Transcriptomic characterization of lamb ovaries and oocytes reveals key biomarkers after superovulation

Superovulated prepubertal lambs serve as an important source of oocytes for Juvenile In Vitro Embryo Transfer (JIVET); however, their ovarian response to gonadotropin stimulation markedly differs from that of adult ewes. The ovaries and oocytes are the primary targets of hormonal-induced superovulation in lambs, and their developmental status directly determines the efficiency of follicular recruitment and maturation. In this study, the in vitro developmental assessment revealed that the maturation rate, cleavage rate, and blastocyst formation rate of lamb oocytes were significantly lower (P < 0.05) than those of adult sheep oocytes. To investigate this disparity, whole transcriptome sequencing (RNA-seq) of ovaries and ultra-low RNA-seq of oocytes collected from adult sheep and lamb were performed. Integrative transcriptomic analysis identified a significant enrichment of differentially expressed genes (DEGs) in the PI3K/Akt signaling pathway across ovarian and oocytes. Both Immunofluorescence and Immunohistochemistry analyses revealed key nodes ERBB3, HRAS proteins in this pathway exhibited elevated expression in both ovarian follicles and oocytes of superovulated lambs. Collectively, ERBB3 and HRAS serve as key biomarkers for the reduced developmental competence of oocytes in lambs following superovulation.