Differential in situ expression of α2(XI) collagen mRNA isoforms in the developing mouse

Type XI collagen is an essential structural component of the extracellular matrix of cartilage and plays a role in collagen fibril formation and skeletal morphogenesis. The expression of all three type XI collagen genes is not restricted to cartilage. In addition, alternative exon usage seems to increase the structural diversity and functional potential of type XI collagen during development. In order to investigate type XI collagen expression during development, we have examined alpha 2(XI) and alpha 1(XI) collagen genes by in situ hybridization in mice. Introduction Transcripts of the alpha 2(XI) collagen gene were first detected in the notochord of mouse embryos after 11.5 days of gestation. Subsequently, alpha 2(XI) mRNA was mainly found in the cartilaginous tissues of the developing limbs and axial skeleton together with transcripts of the alpha 1(XI) gene. The alpha 2(XI) transcripts seemed to be alternatively spliced isoforms lacking exons 6-8, which code for an acidic domain. Expression of alpha 2(XI) outside the cartilage was relatively restricted, whereas expression of the alpha 1(XI) gene was widespread. However, expression of alpha 2(XI) transcripts containing exons 6-8 was found in non-chondrogenic tissues, including the calvarium and periosteum where intramembranous ossification occurs. These results indicate that alpha 2(XI) mRNA isoforms are differentially expressed in various tissues during development. In addition, alpha 2(XI) mRNA isoforms containing alternative exons are present in osteogenic cells, and their expression may be closely related to the formation of bone or cartilage.