Biological Clock Research Articles

Newly discovered harvestmen relict eyes eyeing for their functions.

Most chelicerates operate the world with two kinds of visual organs, the median and lateral eyes of the arthropod ground plan. In harvestmen (Opiliones), however, members of the small and withdrawn suborder Cyphophthalmi lack eyes except for two genera with lateral eyes. In the other suborders (Eupnoi, Dyspnoi, and Laniatores), lateral eyes are absent but median eyes pronounced. To resolve the phylogenetic history of these contrasting trait states and the taxonomic position of a four-eyed harvestmen fossil, visual system development was recently studied in the daddy longleg Phalangium opilio (Eupnoi). This effort uncovered not only a highly regressed and internalized pair of lateral eyes but also a similarly cryptic pair of additional median eyes. After recounting the evo-devo discovery journey of uncompromising harvestmen taxonomists, this review explores comparative evidence that the enigmatic P. opilio relict eyes might serve the multichannel zeitgeber system of the biological clock.

Night Shift Work and Sleep Experiences in Older Night Shift Nurses.

Working at night leads to misalignment between the biological clock and the work/sleep schedule, resulting in sleepiness and impaired performance during the night shift and poor quality, shortened sleep during the day; this is greatly impaired in older individuals. To describe night work and sleep experiences from the perspective of older (aged 50-65) nurses. Seven virtual focus groups were formed comprising 19 older nurses who worked regular 8-hour night shifts (at least 6 consecutive hours between midnight and 6 am) to learn about their shift work and sleep experiences. Two facilitators and 2 research assistants independently reviewed and coded the transcripts using qualitative content analysis. Nine themes were identified in 3 domains: (a) night shift challenges and difficulties, including first night shift is most difficult; never feel rested working nights; and personal health concerns and benefits from working nights; (b) sleep challenges and difficulties, including inconsistent sleep timing when switching between nights and days; extended (24+ hours) time awake before and after consecutive nights; difficulty maintaining long and sound daytime sleep; and napping before night shifts for better performance; and (c) family and social challenges and support, including childcare, family, personal obligations, and social activities affect sleep; aging of self and children influences sleep and prioritization of sleep. The findings help understand challenges and struggles to obtain adequate sleep and safe work performance in older night shift nurses. These insignts are critical for designing and implementing feasible and acceptable interventions to improve sleep in this high-risk occupational group.

Ergonomics in Management of Stress amongst the Night Shift Workers: A Preliminary Review

Working on night shift is basically going against the circadian rhythm. Biological clock inside the human insists to fixed working status on daytime and rest/sleep at night. Ergonomics deals with providing a healthy relation between man machine and environment, where man fits to the job generates ultimate productivity. People in the east who are compromised to adjust in low to middle income are the main sufferers of not having optimum sleep. The population of security services, drivers, loco-pilots, nurses, tele-sales, IT professionals, various millworkers etc. often have shift based jobs and tries to accustom in it by compromising the biological clock. Many research evidences have been showed that alterations in biological clock lead to cause severe insomnia & shift work sleep disorder leading in disturbing occupational health as well as safety. Even sudden alterations in the biological clock lead cause accident, injuries alike from common health distresses. Alteration in the work rest cycle, taking sufficient rest in between the works, getting sufficient scopes in changing postures by arrangements of refreshments in the work place can help in optimizing productivity in the work place. Rotational shift with dynamic posture based work may lower the tendencies of accident and risk associated with night shift based work.

Chronotherapy in head and neck cancer: A systematic review and meta-analysis.

Optimizing the timing of radiotherapy and chemotherapy tailored to the body's biological clock (i.e., chronotherapy) might improve treatment efficacy and reduce side effects. This systematic review evaluated the effect of chrono-radiotherapy and chrono-chemotherapy on treatment efficacy, toxicity and adverse events in head and neck cancer (HNC) patients from prospective and retrospective studies published between the date of database inception until March 2024. The primary outcome measures for chrono-radiotherapy were treatment efficacy and incidence of grade ≥3 oral mucositis, and the main outcome measures for chrono-chemotherapy were objective response rate (ORR) and overall toxicity and adverse events. Of 7349 records identified, 22 studies with 3366 patients were included (chrono-radiotherapy = 9 and chrono-chemotherapy = 13). HNC patients who underwent chrono-radiotherapy had 31% less risk of developing severe oral mucositis (grade ≥3) compared to evening radiotherapy (risk ratio: 0.69, 95% CI: 0.53-0.90, p < 0.05). Further, HNC patients who underwent chrono-chemotherapy using platinum-based and antimetabolite agents had 73% less risk of lower ORR compared to nontime-stipulated chemotherapy (risk ratio: 0.27, 95% CI: 0.09-0.84, p < 0.05). In addition, HNC patients who underwent chrono-chemotherapy had 41% less risk of lower overall toxicity and adverse events in comparison to nontime-stipulated chemotherapy (risk ratio: 0.59, 95% CI: 0.47-0.72, p < 0.05). In conclusion, chrono-chemotherapy studies showed evidence of improved treatment efficacy, while in chrono-radiotherapy it was maintained. Chrono-radiotherapy and chrono-chemotherapy studies provide evidence of reduced toxicity and adverse events. However, optimized circadian-based multicentric clinical studies are needed to support chrono-radiotherapy and chrono-chemotherapy in managing HNC.

How Light at Night Sets the Circalunar Clock in the Marine Midge Clunio marinus.

Many organisms inhabiting the interface between land and sea have evolved biological clocks corresponding to the period of the semilunar (14.77 days) or the lunar (29.53 days) cycle. Since tidal amplitude is modulated across the lunar cycle, these circasemilunar or circalunar clocks not only allow organisms to adapt to the lunar cycle, but also to specific tidal situations. Biological clocks are synchronized to external cycles via environmental cues called zeitgebers. Here, we explore how light at night sets the circalunar and circasemilunar clocks of Clunio marinus, a marine insect that relies on these clocks to control timing of emergence. We first characterized how moonlight intensity is modulated by the tides by measuring light intensity in the natural habitat of C. marinus. In laboratory experiments, we then explored how different moonlight treatments set the phase of the clocks of two C. marinus strains, one with a lunar rhythm and one with a semilunar rhythm. Light intensity alone does not affect the phase of the lunar rhythm. Presenting moonlight during different 2-h or 4-h windows during the night shows that (1) the required duration of moonlight is strain-specific, (2) there are strain-specific moonlight sensitivity windows and (3) timing of moonlight can shift the phase of the lunar rhythm to stay synchronized with the lowest low tides. Experiments simulating natural moonlight patterns confirm that the phase is set by the timing of moonlight. Simulating natural moonlight at field-observed intensities leads to the best synchronization. Taken together, we show that there is a complex and strain-specific integration of intensity, duration and timing of light at night to precisely entrain the lunar and semilunar rhythms. The observed fine-tuning of the rhythms under natural moonlight regimes lays the foundation for a better chronobiological and genetic dissection of the circa(semi)lunar clock in C. marinus.

Daily rhythms of locomotor activity and transcript levels of non-visual opsins in the brain of the blind Mexican cavefish (Astyanax mexicanus)

Most organisms possess endogenous circadian clocks that synchronise their physiology and behaviour with environmental cycles, with the light-dark (LD) cycle being the most potent synchronising signal. Consequently, it can be hypothesised that animals that have evolved in the dark, as in caves or deep sea, may no longer possess a functional light-entrained biological clock. In this research, the blind cavefish Astyanax mexicanus was selected as a model organism to investigate the potential effects of daily light conditions on the circadian timekeeping mechanisms. First, we focused on describing behavioural photic entrainment and the presence of a circadian endogenous rhythmicity by recording locomotor activity rhythms under different lighting regimes: LD 12:12, after a 6-h shift of LD, constant darkness (DD), and constant dim light (LLdim). Secondly, we aimed at characterising the mechanisms of photodetection by analysing the daily rhythms of expression of selected non-visual extraocular opsins (exo-rhod, opn3, rgra, rgrb, tmt1a and tmt1b) in the brain of this blind species using real-time quantitative PCR. Our results revealed that blind Mexican cavefish activity rhythms were entrained to the LD cycle, with a diurnal activity pattern that persisted in a circadian fashion under constant lighting conditions. Additionally, statistically significant daily variations and/or rhythms were observed in three out of the six non-visual opsin genes analysed (opn3, rgra and tmt1b), all of them displaying nocturnal acrophases. These findings suggest that daily rhythms in extraretinal non-visual opsins may be transducing daily photic cycles and contributing to the entrainment of locomotor activity and other light-synchronised rhythms in blind cavefish species.

Efficacy of Ayurveda in the Prevention of Lifestyle Diseases or Non-Communicable Diseases (NCDs)

Lifestyle diseases occur due to an individual's everyday regimen and arise from an incorrect interaction between individuals and their environment. Bad eating habits, physical inactivity and a disrupted biological clock are primarily responsible for such diseases. In this context Ayurveda offers a well-organized system of conventional health care that promotes health maintenance and disease prevention via adherence to a balanced diet and vigorous lifestyle. There has been a strong connection between Ayurveda and Nutrition since ancient times. Interest in Ayurveda has grown across the globe due to its potential for managing and preventing lifestyle disorders. Acknowledged as one of the leading life sciences Ayurveda offers effective solution through Panchakarma, Rasayana, dietary control, lifestyle advice and rejuvenating therapies. The most effective and significant method in use is Ashtanga Yoga, a combination of Yogic and meditation exercises beneficial for regulating one's senses, focus and combating lifestyle disorders. Thus, Ayurveda is a holistic approach to health designed to help people live long, healthy and balanced life free from illness and diseases. This paper examines the causative factor behind certain lifestyle diseases and lays stress on their prevention through Ayurvedic techniques.

Unclocklike Oscillators with Frequency Memory for the Entrainment of Biological Clocks

Entrainment experiments on the vertebrate segmentation clock have revealed that embryonic oscillators actively change their internal frequency to adapt to the driving signal. This is not consistent with either a one-dimensional clock model or a limit-cycle model, but rather it suggests a new “unclocklike” behavior. In this work, we propose simple, biologically realistic descriptions of such internal frequency adaptation, where a phase oscillator activates a memory variable controlling the oscillator's frequency. We study two opposite limits for the control of the memory variable, one with a smooth phase-averaging memory field, and the other with a pulsatile, phase-dependent activation. Both models recapitulate intriguing properties of the entrained segmentation clock, such as very broad Arnold tongues and an entrainment phase plateauing with detuning. We compute analytically multiple properties of such systems, such as entrainment phases and cycle shapes. We further describe new phenomena, including hysteresis in entrainment, bistability in the frequency of the entrained oscillator, and probabilistic entrainment. Our work shows that oscillators with frequency memory can exhibit new classes of unclocklike properties that can be tested through experimental entrainment. Published by the American Physical Society 2024

The Effects of Ghrelin on Spike Activity of the Suprachiasmatic Nucleus Neurones of the Rat

In one of the most important non-photic mechanisms of the circadian biological clock synchronization with environmental geophysical 24 h rhythm, information on feeding schedule, composition and calorie content of food is used. Hormone ghrelin, a product of the neuroendocrine oxyntic cells of the gastric mucosa to be a signal molecule within this mechanism. In experiments on sagittal hypothalamic slices of male Wistar rats, the effects of 25 nM ghrelin on spike activity and parameters of spike information coding were investigated. Application of ghrelin induced an increase in spike frequency and a decrease in entropy of interspike interval distribution in 32.1% of the neurones recorded. In 29.6% of the cells, opposite responses in the form of a reduction of activity and an increase in the entropy of interspike interval distribution were observed. Parameters of spike activity of the reminder 38.3% neurones of the suprachiasmatic nucleus did not change. The observed responses of the entropy of interspike interval distribution indicate the appropriate changes in a degree of irregularity of interspike interval induced by ghrelin. Application of selective high-affinity antagonist of GHS-R1a receptor, JMV 2959 (100 nM) did not induce responses of the investigated parameters of spike activity but completely prevented changes of both, spike frequency and entropy of interspike interval distribution observed in the presence of ghrelin. The obtained data show that hormone ghrelin by a direct influence on the suprachiasmatic nucleus in vitro modulates the activity level and spike code of relatively numerous population of neurones of the nucleus, wherein the effects of ghrelin are implemented via GHS-R1a receptors. The results of the current study provide additional evidence in favour of the hypothesis on the involvement of ghrelin in mechanisms of non-photic entrainment of the circadian biological clock in accordance with severity of food motivation and level of metabolism.

A hematology-based clock derived from the Study of Longitudinal Aging in Mice to estimate biological age.

Biological clocks and other molecular biomarkers of aging are difficult to implement widely in a clinical setting. In this study, we used routinely collected hematological markers to develop an aging clock to predict blood age and determine whether the difference between predicted age and chronologic age (aging gap) is associated with advanced aging in mice. Data from 2,562 mice of both sexes and three strains were drawn from two longitudinal studies of aging. Eight hematological variables and two metabolic indices were collected longitudinally (12,010 observations). Blood age was predicted using a deep neural network. Blood age was significantly correlated with chronological age, and aging gap was positively associated with mortality risk and frailty. Platelets were identified as the strongest age predictor by the deep neural network. An aging clock based on routinely collected blood measures has the potential to provide a practical clinical tool to better understand individual variability in the aging process.

Chronotypes in middle-aged women with polycystic ovary syndrome: A population-based study.

Circadian rhythm disruption has been associated with the risk of polycystic ovary syndrome (PCOS), as the evening chronotype (EC) shares several traits with PCOS, including metabolic disorders, cardiovascular diseases, and psychiatric disorders. It has been suggested that the biological clock could be targeted with new, preventive, and therapeutic strategies for PCOS in women with biorhythm disorders. We evaluated inner circadian rhythmicity in middle-aged women with PCOS in a population-based setting, focusing on whether women with PCOS and an EC have a specific subtype in relation to their clinical characteristics. The data derived from the Northern Finland Birth Cohort, a population-based longitudinal birth cohort of 12 058 individuals born in 1966. We compared the circadian phenotype between 314 women with PCOS (according to the Rotterdam criteria) and 1248 women without PCOS at age 46 years using the validated Finnish shortened 6-item Morningness-Eveningness Questionnaire (sMEQ) and the single-item self-assessed morningness-eveningness question. PCOS was not associated with the EC by the sMEQ (p = 0.495) or self-assessment (p = 0.303). The self-assessed morningness-eveningness values differed from the sMEQ chronotype distribution (p < 0.001), nevertheless, the most frequent chronotype was the intermediate chronotype (IC) determined by both chronotyping methods (sMEQ PCOS 47.7% vs. 45.2% non-PCOS; self-assessment PCOS 66.5% vs. 68.4% non-PCOS). The hyperandrogenic PCOS phenotypes A-C did not differ from the non-hyperandrogenic phenotype D as for the chronotype (p = 0.271). The EC was associated in both groups with depressive and anxiety symptoms (PCOS p = 0.012, non-PCOS p < 0.001) and the use of sleep medication (PCOS p = 0.017, non-PCOS p < 0.001). The EC was not over-represented in middle-aged women with PCOS or in the hyperandrogenic PCOS phenotypes A-C in our study. This does not support the need for chronotyping in the comprehensive assessment of women with PCOS. However, as chronotypes tend to change with aging, cross-sectional studies in different age groups are warranted to draw conclusions on the role of chronotypes in PCOS and the associated metabolic risks.

SPOTLIGHT: Orchestrating nitrogen metabolism: Histone modifications and its interplay with the biological clock

SPOTLIGHT: Orchestrating nitrogen metabolism: Histone modifications and its interplay with the biological clock

Obesity alters circadian and behavioral responses to constant light in male mice

Exposure to artificial light during the night is known to promote disruption to the biological clock, which can lead to impaired mood and metabolism. Metabolic hormone secretion is modulated by the circadian pacemaker and recent research has shown that hormones such as insulin and leptin can also directly affect behavioral outcomes and the circadian clock. In turn, obesity itself is known to modulate the circadian rhythm and alter emotionality. This study investigated the behavioral and metabolic effects of constant light exposure in two models of obesity – a leptin null mutant (OB) and diet-induced obesity via high-fat diet. For both experiments, mice were placed into either a standard Light:Dark cycle (LD) or constant light (LL) and their circadian locomotor rhythms were continuously monitored. After 10 weeks of exposure to their respective lighting conditions, all mice were subjected to an open field assay to assess their explorative behaviors. Their metabolic hormone levels and inflammation levels were also measured. Behaviorally, exposure to constant light led to increased period lengthening and open field activity in the lean mice compared to both obesity models. Metabolically, LL led to increased cytokine levels and poorer metabolic outcomes in both lean and obese mice, sometimes exacerbating the metabolic issues in the obese mice, independent of weight gain. This study illustrates that LL can produce altered behavioral and physiological outcomes, even in lean mice. These results also indicate that obesity induced by different reasons can lead to shortened circadian rhythmicity and exploratory activity when exposed to chronic light.

Post-mortem interval determinations using insects collected from illegally hunted and dehorned rhinoceros in the Republic of South Africa from 2014 to 2021.

Wildlife forensic science is a growing research field globally with application in criminal cases of illegal hunting requiring an estimate of time of death based on insect fauna. The techniques and procedures of forensic entomology acquired over the last 40 years, used in legal cases relating to human remains, can be adapted to decomposing wildlife. Research on carrion utilising the rate of development of insect immatures provides a biological clock from which a minimum post-mortem interval (minPMI) can be derived. The following study concerns 19 rhinoceros that were illegally killed and dehorned in the Republic of South Africa between 2014 and 2021. The paper details 74 samples of insect evidence collected from these rhinoceros remains from which an accurate estimate of their PMI was calculated. The specimens comprised 18 species from 12 families belonging to three insect orders. Many Dipteran and Coleopteran species were found on and around each carcass. The species of fly larvae (family Calliphoridae) used in each case to estimate the PMI are as follows: Chrysomya marginalis (Wiedemann) (13 cases), Chrysomya chloropyga (Wiedemann) (2 cases), Chrysomya albiceps (Wiedemann) (1 case) and Chrysomya megacephala (Fabricius) (1 case). Two species of Coleoptera from the family Dermestidae and Silphidae involved Dermestes maculatus (DeGeer) and Thanatophilus micans (Fabricius), respectively, also were involved in one PMI estimation each. The paper highlights opportunities for improving our global understanding of gaps in procedures and training related to wildlife criminal cases.

A biological age based on common clinical markers predicts health trajectory and mortality risk in dogs.

Predicting aging trajectories through biomarkers of biological aging can guide interventions that optimize healthy lifespan in humans and companion animals. Differences in physiology, genetics, nutrition, and lifestyle limit the generalization of such biomarkers and may therefore require species-specific algorithms. Here, we compared correlations of standard clinical blood parameters with survival probability in humans with those of the two most common mammalian companion animals, cats and dogs, and highlighted universal and species-specific relationships. Based on this comparative analysis, we generated and validated an algorithm that predicts biological age in canines using a longitudinal dataset with health records, blood count, and clinical chemistry from 829 dogs spanning over 12years. Positive deviations of biological from chronological age (AgeDev) measured by this composite score significantly correlated with a decreased survival probability (hazard ratio = 1.75 per 1year of AgeDev, p = 3.7e - 06). Importantly, in nearly half of the dogs whose biological age was accelerated by more than 1year, none or only a single individual marker scored outside its respective reference range, suggesting practical applications for the detection of unfavorable health trajectories. Analyzing samples from a unique 14-year life-long diet restriction study, we show that restricted caloric intake lowers biological age, an effect that can be quantified at midlife years before a difference in survival is observed. Thus, a biological age clock based on clinical blood tests predicts the health trajectories of dogs for use in research and veterinary practice.

Biological clock regulation of blood pressure

Biological clock regulation of blood pressure

Chronopharmacokinetics: A Brief Analysis of the Influence of Circadian Rhythm on the Absorption, Distribution, Metabolism, and Elimination of Drugs

Chronopharmacokinetics is a specialized field within pharmacokinetics that focuses on how the timing of drug administration affects the absorption, distribution, metabolism, and elimination of drugs. The circadian rhythm, governed by the body's biological clock, plays a crucial role in pharmacokinetics, which encompasses the absorption, distribution, metabolism, and elimination of drugs. These pharmacokinetic processes are subject to daily variations influenced by the circadian rhythm. Drug absorption can fluctuate due to changes in gastrointestinal function, such as motility and gastric pH, and blood circulation. Similarly, the distribution of drugs in the body is influenced by factors such as tissue perfusion, plasma protein binding, and cell membrane permeability, all of which are modulated by the circadian rhythm. Metabolism, especially hepatic metabolism, can also experience circadian variations that affect the rate at which drugs are processed and converted into active or inactive metabolites. Finally, the elimination of drugs, primarily through renal function, can show circadian rhythms that impact the excretion of compounds from the body. Understanding these circadian fluctuations is essential to optimize the efficacy and safety of pharmacological treatments, as dosages and administration times could be adjusted to align with the peaks of biological clock activity. Thus, treatments can be more effective and have fewer side effects by leveraging the circadian variability in pharmacokinetic processes.

Time of day effects on consumers’ online review characteristics: Evidence from the homestay platform

Considering the unique mechanism underlying time of day effects due to biological clock on cognition, mood, and behavior, this study seeks to investigate the time of day effects on consumers' online review characteristics in the context of homestay platforms. Mixed approaches were employed, where the textual analysis and econometric analysis were based on the dataset with 189,523 reviews received from Tujia and an online randomized experiment recruited 378 participants. The results show that in the daytime consumers are under high cognitive load and more likely to rely on affective processes rather than cognitive processes when they craft online reviews, and conversely in the nighttime. The emotional expressions extracted from review texts and reflected in online ratings suggest consumers' mood change along time of a day, which further influences their review texts crafting and online ratings posting. Positive (negative) emotions are found to be stronger (weaker) in the daytime than nighttime. This work is conducive to enrichment in extant literature in hospitality academia and numerous rationales and theories in psychology field. Our work suggests important implications for homestay platform operations, hosts' managerial strategies, and consumers’ decision-making.

Knowledge, Attitude, and Practices for Occurrence of Weight Gain Among the Night Shift Working Professionals in Maharashtra, India: A Cross-Sectional Survey

Introduction: The biological clock or circadian rhythm of an organism is a set of regular oscillations. Working at night or on night shifts disrupts the circadian rhythm. When the circadian rhythm is disrupted, concentrations of adiponectin and leptin (satiety hormones) rise at night, leading to overeating and fat gain, while lack of sleep elevates ghrelin levels of the hunger hormone. Thus, the current study sought to explore the knowledge, attitudes, and practices about the dietary and lifestyle factors amongst night-shift working professionals and to assess the influence of knowledge and attitudes on their practices. Methods: A cross-sectional survey was conducted among individuals working night shifts in Maharashtra. A pre-tested questionnaire consisting of questions related to their knowledge, diet, and lifestyle was recorded and scored. Results: Among the 206 participants, a maximum of them were male (57.1%). Approximately 72.8% of respondents were quite young (25-30 years) and had been working the night shift for a period of 9-12 months. The majority (76.6%) of respondents had no medical conditions. Many (42.7%) of the night-shift working professionals were found to be obese. Significance was observed between knowledge and attitude among the overweight BMI category. Conclusion: The participants had good knowledge in terms of dietary habits and lifestyle-related factors. However, this was not reflected in their attitudes and practices. Therefore, interventional research targeting attitudes and behaviors is required to improve behavioral patterns among overweight/ obese people.

PERfect Day: reversible and dose-dependent control of circadian time-keeping in the mouse suprachiasmatic nucleus by translational switching of PERIOD2 protein expression.

The biological clock of the suprachiasmatic nucleus (SCN) orchestrates circadian (approximately daily) rhythms of behaviour and physiology that underpin health. SCN cell-autonomous time-keeping revolves around a transcriptional/translational feedback loop (TTFL) within which PERIOD (PER1,2) and CRYPTOCHROME (CRY1,2) proteins heterodimerise and suppress trans-activation of their encoding genes (Per1,2; Cry1,2). To explore its contribution to SCN time-keeping, we used adeno-associated virus-mediated translational switching to express PER2 (tsPER2) in organotypic SCN slices carrying bioluminescent TTFL circadian reporters. Translational switching requires provision of the non-canonical amino acid, alkyne lysine (AlkK), for protein expression. Correspondingly, AlkK, but not vehicle, induced constitutive expression of tsPER2 in SCN neurons and reversibly and dose-dependently suppressed pPer1-driven transcription in PER-deficient (Per1,2-null) SCN, illustrating the potency of PER2 in negative regulation within the TTFL. Constitutive expression of tsPER2, however, failed to initiate circadian oscillations in arrhythmic PER-deficient SCN. In rhythmic, PER-competent SCN, AlkK dose-dependently reduced the amplitude of PER2-reported oscillations as inhibition by tsPER2 progressively damped the TTFL. tsPER2 also dose-dependently lengthened the period of the SCN TTFL and neuronal calcium rhythms. Following wash-out of AlkK to remove tsPER2, the SCN regained TTFL amplitude and period. Furthermore, SCN retained their pre-washout phase: the removal of tsPER2 did not phase-shift the TTFL. Given that constitutive tsCRY1 can regulate TTFL amplitude and period, but also reset TTFL phase and initiate rhythms in CRY-deficient SCN, these results reveal overlapping and distinct properties of PER2 and CRY1 within the SCN, and emphasise the utility of translational switching to explore the functions of circadian proteins.