Functional Analysis of the Cyclin E Gene in the Reproductive Development of Rainbow Trout (<i>Oncorhynchus mykiss</i>)

As a commercially valuable aquaculture species, rainbow trout (<i>Oncorhynchus mykiss</i>) urgently require solutions to growth inhibition associated with reproductive development. To elucidate the function of the cell cycle regulator Cyclin E genes (<i>CCNE1</i> and <i>CCNE2</i>) in this process, we cloned the genes and analyzed their relative expression across various tissues and gonadal developmental stages. Using RNA interference (RNAi) and overexpression in RTG2 cells, we examined the effects of <i>CCNE</i> on cell viability, proliferation, and meiotic gene expression. Results showed that the open reading frame lengths of <i>CCNE1</i> and <i>CCNE2</i> were 1230 bp and 1188 bp, encoding 408 and 395 amino acids, respectively. Both proteins contain two conserved cyclin boxes, exhibit high structural similarity, and are phylogenetically most closely related to <i>Oncorhynchus tshawytscha</i> and <i>Oncorhynchus kisutch</i>. Expression and localization analyses revealed that <i>CCNE1</i> was highly expressed in the ovary, while <i>CCNE2</i> was highly expressed in the testis. Both proteins were expressed during fertilized egg development and key gonadal stages (at 13, 21, and 35 months post-fertilization). <i>CCNE</i> expression positively correlated with RTG2 cell viability and proliferation, with immunofluorescence confirming that CCNE is localized in the nucleus. Knockdown or overexpression of CCNE induced the differential expression of reproductive-related genes and key meiotic regulators. These findings suggest that <i>CCNE1</i> and <i>CCNE2</i> balance meiosis and gamete development through specific regulatory mechanisms, and their dysregulation may be a key factor underlying meiosis inhibition and reproductive development abnormalities.