Pre-adipocyte 3T3-L1 cells, after an appropriate induction stimulus, proceed through a defined change in morphology as differentiation progresses. Transforming growth factor beta 1 (TGF beta 1) is able to block the morphological and biochemical changes which occur with differentiation of these cells if given within 36-40 h of induction [Ignotz and Massague (1985): Proc Natl Acad Sci USA 82:8530-8534]. To begin to elucidate the role of the extracellular matrix in adipogenesis, as well as the mechanism whereby TGF beta 1 inhibits differentiation, we examined the expression of two extracellular matrix genes, type I (alpha 1) procollagen and fibronectin, as well as endogenous TGF beta 1. Confluent cells were induced to differentiate by treatment with insulin, dexamethasone, and isobutylmethylxanthine in the presence or absence of TGF beta 1. Following 6 days of treatment, the cells in the differentiated group acquired the rounded shape of mature adipocytes; the cytosol of these cells also contained numerous lipid-filled vesicles, as demonstrated by oil red O staining. Cells treated with the differentiation compounds in the presence of TGF beta 1 maintained the fibroblast-like appearance of control cells and did not stain with oil red O. At the level of gene expression, both procollagen and fibronectin mRNAs were down-regulated during differentiation of 3T3-L1 cells. When cells from the control or differentiation groups were treated with TGF beta 1, there was a 2-5-fold induction of procollagen and fibronectin mRNAs throughout the 6-day time course.(ABSTRACT TRUNCATED AT 250 WORDS)