Vitamin D and chick embryonic yolk calcium mobilization: identification and regulation of expression of vitamin D-dependent Ca2(+)-binding protein, calbindin-D28K, in the yolk sac.
The developing chick embryo acquires calcium from two sources. Until about Day 10 of incubation, the yolk is the only source; thereafter, calcium is also mobilized from the eggshell. We have previously shown that during normal chick embryonic development, vitamin D is involved in regulating yolk calcium mobilization, whereas vitamin K is required for eggshell calcium translocation by the chorioallantoic membrane. We have studied here the biochemical action of 1,25-dihydroxy vitamin D3 in the yolk sac by examining the expression and regulation of the cytosolic vitamin D-dependent calcium-binding protein, calbindin-D28K. Two types of embryos are used for this study, normal embryos developing in ovo and embryos maintained in long-term shell-less culture ex ovo, the latter being dependent solely on the yolk as their calcium source. Our findings are (1) calbindin-D28K is expressed in the embryonic yolk sac, detectable at incubation Days 9 and 14; (2) the embryonic yolk sac calbindin-D28K resembles that of the adult duodenum in both molecular weight (Mr 28,000) and isoelectric point, as well as the presence of E-F hand Ca2(+)-binding structural domains; (3) systemic calcium deficiency caused by shell-less culture of chick embryos results in enhanced expression of calbindin-D28K in the yolk sac during late development; (4) yolk sac calbindin-D28K expression is inducible by 1,25-dihydroxy vitamin D3 treatment in vivo and in vitro; and (5) immunohistochemistry revealed that yolk sac calbindin-D28K is localized exclusively to the cytoplasm of the yolk sac endoderm. These findings indicate that the chick embryonic yolk sac is a genuine target tissue of 1,25-dihydroxy vitamin D3.
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Department of Biology, University of Pennsylvania, Philadelphia 19104.
Tuan
R S
RS
D000818:Animals; D015153:Blotting, Western; D064026:Calbindins; D002118:Calcium / Q000502:physiology*; D002642:Chick Embryo; D015180:Electrophoresis, Gel, Two-Dimensional; D004707:Endoderm / Q000378:metabolism; D006706:Homeostasis; D008970:Molecular Weight; D064030:S100 Calcium Binding Protein G / Q000502:physiology*; D014807:Vitamin D / Q000502:physiology*; D015017:Yolk Sac / Q000166:cytology / Q000502:physiology*
D064026:Calbindins; D064030:S100 Calcium Binding Protein G; D014807:Vitamin D; D002118:Calcium