Expression of a 1,25‐Dihydroxyvitamin D3 Membrane‐Associated Rapid‐Response Steroid Binding Protein During Human Tooth and Bone Development and Biomineralization

The calciotropic hormone 1,25‐dihydroxyvitamin D3 [1,25(OH)2D3] has been established to control skeletal tissue formation and biomineralization via the regulation of gene expression. This action involves the well‐characterized nuclear 1,25(OH)2D3 receptor. However, it has been recognized that several cellular responses to 1,25(OH)2D3 may not to be related to the exclusive nuclear receptor. Indeed, this secosteroid is able to generate rapid responses that have been proposed to be mediated by interactions of the ligand, which is a putative cell membrane‐associated rapid‐response steroid (MARRS) binding protein for 1,25(OH)2D3 [1,25D3‐MARRS]. The nongenomic pathway of 1,25(OH)2D3 was studied here in detail by immunolocalization of the 1,25D3‐MARRS during the specific context of human prenatal development. Western blotting with proteins extracted from 4 week‐ to 27‐week‐old embryos was performed, evidencing a 65‐kDa molecular species recognized by antibody Ab 099 generated against synthetic peptides corresponding to the N terminus of the 1,25D3‐MARRS from chick intestinal basolateral membranes. Based on this biochemical conservation of protein in the human species, the temporospatial expression patterns were established in the craniofacial skeleton at the same ages. Comparative analysis was performed in teeth and bones from early morphogenesis to terminal cell differentiation and extracellular biomineralization. The data show the potential implication of 1,25D3‐MARRS in the heterogeneous cell population including ameloblasts, odontoblasts, osteoblasts, and osteoclasts. The epithelial‐mesenchymal cascade related to odontogenesis was coincident with a sequence of up‐ and down‐regulation of immunoreactive 1,25D3‐MARRS. Biomineralization was associated with a striking up‐regulation in the adjoining secretory cells in all tissues. Finally, osteoclasts appeared also to express the 1,25D3‐MARRS during these early phases of bone modeling. Previously obtained data of the nuclear vitamin D receptor (VDR) expression and this study on 1,25D3‐MARRS suggest the existence of cross‐talk between the genomic and nongenomic pathways during human development.