HMN 2025: How Human CLOCK gene enhances mind connectivity and psychological flexibility in mice, study finds

Clock genes are a set of genes identified to contribute to the regulation of the human physique’s inside 24-hour cycle, also called the circadian rhythm. One of those genes is the so-called CLOCK gene, a protein that regulates the exercise of different genes, contributing to recurrent patterns of sleep and wakefulness.

Past findings counsel that this gene can be expressed within the neocortex, a mind area that helps necessary cognitive talents, together with reasoning, decision-making and the processing of language. However, the gene’s potential contribution to those particular mind features stays poorly understood.

Researchers at UT Southwestern Medical Center not too long ago carried out a research on genetically modified mice aimed toward higher understanding how the expression of the CLOCK gene within the human neocortex influences cognitive features. Their findings, published in Nature Neuroscience, counsel that the gene performs a job within the formation of connections between neurons, which in flip affect psychological and behavioral flexibility.

“Comparative genomic research of the neocortex in people and non-human primates have repeatedly recognized human-specific upregulation of the CLOCK gene, suggesting that CLOCK might play a vital position within the evolution of the human mind’s superior cognitive features,” Genevieve Konopka, senior writer of the paper, advised Medical Xpress.

“Intriguingly, though CLOCK is a core circadian regulator, it reveals distinct properties within the human neocortex: it’s extremely expressed in cortical neurons, lacks overt rhythmicity, and regulates a broad set of non-circadian genes. These findings from each evolutionary genomics and circadian biology converge to counsel novel, human-specific neuronal features of CLOCK.”

To discover the potential contributions of the CLOCK gene past the regulation of the circadian rhythm, Konopka and her colleagues first created a humanized mouse model utilizing genetic methods. They particularly modified the expression of the gene within the brains of mice, in order that it intently mirrored its expression within the human neocortex.

The expression patterns that they engineered in mice have been to date solely noticed in people. Therefore, the staff’s speculation was that areas regulating the gene’s expression may need gone via particular adjustments throughout evolution.

“To check this speculation, we used recombineering to edit a human bacterial synthetic chromosome (BAC) containing the full-length CLOCK gene together with its flanking regulatory components,” defined Konopka. “This assemble was used to generate a humanized CLOCK mouse model (HU).

“In customary studying and reminiscence duties, we noticed no vital variations between HU and wild-type mice, probably on account of a ceiling impact. Therefore, we assessed cognitive flexibility utilizing a set-shifting job, which calls for higher-order, rule-based studying.”

To decide when and in what mind areas or varieties of mind cells the CLOCK gene is energetic, the researchers studied the brains of the modified mice at completely different levels of improvement utilizing a mixture of experimental methods. These included immunohistochemistry (IHC), a way that depends on antibodies to detect particular proteins in sections of tissue, and single-nucleus RNA sequencing (snRNA-Seq), a high-resolution software to measure the exercise of genes in particular person cell nuclei.

“To additional establish neuronal features regulated by human CLOCK, we examined neuronal cytoarchitecture and synaptic connectivity utilizing confocal imaging and electrophysiological recordings,” mentioned Konopka. “Finally, to validate our mouse findings in a human context, we employed CRISPR-edited human induced pluripotent stem cell (iPSC) models, confirming the dendritic and backbone phenotypes related to human CLOCK.”

Overall, Konopka and her colleagues discovered that human CLOCK regulates the expression of genes in neurons that contribute to the activation of different cells (i.e., excitatory neurons). They hypothesize that this course of promotes the formation of extra intricate neural networks, that are linked with higher cognitive flexibility.

The adjustments they noticed in mice have been mediated by the altered expression of the gene within the frontal cortex of the “humanized” animals. This means that they efficiently altered the mice to imitate how CLOCK is expressed within the human neocortex.

“Our findings exhibit that CLOCK has undergone evolutionary good points of extra-circadian operate, and that these features might contribute to human-specific mind specializations,” mentioned Konopka. “This work makes a number of novel and necessary contributions to the understanding of CLOCK’s neural operate and its position in human mind evolution.

“First, we developed each a humanized CLOCK mouse model and a CRISPR-mediated CLOCK knockout human iPSC model, which symbolize priceless sources for the broader scientific neighborhood. Second, we recognized a beforehand unrecognized extra-circadian operate of human CLOCK in excitatory neurons of the neocortex.”

This latest study is among the many first to analyze the contribution of a gene identified to help circadian rhythms to different mind features. In the long run, the findings gathered by Konopka and her colleagues may encourage different analysis teams to discover the extra-circadian features of clock genes utilizing humanized animal models.

“We additionally present one of many first strains of proof {that a} novel acquire of operate via altered spatiotemporal gene expression can underlie points of human mind evolution,” added Konopka.

“An intriguing discovering from this study is the elevated cell density, together with each neurons and glia, within the neocortex of HU mice, suggesting that human CLOCK might affect neurogenesis throughout embryonic improvement. Future work will concentrate on characterizing the expression and performance of human CLOCK in neural stem cells.”

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