MESSENGER-RNA LEVELS OF ALPHA-1(VI) COLLAGEN, ALPHA-1(XII) COLLAGEN, AND BETA-IG IN RABBIT CORNEA DURING NORMAL DEVELOPMENT AND HEALING

PURPOSE. Type VI and XII collagens and beta ig, major components of th e interfibrillar matrix, may maintain proper spacing among collagen fi brils, necessary for corneal transparency. During normal corneal strom a development and healing, changes in mRNA levels of these proteins we re measured to determine whether differences in steady state levels ar e indicative of the unique structure produced by each corneal tissue. METHODS. A full-thickness excision wound was made in each cornea of si x adult rabbits and allowed to heal for 1, 2, or 4 weeks. Scar tissue from two rabbits (four scars) were used from each time period and proc essed for RNA extraction. Total RNA from 23-day-old fetal rabbit corne as (equivalent to approximately 1 week of stromal development) and 8-d ay-old neonate corneas (equivalent to approximately 3.5 weeks of strom al development) was also extracted. Relative quantities of alpha 1(VI) collagen, alpha 1(XII) collagen, beta ig, and beta-actin mRNAs were d etermined by competitive reverse transcriptase-polymerase chain reacti on. Glyceraldehyde-3-phosphate dehydrogenase was used as a housekeepin g gene. RESULTS. Increased mRNA levels for alpha 1(VI) and alpha 1(XII ) collagens, beta ig, and beta-actin were seen during the first 2 week s of healing and were followed by a decrease in 4-week-old scars. Simi lar increases were seen in fetal corneas with a further increase in th e neonate. Differences in the beta ig mRNA levels relative to that of alpha 1(XII) collagen in fetal stroma and in comparison with 1-week-ol d wounds suggest a higher production of beta ig in early healing tissu e. CONCLUSIONS. Alterations of mRNA levels during healing and developm ent are consistent with the cellular events and deposition of extracel lular matrices in these corneal tissues. Assuming that extracellular m atrix protein production is regulated at the transcriptional level, re lative changes in beta ig and collagen mRNA levels reflect differences in protein deposition in early fetal and healing tissues. This is con sistent with differences in the organization of the interfibrillar mat rices of these tissues and their transparency.