EXPRESSION OF TRANSFORMING GROWTH-FACTOR-BETA-2 AND BETA-3 MESSENGER-RNAS AND PROTEINS IN THE DEVELOPING CHICKEN-EMBRYO

Specific cDNA probes and antibodies for chicken transforming growth fa ctor (TGF)-beta 2 and beta 3 were used to study expression of TGF-beta 2 and beta 3 mRNAs and proteins in the developing chicken embryo. Exp ression of the mRNAs for both TGF-beta 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-beta 2 and beta 3 mRNAs was detected in every embryonic tissue examined, w ith the level of expression of both isoforms being high in heart, brai n and muscle and low in kidney and liver. Coordinate unidirectional up regulation of expression of TGF-beta 2 and beta 3 mRNAs occurred in mo st embryonic tissues with development except the heart, where the stea dy-state level of expression of TGF-beta 2 mRNA decreased with age, wh ile that of TGF-beta 3 mRNA increased. In situ hybridization analysis detected TGF-beta 2 and beta 3 mRNAs as early as the definitive primit ive streak stage (stage 4). During neurulation (stage 10), TGF-beta 2 and beta 3 mRNAs were detected in cells of all three germ layers; TGF- beta 3 mRNA was detected in neurectoderm as well. Following neurulatio n, TGF-beta 3 mRNA was detected in the neural tube, notochord, ectoder m, endoderm, sclerotome and dermomyotome at stage 16; expression of TG F-beta 2 mRNA was not as prominent as TGF-beta 3 mRNA in these structu res. By stage 29, both TGF-beta 2 and beta 3 mRNAs were localized in s everal tissues including heart, lung, gizzard and feathers. Immunohist ochemical staining analysis detected immunoreactive TGF-beta 2 and bet a 3 proteins in all three germ layers of stage 4 embryos. Staining for TGF-beta 2 and beta 3 proteins was detected in several cell types and tissues in the early developing embryo frequently in the same locatio ns as TGF-beta 2 and beta 3 mRNAs, with staining for TGF-beta 2 being less intense than TGF-beta 3. However, in some cases, localization of TGF-beta 2 and beta 3 proteins was different from that of the mRNAs, i ndicating that a complex mechanism of transcription, translation and s ecretion exits during chicken embryogenesis. These and other results s uggest that TGF-beta 2 and beta 3 may play important roles and act thr ough both autocrine and paracrine mechanisms in the development of man y tissues in the chicken.