Transforming growth factor-beta 1 in the developing mouse pancreas: a potential regulator of exocrine differentiation.

Transforming growth factor-beta 1 (TGF-beta 1) is known to regulate cell growth, differentiation, and function in developing mammalian systems. Altering TGF-beta 1 expression in the developing pancreas has been shown to affect both exocrine and endocrine development, suggesting that it is an important regulator of pancreatic organogenesis. We proposed to examine the ontogeny of TGF-beta 1 mRNA expression in the developing pancreas, as well as characterize the patterns of relative TGF-beta 1 gene expression and activity. We performed in situ hybridization for TGF-beta 1 on pancreas specimens obtained from CD-1 mice on gestational days 12.5 (E12.5), 15.5 (E15.5), and 18.5 (18.5). We also isolated mRNA from the pancreas on each of these days and performed a semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) to assess relative TGF-beta 1 expression as a function of gestational age. Finally, we performed a TGF-beta 1 ELISA with media conditioned by embryonic pancreas from gestational days 15.5 and 18.5. By in situ hybridization, TGF-beta 1 mRNA is expressed exclusively in the E12.5 pancreatic epithelium, sparing the surrounding mesenchyme. As pancreatic organogenesis progresses, TGF-beta 1 mRNA expression localizes predominantly to the developing acini. TGF-beta 1 gene expression appears modest through E15.5 but is upregulated near the end of gestation, at E18.5. TGF-beta 1 activity, by ELISA, is also upregulated at E18.5. TGF-beta 1 may thus be a modulator of pancreatic organogenesis. Modest TGF-beta 1 expression through E15.5 may be permissive for exocrine lineage selection. TGF-beta 1 expression may then become critical for terminal acinar differentiation. Upregulated TGF-beta 1 expression at the end of gestation may be important for islet formation, and it may be necessary to inhibit continued proliferation and differentiation of pluripotent cells within the pancreatic ductal epithelium.