Expression of transforming growth factor-β2 and β3 mRNAs and proteins in the developing chicken embryo

Abstract Specific cDNA probes and antibodies for chicken transforming growth factor (TGF)-β 2 and β 3 were used to study expression of TGF-β 2 and β 3 mRNAs and proteins in the developing chicken embryo. Expression of the mRNAs for both TGF-β isoforms was detected by day 1.5 of incubation (Hamburger and Hamilton stage 10) by RNA Northern blot analysis and increased with developmental age. Expression of TGF-β 2 and β 3 mRNAs was detected in every embryonic tissue examined, with the level of expression of both isoforms being high in heart, brain and muscle and low in kidney and liver. Coordinate unidirectional upregulation of expression of TGF-β 2 and β 3 mRNAs occurred in most embryonic tissues with development except the heart, where the steady-state level of expression of TGF-β 2 mRNA decreased with age, while that of TGF-β 3 mRNA increased. In situ hybridization analysis detected TGF-β 2 and β 3 mRNAs as early as the definitive primitive streak stage (stage 4). During neurulation (stage 10), TGF-β 2 and β 3 mRNAs were detected in cells of all three germ layers; TGF-β 3 mRNA was detected in neurectoderm as well. Following neurulation, TGF-β 3 mRNA was detected in the neural tube, notochord, ectoderm, endoderm, sclerotome and dermomyotome at stage 16; expression of TGF-β 2 mRNA was not as prominent as TGF-β 3 mRNA in these structures. By stage 29, both TGF-β 2 and β 3 mRNAs were localized in several tissues including heart, lung, gizzard and feathers. Immunohistochemical staining analysis detected immunoreactive TGF-β 2 and β 3 proteins in all three germ layers of stage 4 embryos. Staining for TGF-β 2 and β 3 proteins was detected in several cell types and tissues in the early developing embryo frequently in the same locations as TGF-β 2 and β 3 mRNAs, with staining for TGF-β 2 being less intense than TGF-β 3. However, in some cases, localization of TGF-β 2 and β 3 proteins was different from that of the mRNAs, indicating that a complex mechanism of transcription, translation and secretion exits during chicken embryogenesis. These and other results suggest that TGF-β 2 and β 3 may play important roles and act through both autocrine and paracrine mechanisms in the development of many tissues in the chicken.