Evolution, characterization, and expression profile of Egl-9 family hypoxia-inducible factor (<i>egln</i>) in rainbow trout (<i>Oncorhynchus mykiss</i>) under hypoxia stress

Egl-9 family hypoxia-inducible factor (<i>egln</i>), an oxygen-sensing enzyme family, has been thoroughly characterized in mammals and certain fishes, but there is few research on its involvement in reproductive development and hypoxic stress in rainbow trout. In this study, we investigated the gene structure, physicochemical properties, and evolutionary connection of the <i>egln</i> gene family. The expression profile of <i>egln</i> gene family and their regulatory mechanism were explored using bioinformatics analysis and hypoxia treatment experiments. Five <i>egln</i> genes were discovered in the rainbow trout genome in this investigation (<i>egln1</i>, <i>egln2a</i>, <i>egln2b</i>, <i>egln3a</i>, and <i>egln3b</i>). Domain prediction revealed that all <i>egln</i> proteins have p4hc conserved domains, and phylogenetic analysis revealed that rainbow trout <i>egln2</i> and <i>egln3</i> were closely related to <i>Atlantic salmon</i>. The results of real-time quantitative PCR (RT-qPCR) showed that <i>egln</i> genes were generally expressed in all detected tissues, and higher in the ovary, testis, and brain in normoxia. Under hypoxia, the expression level of <i>eglns</i> was significantly down-regulated in most tissues except the liver. Our research contributes to future research on the functional properties of <i>egln</i> genes, as well as the evolution of teleosts and the impact of hypoxia on biological immunity.