Leukaemia inhibitory factor modulates the differentiation of granulosa cells during sheep in vitro preantral to antral follicle development and improves oocyte meiotic competence

In vitro follicle development from cryopreserved ovarian tissue could become an invaluable assisted reproduction technology for women with early ovarian failure. The challenge lies in producing, from small follicles present in the ovarian cortex, high-quality mature oocytes able to sustain embryo development. In vivo, an optimal combination of hormones and other factors coordinates the development of follicles and their enclosed oocyte. We have investigated the effect of the leukaemia inhibitory factor (LIF) cytokine, alone or in combination with FSH, on sheep in vitro follicle development from the preantral stage onwards. LIF did not alter follicle growth or antrum formation, but it modulated the differentiation of granulosa cells, as revealed by decreased production of anti-Müllerian hormone and abolished FSH-induced stimulation of oestradiol secretion. This modulatory role was also reflected in the abundance of mRNA from 35 genes, analysed by reverse-transcription coupled to microfluidic quantitative PCR. LIF stimulated or at least maintained the expression of genes involved in the dialogue between the oocyte and granulosa cells, through gap junctions (GJA4 encoding connexin 37) or paracrine signalling (Bone morphogenetic protein 15, KIT ligand and their receptors). Finally, the presence of both LIF and FSH during follicle growth strongly improved oocyte meiotic competence: most oocytes (56%) underwent subsequent nuclear maturation, a significant increase compared with their counterparts from follicles of similar size (550-900 µm) cultured with FSH only (28%) or developed in vivo (9%). Their ability to sustain embryo development remains to be evaluated. Combined supplementation with FSH and LIF certainly merits investigation with human follicles.