| Phenotypic plasticity is a phenomenon that a genotype expresses different phenotypes,which has been considered to facilitate organisms in response to environmental changes.With global climate change,some species from lowland colonize to high-altitudinal environments,thus have to cope with constant low level of oxygen in the high-altitudinal environments.How phenotypic plasticity contributes to respond to hypoxic condition in the high-altitudinal environments is largely unknown.The Asian house rat(Rattus tanezumi)is a widely distributed and recently has colonized to Qinghai-Tibetan Plateau.To study how phenotypic plasticity has contributed to recent colonization to the Qinghai-Tibetan Plateau,in particular to hypoxic conditions,we acclimated lowland Asian house rats to a hypoxic chamber with a hypoxic condition similar to 3,200 m above sea level.After one-month exposure to hypoxic condition,we compared physiological and gene expression changes between the hypoxia-exposed and control rats.We found hypoxia-exposed rats decreased partial oxygen pressures,and increased mass of lung and heart,and diameters of myocardial fiber,as compared to lowland control rats.We also found the concentration of hemoglobin and erythrocyte pressure of blood have been increased significantly in the hypoxia-exposed than in the control rats.These phenotypic changes have been regarded to increase oxygen diffusion and transportation,thus can facilitate to respond to decrease in the oxygen levels.In the phenotypic change regarding to energy metabolism,we found hypoxia-exposed rats decreased food intake and body weight as compared to lowland controls.This decrease is more significant in the males than in the females.In the phenotypic changes related to metabolic rate,we found hypoxia-exposed rats increases basal metabolic rate and mean mitochondria area in the heart.The mass of brown adipose tissue is also significantly greater in hypoxia-exposed rats than in control rates.This change is more pronounced in the male rats than in female rats.However,we did not found the body surface temperature changed between hypoxia-exposed and control rats.In order to elucidate the regulatory mechanisms of the phenotypic changes,we carried a multi-organ transcriptomic comparison(including heart,lung,hypothalamus,pituitary and adrenal glands)of hypoxia-exposed and lowland control rats.We found that the hypothalamus,as a center of neurohumoral regulation,shows regulatory change in many genes related to angiogenesis and vascular contract.We also found gene expression change in the metabolism.It seems that the Asian house rat seems to be more sensitive to temperature compering to hypoxia,which allows the Asian house rat to activate its BAT tissue under hypoxia to increase regulation of thermogenesis.There is an gender difference in this thermogenic activity mechanism,which was more significant in the hypothalamic-pituitary-thyroid axis.By integrating phenotypic plasticity and transcriptional regulation changes,this study provides novel insight into how phenotypic plasticity of the Asian house rate in response to hypoxia and how this would facilitate to its colonization to the highaltitudinal Qinghai-Tibetan Plateau. |
