The mRNAs for the three chains of human collagen type XI are widely distributed but not necessarily co-expressed: Implications for homotrimeric, heterotrimeric and heterotypic collagen molecules

Abstract

In cartilage collagen type XI exists as heterotrimeric molecules composed of α1(XI), α2(XI) and α3(XI) subunits. Messenger RNAs for some of the α chains of collagen type XI have also been found in non-chondrogenic tissues but the chain composition of the molecule in these sites is not known. Some non-chondrogenic tissues also contain heterotrimers containing collagen α2(V) and α1(XI) chains. We have explored the possibility that collagen type XI could exist in differing trimeric forms in non-chondrogenic tissues and aimed to predict the subunit composition of this collagen in those tissues. The distribution and relative levels of expression of collagen α1(XI), α2(XI) and α3(XI)/α1(II) mRNAs in different human fetal tissues were studied. Expression of mRNAs for all three genes of collagen type XI is not restricted to cartilage but is widespread. However, in some non-chondrogenic tissues, the mRNAs for all three α chains of collagen type XI were not co-expressed, but collagen α1(XI) and α2(XI) mRNAs were found either singly or without collagen α3(XI) transcripts. Collagen type XI may therefore exist as homotrimers and/or heterotrimers composed of two collagen α(XI) chains in some tissues. The distribution of mRNAs for collagen α2(V) and α1(I) were also studied. Co-expression of collagen type XI, α2(V) and α1(I) mRNAs was found for many tissues. These findings have implications for the possibility of additional chain associations for collagen types XI and V in cross-type heterotrimers within heterotypic fibrils.