Targeted disruption of ATF4 discloses its essential role in the formation of eye lens fibres

Background: Activating transcription factor-4 (ATF4)-also termed CREB2, C/ATF, and TAXREB67-is a basic-leucine zipper (bZip) transcription factor that belongs to the ATF/CREB family. In addition to its own family members, ATF4 can also form heterodimers with other related but distinct bZIP proteins such as the C/EBP, AP-1 and Maf families, which may give rise to a variety of combinatorial diversity in gene regulation In order to assess the in vivo essential role of ATF4, we have generated mice lacking ATF4 by gene targeting. Results: ATF4-deficient mice exhibited severe microphthalmia. Although ATF4-deficient eyes revealed a normal gross lens structure up to embryonic day 14.5, later on the ATF4-deficient lens, degenerated due to apoptosis without the formation of lens secondary fibre cells. Retinal development was normal in the mutant mice. The lens-specific expression of ATF4 in the mutant mice led not only to the recovery of lens secondary fibres but also to the induction of hyperplasia of these fibres. Conclusion: These results demonstrated that ATF4 is essential for the later stages of lens fibre cell differentiation.