Repurposing a cyclin dependent kinase 1 (CDK1) mitotic regulatory network to complete terminal differentiation in lens fiber cells

Authors: TAYLOR, ALLEN - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; GU, YUMEI - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; CHANG, MIN-LEE - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; YANG, WENXIN - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; FRANCISCO, SARAH - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; ROWAN, SHELDON - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; BEJARANO, ELOY - University Of Cardenal Herrera-Ceu; PRUITT, STEVEN - Roswell Park Cancer Institute; ZHU, LIANG - Albert Einstein College Of Medicine; WEISS, GRANT - Tufts University; BRENNAN, LISA - Florida Atlantic University; KANTOROW, MARC - Florida Atlantic University; WHITCOMB, ELIZABETH - Jean Mayer Human Nutrition Research Center On Aging At Tufts University

Submitted to: Investigative Ophthalmology and Visual Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2022
Publication Date: 2/3/2023
Citation: Taylor, A., Gu, Y., Chang, M., Yang, W., Francisco, S., Rowan, S., Bejarano, E., Pruitt, S., Zhu, L., Weiss, G., Brennan, L., Kantorow, M., Whitcomb, E. 2023. Repurposing a cyclin dependent kinase 1 (CDK1) mitotic regulatory network to complete terminal differentiation in lens fiber cells. Investigative Ophthalmology and Visual Science. 64(2). https://doi.org/10.1167/iovs.64.2.6.
DOI: https://doi.org/10.1167/iovs.64.2.6

Interpretive Summary: The function of the lens is to focus light on the retina and lens clarity is necessary for proper vision. To achieve clarity, the lens undergoes a programmed removal of its organelles, including the cell nuclei in the central lens fiber cells. We hypothesized that a similar process may be responsible for the removal of nuclei in lens fiber cells. We used a chick lens culture model to demonstrate that compounds which inhibit nuclear envelope breakdown during cell division also inhibit nuclear removal in the lens. Furthermore, using three mouse models, we showed that an inhibitor of cell division also decreased nuclear removal in lens fiber cells. Thus, the lens utilizes proteins involved in cell division to achieve lens clarity by removing rather than replicating nuclei in the central lens fibers.

Technical Abstract: Purpose: During lens fiber cell differentiation, organelles are removed in an ordered manner to insure lens clarity. A critical step in this process is removal of the cell nucleus, however, the mechanisms by which this occurs are unclear. In this study, we investigate the role of a Cyclin dependent kinase 1 (CDK1) regulatory loop in controlling lens fiber cell denucleation (LFCD). Methods: We examined lens differentiation histologically in two different vertebrate models. An embryonic chick lens culture system was used to test the role of CDK1, cell division cycle 25(CDC25), WEE1 and PP2A in LFCD. Additionally, we used three mouse models which express high levels of the CDK inhibitor p27 to test whether increased p27 levels affect LFCD. Results: Using chick lens organ cultures, small molecule inhibitors of CDK1 and CDC25 inhibit LFCD, while inhibiting the CDK1 inhibitory kinase WEE1, potentiates LFCD. Additionally, treatment with an inhibitor of PP2A which indirectly inhibits CDK1 activity also increased LFCD. Three different mouse models that express increased levels of p27 though different mechanisms show impaired LFCD. Conclusions: Here we define a conserved non-mitotic role for CDK1 and its upstream regulators in controlling LFCD. We find that CDK1 functionally interacts with, WEE1, a nuclear kinase that inhibits CDK1 activity, and CDC25 activating phosphatases in cells where CDK1 activity must be exquisitely regulated to allow for LFCD. We also provide genetic evidence in multiple in vivo models that p27, a CDK1 inhibitor, inhibits lens growth and LFCD.