Cloning of cDNA for rat pro alpha 1(III) collagen mRNA. Different expression patterns of type I and type III collagen and fibronectin genes in experimental granulation tissue.

A cDNA clone for rat pro alpha 1(III) collagen mRNA was isolated from a cDNA library constructed for poly(A)+ RNA from 15-day experimental granulation tissue. Two clones, pRGR1 and pRGR5, were characterized by restriction mapping and sequencing. Comparison with human type III collagen sequences revealed 92% identity at the level of translated amino acids, and 88% identity at nucleotide level in the coding region. In the 3'-untranslated sequence the identity was even higher (90%). The clones were used together with cDNA clones for type I collagen chains, fibronectin and gamma-actin to study the expression of the corresponding mRNAs during the development of experimental sponge-induced granulation tissue in rats. These studies revealed a marked activation of type I and type III collagen genes during the second week of granuloma development followed by a transient reduction in their levels during the third week. The mRNA levels for both collagen types remained relatively unchanged from day 25. The molar ratio of pro alpha 1(III) and pro alpha 1(I) collagen mRNAs was at a maximum on day 6, and then decreased to reach a plateau by the end of the third week. Fibronectin mRNA levels were found to increase slower; the maximum value was reached during the fifth week of granuloma development. The mRNA levels of gamma-actin increased continuously up to the end of the fourth week, thus following the cellular maturation of the tissue.