title: Nuclear removal during terminal lens fiber cell differentiation requires CDK1 activity: appropriating mitosis-related nuclear disassembly.
abstract: Lens epithelial cells and early lens fiber cells contain the typical complement of intracellular organelles. However, as lens fiber cells mature they must destroy their organelles, including nuclei, in a process that has remained enigmatic for over a century, but which is crucial for the formation of the organelle-free zone in the center of the lens that assures clarity and function to transmit light. Nuclear degradation in lens fiber cells requires the nuclease DNase IIβ (DLAD) but the mechanism by which DLAD gains access to nuclear DNA remains unknown. In eukaryotic cells, cyclin-dependent kinase 1 (CDK1), in combination with either activator cyclins A or B, stimulates mitotic entry, in part, by phosphorylating the nuclear lamin proteins leading to the disassembly of the nuclear lamina and subsequent nuclear envelope breakdown. Although most post-mitotic cells lack CDK1 and cyclins, lens fiber cells maintain these proteins. Here, we show that loss of CDK1 from the lens inhibited the phosphorylation of nuclear lamins A and C, prevented the entry of DLAD into the nucleus, and resulted in abnormal retention of nuclei. In the presence of CDK1, a single focus of the phosphonuclear mitotic apparatus is observed, but it is not focused in CDK1-deficient lenses. CDK1 deficiency inhibited mitosis, but did not prevent DNA replication, resulting in an overall reduction of lens epithelial cells, with the remaining cells possessing an abnormally large nucleus. These observations suggest that CDK1-dependent phosphorylations required for the initiation of nuclear membrane disassembly during mitosis are adapted for removal of nuclei during fiber cell differentiation.
authors.affiliation: Department of Biology, Miami University, Oxford, OH 45056, USA.
authors.forename: Blake R
authors.initials: BR
authors.lastname: Chaffee
authors.affiliation: Laboratory for Nutrition and Vision Research, Human Nutrition Research Center on Aging, Nutrition &Vision Res-USDA-HNRCA, Tufts University, Boston 02111, MA, USA.
authors.forename: Fu
authors.initials: F
authors.lastname: Shang
authors.affiliation: Laboratory for Nutrition and Vision Research, Human Nutrition Research Center on Aging, Nutrition &Vision Res-USDA-HNRCA, Tufts University, Boston 02111, MA, USA.
authors.forename: Min-Lee
authors.initials: ML
authors.lastname: Chang
authors.affiliation: National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC 27709, USA.
authors.forename: Tracy M
authors.initials: TM
authors.lastname: Clement
authors.affiliation: National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC 27709, USA.
authors.forename: Edward M
authors.initials: EM
authors.lastname: Eddy
authors.affiliation: Department of Biology, Miami University, Oxford, OH 45056, USA.
authors.forename: Brad D
authors.initials: BD
authors.lastname: Wagner
authors.affiliation: Department of Molecular and Cellular Physiology, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Nakahara
authors.affiliation: Department of Medical Chemistry, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Shigekazu
authors.initials: S
authors.lastname: Nagata
authors.affiliation: Department of Biology, Miami University, Oxford, OH 45056, USA robinsm5@miamioh.edu allen.taylor@tufts.edu.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Robinson
authors.affiliation: Laboratory for Nutrition and Vision Research, Human Nutrition Research Center on Aging, Nutrition &Vision Res-USDA-HNRCA, Tufts University, Boston 02111, MA, USA Department of Biological Chemistry, Weizmann Institute of Science, Rehovot, Israel robinsm5@miamioh.edu allen.taylor@tufts.edu.
authors.forename: Allen
authors.initials: A
authors.lastname: Taylor
mesh_terms: D000818:Animals; D016203:CDC2 Protein Kinase / Q000172:deficiency / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002454:Cell Differentiation; D002467:Cell Nucleus / Q000378:metabolism*; D004247:DNA / Q000096:biosynthesis; D004622:Embryo, Mammalian / Q000166:cytology / Q000201:enzymology; D004706:Endodeoxyribonucleases / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D062951:Endoreduplication; D004847:Epithelial Cells / Q000166:cytology / Q000201:enzymology; D005260:Female; D019426:Integrases / Q000378:metabolism; D034882:Lamins / Q000378:metabolism; D007908:Lens, Crystalline / Q000166:cytology* / Q000201:enzymology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008928:Mitochondria / Q000378:metabolism; D008938:Mitosis; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation
chemical_list: D018797:Cell Cycle Proteins; D034882:Lamins; D009687:Nuclear Proteins; C489080:Numa1 protein, mouse; D004247:DNA; D016203:CDC2 Protein Kinase; C045073:Cre recombinase; D019426:Integrases; D004706:Endodeoxyribonucleases; C019329:deoxyribonuclease II
keywords: CDK1; Lens fiber differentiation; Mouse; Organelle-free zone