Aux aurores de la chronobiologie

Le présent article de Mairan, qui date de bientôt trois siècles, est, fait peu courant, encore mentionné dans des articles scientifiques. La plupart des spécialistes voient même ce feuillet d’observations botaniques (sur les ouvertures et fermetures de feuilles) comme la toute première véritable publication, sinon la publication fondatrice, de leur domaine, qui s'est pourtant constitué bien plus tard : la chronobiologie. Ces rythmes circadiens (d’environ 24h) d’ouverture et de fermeture ne sont pas conditionnés par la lumière solaire, mais par un rythme interne à l’organisme vivant, son horloge biologique (ou biochimique), qui s’adapte à l’environnement. Elle peut par exemple s’adapter à des variations jour-nuit fort différentes : on peut obtenir avec une lumière artificielle n’importe quelle période, exactement comme pour le forçage d’un oscillateur en physique. On a pu montrer que la plupart des organismes vivants suivent non seulement les passages jour-nuit, mais celui des saisons en se fiant à la longueur relative du jour, ou de la nuit, au cours des cycles journaliers de 24h : ce qui permet aux agriculteurs et éleveurs d'obtenir la floraison ou la reproduction d'une espèce presque en toute saison, simplement par exposition à des cycles jour-nuit artificiels qui imitent la saison favorable. Notre température interne suit elle-même un rythme circadien, avec un minimum en milieu de nuit, et donc des valeurs un peu plus élevées le soir qu'au réveil, de quelques dixièmes de degrés Celsius. Ces petites variations sont capables de synchroniser d'autres rythmes circadiens au sein de l'organisme ! Important sur le fond, l’article de Mairan a aussi un intérêt épistémologique. Posant une très bonne question d'un point de vue expérimental, il rapporte une observation correcte, qui semble répondre à la question posée. Mais ceci restera une simple observation, tant que manquera le cadre conceptuel qui lui donne sa véritable signification – en d'autres termes, tant que ce ne sera pas vraiment la bonne question ou, si l'on préfère, qu'elle ne sera pas posée pour les bonnes raisons. En tout état de cause, la chronobiologie est aujourd'hui un domaine de recherche fondamentalement pluridisciplinaire, réunissant généticiens et biochimistes, botanistes et zoologistes, neurobiologistes, agronomes, physiciens, mathématiciens, psychologues, médecins...This text by Mairan is that rare thing: a paper dating back almost three centuries which is still mentioned in scientific articles. Most specialists consider this sheet of botanical observations (on the opening and closing of leaves) as the first genuine publication, if not the founding publication, in their field – chronobiology – which emerged only at a much later date. These circadian rhythms (approximately 24 hours long) of opening and closing are not affected by sunlight but by the internal rhythm of the living organism, by its biological (or biochemical) clock, which adapts to the environment. This clock can adapt to very sharp differences – between day and night, for example. Artificial light can be used to create any given period, in the same way as a forced oscillator in physics. It has been shown that most living organisms sense not only the passage of day and night, but also the passing of the seasons by relying on the relative length of the day or night during 24-hour daily cycles. This enables arable and livestock farmers to bring a crop into flower or reproduce a species in almost any season, simply by exposing them to artificial dark/night cycles that imitate those of the desired season. Our internal body temperature itself follows a circadian rhythm, reaching its lowest point in the middle of the night and therefore rising in the evening to values a few tenths of a degree Celsius higher than when one wakes up. It even turns out that these slight variations are able to synchronise other circadian rhythms within the organism! In addition to its scientific importance, Mairan’s article is also interesting in epistemological terms. After posing a very pertinent question from an experimental point of view, it adduces a correct observation, and one that seems to respond to the question being considered. But, in the absence of a conceptual framework capable of elucidating its true significance, it remained just that: an observation. In other words, it remained mere observation just as long as the question was not quite right – or not asked for the right reasons. Today, chronobiology is a fundamentally pluridisciplinary research area, bringing together geneticists, biochemists, botanists, zoologists, neurobiologists, agronomists, physicists, mathematicians, psychologists, doctors, etc

Light Activates Output from Evening Neurons and Inhibits Output from Morning Neurons in the Drosophila Circadian Clock

Animal circadian clocks are based on multiple oscillators whose interactions allow the daily control of complex behaviors. The Drosophila brain contains a circadian clock that controls rest–activity rhythms and relies upon different groups of PERIOD (PER)–expressing neurons. Two distinct oscillators have been functionally characterized under light-dark cycles. Lateral neurons (LNs) that express the pigment-dispersing factor (PDF) drive morning activity, whereas PDF-negative LNs are required for the evening activity. In constant darkness, several lines of evidence indicate that the LN morning oscillator (LN-MO) drives the activity rhythms, whereas the LN evening oscillator (LN-EO) does not. Since mutants devoid of functional CRYPTOCHROME (CRY), as opposed to wild-type flies, are rhythmic in constant light, we analyzed transgenic flies expressing PER or CRY in the LN-MO or LN-EO. We show that, under constant light conditions and reduced CRY function, the LN evening oscillator drives robust activity rhythms, whereas the LN morning oscillator does not. Remarkably, light acts by inhibiting the LN-MO behavioral output and activating the LN-EO behavioral output. Finally, we show that PDF signaling is not required for robust activity rhythms in constant light as opposed to its requirement in constant darkness, further supporting the minor contribution of the morning cells to the behavior in the presence of light. We therefore propose that day–night cycles alternatively activate behavioral outputs of the Drosophila evening and morning lateral neurons

Human Cryptochrome-1 Confers Light Independent Biological Activity in Transgenic Drosophila Correlated with Flavin Radical Stability

Cryptochromes are conserved flavoprotein receptors found throughout the biological kingdom with diversified roles in plant development and entrainment of the circadian clock in animals. Light perception is proposed to occur through flavin radical formation that correlates with biological activity in vivo in both plants and Drosophila. By contrast, mammalian (Type II) cryptochromes regulate the circadian clock independently of light, raising the fundamental question of whether mammalian cryptochromes have evolved entirely distinct signaling mechanisms. Here we show by developmental and transcriptome analysis that Homo sapiens cryptochrome - 1 (HsCRY1) confers biological activity in transgenic expressing Drosophila in darkness, that can in some cases be further stimulated by light. In contrast to all other cryptochromes, purified recombinant HsCRY1 protein was stably isolated in the anionic radical flavin state, containing only a small proportion of oxidized flavin which could be reduced by illumination. We conclude that animal Type I and Type II cryptochromes may both have signaling mechanisms involving formation of a flavin radical signaling state, and that light independent activity of Type II cryptochromes is a consequence of dark accumulation of this redox form in vivo rather than of a fundamental difference in signaling mechanism

The Blursday database as a resource to study subjective temporalities during COVID-19

The COVID-19 pandemic and associated lockdowns triggered worldwide changes in the daily routines of human experience. The Blursday database provides repeated measures of subjective time and related processes from participants in nine countries tested on 14 questionnaires and 15 behavioural tasks during the COVID-19 pandemic. A total of 2,840 participants completed at least one task, and 439 participants completed all tasks in the first session. The database and all data collection tools are accessible to researchers for studying the effects of social isolation on temporal information processing, time perspective, decision-making, sleep, metacognition, attention, memory, self-perception and mindfulness. Blursday includes quantitative statistics such as sleep patterns, personality traits, psychological well-being and lockdown indices. The database provides quantitative insights on the effects of lockdown (stringency and mobility) and subjective confinement on time perception (duration, passage of time and temporal distances). Perceived isolation affects time perception, and we report an inter-individual central tendency effect in retrospective duration estimation

La controverse des horloges biologiques.

ISSN : 0029-567

Le réseau neuronal de l'horloge circadienne dans le cerveau de la drosophile : Organisation fonctionnelle et entraînement par la lumière et la température

LE KREMLIN-B.- PARIS 11-BU Méd (940432101) / SudocSudocFranceF

Étude fonctionnelle et développementale des interactions entre le système visuel et l'horloge circadienne de Drosophila melanogaster

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

L’horloge circadienne à l’heure Nobel

International audienceL’attribution du prix Nobel 2017 de physiologie ou médecine à trois chercheurs américains - Jeffrey C. Hall (né le 3 mai 1945 à New York – University of Maine), Michael Rosbash (né le 7 mars 1944 à Kansas City - Brandeis University, Waltham et Howard Hughes Medical Institute) et Michael W. Young (né le 28 mars 1949 à Miami - Rockefeller University, New York), est difficilement contestable, tant ces chercheurs incarnent depuis près de 35 ans, l’émergence, puis le foisonnement des études moléculaires et cellulaires des rythmes circadiens. Mais ce prix a fait bien plus que trois heureux. Il apporte, en effet, une reconnaissance éclatante à un domaine, la chronobiologie, qui a longtemps fait figure, au mieux pour certains, d’aimable curiosité… La difficulté à identifier les rouages des horloges biologiques qui rythment nos jours et nos nuits, ou même à seulement les imaginer, y a bien sûr contribué. C’est pourquoi les travaux de Hall, Rosbash et Young – récompensés « pour leurs découvertes des mécanismes moléculaires qui contrôlent les rythmes circadiens » – ont revêtu une telle importance, même si la voie leur avait été ouverte un peu plus d’une décennie auparavant. Paradoxalement, le grand public a peut-être admis l’existence de nos horloges internes avant la communauté scientifique, car chacun peut faire l’expérience intime de rythmes journaliers, à commencer par l’alternance veille-sommeil, qui s’imposent à lui

Circadian rhythms of locomotor activity in Drosophila

info:eu-repo/semantics/publishe

A Role for Blind DN2 Clock Neurons in Temperature Entrainment of the Drosophila Larval Brain

Circadian clocks synchronize to the solar day by sensing the diurnal changes in light and temperature. In adult Drosophila, the brain clock that controls rest-activity rhythms relies on neurons showing Period oscillations. Nine of these neurons are present in each larval brain hemisphere. They can receive light inputs through Cryptochrome (CRY) and the visual system, but temperature input pathways are unknown. Here, we investigate how the larval clock network responds to light and temperature. We focused on the CRY-negative dorsal neurons (DN2s), in which light-dark (LD) cycles set molecular oscillations almost in antiphase to all other clock neurons. We first showed that the phasing of the DN2s in LD depends on the pigment-dispersing factor (PDF) neuropeptide in four lateral neurons (LNs), and on the PDF receptor in the DN2s. In the absence of PDF signaling, these cells appear blind, but still synchronize to temperature cycles. Period oscillations in the DN2s were stronger in thermocycles than in LD, but with a very similar phase. Conversely, the oscillations of LNs were weaker in thermocycles than in LD, and were phase-shifted in synchrony with the DN2s, whereas the phase of the three other clock neurons was advanced by a few hours. In the absence of any other functional clock neurons, the PDF-positive LNs were entrained by LD cycles but not by temperature cycles. Our results show that the larval clock neurons respond very differently to light and temperature, and strongly suggest that the CRY-negative DN2s play a prominent role in the temperature entrainment of the networ