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The effects of vitamin D deficiency on the ontogeny of calcium-binding proteins (CaBPs) and the vitamin D receptor (VDR) in the placenta and yolk sac of the mouse were examined. Maternal vitamin D status did not affect the time of appearance of CaBP-D9k (9 kDa) in the yolk sac endoderm or trophoblastic giant cells (TGCs) of the placenta. VDRs were undetectable in TGCs and yolk sac endoderm, but were present in the intraplacental yolk sac. Since yolk sac endoderm and TGCs contain CaBP but not VDR, it is unlikely that CaBP synthesis and/or activity in these cells is controlled by vitamin D. The TGCs, therefore, may be involved in vitamin D-independent transplacental transfer of calcium.

The role of vitamin D in ameloblasts and odontoblasts has been studied experimentally in rodents. Dental dysplasias have also been reported in clinical studies of children with rickets. Vitamin D acts via a nuclear receptor which binds the major metabolite, 1,25-dihydroxyvitamin D3, and positively or negatively controls the expression of specific genes. The most extensively studied markers of 1,25-dihydroxyvitamin D3 action are calbindin-D9k, calbindin-D28k, and osteocalcin. Therefore, to study in more detail the potential role of 1,25-dihydroxyvitamin D3 in human dental development, 1,25-dihydroxyvitamin D3 receptor (VDR) was localized by immunofluorescence in forming teeth (8-26 wk of gestation). Calbindin-D28k was also mapped by immunoperoxidase in antenatal and postnatal forming and formed teeth. VDR were detected in both dental epithelium and mesenchyme of bud, cap, and bell stages of tooth germs. Nuclei of overtly differentiated ameloblasts and odontoblasts were also immunostained. Calbindin-D28k was present in differentiated ameloblasts and odontoblasts. The presence of VDR and calbindin-D28k in ameloblasts and odontoblasts suggests that 1,25-dihydroxyvitamin D3 may contribute to the regulation of enamel and dentin formation, as classically reported for bone formation. Finally, the early appearance of VDR supports the concept that 1,25-dihydroxyvitamin D3 may also control forward stages of tooth crown development in humans.

Levels of calbindin-D28K (CaBP-D28K) mRNA and vitamin D3, 1 alpha, 25(OH)2D3, receptor (VDR) mRNA in the intestine and shell gland were measured in the laying hen during the ovulatory cycle by Northern and slot blot analyses. In addition, effects of presence of an egg and calcium deposition in the shell gland on the levels of both mRNAs were studied either by delay in oviposition (retaining the egg in the shell gland beyond the expected time of oviposition) or premature oviposition (emptying the shell gland and arrest of calcium deposition). During the ovulatory cycle mRNA levels of CaBP-D28K and of VDR remained relatively constant in the intestine. In contrast, both mRNA levels of the shell gland were low when there was an egg in the infundibulum, magnum, and isthmus, but significantly increased when there was an egg in the shell gland during shell formation. The im injection of indomethacin 3 hr before expected ovulation delayed oviposition but increased neither shell thickness nor mRNA levels of CaBP-D28K and of VDR. On the other hand, premature oviposition reduced mRNA levels of both CaBP-D28K and VDR in the shell gland. These results suggest that the presence of an egg and calcium deposition in the shell gland may be a stimulatory factor for synthesis and accumulation of CaBP-D28K mRNA and VDR mRNA in association with calcification.

Using immunohistochemical methods, we detected epitopes of the calcitriol receptor, the ATP-dependent plasma membrane calcium pump and the 28kD vitamin D-dependent calcium-binding protein in sections of the human eye. In retinal photoreceptors, vitamin D receptor, plasma membrane calcium pump and calcium-binding protein epitopes were detected in the outer nuclear layer. Epitopes for the vitamin D receptor and the calcium-binding protein were present in the inner and outer segments of the photoreceptors, where visual transduction occurs. All three proteins were detected in some cells of the ganglion cell layer, the inner nuclear layer, and the retinal pigment epithelium. Epitopes for these proteins also were noted in the ciliary body epithelium. VDR epitopes were seen in lens epithelium. Some immunostaining for VDR, PMCA and calbindin-D28k also was present in the endothelium and in the basal epithelium of the cornea. The presence of these proteins in several tissues of the human eye suggests that the proteins may play a role in the cellular physiology of the eye. Their exact functions in the eye remain undetermined.

Epitopes of the calcitriol receptor, the ATP-dependent plasma membrane calcium pump (PMCA) and the 28-kD vitamin-D-dependent Ca-binding protein (calbindin-D28k) were detected in sections of the albino rat eye using light microscopy and immunohistochemistry of paraffin-embedded tissues. Calcitriol receptor and calbindin-D28k epitopes were detected in both the inner and outer layers of the ciliary body epithelium. PMCA was present in both epithelial cell layers of the ciliary body but was most prominent in the inner layer. Corneal epithelium and endothelium also contained epitopes for calcitriol receptor, PMCA and calbindin-D28k. These Ca-regulatory proteins may play a role in the cellular physiology of the albino rat eye by maintaining appropriate intracellular and aqueous humor Ca concentrations.

The effects of vitamin D3 deficiency on the ontogeny of calcium-binding proteins (CaBPs) and the vitamin D receptor in the duodenum, kidney and cerebellum of the mouse were examined. Maternal vitamin D status did not affect the time of appearance of the fetal 28 kDa CaBP (CaBP-D28k) in the cerebellum, kidney and duodenum, and the 9 kDa CaBP (CaBP-D9k) in the intestine and kidney. Vitamin D receptor was undetectable in all fetal tissues, regardless of maternal vitamin D status, at all stages of gestation examined. Thus it appears that maternal vitamin D status does not affect the ontogeny of CaBP-D9k or CaBP-D28k in the mouse fetus. The factors that influence the appearance of calbindins in the fetus are unclear.