146 Transcriptome characterisation of equine oocyte maturation
A. de la Fuente A B , C. Scoggin C , E. Bradecamp C , H. Ali D , M. Troedsson D , S. Meyers A and P. Dini BA Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California, Davis, CA, USA
B Department of Population Health and Reproduction, University of California, Davis, CA, USA
C LeBlanc Reproduction Center, Rood and Riddle Equine Hospital, Lexington, KY, USA
D Gluck Equine Research Center, University of Kentucky, Lexington, KY, USA
Reproduction, Fertility and Development 34(2) 311-311 https://doi.org/10.1071/RDv34n2Ab146
Published: 7 December 2021
© 2022 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of the IETS
In vitro embryo production (IVP) has become one of the important assisted reproductive techniques for the successful breeding of horses. The most common practice is the retrieval of immature oocytes followed by IVM, intracytoplasmic sperm injection (ICSI), and in vitro culture of zygotes. IVM is one of the limiting steps because only about half of immature oocytes advance to metaphase II and acquire developmental competence, reducing the efficiency of IVP programs. Despite ongoing research on equine oocyte IVM, we still lack a comprehensive understanding of this dynamic event and the elaborated crosstalk between the oocyte and surrounding cumulus cells. This information is key for the optimisation of IVM culture conditions and consequently better IVP outcomes. Thus, the aims of this study were to characterise the transcriptome profile of oocytes (OC) and cumulus cells (CC) derived from immature (MI) and in vitro-matured (MII) cumulus-oocyte complexes (COC) and to elucidate the gene expression dynamic during equine oocyte IVM by identifying differentially expressed genes (DEG). OC or CC from 6 COCs obtained from transvaginal aspiration in live mares (age range: 5–15 years) were pooled into single samples (n), resulting in a total of 15 samples divided in four groups: matured CC (CC-MII, n = 4), immature CC (CC-MI, n = 3), matured OC (OC-MII, n = 4) and immature OC (OC-MI, n = 4). The quality and quantity of extracted RNA were assessed using the Bioanalyzer® 2100 system (Agilent). Then, total RNA was sequenced, generating 6 Gb of raw reads per sample. The reads were trimmed and mapped to EquCab3.0 (https://www.ncbi.nlm.nih.gov/assembly/GCF_002863925.1/). Differentially expressed genes (DEG) were evaluated using DESEqn 2 based upon false discovery rate (FDR) adjusted P-value < 0.05. A total of 15Â 917 genes were expressed in OC, with 407 DEG between OC-MI and OC-MII (183 up-regulated and 224 down-regulated in MII samples compared to MI). In CC, we found 15Â 483 expressed genes with 197 DEG (157 up-regulated and 40 down-regulated in MII samples compared to MI). Gene ontology enrichment analysis revealed that up-regulated genes in OC-MII are involved in the regulation of cellular metabolic processes, component organisation and biogenesis, and nucleic acid-binding, whereas down-regulated genes in OC-MI are related to organelle, nuclear and membrane-enclosed lumen, nucleoplasm, and nucleolus. In CC-MII, up-regulated genes are involved in cell signalling and communication, including cell surface receptor signalling pathways, whereas down-regulated genes in CC-MII are predominantly associated with antigen processing and presentation, endoplasmic reticulum (ER), protein processing in ER, lysosome, and vacuoles. Using the FANTOM5 ligand-receptor database for protein-coding genes, we identified potential crosstalk between the up-regulated follicle-stimulating hormone receptor (FSHR) gene in mature CC and the up-regulated glycoprotein hormone α chain (CGA) gene in mature OC. The information established in this study will help us advance our understanding of oocyte maturation and to further optimise the current IVM culture conditions, ultimately improving equine IVP outcomes.
