Presence of transforming growth factor-beta-like activity in multiple fetal rat tissues

The presence and ontogeny of transforming growth factor-beta (TGF-beta)-like bioactivity in rat tissues was studied. Eight separate tissues were extracted in acetic acid and assayed for TGF-beta-like activity by NRK-49F cell colony formation in soft agar. Bioactivity was present in each tissue during late fetal life, being most abundant in skeletal muscle, liver and lung (7.6-87.3 ng equivalents TGF-beta/g tissue), but fell to barely detectable levels from 12 days after birth. Gel filtration (pH 2.5) on Sephadex G75 of extracted fetal skeletal muscle, or culture medium conditioned by isolated fetal myoblasts demonstrated bioactivity in the molecular weight range 25-40 Kd. The results show that TGF-beta-like activity is selectively present in multiple fetal and neonatal, but not adult, rat tissues. Expression may therefore be developmentally regulated.