(84) Effects of Timing and Pattern of Blastomere Cleavage on Gene Expression Profiles in Bovine in Vitro Fertilized Embryos.

Shunki Ono¹; Hinano Kozuka¹; Kota Okubo¹; Takashi Fujii¹ ; Ken Sawai¹


1.Depertment of Animal Sciences, Faculty of Agriculture, Iwate University, Morioka, Iwate, Japan

Abstract Text:  

   The conception rate after the transfer of bovine in vitro fertilization (IVF) embryos is often lower than that on in vitro-derived (IVD) embryos. Moreover, large-offspring syndrome, characterized by multiple pathologies, including increased birth weight and elevated perinatal mortality rate, is a serious problem in bovine IVF embryos. These problems are thought to be caused by epigenetic status of bovine IVF embryos (Sawai, 2021). On the other hand, it has been suggested that the timing of the first cleavage and the pattern of blastomere cleavage in bovine IVF embryos are related to the fertility of bovine embryos obtained from IVF procedure (Sugimura et al., 2012). However, it is not clear whether timing and pattern of blastomere cleavage is involved in the gene expression status of bovine IVF embryos. In present study, we classified bovine IVF embryos into four categories (Cat.), such as Cat. 1: the first cleavage was completed within 27 h of the start of insemination, Cat. 2: First cleavage occurred within 27 h and cleaved from 1-cell to 2-cell, that did not cleave from 1-cell to 3-cell or more, Cat. 3: Multiple Fragmentation was not detected at 27 h of the start of insemination, Cat. 4: it was 6-cell or higher cell stage at 55 h of the start of insemination. Blastocyst formation rate of embryos that met all Cat. (4 Cat. matched) was 67.9%, and, expanded blastocyst rate (75.0%) of the embryo met all Cat. (4 Cat. matched) was higher than that of all embryos without categorize (42.8%). Gene expression status (IGFBP-2, IGFBP-3, AQP3, OCT-4, SOX2, FGF4, NANOG, TEAD4, CDX2, GATA3, and IFNT) in the 4 Cat. matched embryos were similar to IVD embryos as compared with 3≥ Cat. matched embryos. Blastocyst formation rate (87.3%) of embryos that matched both Cat. 2 and Cat. 4 was higher (P < 0.01) than those of embryos matched only Cat. 2 (50.8%) or did not match both Cat. 2 and Cat. 4 (14.3%). In addition, we evaluated the gene expression status of zygotic gene activation (ZGA)-related genes (ZsCAN4, PIWIL2, EIF1AX, DPPA2, GLIS1, KDM5B, KDM6B, Klf-4, OCT-4, SOX2), because it is well known that 55 h of the start of insemination is time for ZGA. Our results show a relationship between blastomere cleavage and epigenetic status of bovine IVF embryos, will provide new evaluation standard of bovine IVF embryos for preimplantation development and fertility after embryo transfer.