Day-night and seasonal variation of human gene expression across tissues

Circadian and circannual cycles trigger physiological changes whose reflection on human transcriptomes remains largely uncharted. We used the time and season of death of 932 individuals from GTEx to jointly investigate transcriptomic changes associated with those cycles across multiple tissues. For most tissues, we found little overlap between genes changing expression during day-night and among seasons. Although all tissues remodeled their transcriptomes, brain and gonadal tissues exhibited the highest seasonality, whereas those in the thoracic cavity showed stronger day-night regulation. Core clock genes displayed marked day-night differences across multiple tissues, which were largely conserved in baboon and mouse, but adapted to their nocturnal or diurnal habits. Seasonal variation of expression affected multiple pathways and were enriched among genes associated with SARS-CoV-2 infection. Furthermore, they unveiled cytoarchitectural changes in brain subregions. Altogether, our results provide the first combined atlas of how transcriptomes from human tissues adapt to major cycling environmental conditions.

Melatonin and brown adipose tissue: novel insights to a complex interplay

As a chronobiotic molecule, melatonin finely tunes a variety of physiological processes including energy metabolism, reproduction and sleep-wake cycle, collaborating for the survival of the organisms. Since its pineal production occurs exclusively during the night, melatonin is responsible for signaling the circadian and circannual cycles to the organisms. This involves different ways of action that need to be considered when analyzing its effects in a given tissue/organism. Non-shivering thermogenesis (NST) is a crucial process for homeothermic animals and increasing evidences show its importance for the energy metabolic balance due to its influence in body weight control. The highly seasonal brown adipose tissue (BAT) is the site for NST and its metabolism is importantly influenced by melatonin. This review focuses on melatonin actions over BAT and the attention should be given to the relation between this signaling molecule and such a seasonally expressed tissue.

Modeling a Virtual World for the Educational Game Calangos

Ecology plays a central role in biology and deserves special attention in scientific education. Nonetheless, the teaching and learning of ecology face a number of difficulties. In order to tackle these difficulties, electronic games have recently been used to mediate ecology learning. This paper presents an electronic game that fulfills these gaps in order to make the students’ work with ecological concepts more concrete, active, and systematic. The paper presents the computational model of the ecological system included in the game, based on a real ecological case, a sand dune ecosystem located in the semiarid Caatinga biome, namely, the sand dunes of the middle São Francisco River, in the state of Bahia, Brazil. It includes various ecological relationships between endemic lizards and the physical environment, preys, predators, cospecifics, and plants. The engine of the game simulates the physical conditions of the ecosystem (dune topography and climate conditions with their circadian and circannual cycles), its biota (plant species and animal species), and ecological relationships (predator-prey encounters, cospecific relationships). We also present results from one classroom study of a teaching sequence structured around Calangos, which showed positive outcomes regarding high school students’ understanding of thermal regulation in ectothermic animals.

Seasonality in a temperate zone bird can be entrained by near equatorial photoperiods

Birds use photoperiod to control the time of breeding and moult. However, it is unclear whether responses are dependent on absolute photoperiod, the direction and rate of change in photoperiod, or if photoperiod entrains a circannual clock. If starlings ( Sturnus vulgaris ) are kept on a constant photoperiod of 12 h light : 12 h darkness per day (12 L : 12 D), then they can show repeated cycles of gonadal maturation, regression and moult, which is evidence for a circannual clock. In this study, starlings kept on constant 11.5 L : 12.5 D for 4 years or 12.5 L : 11.5 D for 3 years showed no circannual cycles in gonadal maturation or moult. So, if there is a circannual clock, it is overridden by a modest deviation in photoperiod from 12 L : 12 D. The responses to 11.5 L : 12.5 D and 12.5 L : 11.5 D were very different, the former perceived as a short photoperiod (birds were photosensitive for most of the time) and the latter as a long photoperiod (birds remained permanently photorefractory). Starlings were then kept on a schedule which ranged from 11.5 L : 12.5 D in mid-winter to 12.5 L : 11.5 D in mid-summer (simulating the annual cycle at 9 °N) for 3 years. These birds entrained precisely to calendar time and changes in testicular size and moult were similar to those of birds under a simulated cycle at 52 °N. These data show that birds are very sensitive to changes in photoperiod but that they do not simply respond to absolute photoperiod nor can they rely on a circannual clock. Instead, birds appear to respond to the shape of the annual change in photoperiod. This proximate control could operate from near equatorial latitudes and would account for similar seasonal timing in individuals of a species over a wide range of latitudes.

Interactions Between Sleep, Other Body Rhythms, Immune Responses, and Exercise

Biological rhythms can influence both exercise tolerance and immune function. Most studies have focussed upon circadian rhythms, but some circaseptan, circatrigintan, and circannual cycles have also been described. Rhythms may have an endogenous or an exogenous basis. Endogenous rhythms originate in the cells of the suprachiasmatic nucleus. Impulses from this region pass to the pineal gland, where they regulate the production of melatonin, a compound that modulates the sleep/wakefulness cycle. Endocrine, physiological, and psychological parameters all show evidence of periodicity. Most components of the immune system, both cellular and humoral, also show large rhythmic changes. It is not yet clear how far such periodicity is secondary to changes in other body systems. Nevertheless, the magnitude of variation is such that it is vital to obtain experimental and control data at identical time points in both acute and chronic studies of exercise and immune function. Disturbance of the sleep/wakefulness cycle can constitute a form of stress, with adverse consequence for immune function. Key words: circadian rhythms, cytokines, hormones, hypothalamus, leukocytes, melatonin