Comparative transcriptome and adaptive evolution analysis on the main liver and attaching liver of Pareuchiloglanis macrotrema.

Pareuchiloglanis macrotrema is a glyptosternoid fish belonging to the Siluriform family and is endemic to the Qinghai-Tibet Plateau tributaries. P. macrotrema is an ideal model for studying the adaptive evolution of fish at high altitudes. P. macrotrema has two attaching livers connected to the main liver, a common feature in most Sisoridae fishes but is a special phenomenon relative to other vertebrates. Using RNA-Seq, 42 differentially expressed genes were found between the main liver and attaching liver, of which 31 were upregulated and 11 were downregulated in the main liver. The major differentially expressed genes between the main liver and attaching liver of P. macrotrema are related to metabolism, immunity, and digestive processes. Meanwhile, a comparative transcriptome analysis was carried out on P. macrotrema fish and six non-plateau Siluriformes fishes. We found 268 positively selected genes in P. macrotrema that are related to energy metabolism, immunity, and hypoxic responses. The findings of this study highlight the gene expression differences between the main liver and attaching livers of Sisoridae fishes and provide greater insight into the evolution of Tibetan fishes.