The Suprachiasmatic Nucleus of The Reindeer (Rangifer tarandus tarandus) and it’s Circadian Outputs

The Earth is in constant movement around the Sun – this has created environments with changing light throughout the day and year. Through evolution animals have adapted to this change in light and circadian and circannual rhythms have evolved to enhance fitness and survival. Animals living in the Arctic region have a different relationship to light changes as for several months a year the Sun is either above or below the horizon all day creating only a minimum amplitude of light change throughout the day. Consequently, circadian organization may be less important is these animals. However, there are limited research on animals in the Arctic concerning circadian rhythms. This thesis took a closer look at the Norwegian reindeer (Rangifer tarandus). The reindeer suprachiasmatic nucleus (SCN) was characterized with the use of DIG in-situ hybridization and found that arginine vasopressin (AVP) and vasoactive intestinal polypeptide (VIP) are expressed in the SCN, similar to what is seen in sheep. To measure the output physiology – locomotor activity, feeding behavior, rumen temperature, heart rate and cortisol – a forced desynchrony protocol was developed. The reindeer had a weak 24-hour diurnal locomotor activity pattern when a light-dark cycle is present. In constant light this rhythm breaks down and this study did not provide any evidence of a strong circadian rhythm in locomotor activity, feeding behavior or rumen temperature. The most dominant rhythm appears to be ultradian. The limitations of the set-up and devices, and the ultradian rhythmicity in reindeer, resulted in no signs of uncoupling of locomotor activity and feeding behavior from rumen temperature. The three parameters, locomotor activity, feeding behavior and rumen temperature were correlated and this correlation was most apparent at an ultradian level, and the relationship between the parameters did not change throughout the protocol. The reindeer have strong social organization and becomes stressed by being indoors for a longer period of time. As reindeer are ruminants living in the Arctic, both the environment and feeding demands can have contributed to a less important circadian organization

Temporal metabolic partitioning of the yeast and protist cellular networks:the cell is a global scale-invariant (fractal or self-similar) multioscillator

Britton Chance, electronics expert when a teenager, became an enthusiastic student of biological oscillations, passing on this enthusiasm to many students and colleagues, including one of us (DL). This historical essay traces BC’s influence through the accumulated work of DL to DL’s many collaborators. The overall temporal organization of mass-energy, information, and signaling networks in yeast in self-synchronized continuous cultures represents, until now, the most characterized example of in vivo elucidation of time structure. Continuous online monitoring of dissolved gases by direct measurement (membrane-inlet mass spectrometry, together with NAD(P)H and flavin fluorescence) gives strain-specific dynamic information from timescales of minutes to hours as does two-photon imaging. The predominantly oscillatory behavior of network components becomes evident, with spontaneously synchronized cellular respiration cycles between discrete periods of increased oxygen consumption (oxidative phase) and decreased oxygen consumption (reductive phase). This temperature-compensated ultradian clock provides coordination, linking temporally partitioned functions by direct feedback loops between the energetic and redox state of the cell and its growing ultrastructure. Multioscillatory outputs in dissolved gases with 13 h, 40 min, and 4 min periods gave statistical self-similarity in power spectral and relative dispersional analyses: i.e., complex nonlinear (chaotic) behavior and a functional scale-free (fractal) network operating simultaneously over several timescales

Time-course RNASeq of Camponotus floridanus forager and nurse ant brains indicate links between plasticity in the biological clock and behavioral division of labor

Background: Circadian clocks allow organisms to anticipate daily fluctuations in their environment by driving rhythms in physiology and behavior. Inter-organismal differences in daily rhythms, called chronotypes, exist and can shift with age. In ants, age, caste-related behavior and chronotype appear to be linked. Brood-tending nurse ants are usually younger individuals and show “around-the-clock” activity. With age or in the absence of brood, nurses transition into foraging ants that show daily rhythms in activity. Ants can adaptively shift between these behavioral castes and caste-associated chronotypes depending on social context. We investigated how changes in daily gene expression could be contributing to such behavioral plasticity in Camponotus floridanus carpenter ants by combining time-course behavioral assays and RNA-Sequencing of forager and nurse brains. Results: We found that nurse brains have three times fewer 24 h oscillating genes than foragers. However, several hundred genes that oscillated every 24 h in forager brains showed robust 8 h oscillations in nurses, including the core clock genes Period and Shaggy. These differentially rhythmic genes consisted of several components of the circadian entrainment and output pathway, including genes said to be involved in regulating insect locomotory behavior. We also found that Vitellogenin, known to regulate division of labor in social insects, showed robust 24 h oscillations in nurse brains but not in foragers. Finally, we found significant overlap between genes differentially expressed between the two ant castes and genes that show ultradian rhythms in daily expression. Conclusion: This study provides a first look at the chronobiological differences in gene expression between forager and nurse ant brains. This endeavor allowed us to identify a putative molecular mechanism underlying plastic timekeeping: several components of the ant circadian clock and its output can seemingly oscillate at different harmonics of the circadian rhythm. We propose that such chronobiological plasticity has evolved to allow for distinct regulatory networks that underlie behavioral castes, while supporting swift caste transitions in response to colony demands. Behavioral division of labor is common among social insects. The links between chronobiological and behavioral plasticity that we found in C. floridanus, thus, likely represent a more general phenomenon that warrants further investigation

Data integration and analysis for circadian medicine

Data integration, data sharing, and standardized analyses are important enablers for data-driven medical research. Circadian medicine is an emerging field with a particularly high need for coordinated and systematic collaboration between researchers from different disciplines. Datasets in circadian medicine are multimodal, ranging from molecular circadian profiles and clinical parameters to physiological measurements and data obtained from (wearable) sensors or reported by patients. Uniquely, data spanning both the time dimension and the spatial dimension (across tissues) are needed to obtain a holistic view of the circadian system. The study of human rhythms in the context of circadian medicine has to confront the heterogeneity of clock properties within and across subjects and our inability to repeatedly obtain relevant biosamples from one subject. This requires informatics solutions for integrating and visualizing relevant data types at various temporal resolutions ranging from milliseconds and seconds to minutes and several hours. Associated challenges range from a lack of standards that can be used to represent all required data in a common interoperable form, to challenges related to data storage, to the need to perform transformations for integrated visualizations, and to privacy issues. The downstream analysis of circadian rhythms requires specialized approaches for the identification, characterization, and discrimination of rhythms. We conclude that circadian medicine research provides an ideal environment for developing innovative methods to address challenges related to the collection, integration, visualization, and analysis of multimodal multidimensional biomedical data.Peer Reviewe

Multiscale adaptive analysis of circadian rhythms and intradaily variability: Application to actigraphy time series in acute insomnia subjects

Circadian rhythms become less dominant and less regular with chronic-degenerative disease, such that to accurately assess these pathological conditions it is important to quantify not only periodic characteristics but also more irregular aspects of the corresponding time series. Novel data-adaptive techniques, such as singular spectrum analysis (SSA), allow for the decomposition of experimental time series, in a model-free way, into a trend, quasiperiodic components and noise fluctuations. We compared SSA with the traditional techniques of cosinor analysis and intradaily variability using 1-week continuous actigraphy data in young adults with acute insomnia and healthy age-matched controls. The findings suggest a small but significant delay in circadian components in the subjects with acute insomnia, i.e. a larger acrophase, and alterations in the day-to-day variability of acrophase and amplitude. The power of the ultradian components follows a fractal 1/f power law for controls, whereas for those with acute insomnia this power law breaks down because of an increased variability at the 90min time scale, reminiscent of Kleitman&rsquo;s basic rest-activity (BRAC) cycles. This suggests that for healthy sleepers attention and activity can be sustained at whatever time scale required by circumstances, whereas for those with acute insomnia this capacity may be impaired and these individuals need to rest or switch activities in order to stay focused. Traditional methods of circadian rhythm analysis are unable to detect the more subtle effects of day-to-day variability and ultradian rhythm fragmentation at the specific 90min time scale.<br /

An Optimal Time for Treatment-Predicting Circadian Time by Machine Learning and Mathematical Modelling

Tailoring medical interventions to a particular patient and pathology has been termed personalized medicine. The outcome of cancer treatments is improved when the intervention is timed in accordance with the patient's internal time. Yet, one challenge of personalized medicine is how to consider the biological time of the patient. Prerequisite for this so-called chronotherapy is an accurate characterization of the internal circadian time of the patient. As an alternative to time-consuming measurements in a sleep-laboratory, recent studies in chronobiology predict circadian time by applying machine learning approaches and mathematical modelling to easier accessible observables such as gene expression. Embedding these results into the mathematical dynamics between clock and cancer in mammals, we review the precision of predictions and the potential usage with respect to cancer treatment and discuss whether the patient's internal time and circadian observables, may provide an additional indication for individualized treatment timing. Besides the health improvement, timing treatment may imply financial advantages, by ameliorating side effects of treatments, thus reducing costs. Summarizing the advances of recent years, this review brings together the current clinical standard for measuring biological time, the general assessment of circadian rhythmicity, the usage of rhythmic variables to predict biological time and models of circadian rhythmicity

Behavioral, Neurobiological, and Genetic Analysis of the Circadian Mutant Duper

The recently discovered circadian mutant hamster duper has a short period of ~23 hours and exhibits exaggerated phase shifts in response to a 15-min light pulse. To increase the understanding of the duper mutation, I performed behavioral, neurobiological, and genetic experiments. Behavioral studies using photic and non-photic stimuli found that large phase shifts exhibited by duper hamsters are specific to photic cues, but not to phase. Additionally, 2/3 of duper hamsters, but no WTs, displayed transient ultradian wheel-running patterns when transferred from light to dark at CT 18. This suggests that the mutation may weaken coupling among components of the circadian pacemaker. Anatomical and immunocytochemical analysis of the SCN was used to examine the neurobiological mechanisms of large light-induced phase shifts in dupers. Brains were collected from duper and WT hamsters at CT 12 and 15 as well as 1, 2, 3, 6 and 9 hours following a light pulse, or control handling, at CT 15. Surprisingly, the only difference in PER1 (a core clock protein) expression in the SCN between dupers and WTs was seen 2-hours after a light pulse; duper hamsters displayed a significantly greater percentage of retinorecipient VIP cells co-labeled with PER1 compared to WTs. Additional differences between genotypes occurred 9 hours after CT15 (controls). In the SCN, the number of PER1-ir cells was significantly greater in WT than duper hamsters, however this finding was reversed in the PVN. This anatomical mismatch suggests the mutation may affect signaling between the SCN and extra-SCN oscillators. Finally, to identify the genetic basis of the duper phenotype, I crossed dupers with a novel ecotype in order to perform fast homozygosity mapping. Duper transmitted onto the novel ecotype with the predicted Mendelian inheritance of phenotype. I collected DNA from F2 duper hamsters, and expect fast homozygosity mapping will identify candidate genetic regions of the duper mutation. Additional behavioral experiments in F2 dupers demonstrated that duper hamsters are resistant to jet lag. As duper is a unique circadian mutation, understanding of the behavioral phenotype, neurobiological mechanism, and genetic basis of the duper mutation will greatly increase our knowledge of the circadian system

Role of biological clocks in ant behavioral plasticity and parasitic manipulation of ant behavior

Living organisms exhibit daily rhythms as a way to anticipate predictable fluctuations in their environment. Such daily rhythmicity is the phenotypic outcome of oscillating genes and proteins, driven by an endogenous biological clock. Clock-controlled behavioral rhythms are inherently flexible since their phase, amplitude, and period can change throughout an animal\u27s life hallmarked by changes in so-called chronotype. How this inherent plasticity of clock-controlled rhythms is linked to plasticity of behavior is still an open question in biology. Characterizing the various mechanistic links between plasticity of the animal clock and behavioral state will not only shed light on the molecular underpinnings of animal behavior, but also lead to novel chronotherapeutic interventions to treat human disorders that affect the behavioral state such as bipolar disorder and Alzheimer\u27s. While clock-controlled behavioral plasticity is crucial to a species\u27 survival and fitness, it has also been hypothesized to be a target for manipulative parasites that need to induce timely changes in host behavior to facilitate growth and transmission. Using the Florida carpenter ant Camponotus floridanus as a model, this dissertation attempts to bridge some of the existing knowledge gaps in sociobiology, chronobiology, and parasitology. In the first chapter, we have identified a mechanistic link between plasticity of the C. floridanus clock and its behavioral state. Subsequently, in chapter two, we have provided evidence showing that Ophiocordyceps camponoti-floridani, a fungal parasite that induces timely changes in C. floridanus behavior targets the pre-existing links between host behavior and chronobiological plasticity we have found in chapter one. In the final chapter, we characterize how the clock of O. camponoti-floridani functionally differs from the clock of a non-manipulating fungal parasite, Beauveria bassiana, and put forward a regulatory mechanism via which the manipulating parasite\u27s clock might be inducing timely changes in host behavior