Abstract
Simple SummaryThe yak is a multipurpose domesticated animal that serves as a protein source for local herders and a sacred carrier of culture and religion. Besides their economic significance, yaks harbor special morphological, physiological, biochemical, and genetic adaptations for tolerance to high-altitude stress. Morphologically, yaks have large hearts and lungs, compact bodies, thick outer hair covering, and nonfunctional sweat glands, which help to withstand hypoxia and cold stress. A reduced heat production, decreased respiration and sweating, reduced metabolism, and efficient nitrogen utilization are the major physiological and biochemical mechanisms for yak survival at high altitudes. Furthermore, the yak has undergone long-term natural selection and developed a unique genetic architecture that favors survival in hostile environments. The yak expresses the HIF-1α pathway-related genes (ADAM17, ARG2, and MMP3) putatively involved in hypoxia response and nutrition pathways genes (CAMK2B, GENT3, HSD17B12, WHSC1, and GLUL) for nutritional assimilation at high altitudes.Living at a high altitude involves many environmental challenges. The combined effects of hypoxia and cold stress impose severe physiological challenges on endothermic animals. The yak is integral to the livelihood of the people occupying the vast, inhospitable Qinghai–Tibetan plateau and the surrounding mountainous region. Due to long-term selection, the yak exhibits stable and unique genetic characteristics which enable physiological, biochemical, and morphological adaptations to a high altitude. Thus, the yak is a representative model for mammalian plateau-adaptability studies. Understanding coping mechanisms provides unique insights into adaptive evolution, thus informing the breeding of domestic yaks. This review provides an overview of genetic adaptations in Bos grunniens to high-altitude environmental stress. Combined genomics and theoretical advances have informed the genetic basis of high-altitude adaptations.
Highlights
The Qinghai–Tibetan Plateau ecological environment is characterized by low atmospheric oxygen pressure, cold, and limited feed supplies [1,2]
The significant reduction in heat production of yaks during winter might result from their adaptation to low oxygen concentrations in the air, the cold environment, and the long-term under nutrition prevalent in the sixmonths-long cold season of the Tibetan plateau [5]
During periods of reduced O2 availability, changes in gene expression are mediated by a specific family of transcription factors called the “master regulator” of O2 homeostasis. These genes are collectively known as hypoxia-inducible factors (HIF) [70,71]
Summary
The Qinghai–Tibetan Plateau ecological environment is characterized by low atmospheric oxygen pressure, cold, and limited feed supplies [1,2]. Endothermic animals endure impaired oxygen supplies, which compromise cellular functions and physiologic performance under high-altitude environments. These high-altitude mountains are more sensitive and vulnerable to climate change, a huge threat to biodiversity and the ecosystem [3]. The yak supplies (milk, meat, hair, hides, and manure) and services (draft, packing, and riding) the pastoralists and agro-pastoralists occupying these areas They are means of financial security and cultural functions (status, dowry, religious festivals) [6]. This review attempts to collate and synthesize current knowledge on the mechanisms of yak adaptation to high altitudes It can provide new avenues for in vitro and in vivo studies to further test hypotheses arising from previous investigations and options for designing and implementing interventions for improved yak productivity and resilience in high altitudes
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