The Influence of Morphology, Follicle Size and Bcl‐2 and Bax Transcripts on the Developmental Competence of Bovine Oocytes

Abstract

This study analysed two non-invasive oocyte selection methods in relation to in vitro embryo development capacity and expression of apoptosis-related genes. Selection was based on morphological quality of oocytes or follicle diameter. Oocytes were classified as grade I (GI ≥3 layers compact cumulus cells and homogeneous cytoplasm; grade II (GII ≤3 layers compact cells and homogeneous cytoplasm;, and grade III (GIII ≥3 layers, but cells with slight expansion and slightly granulated cytoplasm). Blastocyst development was lower for GII (28.5%) than for GIII (47.7%, p < 0.05), and GI was similar to both (36.9%, p > 0.05). Relative expression of Bcl-2 gene was lower in the GI (1.0, p < 0.05) than in the GII (1.8) and GIII (2.2), which were not different (p > 0.05). There was no difference (p > 0.05) between GI (1.0), GII (0.92) and GIII (0.93) regarding the Bax transcript. However, the Bax and Bcl-2 transcript ratios in GII (Bax; 0.92 and Bcl-2; 1.8) and GIII (Bax; 0.93 and Bcl-2; 2.2) were different (p < 0.05). Regarding oocytes from follicles of different sizes, cleavage and blastocyst rates for 1-3 mm (82.5; 23.7%) were lower (p < 0.05) than for 6-9 mm (95.6; 41.1%), but similar (p > 0.05) to 3-6 mm (93.7; 35.4%), which were not different (p > 0.05). Regarding Bax and Bcl-2 expression, the oocytes were similar (p > 0.05) for 1-3 mm (Bax; 1.0 and Bcl-2; 1.0), 3-6 mm (Bax; 1.0 and Bcl-2; 0.93) and 6-9 mm (Bax; 0.92 and Bcl-2; 0.91). In conclusion, oocyte selection based on morphological appearance does not guarantee the success of embryonic development. Additionally, the absence of apoptosis is not necessarily a benefit for the development of oocytes. Bovine COCs with initial signs of atresia may be used for the in vitro production of embryos, and COCs taken from follicles >3 mm in diameter are better suited to in vitro embryo development.

Oxidative homeostasis in oocyte competence for in vitro embryo development

“…In addition, GSH is directly involved in the acquisition of oocyte competence and thus, its cytoplasmic level may be a reliable indicator of oocyte viability (Curnow, Ryan, Saunders, & Hayes, 2010;Sovernigo et al, 2017). However, besides ROS and GSH, the oocyte competence in maturation is also related to other factors, such as cumulus cell expansion, gene expression, structural organization, and mitochondrial replication, among many others (De Bem et al, 2014;Kahraman et al, 2018;Lamas-Toranzo, Pericuesta, & Bermejo-Alvarez, 2018;Nivet, Leveille, Leader, & Sirard, 2016 ROS and GSH seem to be of fundamental importance for the optimization of in vitro production of embryos (Luberda, 2005;Sovernigo et al, 2017). Since ROS and GSH play important roles in maturation, fertilization, and oocyte development, (Liang et al, 2018;Luberda, 2005;Sovernigo et al, 2017) another relevant point for oocyte competence appears to be oxidative homeostasis.…”

“…Follicles located in the cortical region ( Figure 1) were measured with the aid of a digital caliper and classified according to their diameter: follicles within size range 2-8 mm as general; 4-8 mm as large; and 2 < 4 mm as small. The oocytes aspirated from the follicles (general, large, and small) were evaluated under stereomicroscope and those viable and containing more than two layers of cumulus cells and uniform cytoplasm were used in the experiments (De Bem et al, 2014). To perform the study, 268 ovaries were used and an average of 10 follicles was aspirated per ovary, comprising 1,353 viable oocytes in total.…”

Effects of sexed semen and interactive effects on commercial in vitro embryo production when oocytes are collected from cows of Bos indicus, and Bos taurus breeding and crossbred cows of these subspecies

“…Additionally, personal observations of morphological characteristics of oocytes from cows with BT breeding were that these oocytes were of lesser quality compared with morphological classification of oocytes from cows of BI breeding, thus, this could account for the lesser cleavage rates and blastocyst development rates when oocytes were from BI/BT crossbred cows in the present study. A recent report provides evidence to corroborate this hypothesis (De Bem et al, 2014).…”

Influência Do Método De Recuperação Oocitária Sobre Os Parâmetros Quanti-Qualitativos De Oócitos Bovinos

“…Em geral, a maior recuperação alcançada pela técnica de slicing pode estar associada ao procedimento que favorece a colheita de oócitos oriundos de folículos com pequeno diâmetro, os quais normalmente não são utilizados na aspiração folicular (SIANTURI et al, 2002). A seleção de folículos com diâmetro maior, até 8 mm, durante a colheita favorece a obtenção de oócitos mais competentes, uma vez que folículos pequenos provavelmente não receberam estímulo suficiente de hormônios in vivo para o desenvolvimento posterior (DE BEM et al, 2014). Assim, o uso da técnica de slicing pode ser vantajoso quando se deseja uma alta taxa de recuperação e em casos de pouca disponibilidade de ovários para colheita.…”

“…A produção in vitro de embriões (PIVE) possibilita vários benefícios para a reprodução animal em setores científicos, produtivos e tecnológicos (DE BEM et al, 2014). Essa biotécnica compreende várias etapas e cada uma tem influência direta no resultado final.…”