Possible roles for stanniocalcin during early skeletal patterning and joint formation in the mouse

Stanniocalcin (STC) is a polypeptide hormone discovered first in fish and m ore recently in mammals. In mammals, the gene is widely expressed and the h ormone is, so far, known to be involved in regulating the transport of calc ium or phosphate across retial and gut epithelia, and into neuronal cells. Gene expression is also high during development, and in an earlier study we mapped the temporal and spatial pattern of gene expression in the mouse ur ogenital system. Our data suggested that STC probably acted as a signaling molecule that was produced in mesenchyme cells and targeted to epithelial c ell layers in both kidney and testes. Here we have examined STC mRNA and pr otein distributions between develop in en tal stages E10.5 and E18.5 in the axial and appendicular skeleton. In the axial skeleton, STC was transientl y expressed in a rostral-caudal fashion during vertebral development protei n appeared to be made in intervertebral disc mesenchyme cells and targeted to vertebral hypertrophic and prehypertrophic chondrocytes. By stage E18.5, the STC gene was active only in vertebral perichondrocytes. The pattern of expression in the appendicular skeleton was equally striking. Early in dev elopment, STC gene expression defined the initial lengths of bone primordia . The gene was expressed in mesenchyme cells at either ends of precartilagi nous condensations defining future long bones and the secreted protein was targeted to the chondroblasts. Later on during joint formation, STC was hig hly expressed in interzone cells that defined all future joints. After cavi tation, STC gene expression was greatest in perichondrocytes lining the joi nts. Underlying resting, proliferative and prehypertrophic chondrocytes app eared to be the targets of STC both during and after cavitation, Therefore, its pattern of expression was indicative of a role in early skeletal patte rning and joint formation. Moreover, as occurs during urogenital developmen t, it appeared that STC is made in undifferentiated mesenchyme cells and se questered by those destined to differentiate.