EXPRESSION OF THE GENE FOR TRANSFORMING GROWTH-FACTOR-BETA IN AVIAN DYSCHONDROPLASIA

Previous immunolocalisation studies of dyschondroplasia have indicated that there is a reduction in the number of growth plate chondrocytes containing the protein transforming growth factor beta 3 (TGF-beta 3). The reduction in TGF-beta 3 in dyschondroplasia is likely to be a dir ect result of a reduction in the expression of the TGF-beta 3 gene. mR NA was extracted from small (0 . 09 g) samples of growth cartilage fro m the proximal tibiotarsus of three-week-old broiler chicks. The carti lage samples contained cells from all three zones of the growth plate (proliferative, transitional and upper hypertrophic) and were collecte d from normal and dyschondroplastic growth plates. The dyschondroplast ic growth plates were identified by an accumulation of transitional ch ondrocytes which were considered to be a result of a failure to differ entiate to the hypertrophic phenotype. A semi-quantitative polymerase chain reaction (PCR) was used to estimate the quantity of mRNA specifi c for glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and for each of the three isoforms of TGF beta (TGF-beta 1, TGF-beta 2, and TGF-beta 3) in each of the cartilage samples. The levels of expression of mRNA for GAPDH, TGF-beta 1 and TGF-beta 2 were similar in the two groups, b ut the expression of TGF-beta 3 mRNA was significantly reduced in the samples from the dyschondroplastic growth plates. The reduction in TGF -beta 3 levels is thought to be associated with the failure of chondro cyte hypertrophy in dyschondroplasia, and provides in vivo evidence th at TGF-beta 3 is part of the cascade of events associated with the dif ferentiation of chondrocytes during endochondral ossification in the c hick.