The effect of leukaemia inhibitory factor (LIF) on embryogenesis.

Leukaemia inhibitory factor (LIF) was originally identified as a haemopoetic factor that induced the differentiation of certain myeloid leukaemia cell lines. In contrast to this action, LIF was subsequently shown to inhibit the spontaneous differentiation of murine embryonic stem cells in culture, thus maintaining their pluripotency and ability to contribute to the germline of chimaeric mice. In the mouse, mRNA for LIF is expressed by the endometrial glands of the uterus coincident with the time of blastocyst implantation and receptors have been found on the preimplantation blastocyst. The signal for LIF expression appears to be of maternal origin, perhaps regulated by oestradiol. Recombinant LIF improves the development of murine and ovine blastocysts in culture although there is some species specificity with respect to the type of LIF that is bioactive. It is proposed here that LIF acts on the trophectoderm of the rapidly expanding blastocyst and improves the implantation rate of otherwise compromised embryos. Further studies in livestock should elicit therapeutic uses for LIF in embryo culture, embryo transfer and embryo survival in vivo.