Current Issue

Volume 19, Number 3, Oct-Dec (Autumn) 2017, Serial Number: 75 Pages: 482-491

Evidence of Oocyte Polarity in Bovine; Implications for Intracytoplasmic Sperm Injection and Somatic Cell Nuclear Transfer


Seyed Morteza Hosseini, Ph.D., 1, 2, Fariba Moulavi, B.Sc., 2, Nima TanhaieVash, B.Sc., 2, Naser Shams-Esfandabadi, Ph.D., 1, Mohammad Hossein Nasr-Esfahani, Ph.D., 2, *, Abolfazl Shirazi, Ph.D., 1, 3, *,
Research Institute of Animal Embryo Technology, Shahrekord University, Shahrekord, Iran
Department of Reproductive Biotechnology, Reproductive Biomedicine Research Center, Royan Institute for Biotechnology, ACECR, Isfahan, Iran
Reproductive Biotechnology Research Center, Avicenna Research Institute, ACECR, Tehran, Iran
*Corresponding Address: Department of Reproductive Biotechnology Reproductive Biomedicine Research Center Royan Institute for Biotechnology ACECR Isfahan Iran Research Institute of Animal Embryo Technology Shahrekord University Shahrekord Iran Emails: mh.nasr-esfahani@royaninstitute.org, shiraziabbas@yahoo.com

Abstract

Objective

We recently demonstrated spatial regionalization of maternal transcripts and proteins within unfertilized ovine oocyte. Here, we investigated the likelihood of oocyte polarity for the first time in bovine.

Materials and Methods

In this experimental study, in vitro matured bovine oocytes were used for manual bisection [into oocyte halve that were near-to (HNS) and far-from (FS) spindle] or trisection [into MII-spindle (S), the spindle-side half (NS), and the distal half unassociated with the spindle (FS)]. Prepared pools of oocyte substructures were used for comparative quantitative real-time polymerase chain reaction (RT-qPCR). To map the possible preferential sperm entry point (SEP), the spatial relationship between SEP and MII-spindle was measured 5 hours post-fertilization.

Results

The proportional amount of maternal mRNA in S oocyte fragment was estimated to be 6 to 11-fold higher than NS and FS counterparts. The relative abundances of Nanog, Oct4, Fgf4 and Tead4 were significantly higher in HNS oocyte fragment compared t0 FS. The relative abundances of Ctnb, Carm1, Rex1, Sox2 and Cdx2 were comparable between HNS and NS oocyte fragments. FS oocyte fragment possessed significantly higher transcripts of Gata4 compared to HNS. The distribution of certain transcripts related to pluripotency and lineage commitment were different depending upon the region of the oocyte; either enriched at S (Tead4, Nanog, Ctnb and Sox2), NS (Oct4), or FS (Gata6). The SEP in almost (90%) fertilized oocytes was located in MII-hemisphere.

Conclusion

The observation of spatial restriction of mRNAs and SEP within MII-oocyte may indicate that the principal forces of oocyte polarity are evolutionary conserved. This may in turn highlight the need for refinements in the methodology of intracytoplasmic sperm injection (where a sperm is injected far from the MII-spindle) and somatic cell nuclear transfer (where a major amount of regulative mRNAs that are associated with MIIspindle is removed during enucleation).