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. Necessary to mediate a specific antagonistic effect of inhibin B on activin-stimulated transcription (By similarity). Interacts with INHA; the interaction is not confirmed by standard receptor binding assays (By similarity). 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 (By similarity). Interacts with HECTD1 (By similarity). Expressed at embryonic day (E) 12.5 in embryo. Mice are viable and fertile and show no alterations in FSH synthesis or secretion or in ovarian and testicular function. According to PubMed:23143598 male mice show diminished pituitary and serum thyroid-stimulating hormone (TSH) concentrations, reduced pituitary thyrotropin-releasing hormone (TRH) receptor expression, decreased triiodothyronine concentrations and increased body mass. Produced by alternative promoter usage. Produced by alternative splicing of isoform 1. Produced by alternative splicing of isoform 1. Produced by alternative splicing of isoform 1. Produced by alternative promoter usage. It is uncertain whether Met-1 or Met-2 is the initiator. Extended N-terminus.