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The circadian field has come a long way since I started as a postdoctoral fellow ~30 years ago. At the time, the only known animal clock gene was period, so I had the privilege of witnessing, and participating in, the molecular revolution that took us from the discovery of the circadian clock mechanism to the identification of pathways that link clocks to behavior and physiology. This lecture highlights my role and perspective in these developments, and also demonstrates how the successful use of Drosophila for studies of circadian rhythms inspired us to develop a fly model for sleep. I also touch upon my experiences as a non-white immigrant woman navigating my way through the US science and education system, and hope my story will be of interest to some.

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A diverse range of species, from cyanobacteria to humans, evolved endogenous biological clocks that allow for the anticipation of daily variations in light and temperature. The ability to anticipate regular environmental rhythms promotes optimal performance and survival. Herein we present a brief historical timeline of how circadian concepts and terminology have emerged since the early observation of daily leaf movement in plants made by an astronomer in the 1700s.

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The pursuit of mechanistic explanations in biology has produced a great deal of knowledge about the parts, operations, and organization of mechanisms taken to be responsible for biological phenomena. Holist critics have often raised important criticisms of proposed mechanistic explanations, but until recently holists have not had alternative research strategies through which to advance explanations. This paper argues both that the results of mechanistic strategies has forced mechanists to confront ways in which whole systems affect their components and that new representational and modeling strategies are providing tools for understanding these effects of whole systems upon components. Drawing from research on the mechanism responsible for circadian rhythms in mammals, I develop two examples in which mechanistic analysis is being integrated into a more holist perspective: research revealing intercellular integration of circadian mechanisms with those involved in cell metabolism and research revealing that stable␣rhythms are dependent on how individual cells in the suprachiasmatic nucleus synchronize with each other to generate regular rhythms. Tools such as network diagramming and computational modeling are providing means to integrate mechanistic models into accounts of whole systems.

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There are three common periodic intervals in the life of each human being from time immemorial: the day, the week and the year. The first one is given by the Earth´s rotation, the latter one by its revolution around the Sun. These both do have clear biomedical counterparts. The 7-day week, basically linguistically "period of change" (or a similar period, e.g.10 days in Egypt or 8 days in Etrutria) was obviously originally considered mainly as a product of a societal agreement. Two groups of Czechoslovak clinicians-scientists, however, noted in forties of the XXth century an approximately week period in human laboratory data, after similar attempts abroad a few years earlier. In fifties, L.Dérer, respecting the mathematical and biological principles in medicine and supported by the mathematician A.Huta, demonstrated the presence of the "6-day" rhythm in blood leukocyte counts in patients with leukemia, treated by cytostatics. Posing the question "Where is it from?", he considered also cosmic influences but was unable to study this issue more deeply due to his premature decease. Two decades later, the "Dérer´s circaseptans" found wide confirmation not only in human medicine but also in biology. The pioneering role here belongs to Franz Halberg, USA, the godfather of the "circadians" (originally "Halberg´s paranoia") since the fifties. The possible geocosmic roots of circaseptans are supposed in the geomagnetic activity from interplanetary space, generating under the influence of the Sun rotation the periods around 6-7 days. This is presently documented, surprisingly, also by analysing the Dérer´s original data using more advanced, inferentially statistical method - the Halberg cosinor regression. Thus, the optimal approximation has been achieved for the period of 6.75 days - the 4th harmonics of the Bartels solar rotation cycle. Accordingly, the week can be now, after Dérer and Halberg, understood also - same as day and year - as a biological - geocosmic phenomenon, a geomagnetic week, genetically acquired in the course of billions years´ of evolution, encoded in our chronome. The personality of Ladislav Dérer should, in the history of the Czech and Slovak biomedical sciences, be permanenly standing by such giants as the well known Jan Evangelista Purkyne ("Purkinje") or as Bohumil Nemec, discoverer of the mechanism of positive geotropism of plant roots (Fig. 3, Ref. 28).

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The detection of ultraweak light emission in seedlings has been explored in toxicological and chronobiological studies. The main studies in this area are reviewed briefly, including a report on applied tests held in the last 7 years at LaFA--UNICAMP (Brazil). In general, results indicate that a linear relation for total light emission versus germination performance is found if only strong stress situations are considered, when external factors depress a seedling's development, even when considering a sequential series of tests. Light emitted by a single seedling was detected in a compact apparatus, and data are presented here for the first time showing pronounced circadian cycles are evident, with similar time and frequency profiles as those of the local gravimetric tide.

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Chronomedicine may be conceptualized as dealing with the prevention, causation, diagnosis, and treatment of diseases in humans with a particular focus on the role "time" [Greek: chrónos] plays in our physiology, endocrinology, metabolism and behavior at many organizational levels. While it has been used as a term and somewhat pursued as a discipline for decades, it appears that chronomedicine has captured a broader interest as a promising specialty only more recently. This commentary addresses roots of chronomedicine in the 1900s and perspectives for chronomedicine in the 21st century. Classical terms of chronobiology, e.g., Zeitgeber, melatonin and circadian, may be traced back to Aschoff, Lerner, and Halberg, respectively, but who actually coined the term "chronomedicine" and used it first in a publication remains unclear. Importantly, it could be(come) rather straightforward to transfer abundant insights gained from chronobiology to strategies in chronomedicine as animal models have been increasingly developed to understand human health and disease. Perspectively, chronomedicine should comprise "clinical chronomedicine" (individual-based) and "preventive chronomedicine" (population-based). Overall, due to the "maturing" of chronomedicine as a field, the near future might bring a section dedicated to chronomedicine in existing journals, or even a "Journal of Chronomedicine" as vectors of ideas and research.

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