description
Activin was initially discovered as an activator of follicle stimulating hormone in the pituitary gland. It has since been shown to be an important participant in the differentiation of embryonic cells into mesodermal and endodermal layers. Activin binds the Activin receptor and triggers downstream events: phosphorylation of SMAD2 and SMAD3 followed by activation of gene expression (reviewed in Attisano et al. 1996, Willis et al. 1996, Chen et al. 2006, Hinck 2012). Activins are dimers comprising activin A (INHBA:INHBA), activin AB (INHBA:INHBB), and activin B (INHBB:INHBB). Activin first binds the type II receptor (ACVR2A, ACVR2B) and this complex then interacts with the type I receptor (ACVR1B, ACVR1C) (Attisano et al. 1996). The type II receptor phosphorylates the type I receptor and then the phosphorylated type I receptor phosphorylates SMAD2 and SMAD3. Dimers of phosphorylated SMAD2/3 bind SMAD4 and the resulting ternary complex enters the nucleus and activates target genes

external resources
NCBI:1269621
REACTOME:R-HSA-1502540
PUBMED:8622651
PUBMED:16636301
PUBMED:22651914
PUBMED:8721982

genes
ACVR1B , ACVR2A , ACVR2B , INHBA , INHBB , SMAD2 , SMAD3 , SMAD4 , FOXH1 , FSTL3 , FST , DRAP1 , ACVR1C ,