Abstract
The ability to mature oocytes in vitro provides a tool for creating embryos by parthenogenesis, fertilization, and cloning. Unfortunately the quality of oocytes matured in vitro falls behind that of in vivo matured oocytes. To address this difference, transcriptional profiling by deep sequencing was conducted on pig oocytes that were either matured in vitro or in vivo. Alignment of over 18 million reads identified 1,316 transcripts that were differentially represented. One pathway that was overrepresented in the oocytes matured in vitro was for Wingless-type MMTV integration site (WNT) signaling. In an attempt to inhibit the WNT pathway, Dickkopf-related protein 1 was added to the in vitro maturation medium. Addition of Dickkopf-related protein 1 improved the percentage of oocytes that matured to the metaphase II stage, increased the number of nuclei in the resulting blastocyst stage embryos, and reduced the amount of disheveled segment polarity protein 1 protein in oocytes. It is concluded that transcriptional profiling is a powerful method for detecting differences between in vitro and in vivo matured oocytes, and that the WNT signaling pathway is important for proper oocyte maturation.
Highlights
In vitro maturation (IVM) of mammalian oocytes has long been a problematic step for the in vitro production of embryos
After mining through this data we noted that there were several genes related to the Wingless-type MMTV integration site (WNT) pathway that were over represented in IVM oocytes; WNT7A, FZD4, and DVL1
In a previous study evaluating transcript abundance in oocytes from cyclic versus prepubertal females, it was shown that development was lower from the prepubertal derived oocytes and about 10% of the transcriptome was different between the two groups of oocytes [17]
Summary
In vitro maturation (IVM) of mammalian oocytes has long been a problematic step for the in vitro production of embryos. While there have been major advances in improving both oocyte maturation and embryo culture over the past decades, and oocytes can successfully be matured in vitro, the rate of maturation and extent of maturation is lower than in vivo matured oocytes. Maturation of pig oocytes in vitro is even lower as compared to other livestock species [1,2]. While IVM pig oocytes are capable of being fertilized, developing to the blastocyst stage and producing offspring after transfer to a surrogate, the developmental competence of these oocytes is lower than in vivo produced oocytes; partially due to a lower number of nuclei in the resulting blastocyst [3], implying that the quality of the blastocyst is lower. By improving the oocyte’s overall health in vitro, the stage could be set for improved development by providing the oocytes most of what they need to be developmentally competent
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