S100A2 and neoplasm: In the red module significantly associated with 2.5 years old, hub genes such as S100A2, KRT6A, TGFA, and KLK7 [44,45,46,47] were reported to play roles in skin damage repair, inflammation, and the immune response, which may be related to the enhancement of the barrier and immune function of the yak skin at 2.5 years old.