Tissue‐specific expression of calbindin‐D_28K gene during ontogeny of the chicken

The vitamin D₃‐dependent calcium binding protein, calbindin‐D₂₈K (CaBP‐D28K), plays an important role in transepithelial calcium translocation. To evaluate its role in chick embryonic calcium metabolism, steady‐state levels of CaBP‐D28K mRNA in various tissues of the chick embryo were determined by Northern blot and slot blot analyses, and CaBP‐D28K concentrations in the examined tissues and plasma were estimated by RIA. High levels of CaBP‐D28K mRNA were found in the embryonic kidney (mesonephros) on embryonic day (E) 10 and E12 and thereafter gradually decreased until hatching. CaBP‐D28K mRNA levels were low in the yolk sac until E16 but increased on E18 and reached a maximum on E20. A steady increase in CaBP‐D28K mRNA levels was observed in the cerebellum during the development from E10 to post‐hatching. CaBP‐D28K mRNA levels in the intestine were very low during the incubation period but significantly increased on days 1 and 7 after hatching. By Northern blot analysis, CaBP‐D28K mRNA was barely detectable in liver, heart, and chorioallantoic membrane of the embryonic chick. Changes in immunoreactive CaBP‐D28K of each tissue paralleled observed changes in mRNA levels. In plasma, measurable levels of CaBP‐D28K were found as early as E8 and were stable until E18, when 6.5‐fold increase was observed compared to E16. The highest level of CaBP‐D28K in plasma was found on E20 and decreased after hatching. These temporal profiles of CaBP‐D28K suggest that it may play an important role in the regulation of chick embryonic calcium homeostasis. © 1994 Wiley‐Liss, Inc.