Comparative transcriptomic analysis across ovarian developmental stages in Sepiella japonica provides novel insights...

Sepiella japonica is a cephalopod of significant commercial value, commonly found throughout China's coastal waters, ranging from southern Hong Kong to the Korean Peninsula and western regions of Japan. However, under captive conditions, S. japonica frequently exhibits precocious sexual maturation, which can result in reduced adult body size and severely limit aquaculture development. Therefore, elucidating the molecular mechanisms on ovarian development has become a critical priority. In this study, RNA sequencing was performing of the ovary tissue of female S. japonica collected across four key ovarian developmental stages: oogonium production (stage I), protoplasmic growth (stage II), interstitial growth (stage III), and trophoplasmic growth (stage IV). A total of 354,393,214 clean reads (Q20>98.58%) were obtained from 16 samples. Pairwise comparative analyses of I vs II, II vs III, and III vs IV identified 10050, 2564, 2278 differentially expressed genes (DEGs), respectively. Through differential expression analysis, we identified 13,319 differentially expressed genes (DEGs), among of which exhibited consistently high expression across four developmental stages, such as FOXL2, HSD17B2, and BMP1, suggesting their critical roles in regulating ovarian development in S. japonica. Gene Ontology (GO) enrichment analysis showed that these DEGs were significantly enriched in processes including protein targeting to the ER, response to estradiol, oxidative phosphorylation, and female pregnancy. KEGG pathway analysis revealed that DEGs were significantly enriched in key functional pathways, such as Ribosome, Prolactin signaling, FOXO signaling, and Lysosome. Furthermore, the "response to estradiol" pathway was consistently enriched across multiple developmental stage comparisons, suggesting that genes associated with steroid-related signaling may play conserved roles during ovarian development in S. japonica. This study clarified the regulation of transcript expression and molecular mechanisms in the ovary of S. japonica at different ovarian development stages, thereby offering theoretical guidance for enhancing reproductive efficiency in mollusk aquaculture.