Expression pattern of type II collagen mRNA during early vertebral development in the human embryo

The role of extracellular matrix molecules in ontogenetic differentiation processes is a matter of increasing interest. In cartilage development, type II collagen is suspected of promoting chondrogenic differentiation, since its expression has been demonstrated in a range of precartilaginous tissues of vertebrate species. Up to now, no studies supplying a coherent description of type II collagen expression in the skeletogenesis of human embryos including early embryonic stages have been published. In this work, we examine the temporal and spatial distribution of type II collagen mRNA during vertebral column development in human embryos from 4 to 12 weeks of gestation using non-radioactive in situ hybridization. The onset of gene expression was demonstrable in the 5th week in precartilaginous mesenchymal cells and in notochordal cells. Additionally, we found a weaker hybridization signal in the mesenchymal precursors of the intervertebral discs. In the anlagen of the axial skeleton, type II collagen expression decreased during osteogenic reconstruction in the 11th/12th week, whereas expression continued in the notochordal remnants of the future nuclei pulposi. The results suggest a relatively late occurrence of type II collagen in human vertebral development compared with other vertebrate species. The distribution of gene expression is concordant with a possible role of this molecule in promoting differentiation of mesenchymal cells into chondrocytes. The mechanism of this influence remains to be established.