DIFFERENTIAL EXPRESSION OF ALPHA-A-CRYSTALLIN AND ALPHA-B-CRYSTALLIN DURING MURINE OCULAR DEVELOPMENT

Purpose. To compare the temporal and spatial expression patterns of al pha A- and alpha B-crystallin mRNA during ocular development. Methods. Tissue samples from embryonic clay 9.5 (E9.5) through postnatal day 1 4 were collected from FVB/N strain mice. The specimens were fixed in p araformaldehyde, histologically processed, and assayed for alpha A- an d alpha B-crystallin mRNA expression by in situ hybridization. Results . During ocular development, alpha B-crystallin transcripts are presen t in the lens placode at E9.5. Transcripts of alpha Acrystallin are fi rst observed in the lens cup at E10 to 10.5. During subsequent develop ment of the lens, alpha A crystallin transcripts are most abundant in the fiber cells, and alpha B crystallin mRNA is preferentially express ed in epithelial cells. Transcripts of alpha A-crystallin were detecte d only in the lens. In contrast, alpha B-crystallin transcripts are pr esent in retinal pigment epithelium, optic nerve, extraocular muscle, iris, ciliary body, cornea, and several nonocular sites, such as heart and nasal epithelium. Conclusions. Transcription of alpha B-crystalli n precedes the expression of alpha A-crystallin during murine ocular d evelopment. Furthermore, the patterns of alpha A- and beta B-crystalli n expression in the lens are distinctive: alpha A is upregulated and a lpha B is downregulated during prenatal fiber cell differentiation. Th ese results indicate that the alpha-crystallin genes are not identical ly regulated either within or outside the lens.