Competence of 1ƒ¿, 25-dihydroxyvitamin D3 Receptor System in Embryonic Chick Intestine1

The competence of the duodenal 1ƒ¿, 25-(OH)2-D3 receptor system in embryonic chicks was studied in the reconstituted cytosol-chro matin system. The sucrose density gradient centrifugation following incubation of duodenal cytosol with 1x,25-dihydroxy-[3H]-vitamin D3 revealed that a cytosol 1x,25-dihydroxyvitamin D3 receptor existed in the duodenum of 18-day-old embryos. In the duodenum of 14-day-old embryos, however, the cytosol 1ƒ¿ ,25-dihydroxyvitamin D3 receptor was not detected. In the reconstituted cytosol-chromatin system, duodenal cytosol of 18 day-old embryos stimulated the association of 1ƒ¿, 25-dihydroxy-[3H] vitamin D3 with chromatin of the vitamin D-deficient chick duodenum. The association of 1ƒ¿, 25-dihydroxy-[3H]-vitamin D3 was shown to be saturable and temperature dependent. In a system where duodenal chromation of 18-day-old embryos was reconstituted with cytosols, 1ƒ¿, 25-dihydroxy-[3H]-vitamin D3 was re vealed to associate specifically with the chromatin in the presence of duodenal cytosol obtained from 18-day-old embryos or vitamin D deficient chicks. No significant association of 1ƒ¿, 25-dihydroxy-[3H] vitamin D3 with duodenal chromatin of 18-day-old embryos occurred in the absence of duodenal cytosol. From these results, it was strongly suggested that the intestinal 1ƒ¿, 25 dihydroxyvitamin D3 receptor system in embryonic chicks has become competent for the intracellular transfer of 1ƒ¿, 25-(OH)2-D3 before hatching.