Purpose: To compare the temporal and spatial expression patterns of alpha A- and alpha B-crystallin mRNA during ocular development.
Methods: Tissue samples from embryonic day 9.5 (E9.5) through postnatal day 14 were collected from FVB/N strain mice. The specimens were fixed in paraformaldehyde, histologically processed, and assayed for alpha A- and alpha B-crystallin mRNA expression by in situ hybridization.
Results: During ocular development, alpha B-crystallin transcripts are present in the lens placode at E9.5. Transcripts of alpha A-crystallin are first observed in the lens cup at E10 to 10.5. During subsequent development of the lens, alpha A crystallin transcripts are most abundant in the fiber cells, and alpha B crystallin mRNA is preferentially expressed in epithelial cells. Transcripts of alpha A-crystallin were detected only in the lens. In contrast, alpha B-crystallin transcripts are present 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-crystallin precedes the expression of alpha A-crystallin during murine ocular development. Furthermore, the patterns of alpha A- and alpha B-crystallin expression in the lens are distinctive: alpha A is upregulated and alpha B is downregulated during prenatal fiber cell differentiation. These results indicate that the alpha-crystallin genes are not identically regulated either within or outside the lens.