Effect of follicular diameter, time of first cleavage and H3K4 methylation on embryo production rates of Bos indicus cattle

Abstract

This study aimed investigate the relationship between epigenetics, follicular diameter and cleavage speed, by evaluating the developmental potential and occurence of H3K4 monomethylation of early-, intermediate-and late-cleaving Bos indicus embryos from in vitro fertilized oocytes originating from follicles up to 2 mm in diameter or between 4 and 8 mm in diameter. Oocytes (n = 699) from small follicles (≤ 2 mm) and 639 oocytes from large follicles (4-8 mm) were punched from 1,982 Bos indicus' slaughterhouse ovaries. After maturation and in vitro fertilization (IVF), the cultured embryos were separated into early (≤ 28 h post-IVF), intermediate (> 28 h and ≤ 34 h post-IVF) and late (> 34 h and ≤ 54 h post-IVF) cleavage groups. Blastocysts were subjected to an immunofluorescence assessment for H3K4me investigation. The blastocyst rate for large follicles (36.3%) was higher than that for small follicles (22.9%, P<0.05). In addition, blastocyst rates for early and intermediate cleavage groups (45.3% and 33.8%, respectively) were higher than that for late cleavage group (13.5%, P < 0.05). The blastocysts from all groups displayed H3K4me staining by immunofluorescence, particularly intense in what seemed to be trophectoderm cells and weak or absent in cells seemingly from the inner cell mass. For the first time for indicus embryos, data from this study demonstrate that higher blastocyst embryo rates are obtained from embryos that cleave within 34 h after fertilization and from those produced from follicles of 4-8 mm in diameter, indicating a greater ability of these embryos to develop to the stage of embryonic preimplantation. This is the first article demonstrating the occurrence of H3K4me in cattle embryos; its presence in all the evaluated blastocysts suggests that this histone modification plays a key role in maintaining embryo viability at preimplantation stage. Key words: Bovine. Early cleavage. Follicular size. Late cleavage. Histone modifications. ResumoEste estudo teve como objetivo investigar a relação entre a epigenética, o diâmetro folicular e a velocidade de clivagem, avaliando o potencial de desenvolvimento e a ocorrência de monometilação da H3K4 em embriões Bos indicus de clivagem precoce, intermediária e tardia produzidos a partir de oócitos fertilizados in vitro oriundos de folículos de até 2 mm de diâmetro ou entre 4 e 8 mm de diâmetro.

Effect of Combination of Follicle Size, FSH and Cysteamine on In Vitro Production of Sheep Embryos

“…Perhaps these vital roles of cysteamine are the main reason for the low rates of arrest presented in our study (Table 3), specifically in embryos resulting from oocytes that have been matured in B medium (LF group). In general, the results of the current study related to the rates of cleavage and blastocyst stage can be compared with the results of some studies (Lojkić et al 2016;Shabankareh et al 2015;Muasa 2010;Lunardelli et al 2016;Merton et al 2013;Shabankareh & Zandi 2010;Ranjbar et al 2018) summarized in Table 5 according to the studied factors.…”