FIGURE 1.

Variant cell cycles and polyploidy in neurons. (A) Cartoons showing the progression of the canonical cell cycle and two variant cell cycles: the endocycle and the endomitotic cycle. Multiple repeated canonical cell cycles result in numerous daughter cells with diploid DNA content, whereas endocycles result in cells with tetraploid or greater (>4C) DNA content and endomitosis can result in either binucleate or multinucleate cells. (B–F) Examples of polyploid neurons from the literature. (B) Nuclear DAPI staining and quantification showing larger, polyploid pyramidal neurons in the rat cortical layer https://doi.org/10.1016/j.celrep.2017.08.069. Scale bars = 25 and 5 μM for inset. (C) Polyploid neurons in the developing mouse neocortex from https://doi.org/10.1093/texcom/tgaa063. This study used a combination of flow cytometry and FISH combined with immunostaining against various neuronal markers to determine polyploidy. NeuO is a neuronal marker. Mouse neocortex has both polyploid neurons and non-neurons, both show increased number of red and green foci (FISH probes against loci on chromosomes 11 and 2, respectively). (D) Large polyploid purkinje neurons from rat cerebellum, outlined in red. Reprinted from Herman and Lapham (1973) with permission from Elsevier. License Number 5079560753665 (to author LB). (E) Red outlines and black arrows indicate polyploid supramedullary neurons of pufferfish Diodon holancthus stained with toluidine blue. Scale bar = 100 μM. Reprinted from Cuoghi and Marini (2001) with permission from Elsevier. License number 5053261503241 (to author SN). (F) Giant neurons in an Aplysia (slug) brain, positive for BrdU in green. Nuclei are stained with DAPI in blue and cyan, and red staining indicates FISH against mRNA of neurotransmitter achatin. Data from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6622835. Scale bar = 125 μM.