ACVR2A and infectious otitis media: In contrast, a significant decrease was observed in the expression of activin βB-subunit (Fig. 2; middle column), activin type IIA receptor (Fig. 2; right column), p-smad2 (Fig. 3; middle column), p-smad3 (Fig. 3; right column), smad4 (Fig. 4; left column) and smads 6&7 (Fig. 4; middle column) in both short and long AOM compared with normal colons.