Role of retinoic acid in regulation of mRNA expression of CaBP-D28k in the cerebellum of the chicken

In contrast to vitamin D₃-dependent gene expression of calbindin (CaBP- D(28k)) in intestine and kidney, the cerebellar mRNA expression seems independent of vitamin D₃. The present study was conducted to elucidate correlation of mRNA expression of CaBP-D(28k) and vitamin D₃ receptor (VDR) in the kidney and cerebellum of the developing chick by Northern blot analysis, localization of CaBP-D28k mRNA within the cerebellum by in situ hybridization, and effect of retinoic acid in ovo on CaBP-D(28k) mRNA levels. CaBP-D(28k) mRNA levels were low in the cerebellum until embryonic day 16 (E16) but markedly increased on E18 and reached plateau levels on E20. VDR mRNA levels were low until E16 and significantly increased on E18 but decreased on E20 and remained low on 1 and 7 days after hatching. In the mesonephros, CaBP-D(28k) mRNA levels were high until E16 but abruptly decreased on E18, while VDR mRNA levels remained relatively constant throughout the examined period between E10 and 20. In situ hybridization analysis clearly demonstrated CaBP-D(28k) mRNA signals within the Purkinje cells of the cerebellum in the embryo on E12-E18. Although 1,25 dihydroxyvitamin D₃ [1,25(OH)₂D₃, 3 x 10^-10 M] injected in ovo on E15 increased CaBP-D(28k) mRNA levels in the mesonephros on E16 but had no effect on those in the cerebellum. On the contrary, in ovo injection of retinoic acid (10^-10 and 10^-8 M) caused no effect on CaBP-D(28k) mRNA levels in the mesonephros but significantly increased those in the cerebellum. The results indicate a regulatory role of retinoic acid on mRNA expression of CaBP-D(28k) in the cerebellar Purkinje cells of the chicken embryo.