Influence of follicle size on bovine oocyte lipid composition, follicular metabolic and stress markers, embryo development and blastocyst lipid content

Abstract

This study assessed the lipid composition of oocytes from different follicle sizes and compared the expression of lipid-related genes and follicular fluid (FF) molecules between groups. We also investigated the functional consequences of differences on embryo development and blastocyst lipid deposits. Oocytes and FF were recovered from different follicle sizes. Oocytes from small (≤5mm) and large (≥6mm) bovine follicles were used to produce Day 7 expanded blastocysts (Day7Ex) and blastocysts that only became expanded at Day 8 (Day8Ex) after insemination. Oocytes from >8mm follicles had the highest lipid content. Few oocyte phospholipid variations were identified between groups. Very long chain fatty acid elongase 6 (ELOVL6) mRNA abundance was reduced in larger follicle-derived oocytes compared with the ≤2mm group. Increased levels of glucose, reactive oxygen species, glutathione and superoxide dismutase activity were also identified in FF from larger follicles. Large follicle-derived embryo development and lipid content of Day7Ex were greater than those derived from small follicles. Day8Ex had greater lipid deposition than Day7Ex. Oocytes and blastocysts exhibited follicle size-specific lipids. Large-follicle oocytes had increased lipid content and became Day7Ex with greater lipid deposition whereas delayed blastocoel expansion associated with a prolonged period of culture determined the lipid accumulation of Day8Ex. The FF microenvironment of large follicles seems to favour embryo development.

Coenzyme and cofactor metabolism belongs to biochemical processes significantly regulated in human granulosa cells collected after IVF during long-term primary in vitro culture

“…A studies provided by Annes et al compared the expression of lipid-related genes and follicular fluid molecules between different bovine follicle sizes. It was demonstrated that ELOVL6 showed lower transcript levels in larger follicle-derived (≥6 mm) oocytes compared with the ≤2 mm group [26]. Another study provided a comprehensive description of stage-specific lipidome signatures in early bovine embryo development, via assessment the mRNA abundance of lipid metabolism-related genes (including both ELOVL5 and ELOVL6).…”

Embryo competence and cryosurvival: Molecular and cellular features

“…Any type of stress conditions that oocytes face can potentially disrupts embryo development. Differences in the morphology (Nagai et al, 2015;Nagano, 2019), lipid composition, transcriptome, and embryo development (Labrecque et al, 2016;Annes et al, 2018) had already been described in the oocytes recovery from different follicle sizes. The bovine oocytes used for IVPE are recovered from follicles with 2 to 8 mm of diameter, before follicle divergence.…”

“…The bovine oocytes used for IVPE are recovered from follicles with 2 to 8 mm of diameter, before follicle divergence. Generally, oocytes recovered from large follicles (> 6mm) present a greater potential of reaching blastocysts compared to oocytes recovered from follicles of 2 to 6 mm (Rizos et al, 2002;Fair, 2003;Labrecque et al, 2016;Annes et al, 2018).…”

“…In the commercial IVPE programs, the ultrasound-guided follicular aspiration (OPU) is routinely used for oocyte recovery, this biotechnology allows access a large number of female gametes in mono-ovulatory species favoring the multiplication of animals with exponentially genetic merit (Nagai et al, 2015;Nagano, 2019). Investigations on the influence of the follicle microenvironment and size in the establishment of competent embryos have been conducted (Annes et al, 2018;Labrecque et al, 2016;Lonergan et al, 2016).…”

“…Despite embryo culture conditions is crucial for embryo quality and cryosurvival determination , blastocysts that originate from oocytes matured in vitro result in lower rates of gestation compared to their in vivo counterparts (Peterson and Lee, 2003). Additionally, we recently identified a relationship between the cytoplasmic lipid content of oocytes and the lipid deposit of expanded blastocysts (Annes et al, 2018), i.e., oocytes derived from large follicles and containing greater amount of lipid droplets, originated day 7 expanded blastocysts, after IVPE, with increased lipid deposit. An experiment evaluating the cryosurvival of these blastocysts is still lacking, however, it is fair to speculate that this increased lipid deposit negatively impact embryo cryosurvival (Abe et al, 2002).…”