Determination of the complete cDNA sequence of rat type II collagen and evaluation of distinct expression patterns of types IIA and IIB procollagen mRNAs during fracture repair in rats.

Elucidating the molecular mechanisms that underlie fracture healing is crucial to understanding and devising strategies for the management of fractures, especially those associated with a pathological condition such as diabetes or old age. Cartilage formation, and therefore the expression of type II collagen by chondrocytes, is a critical step in frac-ture healing. Two forms of type II collagen, IIA and IIB, are known to be produced by alternative splicing of the Alpha(1) (II) procollagen gene. We have followed the patterns of expression of these two forms of type II collagen to determine the nature of chondrocyte recruitment during fracture healing. First, we sequenced the rat collagen type II cDNA to design the primers. Second, using a competitive quantitative reverse transcription-mediated polymerase chain reaction, we provide evidence that (1) there is a basal level of type IIA collagen expression during the early stages of fracture healing; (2) transient but sharp up-regulation of IIA expression occurs concomitant with chondrogenesis and endochondral ossification; and (3) type IIB collagen is the predominant mRNA variant expressed at virtually all times during fracture repair.