Aneuploid neurons are functionally active and integrated into brain circuitry

Abstract

The existence of aneuploid cells within the mammalian brain has suggested the influence of genetic mosaicism on normal neural circuitry. However, aneuploid cells might instead be glia, nonneural, or dying cells, which are irrelevant to direct neuronal signaling. Combining retrograde labeling with FISH for chromosome-specific loci, distantly labeled aneuploid neurons were observed in expected anatomical projection areas. Coincident labeling for immediate early gene expression indicated that these aneuploid neurons were functionally active. These results demonstrate that functioning neurons with aneuploid genomes form genetically mosaic neural circuitries as part of the normal organization of the mammalian brain.cerebral cortex ͉ chromosome paint ͉ mosacism A neuploidy, the loss and͞or gain of chromosomes producing numerical deviation from haploid multiples, has documented effects on cellular physiology, particularly in pathophysiological settings such as cancer and Down's syndrome (1, 2). Whereas even the quantitative change of a single-gene product can produce major changes in cellular signaling (3), the effects associated with loss or gain of Ϸ1,000 gene copies on an average chromosome should have even more pronounced changes on a cell's physiology. Approximately 33% of neural progenitor cells display genetic variability, manifested as chromosomal aneuploidy that encompasses both loss and gain of chromosomes (4-7). In the mature brain, aneuploid cells that express neuronal markers have been observed (4, 6). However, an unanswered question is whether these neurons represent functional rather than dying cells, with death being a common fate for aneuploid cells in other systems (8,9). Toward determining their relevance for adult brain function, we examined aneuploid cells in the normal brain for anatomical connectivity and functional activity. MethodsProcedures involving live animals were conducted at the University of California at San Diego (UCSD), approved by the Animal Subjects Committee at UCSD, and conform to National Institutes of Health guidelines and public law.Activation Paradigm for Immediate Early Gene (IEG) Induction. All animals were transferred from the home cage to a clean cage 1 h before killing. To maximize the activation of cortical cells, two mice received additional stimulation that included exposure to a novel male (10) and to various odors (11). Specifically, a novel male was placed in the same cage as the subject male, and the males were allowed to interact for 1-3 min. After the removal of the novel male, subject males were then exposed sequentially to peppermint and banana odors for 15 min each while remaining in the clean cage. Animals were killed 1 h after the beginning of the exposure paradigm, perfused with 0.9% saline, followed by 4% paraformaldehyde in 0.1 M PBS (pH 7.4), and brain tissue was processed as described below.Retrograde Tracer Injections. Ten male 8-week-old mice from three different strains (BalbC͞CR, Swiss Webster, and c129SvJ) received tracer injections. Mice were ane...

Alzheimer's presenilin 1 causes chromosome missegregation and aneuploidy

“…Several possibilities can be envisioned and are the subject of current investigations. For example, the process of mitotic spindle malformation/disruption and consequent chromosome missegregation in neural stem cells could trigger a cell cycle checkpoint that leads to apoptosis and/or reduced neurogenesis, although recent work in mice suggests that aneuploid neurons survive and function well [19]. Also, the evident PS-induced disruption of the microtubule network indicates that PS overexpression or mutation likely interferes with microtubule formation or function, possibly through an effect on microtubule associated proteins such as Tau.…”

“…Interestingly, age itself is the greatest risk factor for developing AD, and low levels of aneuploidy have also been shown to develop in mature brain neurons because of mitotic defects in neural precursor cells [19,34,51]. The fact that chromosome segregation defects underlie another disease of aging-cancer [4]-suggests that perhaps microtubule disfunction leading to different degrees and types of aneuploidy underlie many manifestations of "normal" aging in addition to predisposing to Alzheimer's disease when chromosome 21 is affected [32].…”

Donor cell differentiation, reprogramming, and cloning efficiency: Elusive or illusive correlation?

“…This failure is significant but does not necessarily reflect lower reprogrammability of neurons. Instead, the fact that an unknown proportion of functional adult neurons are aneuploid (Kingsbury et al, 2005) may account for their apparent loss of totipotency after NT. If this was indeed the reason, the data could not be interpreted in light of the high differentiation-low reprogrammability hypothesis since genetic errors are unlikely to be reversible by reprogramming.…”

Single cell sequencing reveals low levels of aneuploidy across mammalian tissues

“…Subsequent studies using FISH indicated that approximately 20% of adult mouse and human brain cells were aneuploid (16)(17)(18)(19)(20). These aneuploid cells were believed to arise from chromosome mis-segregation events in neural progenitor cells and were shown to integrate into brain circuitry (21,22). These high levels of aneuploidy were proposed to provide the brain with its notable phenotypic diversity while simultaneously predisposing the organ to neurodegeneration (23)(24)(25)(26).…”