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Vertebrate reproductive science and technology
RESEARCH ARTICLE

Maternal age and in vitro culture affect mitochondrial number and function in equine oocytes and embryos

W. Karin Hendriks A F , Silvia Colleoni C , Cesare Galli C D , Damien B. B. P. Paris A G , Ben Colenbrander A , Bernard A. J. Roelen A B and Tom A. E. Stout A B E H
+ Author Affiliations
- Author Affiliations

A Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 114, 3584 CM Utrecht, The Netherlands.

B Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 104, 3584 CM Utrecht, The Netherlands.

C Avantea, Laboratorio di Tecnologie della Riproduzione, Via Porcellasco 7f, 26100 Cremona, Italy.

D Department of Veterinary Medical Sciences, University of Bologna, Via Tolara di Sopra 50, 40064 Ozzano Emilia, Italy.

E Section of Reproduction, Faculty of Veterinary Science, University of Pretoria, Private Bag XO4, Onderstepoort, 0110, South Africa.

F Present address: Hendriks EQ Repro Consultancy, Zutphensestraatweg 32, 6955 AH Ellecom, The Netherlands.

G Present address: College of Public Health, Medical and Veterinary Sciences, James Cook University, Solander Drive, Townsville, Qld 4814, Australia.

H Corresponding author. Email: t.a.e.stout@uu.nl

Reproduction, Fertility and Development 27(6) 957-968 https://doi.org/10.1071/RD14450
Submitted: 18 November 2014  Accepted: 6 March 2015   Published: 17 April 2015

Abstract

Advanced maternal age and in vitro embryo production (IVP) predispose to pregnancy loss in horses. We investigated whether mare age and IVP were associated with alterations in mitochondrial (mt) DNA copy number or function that could compromise oocyte and embryo development. Effects of mare age (<12 vs ≥12 years) on mtDNA copy number, ATP content and expression of genes involved in mitochondrial replication (mitochondrial transcription factor (TFAM), mtDNA polymerase γ subunit B (mtPOLB) and mitochondrial single-stranded DNA-binding protein (SSB)), energy production (ATP synthase-coupling factor 6, mitochondrial-like (ATP-synth_F6)) and oxygen free radical scavenging (glutathione peroxidase 3 (GPX3)) were investigated in oocytes before and after in vitro maturation (IVM), and in early embryos. Expression of TFAM, mtPOLB and ATP-synth-F6 declined after IVM (P < 0.05). However, maternal age did not affect oocyte ATP content or expression of genes involved in mitochondrial replication or function. Day 7 embryos from mares ≥12 years had fewer mtDNA copies (P = 0.01) and lower mtDNA : total DNA ratios (P < 0.01) than embryos from younger mares, indicating an effect not simply due to lower cell number. Day 8 IVP embryos had similar mtDNA copy numbers to Day 7 in vivo embryos, but higher mtPOLB (P = 0.013) and a tendency to reduced GPX3 expression (P = 0.09). The lower mtDNA number in embryos from older mares may compromise development, but could be an effect rather than cause of developmental retardation. The general down-regulation of genes involved in mitochondrial replication and function after IVM may compromise resulting embryos.

Additional keywords: ATP, gene expression, mitochondrial quantity, mitochondrial replication.


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