Regulation of mouse lens maturation and gene expression by Krüppel-like factor 4.

Conditional disruption of Klf4 in the surface ectoderm-derived tissues of the eye results in defective cornea, conjunctiva and the lens. This report describes the effects of disruption of Klf4 in the lens in greater detail. Expression of Klf4, first detected in the embryonic day-12 (E12) mouse lens, peaked at E16 and was decreased in later stages. Early embryonic disruption of Klf4 resulted in a smaller lens with cortical vacuolation and nuclear opacity. Microarray comparison of Klf4CN and WT lens transcriptomes revealed fewer changes in the E16.5 (59 increases, 20 decreases of >1.5-fold) than the PN56 Klf4CN lens (239 increases, 182 decreases of >2-fold). Klf4-target genes in the lens were distinct from those previously identified in the cornea, suggesting disparate functions for Klf4 in these functionally related tissues. Transcripts encoding different crystallins were down-regulated in the Klf4CN lens. Shsp/αB-crystallin promoter activity was stimulated upon co-transfection with pCI-Klf4. Mitochondrial density was significantly higher in the Klf4CN lens epithelial cells, consistent with mitochondrial dysfunction being the most significantly affected pathway within the PN56 Klf4CN lens. The Klf4CN lens contained elevated levels of Alox12 and Alox15 transcripts, less reduced glutathione (GSH) and more oxidized glutathione (GSSG) than the WT, suggesting that it is oxidatively stressed. Although the expression of 2087 genes was modulated during WT lens maturation, transcripts encoding crystallins were abundant at E16.5 and remained stable at PN56. Among the 1065 genes whose expression increased during WT lens maturation, there were 104 Klf4-target genes (9.8%) with decreased expression in the PN56 Klf4CN lens. Taken together, these results demonstrate that Klf4 expression is developmentally regulated in the mouse lens, where it controls the expression of genes associated with lens maturation and redox homeostasis.