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Trophic effects of myeloid leukaemia inhibitory factor (LIF) on mouse embryos

Myeloid leukaemia inhibitory factor (LIF) is expressed at highest concentrations in the maternal endometrial glands at about the stage of blastocyst implantation. LIF is also expressed by the extraembryonic membranes of the early mouse embryo. Embryos of different ages were cultured with, or without, LIF, and embryo growth in vivo and in vitro was examined to determine whether LIF is important for embryo development. Supplementing embryo culture media with 1000 U recombinant human LIF ml^–1 increased the number of eight-cell mouse embryos developing beyond the hatched blastocyst stage in vitro from 62.1% to 85.1% (P < 0.05). LIF significantly increased the number of embryos hatching (33.8% versus 7.65% for controls 96 h after hCG injection, P < 0.001), completely hatching (85.1% versus 62.1%, P < 0.05), and exhibiting trophoblast outgrowth (13.5% versus 0% 120 h after hCG treatment, 85.1% versus 47.0% 144 h after hCG treatment, P < 0.001) in vitro. LIF-treated embryos also displayed a significantly greater area of trophoblast outgrowth than did controls as early as day 5 in culture (P < 0.005). These data show that LIF enhances mouse eight-cell embryo development in vitro, as seen by the accelerated rate of embryo hatching and trophoblast outgrowth. In addition, enhanced embryo survival in vivo is shown, following the transfer of LIF-treated embryos into a pseudopregnant recipient female. Expression of mRNA encoding LIF was detected in endometrial cells cultured in monolayer from uteri of day 3 pregnant females, explaining the known embryotrophic effects of endometrial coculture. This expression was not enhanced significantly by treatment with oestradiol (3.7 x 10^–5 mol l^–1) or progesterone (3.2 x 10^–6 mol l^–1) or both hormones. These results indicate that LIF could have a dual action in early embryogenesis as an embryotrophin and as a factor required for embryo implantation. Multiple roles for LIF are consistent with the expression of this factor at embryonic, extraembryonic and maternal sites during early embryogenesis.