Regulation of ovarian maturation in Macrobrachium nipponense by the ribonucleotide reductase M1 subunit

Ribonucleotide reductase large subunit (RRM1) functions as the catalytic subunit of ribonucleotide reductase (RR), which is a rate-limiting enzyme involved in DNA synthesis and repair. In this study, an RRM1 gene was identified from Macrobrachium nipponense and designated as MnRRM1. Its complete cDNA sequence was 2941 bp, encoding 812 amino acids. Quantitative real-time PCR (qRT-PCR) indicated that MnRRM1 expression was most pronounced in stage Ⅴ of ovary development compared to the other stages. Fluorescence in situ hybridization localized the MnRRM1 mRNA to the oocyte cytoplasm and to the follicular cells surrounding the oogonia and previtellogenic oocytes. Immunohistochemistry (IHC) localized the MnRRM1 protein to the nucleus of oogonia, as well as the cytoplasm and nucleus of oocytes. Ovarian explant incubation with AICA riboside (AICAR) and in vivo injection with 5-hydroxytryptamine (5-HT) upregulated the expression of the cell cycle protein B (MnCYCLIN B), cell division cyclin 2 (MnCDC2), and mitogen-activated protein kinase (MnMAPK) genes. In contrast, the wee1 protein (MnWEE1) and nm23 nucleoside diphosphate kinase (MnNM23) genes were downregulated. However, the outcomes of gemcitabine (GEM) incubation and RNA interference (RNAi) demonstrated an inverse pattern. Furthermore, RNAi-based MnRRM1 knockdown delayed oocyte maturation. These findings imply that MnRRM1 plays a potentially crucial role in promoting ovarian maturation in M. nipponense by facilitating DNA synthesis and energy provision during oocyte development and maturation.