passages.id: split_8_test_3271_passage
passages.type: progene_text
passages.text: Activin type II receptors ( ActRIIs ) including ActRIIA and ActRIIB are serine / threonine kinase receptors that form complexes with type I receptors to transmit intracellular signaling of activins , nodal , myostatin and a subset of bone morphogenetic proteins .