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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #322327
Title: Effect of ovulatory follicle diameter on the oocyte transcriptome in beef cows

Author
item DICKINSON, SARA - University Of Missouri
item GREEN, J - University Of Missouri
item Geary, Thomas
item POHLER, K - University Of Missouri
item SMITH, M - University Of Missouri

Submitted to: Reproduction, Fertility and Development
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/2015
Publication Date: 12/3/2015
Citation: Dickinson, S.E., Green, J.A., Geary, T.W., Pohler, K.G., Smith, M.F. 2015. Effect of ovulatory follicle diameter on the oocyte transcriptome in beef cows[Abstract]. Reproduction, Fertility and Development. 28(2):203. doi:10.1071/RDv28n2Ab147.

Interpretive Summary:

Technical Abstract: Inadequate oocyte competence is a potential explanation for reduced pregnancy rates and(or) embryonic/fetal mortality when small dominant follicles are induced to ovulate prematurely with gonadotropin releasing hormone (GnRH). Our hypothesis was that the physiological status of an ovulatory follicle has a direct effect on competence of the oocyte and resulting embryo. The objective was to determine if the transcriptome of oocytes differ depending on whether they are collected from small or large dominant follicles following a GnRH-induced gonadotropin surge. Suckled beef cows (n=350) were pre-synchronized with a 5-day CIDR protocol. Following pre-synchronization, GnRH1 was administered on day -9, prostaglandin F on day -2, GnRH2 (to initiate the ovulatory process) on day 0, and dominant follicles were transvaginally aspirated on day 1 before follicular rupture. On day 0, cows were divided into small (<11.7mm; no estrus expression), or large (>12.5 mm; no estrus expression) groups based on dominant follicle diameter. Oocytes were individually collected after aspiration, and RNA was later extracted from pools of 4 oocytes (n= 6 oocyte pools from both small and large follicles) and sequenced on an Illumina HiSeq 2000 (single reads, 100 bases). The sequences were tiled against a ~23,500 member bovine transcript reference obtained from NCBI. Tiling to target transcripts required a minimum match of 50 bases with at least 96% identity. Tiling counts were displayed as RPKM values which were obtained by correcting for the length of each target (in kbp) and the number of total tiled reads (in millions). Differences between groups were defined by two-tailed T-test and gene lists were selected based on P values <0.02. Numerous differences in transcript abundance were characterized between oocytes from small and large dominant follicles. Follistatin-like 5 expression was increased (P < 0.02) in oocytes collected from large dominant follicles compared to oocytes collected from small dominant follicles. There were several genes associated with the ubiquitin pathway (e.g. ubiquitin conjugating enzyme, ubiquitin like protein -7) that were upregulated (P < 0.02) in oocytes from large versus small dominant follicles. In addition, there were four members of the zinc finger protein family that were upregulated (P < 0.02) and four members that were downregulated (P < 0.02) in oocytes from large compared to small dominant follicles. In summary, some of the genes that were highly differentially regulated in bovine oocytes between small and large dominant follicles included members of the zinc finger and ubiquitin pathways which may reflect differences in transcriptional regulation and protein turnover, respectively, between oocytes collected from large and small follicles. AFRI Grant no. 2013-67015-21076 from the USDA National Institute of Food and Agriculture.