ABSTRACT
This chapter focuses on the combined application of molecular, biochemical, and morphologic approaches that have contributed to defining the multiple effects of vitamin D on bone cell growth and differentiation. The osteocalcin gene is representative of a series of genes that are vitamin D- responsive, and stringently regulated during progressive development of the osteoblast phenotype. Numerous studies have established that osteoclasts are formed by the differentiation and fusion of progenitors derived from hematopoietic stem cells. The chapter illustrates how experimental approaches have been effectively integrated to address the structural and functional properties of vitamin D regulation of osteocalcin in bone. Vitamin D affects numerous osteoblast products, including cell growth related genes, nuclear and cytoskeletal proteins, structural proteins involved in bone matrix formation, and mineralization, enzymes, and plasma membrane proteins such as alkaline phosphatise. When vitamin D-deficient animals are treated with 1-a-25-dihydroxyvitamin D3, osteoclastic bone resorption is enhanced and the number of osteoclasts increases.
