| Summary: | Elephant seals undergo an annual catastrophic molting phase during which they shed all of their pelage (skin and fur) within one month. Molting occurs on dry land because blood flow has to be directed towards the surface of the skin for rapid regeneration, whereas it is directed toward internal organs in the water. Since seals cannot forage while they are at the rookery, they fast while molting, during which they rely heavily on fats stored within their blubber, a specialized type of fat tissue, for energy. The outer layer of the blubber is used for thermoregulation, while the inner layer serves to store energy. While most studies on seal metabolism have been conducted using inner blubber, the blubber layers are not well-defined morphologically. In this study, we characterized rapid hair follicle regeneration during molting in seals using histology. We found that during the early molting phase, most of the hair follicles were in the telogen phase of the hair cycle, while during the late molt phase, most were in anagen phase. We also distinguished inner and outer blubber layers using proteomics. We identified 1,369 proteins in the seal blubber proteome by mass spectrometry and found six proteins that were differentially abundant between the inner and outer blubber layers. The proteins RPL35 and ADH3 were more abundant in inner blubber, while ASPN, GIMAP4, PRKAR2A, and EVPL were more abundant in outer blubber. Our study allows us to gain a more in-depth understanding of the mechanisms regulating extremely rapid skin regeneration, which furthers our understanding of human skin diseases and disorders and their possible treatments. It also provides us with molecular markers to distinguish visibly similar but functionally distinct blubber layers in seals, as well as understand the evolution of blubber in mammals.
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