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The dominant follicle: the final frontier in oocyte development

ABSTRACT: The acquisition of oocyte competence, involving both cytoplasmic and nuclear maturation, is critical for successful fertilization and embryonic development in mammals. Discrepancies between in vivo and in vitro studies underline the potential impact of assisted reproductive technologies (ARTs), such as FSH stimulation and in vitro maturation, on oocyte quality and the molecular integrity of bovine oocytes. These insights underscore the importance of optimizing ART conditions to enhance reproductive success in cattle production. Therefore, this study focuses on the gene expression and DNA methylation dynamics in bovine oocytes from dominant follicles, utilising single-cell bisulfite conversion and RNA sequencing (scG&T), without ovarian stimulation. Samples were collected from synchronized heifers during three time points from 24hr to 2hr before ovulation and submitted to scG&T and compared with a dataset of >120 um in diameter oocytes collected by ovary slicing. Our findings from the single-cell RNA sequencing highlight significant changes in oxidative phosphorylation transcripts, indicating the importance of energy metabolism during oocyte capacitation. Additionally, small changes in global CpG methylation and methylation over genomic features were observed. However, modest modifications in CpG windows suggest a less stable epigenome than previously assumed in fully-grown oocytes. In conclusion, the present study brings new insights into molecular changes in bovine oocytes collected from dominant follicles, which can contribute to oocyte quality improvement in cattle production.

ORGANISM(S): Bos taurus

PROVIDER: GSE297927 | GEO | 2025/07/14

REPOSITORIES: GEO

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Project description:Developmental competences of oocytes derived from prepubertal heifers are lower than those derived from adult counterparts. The objective of this study was to identify a range of genes associated with reduced oocyte competence that are differentially expressed between adult versus prepubertal donors. Microarray experiments were conducted using total RNA isolated from GV and MII stages oocytes collected from adult and prepubertal animals using Affymetrix GeneChip Bovine Genome Array containing 24,072 probe sets representing over 23,000 transcripts. A total of 549 and 333 genes were differentially expressed between prepubertal versus adult bovine MII and GV stages oocytes respectively. Out of these, 312 and 176 genes were up-regulated, while 237 and 157 were down-regulated in prepubertal when compared with adult MII and GV oocytes respectively. Ontological classification of the differentially expressed genes revealed that up-regulated genes in adult oocytes were involved in signal transduction, regulation of transcription DNA-dependent, and transport. Results from the present study indicated that significant number of genes were differentially expressed (>2-fold, p<0.01) between the two groups. Thus the decreased developmental competence of oocytes from prepubertal heifers may be induced due to difference in gene expression abundance as observed in our study. In conclusion, transcript abundance analyses of oocytes using microarray approach have been carried out in bovine and several other species. However, to our knowledge, this is the first study carried out to examine genes expression differential abundance in oocytes derived from perpubertal versus adult Japanese Black Cattle. Bovine 4b PP biological rep1, Bovine 78b PP biological rep2, Bovine 79 PP biological rep3 represents GV stage oocytes derived from Prepubertal (PP) heifer group, while Bovine 74b A biological rep1, Bovine 80b A biological rep2, Bovine 81 A biological rep3 represents GV stage oocytes derived from Adult (A) cow group. Bovine 7 PP biological rep1, Bovine 53 PP biological rep2, Bovine 57 PP biological rep3 represents MII stage oocytes derived from Prepubertal heifer group, while Bovine 59 A biological rep1, Bovine 70 A biological rep2, Bovine 71 A biological rep3 represents MII stage oocytes from Adult cow group. The ovaries of adult cows (Japanese black cattle) were collected from local abattoir while ovaries of prepubertal Japanese black heifers (9 to 12 months old) were collected by spay device at several commercial farms. The collected ovaries of both the adult cows and prepubertal heifers groups were transported to the research laboratory in 0.67% (w/v) NaCl solution containing 100 mg/L kanamycin sulfate (Meiji Seika, Tokyo, Japan). For both groups, cumulus oocyte complexes (COCs) from ovarian follicles 2 to 8M-BM- mm in diameter were aspirated by using an 18 gauge needle (Terumo co, Tokyo, Japan) attached to a 5 ml disposable syringe (Nipro, Osaka, Japan). After collection, the COCs were washed twice with Tyrode-lactate-pyruvate-polyvinylalcohol (Hepes-TLP-PVA) and TCM 199 (Invitrogen, Gibco, NY, USA) supplemented with 10% heat-inactivated fetal bovine serum (maturation medium). Only COCs with evenly granulated cytoplasm surrounded by multiple layers of compact cumulus cells were used in all the experiments. The COCs (70 to 80) were placed in 200 M-BM-5L drop of the maturation medium in petri dish (35x10mm, Becton Dickinson Labware, Oxnard, CA, USA) covered with paraffin liquid (Nacalai Tesque Inc, Kyoto, Japan) and cultured at 38.5M-BM-0C in a humidified atmosphere of 5% CO2 in air for 20 to 22 h for maturation.

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The dominant follicle: the final frontier in oocyte development

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