Abstract
BackgroundWork in other species suggests that interleukin-6 (IL6) promotes early embryo development. It was unclear whether IL6 serves as an embryokine in cultured bovine embryos. This work was undertaken to elucidate the role of IL6 during in vitro bovine embryo production.ResultsTranscripts for IL6 and its two cognate receptor subunits (IL6R, IL6ST) were confirmed in bovine embryos from the 1-cell to blastocyst stages. Supplementing 100 ng/ml recombinant bovine IL6 to in vitro-produced bovine embryos at day 1, 3 or 5 increased (P < 0.05) inner cell mass (ICM) cell number and the ICM:trophectoderm (TE) ratio but not TE cell number. No increase in ICM or TE cell number was observed after supplementation of 1 or 10 ng/ml IL6 beginning at either day 1 or 5. Sequential supplementation with 100 ng/ml IL6 at both day 1 and 5 (for a total of 200 ng/ml IL6) increased (P < 0.05) ICM cell number to a greater extent than supplementing IL6 at a single time period in one study but not a second study. Additionally, providing 200 ng/ml IL6 beginning at day 1 or 5 yielded no further increase on ICM cell numbers when compared to supplementing with 100 ng/ml IL6. IL6 treatment had no effect on cleavage or blastocyst formation in group culture. However, IL6 supplementation increased cleavage and day 8 blastocyst formation when bovine embryos were cultured individually.ConclusionsThese results implicate IL6 as an embryokine that specifically increases ICM cell numbers in bovine embryos and facilitates bovine blastocyst development in embryos cultured individually.
Highlights
Work in other species suggests that interleukin-6 (IL6) promotes early embryo development
Similar scenario exists in cattle, where the current consensus is that bovine embryo culture conditions fail to adequately promote proper inner cell mass (ICM) development, and this contributes to at least some of the pregnancy losses that occur after transfer of in vitro-produced (IVP) bovine embryos [6, 7]
Fewer pregnancies are maintained by IVP conceptuses that lack visible embryonic disks when compared with IVP conceptuses containing prominent embryonic disks [6]
Summary
Work in other species suggests that interleukin-6 (IL6) promotes early embryo development. It was unclear whether IL6 serves as an embryokine in cultured bovine embryos. A similar scenario exists in cattle, where the current consensus is that bovine embryo culture conditions fail to adequately promote proper ICM development, and this contributes to at least some of the pregnancy losses that occur after transfer of in vitro-produced (IVP) bovine embryos [6, 7]. Bovine IVP blastocysts have fewer ICM cells, elevated apoptosis in the ICM, and produce smaller embryonic disks than their in vivo-produced counterparts [8, 9]. The embryonic and uterinederived factors controlling ICM specification and development remain largely unknown in cattle, humans and other mammals
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