Expression of Leukemia inhibitory factor and its receptor during oocyte maturation of adult and pre pubertal sheep

Leukemia inhibitory factor (LIF ) is expressed in the mouse uterus at ovulation and prior to implantation. The presence of LIF and its receptor (LIFR) has also been reported in the ovary in human, mouse and rat at different stages of follicular development. A beneficial influence of this cytokine on pre-implantation embryo development has been shown in several species; however LIF direct effect on the oocyte has not been studied yet. Aim of the present experiments was to investigate the expression of this cytokine specifically in GV and MII stage sheep oocytes, and their surrounding cumulus cells, both in adult and pre pubertal sheep. For this purpose, RNA was extracted and subsequently reverse transcribed. PCR was carried out with primers that were designed based on bovine and human deposited sequences. GV oocytes were matured: a) in the presence of LIF, b) LIF +anti-LIF antibody c) in control conditions. Following maturation, part of the oocytes was assessed for molecular studies, part for immunolocalization, while the remaining eggs were activated and cultured to the blastocyst stage in standard media. The proportion of developed embryos was evaluated for each group. PCR studies demonstrated the presence of the LIF/LIFR system in sheep oocytes and in cumulus cells, both at GV stage and at the end of maturation. These results were common to adult and pre-pubertal animals. The system appears to be biologically active and responsive since LIF putative action on cumulus oocyte complexes was inhibited by the antibody against this cytokine. This inhibition involves a reduction of LIFR density on the oocyte membrane, as evidenced by immunostaining. Altogether, these findings demonstrate the presence of the LIF/LIFR system in ovine cumulus oocyte complexes and indicate an autocrine/paracrine mechanism of action of this cytokine during the final stages of development of the female gamete