bims-ciryme 2023-07-16 papers

bioRxiv. 2023 Jun 28. pii: 2023.06.26.546624. [Epub ahead of print]

The circadian molecular clock in the suprachiasmatic nucleus is necessary but not sufficient for fear entrainment in the mouse.

Ivana L Bussi, Miriam Ben-Hamo, Luis E Salazar Leon, Leandro P Casiraghi, Victor Y Zhang, Alexandra F Neitz, Jeffrey Lee, Joseph S Takahashi, Jeansok J Kim, Horacio O de la Iglesia.

Nocturnal aversive stimuli presented to mice during eating and drinking outside of their safe nest can entrain circadian behaviors, leading to a shift toward daytime activity. We show that the canonical molecular circadian clock is necessary for fear entrainment and that an intact molecular clockwork in the suprachiasmatic nucleus (SCN), the site of the central circadian pacemaker, is necessary but not sufficient to sustain fear entrainment of circadian rhythms. Our results demonstrate that entrainment of a circadian clock by cyclic fearful stimuli can lead to severely mistimed circadian behavior that persists even after the aversive stimulus is removed. Together, our results support the interpretation that circadian and sleep symptoms associated with fear and anxiety disorders may represent the output of a fear-entrained clock.
One-Sentence Summary: Cyclic fearful stimuli can entrain circadian rhythms in mice, and the molecular clock within the central circadian pacemaker is necessary but not sufficient for fear-entrainment.

DOI: https://doi.org/10.1101/2023.06.26.546624

Proc Natl Acad Sci U S A. 2023 07 18. 120(29): e2303779120

Dissecting neuron-specific functions of circadian genes using modified cell-specific CRISPR approaches.

Shlesha Richhariya, Daniel Shin, Jasmine Quynh Le, Michael Rosbash.

Circadian behavioral rhythms in Drosophila melanogaster are regulated by about 75 pairs of brain neurons. They all express the core clock genes but have distinct functions and gene expression profiles. To understand the importance of these distinct molecular programs, neuron-specific gene manipulations are essential. Although RNAi based methods are standard to manipulate gene expression in a cell-specific manner, they are often ineffective, especially in assays involving smaller numbers of neurons or weaker Gal4 drivers. We and others recently exploited a neuron-specific CRISPR-based method to mutagenize genes within circadian neurons. Here, we further explore this approach to mutagenize three well-studied clock genes: the transcription factor gene vrille, the photoreceptor gene Cryptochrome (cry), and the neuropeptide gene Pdf (pigment dispersing factor). The CRISPR-based strategy not only reproduced their known phenotypes but also assigned cry function for different light-mediated phenotypes to discrete, different subsets of clock neurons. We further tested two recently published methods for temporal regulation in adult neurons, inducible Cas9 and the auxin-inducible gene expression system. The results were not identical, but both approaches successfully showed that the adult-specific knockout of the neuropeptide Pdf reproduces the canonical loss-of-function mutant phenotypes. In summary, a CRISPR-based strategy is a highly effective, reliable, and general method to temporally manipulate gene function in specific adult neurons.

Keywords: adult-specific CRISPR; cell type–specific CRISPR; circadian; clock neurons; cryptochrome

DOI: https://doi.org/10.1073/pnas.2303779120

Cell Mol Life Sci. 2023 Jul 08. 80(8): 200

Artificial induction of circadian rhythm by combining exogenous BMAL1 expression and polycomb repressive complex 2 inhibition in human induced pluripotent stem cells.

Hitomi Kaneko, Taku Kaitsuka, Kazuhito Tomizawa.

Understanding the physiology of human-induced pluripotent stem cells (iPSCs) is necessary for directed differentiation, mimicking embryonic development, and regenerative medicine applications. Pluripotent stem cells (PSCs) exhibit unique abilities such as self-renewal and pluripotency, but they lack some functions that are associated with normal somatic cells. One such function is the circadian oscillation of clock genes; however, whether or not PSCs demonstrate this capability remains unclear. In this study, the reason why circadian rhythm does not oscillate in human iPSCs was examined. This phenomenon may be due to the transcriptional repression of clock genes resulting from the hypermethylation of histone H3 at lysine 27 (H3K27), or it may be due to the low levels of brain and muscle ARNT-like 1 (BMAL1) protein. Therefore, BMAL1-overexpressing cells were generated and pre-treated with GSK126, an inhibitor of enhancer of zest homologue 2 (EZH2), which is a methyltransferase of H3K27 and a component of polycomb repressive complex 2. Consequently, a significant circadian rhythm following endogenous BMAL1, period 2 (PER2), and other clock gene expression was induced by these two factors, suggesting a candidate mechanism for the lack of rhythmicity of clock gene expression in iPSCs.

Keywords: BMAL1; Circadian rhythm; GSK126; H3K27 me3; PRC2; iPSCs

DOI: https://doi.org/10.1007/s00018-023-04847-z

Neurochem Res. 2023 Jul 14.

The Dopaminergic System Modulates the Electrophysiological Activity of the Suprachiasmatic Nucleus Dependent on the Circadian Cycle.

Somaye Mesgar, Kiarash Eskandari, Habib Karimian-Sani-Varjovi, Paria Salemi-Mokri-Boukani, Abbas Haghparast.

The suprachiasmatic nucleus of the hypothalamus (SCN) controls mammalian circadian rhythms. Circadian rhythms influence the dopaminergic system, and dopaminergic tone impresses the physiology and behavior of the circadian clock. However, little is known about the effect of dopamine and dopamine receptors, especially D1-like dopamine receptors (D1Rs), in regulating the circadian rhythm and the SCN neuron's activity. Therefore, the present study aimed to investigate the role of the D1Rs in SCN neural oscillations during the 24-h light-dark cycle using local field potential (LFP) recording. To this end, two groups of rats were given the SKF-38393 (1 mg/kg; i.p.) as a D1-like receptor agonist in the morning or night. LFP recording was performed for ten minutes before and two hours after the SKF-38393 injection. The obtained results showed that diurnal changes affect LFP oscillations so that delta relative power declined substantially, whereas upper-frequency bands and Lempel-Ziv complexity (LZC) index increased at night, which is consistent with rodents' activity cycles. The D1Rs agonist administration in the morning dramatically altered these intrinsic oscillations, decreasing delta and theta relative power, and most of the higher frequency bands and LZC index were promoted. Some of these effects were reversed at the night after the SKF-38393 injection. In conclusion, findings showed that the SCN's neuronal activities are regulated based on the light-dark cycle in terms of population neural oscillatory activity which could be affected by dopaminergic stimulation in a time-dependent way.

Keywords: Circadian clock; D1-like dopamine receptor; Dopamine; Local Field Potential; Rat; Suprachiasmatic nucleus

DOI: https://doi.org/10.1007/s11064-023-03988-8

J Biol Rhythms. 2023 Jul 10. 7487304231180953

Modeling the Effects of Napping and Non-napping Patterns of Light Exposure on the Human Circadian Oscillator.

Shelby R Stowe, Monique K LeBourgeois, Cecilia Diniz Behn.

In early childhood, consolidation of sleep from a biphasic to a monophasic sleep-wake pattern, that is, the transition from sleeping during an afternoon nap and at night to sleeping only during the night, represents a major developmental milestone. Reduced napping behavior is associated with an advance in the timing of the circadian system; however, it is unknown if this advance represents a standard response of the circadian clock to altered patterns of light exposure or if it additionally reflects features of the developing circadian system. Using a mathematical model of the human circadian pacemaker, we investigated the impact of napping and non-napping patterns of light exposure on entrained circadian phases. Simulated light schedules were based on published data from 20 children (34.2 ± 2.0 months) with habitual napping or non-napping sleep patterns (15 nappers). We found the model predicted different circadian phases for napping and non-napping light patterns: both the decrease in afternoon light during the nap and the increase in evening light associated with napping toddlers' later bedtimes contributed to the observed circadian phase difference produced between napping and non-napping light schedules. We systematically quantified the effects on phase shifting of nap duration, timing, and light intensity, finding larger phase delays occurred for longer and earlier naps. In addition, we simulated phase response curves to a 1-h light pulse and 1-h dark pulse to predict phase and intensity dependence of these changes in light exposure. We found the light pulse produced larger shifts compared with the dark pulse, and we analyzed the model dynamics to identify the features contributing to this asymmetry. These findings suggest that napping status affects circadian timing due to altered patterns of light exposure, with the dynamics of the circadian clock and light processing mediating the effects of the dark pulse associated with a daytime nap.

Keywords: circadian oscillator; early childhood; light; mathematical model; napping; phase response curve

DOI: https://doi.org/10.1177/07487304231180953