Interleukin-6 and leukemia inhibitory factor differentially modify embryonic disk composition in post hatching bovine embryos

Proper formation of the embryonic disk is essential for pregnancy survival. This study examined whether supplementing interleukin-6 (IL6) or leukemia inhibitory factor (LIF) influence epiblast (EPI) and hypoblast (HYPO) development as well as other facets of post-hatching bovine embryo development in an extended culture system. A series of three studies were completed where in vitro-produced (IVP) embryos were treated with IL6 or LIF from days 5-12, 5-7, or 7-12 post-fertilization. Survival and hatching were monitored from days 7-12, then embryos were fixed for immunofluorescent assessments. Non-treated IVP embryos were transferred at day 7 and collected on day 12 post-estrus (IVP-ET) for use an in-utero reference for the days 7-12 culture group. Neither IL6 nor LIF affected survival or hatching. Supplementing IL6 from days 5-12 increased EPI cell number and reduced HYPO formation whereas LIF had no effect. Supplementing IL6 from days 7-12 produced similar responses, and EPI cell numbers matched those of the IVP-ET day 12 embryos. By contrast, supplementing IL6 from days 5-7 had no effects, indicating that IL6 exposure is unnecessary before blastocyst formation but required afterward to elicit these outcomes. In conclusion, IL6 supplementation after blastocyst formation enhances EPI development to levels comparable to in utero embryos, although this may occur at the expense of HYPO formation. It was equally intriguing that LIF did not mimic the effects of IL6 but rather failed to exhibit any noteworthy effects on the EPI and HYPO lineages.