The molecular oscillations underlying the generation of circadian rhythmicity in mammals develop gradually during ontogenesis. However, the developmental process of mammalian cellular circadian oscillator formation remains unknown. In differentiated somatic cells, the transcriptional-translational feedback loops (TTFL) consisting of clock genes elicit the molecular circadian oscillation. Using a bioluminescence imaging system to monitor clock gene expression, we show here that the circadian bioluminescence rhythm is not detected in the mouse embryonic stem (ES) cells, and that the ES cells likely lack TTFL regulation for clock gene expression. The circadian clock oscillation was induced during the differentiation culture of mouse ES cells without maternal factors. In addition, reprogramming of the differentiated cells by expression of Sox2, Klf4, Oct3/4, and c-Myc genes, which were factors to generate induced pluripotent stem (iPS) cells, resulted in the re-disappearance of circadian oscillation. These results demonstrate that an intrinsic program controls the formation of the circadian oscillator during the differentiation process of ES cells in vitro. The cellular differentiation and reprogramming system using cultured ES cells allows us to observe the circadian clock formation process and may help design new strategies to understand the key mechanisms responsible for the organization of the molecular oscillator in mammals.circadian clock | induced pluripotent stem cells | real-time monitor T he circadian rhythm is a fundamental biological system in mammals involved in the regulation of various physiological functions such as the sleep-wake cycle, energy metabolism, and the endocrine system (1, 2). These physiological rhythms develop gradually in the first year of life in humans (3). It is well known that the human sleep-wake rhythm is generated within a few months after birth. However, a weak circadian rhythm of core body temperature is present immediately after birth, suggesting that the development of the human circadian rhythms starts during fetal life. In fact, recent studies in rodents have suggested the appearance of circadian molecular rhythms in the suprachiasmatic nucleus (SCN) a few days before birth (4). However, little information is available on the development of the mammalian cellular circadian oscillator.In mammals, molecular oscillation of the circadian clock consists of interlocked positive and negative transcription/translation feedback loops (TTFL) involving a set of clock genes and clock-controlled output genes that link the oscillator to the clock-controlled processes (5). CLOCK and BMAL1 are basic-helix-loop-helix (bHLH) PAS transcription factors that heterodimerize and transactivate the core clock genes such as Period (Per1, -2, and -3), Cryptochrome (Cry1 and Cry2), and Rev-Erbα (2, 5, 6). PER and CRY proteins suppress the activity of the CLOCK/BMAL1, whereas REV-ERBα suppresses Bmal1 gene expression.In this study, we focused on the development of the mammalian circadian oscillator du...
The circadian clock is driven by cell-autonomous transcription͞ translation feedback loops. The BMAL1 transcription factor is an indispensable component of the positive arm of this molecular oscillator in mammals. Here, we present a molecular genetic screening assay for mutant circadian clock proteins that is based on real-time circadian rhythm monitoring in cultured fibroblasts. By using this assay, we identified a domain in the extreme C terminus of BMAL1 that plays an essential role in the rhythmic control of E-box-mediated circadian transcription. Remarkably, the last 43 aa of BMAL1 are required for transcriptional activation, as well as for association with the circadian transcriptional repressor CRYPTO-CHROME 1 (CRY1), depending on the coexistence of CLOCK protein. C-terminally truncated BMAL1 mutant proteins still associate with mPER2 (another protein of the negative feedback loop), suggesting that an additional repression mechanism may converge on the N terminus. Taken together, these results suggest that the C-terminal region of BMAL1 is involved in determining the balance between circadian transcriptional activation and suppression.circadian clock ͉ real-time monitor T he mammalian circadian clock is a highly dynamic system that generates periodic fluctuations in the mRNA expression levels of hundreds of genes to confer near 24-h rhythmicity to behavior, physiology, and metabolic processes, thereby allowing mammals to anticipate the momentum of the day (1). The master clock resides in the suprachiasmatic nuclei (SCN) of the brain and, in turn, synchronizes circadian clocks in peripheral tissues (2). Even fibroblasts in culture contain an active circadian clock that has the same genetic makeup of the central clock in the SCN (3-6). To keep pace with the day-night cycle, the SCN clock, but not peripheral clocks, are entrained by light.Circadian rhythms are generated by a molecular oscillator that consists of intertwined positive and negative transcription͞ translation feedback loops involving a set of clock genes (7) and clock-controlled output genes that link the oscillator to clockcontrolled processes (8). BMAL1 (MOP3) and CLOCK are basic helix-loop-helix PAS transcription factors that heterodimerize and (by means of binding to E-box promoter elements) transactivate the Period (Per1 and Per2) and Cryptochrome (Cry1 and Cry2) genes and an orphan nuclear receptor Rev-Erb␣ core oscillator gene. Subsequently, PER and CRY proteins act as negative elements by inhibiting the activity of the CLOCK͞BMAL1 heterodimer, whereas REV-ERB␣ negatively regulates Bmal1 gene expression (1, 9). The above feedback mechanism is supported by biochemical, molecular, and genetic evidence; however, formal proof of its requirement in the maintenance of circadian clock oscillations has not been shown thus far.Genetic ablation of mBmal1 results in complete disruption of the mammalian circadian clock at the behavioral and molecular levels (10). However, except for the PAS elements, which are required for association with CLOCK (11)...
The synthesis and functional analysis of KL001 derivatives, which are modulators of the mammalian circadian clock, are described. By using cutting-edge C-H activation chemistry, a focused library of KL001 derivatives was rapidly constructed, which enabled the identification of the critical sites on KL001 derivatives that induce a rhythm-changing activity along with the components that trigger opposite modes of action. The first period-shortening molecules that target the cryptochrome (CRY) were thus discovered. Detailed studies on the effects of these compounds on CRY stability implicate the existence of an as yet undiscovered regulatory mechanism.
Glycine is a major inhibitory neurotransmitter in the spinal cord and brainstem. Recently, in vivo analysis of glycinergic synaptic transmission has been pursued in zebrafish using molecular genetics. An ENU mutagenesis screen identified two behavioral mutants that are defective in glycinergic synaptic transmission. Zebrafish bandoneon (beo) mutants have a defect in glrbb, one of the duplicated glycine receptor (GlyR) β subunit genes. These mutants exhibit a loss of glycinergic synaptic transmission due to a lack of synaptic aggregation of GlyRs. Due to the consequent loss of reciprocal inhibition of motor circuits between the two sides of the spinal cord, motor neurons activate simultaneously on both sides resulting in bilateral contraction of axial muscles of beo mutants, eliciting the so-called ‘accordion’ phenotype. Similar defects in GlyR subunit genes have been observed in several mammals and are the basis for human hyperekplexia/startle disease. By contrast, zebrafish shocked (sho) mutants have a defect in slc6a9, encoding GlyT1, a glycine transporter that is expressed by astroglial cells surrounding the glycinergic synapse in the hindbrain and spinal cord. GlyT1 mediates rapid uptake of glycine from the synaptic cleft, terminating synaptic transmission. In zebrafish sho mutants, there appears to be elevated extracellular glycine resulting in persistent inhibition of postsynaptic neurons and subsequent reduced motility, causing the ‘twitch-once’ phenotype. We review current knowledge regarding zebrafish ‘accordion’ and ‘twitch-once’ mutants, including beo and sho, and report the identification of a new α2 subunit that revises the phylogeny of zebrafish GlyRs.
In mammalian circadian rhythms, the transcriptional-translational feedback loop (TTFL) consisting of a set of clock genes is believed to elicit the circadian clock oscillation. The TTFL model explains that the accumulation and degradation of mPER and mCRY proteins control the period-length (tau) of the circadian clock. Although recent studies revealed that the Casein Kinase Iεδ (CKIεδ) regurates the phosphorylation of mPER proteins and the circadian period-length, other kinases are also likely to contribute the phosphorylation of mPER. Here, we performed small scale screening using 84 chemical compounds known as kinase inhibitors to identify candidates possibly affecting the circadian period-length in mammalian cells. Screening by this high-throughput real-time bioluminescence monitoring system revealed that the several chemical compounds apparently lengthened the cellular circadian clock oscillation. These compounds are known as inhibitors against kinases such as Casein Kinase II (CKII), PI3-kinase (PI3K) and c-Jun N-terminal Kinase (JNK) in addition to CKIεδ. Although these kinase inhibitors may have some non-specific effects on other factors, our mini screening identified new candidates contributing to period-length control in mammalian cells.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.