PROMOTER AND TRANSCRIPTION OF TYPE-X COLLAGEN GENE IN BROILER-CHICKENS WITH TIBIAL DYSCHONDROPLASIA

Type X collagen is produced exclusively in hypertrophic chondrocytes o f the growth plate of the proximal tibiotarsus and is believed to play an important role during normal development from chondrogenesis to os teogenesis. Chondrocytes of chickens with tibial dyschondroplasia (TD) fail to attain full hypertrophy and the amount of type X collagen, be ing a marker of hypertrophy, is Likely to be reduced. It is not clear whether transcriptional regulation is functional for expression of the type X collagen gene in TD birds. Nucleotide sequence of the type X c ollagen gene promoter was determined by sequencing PCR-based DNA clone s. Nucleotide identity of this fragment between the normal and TD carr iers was 97.6%. Both normal and TD birds were similar in a putative tr anscription start site, the site of TATAA box, and neither had a CCAAT box. However, there were two gaps in TD carriers, four gaps in normal s, and five nucleotide substitution sites. By rapid amplification of c DNA ends by PCR (RACE-PCR), transcription of the gene was assessed usi ng total RNA and mRNA from both normal chondrocytes and TD lesions at 3 and 4 wk of age. The RACE-PCR product for type X collagen mRNA was d etectable in both normal and TD birds at two stages. No difference was found between them. This result does not support the hypothesis that transcriptional regulation of type X collagen gene is important in TD development of chickens. Variations in the promoter region did not aff ect transcription of type X collagen gene in TD carrier chickens.