GENETIC VARIATION IN HAEMOGLOBIN ALTERS CONTROL OF BREATHING IN HIGH-ALTITUDE DEER MICE

Haemoglobin (Hb)-O2 affinity has been a pervasive target of selection in many high-altitude taxa and is often presumed to safe-guard arterial O2 saturation in hypoxia, but the effect of genetic variation in globins on other aspects of respiratory physiology is poorly understood. We investigated the influence of the high-altitude variants in alpha- and beta-globins of North American deer mice (Peromyscus maniculatus) on control of breathing. We created a hybrid population of deer mice using a F2 intercross breeding design, which disrupts the linkages between loci that result from population genetic structure, so the effects of globin genotype on breathing, metabolism, and arterial O2 saturation during hypoxia could be compared on an admixed genetic background. Alpha-globin genotype had a significant influence on breathing pattern, with highland homozygotes breathing deeper but less frequently across a range of inspired O2. The ventilatory response to hypoxia was augmented in mice that were homozygous for highland beta-globin. These differences in breathing did not appear to be caused by genetically based differences in blood-O2 affinity, because treatment with efaproxiral to reduce Hb-O2 affinity had no effect on breathing in normoxia or hypoxia. Globins were not expressed in the brainstem, and globin genotype had little effect on gene expression in the medulla (assessed using RNA-Seq), so differences in control of breathing were not caused by non-erythroid expression of globins in these key sites of ventilatory control. Our findings suggest that the evolution of globin genes may have pervasive effects on multiple respiratory phenotypes, and may contribute to environmental adaptation via physiological mechanisms that are not commonly ascribed to this protein.

血红蛋白（Haemoglobin, Hb）与氧气的亲和力是众多高海拔类群中普遍存在的选择靶标，学界通常认为其可在低氧环境中维持动脉血氧饱和度，但球蛋白的遗传变异对呼吸生理学其他方面的影响仍知之甚少。本研究以北美鹿鼠（Peromyscus maniculatus）的α-和β-球蛋白高海拔变异体为研究对象，探究其对呼吸调控的影响。我们采用F2互交育种策略构建鹿鼠杂交种群，以此打破群体遗传结构带来的位点连锁不平衡，从而可在混杂遗传背景下，比较球蛋白基因型对低氧条件下呼吸、代谢及动脉血氧饱和度的影响。α-球蛋白基因型对呼吸模式存在显著影响：在不同吸入氧浓度条件下，高海拔纯合子小鼠的呼吸更深但频率更低。携带高海拔β-球蛋白纯合基因型的小鼠，其低氧通气反应更为显著。此类呼吸差异似乎并非由血液氧亲和力的遗传差异所致：使用依法普司（efaproxiral）降低Hb-O2亲和力后，无论常氧还是低氧条件下，小鼠的呼吸均未发生明显变化。脑干中并无球蛋白表达，且球蛋白基因型对延髓的基因表达（通过RNA测序（RNA-Seq）评估）影响极小，因此呼吸调控的差异并非由通气调控关键位点中非红系表达的球蛋白所导致。本研究结果表明，球蛋白基因的演化可能对多种呼吸表型产生广泛影响，并可通过以往未被归因于该蛋白的生理机制，助力物种的环境适应。