertain whether Met-1 or Met-12 is the initiator.