Control of lens fiber cell denucleation by CDK1 and its regulators

Abstract

Purpose : The lens of the eye undergoes a regulated differentiation process whereby organelle removal in the fiber cells is necessary for lens clarity. The mechanisms by which this occurs are unclear. Previous work in our lab demonstrated that impaired lens fiber cell denucleation (LFCD) was associated with increased levels of the CDK inhibitor p27. Additionally, we showed that deletion of CDK1 in the lens impaired LFCD. These data indicate that CDK activity is crucial for denucleation. In this study, we examine the role of CDK activators and inhibitors in the denucleation process.

Methods : We used three different mouse models to ask whether increased p27 levels affects lens differentiation. The first model expresses a drug inducible p27 transgene. We induced expression of the transgene during pregnancy to increase p27 during a crucial phase of lens differentiation. The second model is a Skp2-/-. Skp2 is part of a ubiquitin ligase complex that is known to ubiquitinate p27 and target it for proteasomal degradation; these mice constitutively express high levels of p27. The third model expresses a degradation resistant mutant p27. To determine how CDK1 regulators are involved in LFCD, we used a chick lens culture model and treated lenses with small molecule drugs that affect the activities of Cdc25, Wee1, CDK1 and PP2A.

Results : Expression of increased levels of p27 led to impaired LFCD in all three mouse models. Inhibition of the CDK1 activator Cdc25 inhibits LFCD, whereas inhibition of the CDK1 inhibitor Wee1 potentiates LFCD in chick lenses. PP2A inhibits CDK1 activity: activation of PP2A inhibits LFCD while inhibition of PP2A increases LFCD.

Conclusions : Inhibition of CDK1 activity by increased p27 protein levels, activation of PP2A or inhibition of Cdc25 inhibits LFCD. Inhibiting CDK1 inhibitors Wee1 and PP2A, led to increased LFCD. Thus, CDK1 activity is a crucial regulator of LFCD.

This is a 2020 ARVO Annual Meeting abstract.