Constitutively active forms of ALK4 and ALK7 stimulate Fshb mRNA expression and Smad2/3 phosphorylation. A, LβT2 cells were transfected as described with constitutively active (TD) forms of ALK4 and ALK7. RNA was isolated and Fshb mRNA levels measured by RT-PCR. Rpl19 was used as a loading control. B, LβT2 cells in 6-well plates were transfected with ALK4(TD) or ALK7(TD) along with pcDNA3 (V), Flag-Smad2 (2), or Flag-Smad3 (3). Whole cell protein lysates were subjected to immunoblotting with the indicated antibodies. Molecular weight markers (in kDa) are indicated at the left.