p27(Kip1) participates in the regulation of endoreplication in differentiating chick retinal ganglion cells

• Published in: Cell cycle (Georgetown, Tex.) Vol. 14; no. 14; pp. 2311 - 2322
• Main Authors: Ovejero-Benito, María C, Frade, José M
• Format: Journal Article
• Language: English
• Published: United States 01.01.2015
• Subjects: Animals; Cell Differentiation; Chick Embryo; Chickens; Cyclin-Dependent Kinase 4 - antagonists & inhibitors; Cyclin-Dependent Kinase 4 - metabolism; Cyclin-Dependent Kinase 6 - antagonists & inhibitors; Cyclin-Dependent Kinase 6 - metabolism; Cyclin-Dependent Kinase Inhibitor p27 - antagonists & inhibitors; Cyclin-Dependent Kinase Inhibitor p27 - genetics; Cyclin-Dependent Kinase Inhibitor p27 - metabolism; Down-Regulation; Endoreduplication; Immunohistochemistry; Mice; Mice, Knockout; Minichromosome Maintenance Complex Component 7 - chemistry; Minichromosome Maintenance Complex Component 7 - metabolism; Ploidies; Receptor, trkB - metabolism; Retinal Ganglion Cells - cytology; Retinal Ganglion Cells - metabolism; Retinoblastoma Protein - metabolism; RNA Interference; RNA, Small Interfering - metabolism; polyploidy; cell cycle; endoreduplication; retina; endocycle; neurogenesis; vertebrate; RGC
• ISSN: 1551-4005
• DOI: 10.1080/15384101.2015.1044175

Nuclear DNA duplication in the absence of cell division (i.e. endoreplication) leads to somatic polyploidy in eukaryotic cells. In contrast to some invertebrate neurons, whose nuclei may contain up to 200,000-fold the normal haploid DNA amount (C), polyploid neurons in higher vertebrates show only 4C DNA content. To explore the mechanism that prevents extra rounds of DNA synthesis in these latter cells we focused on the chick retina, where a population of tetraploid retinal ganglion cells (RGCs) has been described. We show that differentiating chick RGCs that express the neurotrophic receptors p75 and TrkB while lacking retinoblastoma protein, a feature of tetraploid RGCs, also express p27(Kip1). Two different short hairpin RNAs (shRNA) that significantly downregulate p27(Kip1) expression facilitated DNA synthesis and increased ploidy in isolated chick RGCs. Moreover, this forced DNA synthesis could not be prevented by Cdk4/6 inhibition, thus suggesting that it is triggered by a mechanism similar to endoreplication. In contrast, p27(Kip1) deficiency in mouse RGCs does not lead to increased ploidy despite previous observations have shown ectopic DNA synthesis in RGCs from p27(Kip1-/-) mice. This suggests that a differential mechanism is used for the regulation of neuronal endoreplication in mammalian versus avian RGCs.