International Journal of Aquaculture, 2024, Vol.14, No.4, 184-194 http://www.aquapublisher.com/index.php/ija 186 al., 2021; Yuan et al., 2021). The loss of the UCP1 locus in many marine mammals indicates a shift in their thermostatic strategy from enhancing heat production to limiting heat loss, further highlighting the role of GRNs in evolutionary adaptation. The gene plays a crucial role in determining whether adipocytes develop into energy-storing white fat cells or heat-producing brown fat cells by regulating adipocyte differentiation. In brown fat cells, the action of the UCP1 protein can convert stored energy into heat, which is vital for maintaining body temperature in cold aquatic environments. Research has found convergent amino acid substitutions in the NFIA gene across multiple marine mammal species, suggesting that these species may promote the formation of adipose tissue through similar mechanisms to adapt to aquatic environments. Additionally, the SEMA3Egene plays an important role in vascular development. The vascular structures of marine mammals, such as the complex retia mirabilia, are crucial for thermoregulation, effectively reducing heat loss in water. Studies show that the convergent evolution of the SEMA3E gene may help these animals develop their vascular systems more effectively to maintain body temperature in cold environments. Figure 1 Convergent evolution of thermoregulation in marine mammals (Adopted from Yuan et al., 2021) Image caption: (A) Schematic diagram of thermoregulation in marine mammals. Up- or down-regulation of nuclear factor I A (NFIA) affects the cell fate of mesenchymal precursors, the integrity of UCP1 gene affects the fate of brown adipocyte, and the well-developed retia mirabilia in marine mammal aids in the heat transfer to maintain body temperature balance. VSMC, vascular smooth muscle cell; EC, endothelial cell. (B) A unique amino acid change in the NFIAgene of marine mammals. Shared amino acid change are highlighted in blue, IP, Indo-Pacific. (C) A unique amino acid change in the SEMA3E gene of cetaceans and pinnipeds. Blue highlighting indicates the shared amino acid change. (D) VISTA sequence conservation plot of the UCP1 gene, using goat (ARS1) as a reference (Adopted from Yuan et al., 2021) 3.2 Epigenetic modifications Epigenetic modifications, including DNA methylation and histone modifications, are pivotal in regulating gene expression without altering the underlying DNA sequence. These modifications can lead to phenotypic changes that are essential for the adaptation to new environments. In the context of aquatic life forms, epigenetic changes may influence the expression of genes involved in critical physiological processes such as thermoregulation, diving, and navigation. For example, the unique changes in genes like NFIA and SEMA3E in marine mammals
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