MOLECULAR ASPECTS OF TIBIAL DYSCHONDOPLASIA IN THE CHICKEN .1. EXPRESSION OF CALBINDIN-D-28K GENE

Avian tibial dyschondroplasia (TD) is a skeletal disorder characterize d by a cartilage plug in the proximal metaphysis of the tibiotarsus. E xperiments were carried out to investigate whether the expression of c albindin-D-28k gene is altered in this disease or in the presence of v itamin D metabolites. The intestinal mRNA levels for calbindin-D-28k i n normal and TD chicks were determined by northern blot analysis, and the distribution of calbindin-D-28k in the normal growth plate (LTD) a nd tibial dyschondroplastic cartilage of chicks were examined immunocy tochemically. There were no differences in the intestinal calbindin-D- 28k mRNA levels between LTD and TD chicks fed diets sufficient in vita min D-3. However, reduced calbindin-D-28k mRNA levels were found in TD chicks fed a diet supplemented with 10 mu g/kg 1,25 (OH)(2)D-3 as com pared to LTD chicks. Calbindin-D-28k was distributed throughout the gr owth plate, but concentrated in the hypertrophic zones. Depletion of v itamin D resulted in the absence of calbindin-D-28k in rachitic growth plates. These findings suggest that calbindin-D-28k is vitamin D depe ndent in this tissue. This protein was also found to be present in the TD-associated epiphyseal growth plate, but appeared to be less intens ely concentrated than that in LTD growth plate. The proximal part of t he dyschondroplastic cartilage was lightly stained, and no evidence of calbindin was found in the middle and distal parts of the lesion. The se results suggest that decreased calbindin-D-28k gene expression is o bserved in the TD lesion. (C) 1998 Elsevier Science Inc.