Intrauterine expression of LIF and its receptors in the cycling and early pregnant mare

Abstract

Leukaemia Inhibitory Factor (LIF) plays a critical role in blastocyst development and implantation, as clearly demonstrated by the failure of wild-type mouse embryos to implant in the uterus of LIF-knockout female mice unless the latter receive LIF supplementation. Expression of LIF and its receptors (LIF-R and gp130) in the early pregnant horse have not been described. However, the horse may be an interesting animal in which to study such ‘implantation factors’ because various aspects of implantation occur both unusually late and in a temporally distinct fashion in this species. The aim of this study was to examine LIF, LIF-R and gp130 gene expression in the endometrium of cycling and early pregnant mares, and in the early conceptus. Endometrial biopsies were recovered from 4 mares at each of late oestrus, days 7 and 14 of dioestrus (cycling mares), and days 7, 14 and 21 of gestation. Conceptuses were recovered by uterine lavage (day 7) or using a video-endoscopically guided net (days 14 and 21). For day 14 and 21 conceptuses, only the bilaminar trophoblast was used in gene expression studies. Expression of mRNA for LIF, LIF-R and gp130 was analysed by rtPCR, with relative expression calculated with respect to the 3 most stable housekeeping genes using GeNorm analysis. A dramatic increase in LIF mRNA expression (p<0.01) was observed in both the endometrium and the trophoblast on day 21 of pregnancy. Expression of LIF-R and gp 130 increased significantly in the trophoblast on day 21 (p<0.01), but did not vary in the endometrium at the various stages examined. We propose that LIF plays a role in the adhesion between trophoblast and endometrium which, in the mare, cannot begin until the blastocyst capsule is dissolved somewhere between days 18 and 22 of gestation