Developmental patterns of two α1(IX) collagen mRNA isoforms in mouse

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Abstract
Northern blot hybridization, reverse‐transcription polymerase chain reaction (RT‐PCR), and RNase protection assays were used to examine the expression of twoα1(IX) collagen mRNA species (long and short form) in developing mouse tissues. Furthermore, in situ hybridization was used to identify cells expressing the Col9a1 gene during eye development. The results indicate that during embryonic development eye and heart preferentially express the short form; lung and cartilage express the long form; whereas liver expresses a very low level of long formα1(IX) mRNA which can only be detected by RT‐PCR. In situ hybridization demonstrated that at 10.5 day postcoitum (d.p.c.), theα1(IX) collagen mRNAs were first expressed in optic cup (neural ectoderm) but not in lens vesicle (surface ectoderm). By 13.5 d.p.c., the cells that express theα1(IX) mRNA progressively were concentrated to ward the anterior part of the neural retina. By 16.5–18.5 d.p.c., the hybridization signals were found exclusively in the inner non‐pigmented layer of the presumptive ciliary epithelium. As ciliary epithelial cells become well differentiated 3 weeks after birth, cells expressing the Col9a1 gene were limited to the junction between mature ciliary folds and the neural retina. No hybridization signal could be detected in ocular tissues of mouse older than 6 weeks. It is of interest to note that a hybridization signal was not detected in cornea at the various developmental stages examined, suggesting that mouse cornea does not significantly expressα1(IX) mRNA during embyronic development. This differs from that of chick cornea development. In summary, the expression of the Col9a1 gene shows a temporospatial pattern throughout mouse eye development. It is suggested that the short form collagen IX may play an important role in eye development.

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