Type X collagen gene expression is transiently up-regulated by retinoic acid treatment in chick chondrocyte cultures.
During endochondral ossification, resting and proliferating chondrocytes mature into hypertrophic chondrocytes that initiate synthesis of type X collagen. The mechanisms regulating the differential expression of type X collagen gene were examined in confluent Day 12 secondary cultures of chick vertebral chondrocytes in monolayer treated with the vitamin A analog retinoic acid (RA). Preliminary results showed that major effects of RA on chondrocyte gene expression occurred between 24 and 48 h of treatment. Thus in subsequent experiments cultures were treated for 24, 30, 36, 42, 48, 72, 96, and 120 h. Total RNAs were isolated and analyzed by hybridization with 32P-labeled plasmid probes coding for five matrix macromolecules including type X collagen. We found that the steady-state levels of mRNAs for the large keratan sulfate/chondroitin sulfate proteoglycan (KS:CS-PG) core protein and type II collagen decreased several fold between 24 and 48 h of treatment compared to untreated cells, and remained low with further treatment. In sharp contrast, the level of type X collagen mRNA increased threefold by 42 h of treatment; thereafter it began to decrease and reached minimal levels by 72-120 h of treatment. The changes in steady-state mRNA levels during RA regimen paralleled similar changes in relative rates of protein synthesis. The transient up-regulation of type X collagen gene expression at 42 h of treatment was preceded by a five-fold increase in fibronectin gene expression, was followed by a several fold increase in type I collagen gene expression, and was accompanied by cell flattening and loss of the pericellular proteoglycan matrix. Thus, RA treatment leads to a unique biphasic modulation of type X collagen gene expression in maturing chondrocyte cultures. The underlying, RA-sensitive mechanisms effecting this modulation may reflect those normally regulating the differential expression of this collagen gene during endochondral ossification.
Oettinger
H F
HF
Department of Anatomy and Histology, School of Dental Medicine, University of Pennsylvania, Philadelphia 19104-6003.
Pacifici
M
M
D000818:Animals; D002356:Cartilage / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D002642:Chick Embryo; D002809:Chondroitin Sulfates / Q000235:genetics / Q000378:metabolism; D003094:Collagen / Q000235:genetics* / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005455:Fluorescent Antibody Technique; D015870:Gene Expression / Q000187:drug effects*; D007632:Keratan Sulfate / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D014212:Tretinoin / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects* / Q000502:physiology
D012333:RNA, Messenger; D014212:Tretinoin; D002809:Chondroitin Sulfates; D003094:Collagen; D007632:Keratan Sulfate