176 EFFECT OF LEUKEMIA INHIBITORY FACTOR FROM HUMAN AND MOUSE ORIGIN ON THE DEVELOPMENT OF BOVINE EMBRYOS PRODUCED IN VITRO

Abstract

Leukemia Inhibitory Factor (LIF) is a cytokine with potential to influence embryonic quality and proliferation within the inner cell mass (ICM). However, conflicting effects of LIF have been reported with in vitro-produced (IVP) bovine embryos, in spite of LIF receptor (LIFr) and gp130 transcripts being expressed at all stages during pre-implantation development (Niemann and Wrenzycki 2000 Theriogenology 53, 21–34). As there is no commercially available bovine LIF (bLIF), researchers have used human LIF (hLIF) because of its greater sequence homology compared to murine LIF (mLIF). However, mLIF has been not compared with hLIF in culture with bovine embryos; thus this was the aim of this study. Cumulus–oocyte complexes from slaughterhouse ovaries were matured and fertilized in vitro and presumptive zygotes cultured in modified synthetic oviduct fluid with 6 g L^-1 BSA. At 139 h post-insemination (Day 6), a total of 423 morulae (>90%) and early blastocysts were cultured for 48 h with: (1) 100 ng mL^-1 recombinant mLIF (Sigma-Aldrich Quimica SA, Madrid, Spain); (2) 100 ng mL^-1 recombinant hLIF (Sigma); and (3) no LIF. Data (6 replicates) were processed by GLM and Duncan's test, and expressed as LSM ± SE (^ab: P < 0.05; ^xy: P < 0.01). Development was recorded up to the hatched blastocyst stage and cells were differentially counted in the ICM and trophectoderm (TE) following the method described by Thouas et al. (2001 Reprod. Biomed. Online 3, 25–29). There were no differences within developmental rate on Day 7, but reduced blastocyst rates were observed on Day 8 between hLIF (42.0 ± 3.9^a and 27.2 ± 3.3^a) and controls (57.7 ± 3.9^b and 38.9 ± 3.3^b) at the medium and expanded stages, respectively, whereas mLIF had no effect (47.4 ± 3.9 and 32.3 ± 3.3). Contrary to development, Day 8 blastocysts showed decreased cell counts in both the ICM and the ICM/total cell proportions in the presence of mLIF (19.1 ± 3.1^x and 13.8 ± 2.4^x vs. 32.6 ± 3.0^y and 24.8 ± 2.3^y for controls, respectively), whereas hLIF had no effect (29.7 ± 3.1^y and 20.9 ± 2.4^y). No changes were seen in TE and total cell counts. The disparate effects exhibited by hLIF and mLIF during blastocyst formation may reflect the fact that these compounds are inappropriate to replace bLIF, and/or endogenous LIF probably suffices during bovine development. In fact, mouse embryonic development and blastocyst cell numbers decrease in murine embryos injected with LIF antisense nucleotides (Cheng et al. 2004 Biol. Reprod. 70, 1270–1276). Furthermore, embryonic stem (ES)-like cell derivation in bovine is possible with (Saito et al. 2003 Biochem. Biophys. Res. Com. 309, 104–113) and without (Mitalipova et al. 2001 Cloning 3, 59–67) exogenous LIF. Therefore, strategies to investigate LIF signalling in bovine embryos and stem cells should be reconsidered.

This work was supported by Grant AGL2005-04479.