Genome-wide characterization of HSP70 and HSP90 subfamilies in Yak (Bos grunniens): expression patterns under cold and chemical hypoxia conditions.

The yak (Bos grunniens), a typical alpine species, exhibits distinctive adaptations to extreme environments, including a dense coat system and robust tolerance to hypoxia and low temperatures. Within this context, the heat shock protein (HSP) gene family likely plays a core role in the high-altitude adaptive evolution of yaks. By regulating protein homeostasis and mediating cellular stress responses, HSPs critically support cellular physiological functions, particularly under hypoxic and cold stress conditions. The physicochemical properties of the HSP70 and HSP90 subfamilies were systematically evaluated, and their subcellular localization was simulated. Protein-protein interaction (PPI) networks were constructed and RNA sequencing (RNA-seq) data were processed to assess tissue-specific expression patterns in yaks. To evaluate the stress response, yak preadipocyte cells were subjected to cold exposure and chemical hypoxia induction using CoCl2, followed by quantification of HSP70 and HSP90 gene expression using reverse transcription quantitative polymerase chain reaction (RT-qPCR). This genome-wide comparative analysis of HSP70 and HSP90 genes across five bovine species identified four evolutionarily conserved subfamilies exhibiting lineage-specific structural variations, including chromosomal rearrangements and duplication events. In yaks, 14 HSP70/90 genes with different structural configurations and species-specific expression profiles were identified. PPI network analyses revealed novel functional associations between previously uncharacterized HSP members and core regulatory partners. Tissue-specific expression profiling demonstrated ubiquitous HSP gene expression across multiple yak tissues, indicative of a diverse range of physiological functions. Furthermore, the HSP genes exhibited three distinct expression patterns under combined chemical hypoxia induction using cold and CoCl2 stress conditions. This study systematically elucidated the functional significance of HSP genes—particularly HSP70 and HSP90—in the high-altitude adaptation of yaks. Our findings establish a molecular framework for understanding the genetic basis of cold resistance and hypoxia tolerance in bovids, with implications for germplasm improvement.