SKR2 Acvr1b + http://identifiers.org/mgd/MGI:1338944 ActR-IB SKR2|ActRIB|ActR-IB|Acvrlk4|Alk4 O genetic mapping Alk4 MGI:1338944 Gene ActRIB activin A receptor, type 1B Acvrlk4 protein coding gene