Simple Summary
In vitro-produced (IVP) bovine embryos have reduced developmental potential and post-transfer survival. One reason this may occur is because of the lack of growth, differentiation factors, and cytokines that are present within the follicle but absent within oocyte maturation culture systems. This work explored whether supplementing selective members of the interleukin-6 (IL6) cytokine family during in vitro bovine oocyte maturation affects maturation success, cumulus–oocyte complex (COC) gene expression, fertilization success, and embryo development potential. Human recombinant proteins for IL6, IL11, and leukemia inhibitory factor (LIF) were supplemented to COCs during the maturation period, then fertilization and embryo culture commenced without further cytokine supplementation. Several key outcomes were observed. Both LIF and IL11 increased one COC transcript associated with oocyte competency whereas IL6 did not produce this effect. None of the cytokines influenced fertilization success but supplementing COCs with LIF or IL11 increased the ability of these oocytes to generate blastocyst stage embryos. No effect of IL6 supplementation was detected. Collectively, this work provides evidence that supplementing LIF or IL11 during in vitro oocyte maturation complexes improves oocyte competency, but no such effects were detected when IL6 was supplemented during maturation.
Abstract
This work explored whether supplementing selective members of the interleukin-6 (IL6) cytokine family during in vitro bovine oocyte maturation affects maturation success, cumulus–oocyte complex (COC) gene expression, fertilization success, and embryo development potential. Human recombinant proteins for IL6, IL11, and leukemia inhibitory factor (LIF) were supplemented to COCs during the maturation period, then fertilization and embryo culture commenced without further cytokine supplementation. The first study determined that none of these cytokines influenced the rate that oocytes achieved arrest at meiosis II. The second study identified that LIF and IL11 supplementation increases AREG transcript abundance. Supplementation with IL6 supplementation did not affect AREG abundance but reduced HAS2 transcript abundance. Several other transcriptional markers of oocyte competency were not affected by any of the cytokines. The third study determined that supplementing these cytokines during maturation did not influence fertilization success, but either LIF or IL11 supplementation increased blastocyst development. No effect of IL6 supplementation on subsequent blastocyst development was detected. The fourth experiment explored whether each cytokine treatment affects the post-thaw survivability of cryopreserved IVP blastocysts. None of the cytokines supplemented during oocyte maturation produced any positive effects on post-thaw blastocyst re-expansion and hatching. In conclusion, these outcomes implicate IL11 and LIF as potentially useful supplements for improving bovine oocyte competency.