Neofunctionalization of the UCP1 mediated the non-shivering thermogenesis in the evolution of small-sized placental mammals

Evolution of UCP1 Gene and Its Significance to Temperature Adaptation in Rodents

Adaptive thermogenesis comprises shivering thermogenesis dependent on skeletal muscles and non-shivering thermogenesis (NST) mediated by uncoupling protein 1 (UCP1). Although the thermogenic function of UCP1 was adopted early in some placental mammals, positive selection predominantly occurred in the ancestral branches of small-bodied species. Some previous studies have revealed that rodents living in northern or high mountain regions adapt to cold environments by increasing NST, whereas those living in tropical and subtropical regions that are not exposed to cold stress express low concentrations of UCP1, indicating that UCP1 may have evolved to adapt to ambient temperatures. In this study, we explored the evolution of UCP1 and its significance to temperature adaptation by performing detailed evolutionary and statistical analyses on 64 rodents with known genomes. As a result, a total of 71 UCP1 gene sequences were obtained, including 47 intact genes, 22 partial genes, and 2 pseudogenes. Further, 47 intact genes and 3 previously published intact UCP1 genes were incorporated into evolutionary analyses, and correlation analyses between evolutionary rate and ambient temperatures (including average annual temperature, maximum temperature, and minimum temperature) of the rodent survives were conducted. The results show that UCP1 is under purifying selection (ω = 0.11), and among rodents with intact UCP1 sequences, Urocitellus parryii and Dicrostonyx groenlandicus-the two species with the lowest ambient temperatures among the rodents used here-have higher evolutionary rates than others. In the statistical analyses, in addition to ambient temperatures, body weight and weight at birth were also taken into account since weight was previously proposed to be linked to UCP1 evolution. The results showed that after controlling for the phylogenetic effect, the maximum temperature was significantly negatively correlated with the evolutionary rate of UCP1, whereas weight did not have a relationship with UCP1 evolutionary rate. Consequently, it is suggested that ambient temperature can drive the evolution of rodent UCP1, thereby enhancing NST adaptation to cold stress.

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 3: Heat and cold tolerance during exercise

In this third installment of our four-part historical series, we evaluate contributions that shaped our understanding of heat and cold stress during occupational and athletic pursuits. Our first topic concerns how we tolerate, and sometimes fail to tolerate, exercise-heat stress. By 1900, physical activity with clothing- and climate-induced evaporative impediments led to an extraordinarily high incidence of heat stroke within the military. Fortunately, deep-body temperatures > 40 °C were not always fatal. Thirty years later, water immersion and patient treatments mimicking sweat evaporation were found to be effective, with the adage of cool first, transport later being adopted. We gradually acquired an understanding of thermoeffector function during heat storage, and learned about challenges to other regulatory mechanisms. In our second topic, we explore cold tolerance and intolerance. By the 1930s, hypothermia was known to reduce cutaneous circulation, particularly at the extremities, conserving body heat. Cold-induced vasodilatation hindered heat conservation, but it was protective. Increased metabolic heat production followed, driven by shivering and non-shivering thermogenesis, even during exercise and work. Physical endurance and shivering could both be compromised by hypoglycaemia. Later, treatments for hypothermia and cold injuries were refined, and the thermal after-drop was explained. In our final topic, we critique the numerous indices developed in attempts to numerically rate hot and cold stresses. The criteria for an effective thermal stress index were established by the 1930s. However, few indices satisfied those requirements, either then or now, and the surviving indices, including the unvalidated Wet-Bulb Globe-Thermometer index, do not fully predict thermal strain.

Comparative genomics provides insights into the aquatic adaptations of mammals

Divergent lineages can respond to common environmental factors through convergent processes involving shared genomic components or pathways, but the molecular mechanisms are poorly understood. Here, we provide genomic resources and insights into the evolution of mammalian lineages adapting to aquatic life. Our data suggest convergent evolution, for example, in association with thermoregulation through genes associated with a surface heat barrier (NFIA) and internal heat exchange (SEMA3E). Combined with the support of previous reports showing that the UCP1 locus has been lost in many marine mammals independently, our results suggest that the thermostatic strategy of marine mammals shifted from enhancing heat production to limiting heat loss.

The ancestors of marine mammals once roamed the land and independently committed to an aquatic lifestyle. These macroevolutionary transitions have intrigued scientists for centuries. Here, we generated high-quality genome assemblies of 17 marine mammals (11 cetaceans and six pinnipeds), including eight assemblies at the chromosome level. Incorporating previously published data, we reconstructed the marine mammal phylogeny and population histories and identified numerous idiosyncratic and convergent genomic variations that possibly contributed to the transition from land to water in marine mammal lineages. Genes associated with the formation of blubber (NFIA), vascular development (SEMA3E), and heat production by brown adipose tissue (UCP1) had unique changes that may contribute to marine mammal thermoregulation. We also observed many lineage-specific changes in the marine mammals, including genes associated with deep diving and navigation. Our study advances understanding of the timing, pattern, and molecular changes associated with the evolution of mammalian lineages adapting to aquatic life.

Genetic and Functional Characterization of Novel Brown-Like Adipocytes Around the Lamprey Brain

During the process of vertebrate evolution, many thermogenic organs and mechanisms have appeared. Mammalian brown adipose tissue (BAT) generates heat through the uncoupling oxidative phosphorylation of mitochondria, acts as a natural defense against hypothermia and inhibits the development of obesity. Although the existence, cellular origin and molecular identity of BAT in humans have been well studied, the genetic and functional characteristics of BAT from lampreys remain unknown. Here, we identified and characterized a novel, naturally existing brown-like adipocytes at the lamprey brain periphery. Similar to human BAT, the lamprey brain periphery contains brown-like adipocytes that maintain the same morphology as human brown adipocytes, containing multilocular lipid droplets and high mitochondrion numbers. Furthermore, we found that brown-like adipocytes in the periphery of lamprey brains responded to thermogenic reagent treatment and cold exposure and that lamprey UCP2 promoted precursor adipocyte differentiation. Molecular mapping by RNA-sequencing showed that inflammation in brown-like adipocytes treated with LPS and 25HC was enhanced compared to controls. The results of this study provide new evidence for human BAT research and demonstrate the multilocular adipose cell functions of lampreys, including: (1) providing material energy and protecting structure, (2) generating additional heat and contributing to adaptation to low-temperature environments, and (3) resisting external pathogens.