Transcriptome profiles of in vivo matured bovine cumulus-oocyte complexes reveal unique gene expression between the oocyte and cumulus cells

Authors: HESSOCK, EMMA - University Of Tennessee; SMITH, MICHAEL - University Of Missouri; Geary, Thomas; POHLER, KY - Texas A&M University; GREEN, JONATHAN - University Of Missouri; BEHURA, SUSANTA - University Of Missouri; STOKES, ALLYSON - University Of Tennessee; MOOREY, SARAH - University Of Tennessee

Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The oocyte and cumulus cells (CC) are intimately associated throughout folliculogenesis. They communicate bidirectionally to transfer important substrates such as metabolic components and RNA transcripts between cell types. It is well understood that the oocyte and CC play distinct roles throughout the development of the follicle and oocyte. Intercellular communication is vital for the oocyte’s successful trajectory through maturation, fertilization, and early embryo development. Previous in vitro studies revealed different gene expression profiles between the oocyte and CC, highlighting differences in function of the cells. However, to our knowledge, RNA-sequencing derived gene expression profiles unique to the oocyte and CC have yet to be explored in an in vivo matured, pre-ovulatory follicle model. We hypothesized that characterization of transcript profiles from in vivo matured bovine oocytes and CC will reveal essential functions of each cell type that occur during the latter stages of in vivo oocyte maturation. Our objectives were to identify transcripts exclusively and differentially expressed in in vivo matured bovine oocytes and CC, determine pathways and gene ontologies significantly enriched with exclusively or differentially expressed transcripts, and compare our results to those identified from in vitro models. We utilized RNA-sequencing data from pools of 4 oocytes (n=4) and their corresponding CC (n=5) collected via transvaginal aspiration of the pre-ovulatory follicle ~23 hours after estrus onset. We normalized expression levels to counts per million (CPM) and retained transcripts expressed (>1 CPM) in both cell types or exclusively expressed in oocytes or CC. We retained a total of 11,802 gene transcripts among all samples. There were 1,387 transcripts exclusively in the oocyte and 2,765 exclusively in the CC, whereas 7,655 transcripts were retained in both. Of the transcripts present in both cells, 4,298 were differently expressed with 2,553 upregulated in the oocyte and 1,745 upregulated in the CC. We then performed pathway and gene ontology enrichment analysis of the transcripts exclusively and differentially expressed between cell types. Transcripts exclusively expressed in oocytes were significantly enriched in multiple ontologies, including gene silencing or transcriptional processes (‘piRNA process’, ‘DNA methylation’, ‘transcriptional activator’) and ‘plasma membrane’ (FDR<0.01). Transcripts expressed exclusively in CC were enriched in metabolic pathways and cellular components such as ‘extracellular exosomes’ and ‘mitochondrion’ (FDR<0.04). Transcripts detected in both cell types but upregulated in CC were enriched in ‘oxidative phosphorylation’, ‘glycolysis’, ‘fatty acid metabolism’, and ‘steroid biosynthesis’ pathways, whereas pathways of ‘oocyte meiosis/maturation’ and ‘cell cycle’ were enriched with transcripts upregulated in oocytes (FDR<0.05). Compared to transcripts exclusive to in vitro matured bovine oocytes and CC there is overlap of significant enrichment of the ‘apical plasma membrane’ or ‘metabolic pathways’, ‘extracellular exosomes’, and ‘PI3K-Atk signaling pathway’. Additional pathways highlighted in our dataset related to transcriptional processes in the oocyte and potential mitochondrial function in CC provide a base for further studies comparing the developmental competency and transcriptome profiles of in vitro and in vivo matured oocytes. This research is/was supported by the USDA NIFA (AFRI Grant no. 2013-67015-21076), Hatch project 1022068 and UT AgResearch/the Department of Animal Science.