DEVELOPMENTAL-CHANGES IN SKIN COLLAGEN BIOSYNTHESIS PATHWAY IN POSTHATCH MALE AND FEMALE CHICKENS

The developmental changes in skin collagen biosynthesis pathway in mal e and female chickens were evaluated. Concentration of collagen, level s of mRNA for collagen type I subunits and for lysyl hydroxylase, and the level of three lysyl oxidase-derived cross-links: dehydro-dihydrox ylysinonorleucine (DHLNL), dehydro-hydroxylysinonorleucine (HLNL), and dehydro-histidinohydroxymerodesmosine (HHMD) were determined during 4 wk posthatching. Skin collagen content increased with age and was hig her in males than in females. In both sexes, the expression of the gen es coding for alpha 1 and alpha 2 of collagen type I decreased with ag e: alpha 1 (I) gene expression decreased from Day 3 onwards, whereas t he reduction in alpha 2(I) gene expression started 1 wk later. At all ages examined, the expression of both genes was higher in male than in female skin, Males and females lysyl hydroxylase gene expression rema ined low until Day 16, after which an increase in the enzyme gene expr ession was observed. An increase in skin HLNL content was observed fro m Day 3 in both sexes reaching a peak in males at Day 9 and in females 1 wk later. The DHLNL content, which was higher in males than in fema les at all ages tested, dramatically decreased in both male and female skin from 3 d of age, reaching its lowest level at Day 16, and remain ed at that low level thereafter. The skin content of HHMD in males and females followed an oscillatory behavior with higher peaks in the mal e skin. The results suggest that the higher tensile strength of male s kin than female skin may be due to the elevated skin collagen content that resulted from increased expression in collagen type I genes on th e one hand, and from the higher amounts of various collagen cross-link s on the other.