Pattern of expression of transforming growth factor‐β4 mRNA and protein in the developing chicken embryo

Expression of TGF‐β4 mRNA and protein was studied in the developing chicken embryo using specific cDNA probes and antibodies for chicken TGF‐β4. Expression of TGF‐β4 mRNA was detected by day 4 of incubation (Hamburger and Hamilton stage 22, E4) by RNA Northern blot analysis and increased with developmental age until day 12 of incubation (stage 38, E12) where it was detected in every embryonic tissue examined, with expression being highest in smooth muscle and lowest in the kidney. The steady‐state level of expression of TGF‐β4 mRNA remained relatively constant in most embryonic tissues through day 19 (stage 45, E19). In situ hybridization analysis detected TGF‐β4 mRNA as early as the “definitive primitive streak” stage (stage 4); during neurulation (stage 10), TGF‐β4 mRNA was detected in all three germ layers, including neuroectoderm. Following neurulation, TGF‐β4 mRNA was detected in the neural tube, notochord, ectoderm, endoderm, sclerotome, and myotome, but not dermotome at stage 16. By day 6 of incubation (stage 29, E6), TGF‐β4 mRNA was localized in several tissues including heart, lung, and gizzard. Immunohistochemical staining analysis also showed expression of TGF‐β4 protein in all three germ layers as early as stage 4 in various cell types in qualitatively similar locations as TGF‐β4 mRNA. These results suggest that TGF‐β4 may play an important role in the development of many tissues in the chicken. © 1993 Wiley Liss, Inc.