Abstract：Pregnant mare serum gonadotropin (PMSG) combined with gonadotropin-releasing hormone (GnRH) can improve reproductive efficiency by stimulating the ovaries of mice (Mus musculus), but its effect on embryo implantation remains unclear. This study aimed to explore the effect of PMSG combined with GnRH on embryo implantation in mice. In the experiment group, mice were used to inject 3.5 µg of GnRH agonist leuprorelin 48 h after 7.5 IU of PMSG injection (referred to as P+G group), and the control group was injected twice with saline. Normal blastocysts were transferred into the uterus of pseudo-pregnant mice in the P+G and control groups, then embryo implantation rates were analyzed after 5 d embryo transfer, and the expression of endometrial receptivity marker gene - leukemia inhibitory factor (Lif) was detected. Transcriptome sequencing data were analyzed to reveal the effect of P+G on endometrial receptivity, and qRT-PCR and Western blot were used to verify the data accuracy. The results showed that the embryo implantation rate of P+G group was significantly lower than that of the control group (P<0.05), and the expression of endometrial receptivity marker gene Lif was significantly reduced (P<0.05) in the P+G group. Transcription group sequencing analysis found 751 differentially expressed genes (DEGs), of which 587 up-regulated and 164 down-regulated. GO and KEGG analysis found that DEGs mainly enriched in the immune response, immune system process, cell adhesion molecules (CAMs), and cytokine-cytokine receptor interaction pathways. The results of qRT-PCR and Western blot showed that the expression of Lif gene and protein were down-regulated and the expression of Lcn2 and Prap1 gene and protein were up-regulated in the P+G group, which was consistent with the results of transcriptome sequencing. This study provides a certain theoretical basis for in- depth exploration of the regulatory mechanism of PMSG and GnRH involved in embryo implantation.
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