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Vertebrate reproductive science and technology
RESEARCH ARTICLE

A prematuration approach to equine IVM: considering cumulus morphology, seasonality, follicle of origin, gap junction coupling and large-scale chromatin configuration in the germinal vesicle

Valentina Lodde A , Silvia Colleoni B , Irene Tessaro A , Davide Corbani A , Giovanna Lazzari B C , Alberto M. Luciano A , Cesare Galli B C and Federica Franciosi https://orcid.org/0000-0001-8742-0291 A D
+ Author Affiliations
- Author Affiliations

A Dipartimento di Scienze Veterinarie per la Salute la Produzione Animale e la Sicurezza Alimentare ‘Carlo Cantoni’, Reproductive and Developmental Biology Lab, Università degli Studi di Milano, via Celoria, 10 20133 Milano, Italy.

B Laboratory of Reproductive Technologies, Avantea, Cremona, Via Porcellasco, 7f 26100 Cremona, Italy.

C Fondazione Avantea, Via Porcellasco, 7f 26100 Cremona, Italy.

D Corresponding author. Email: federica.franciosi1@unimi.it

Reproduction, Fertility and Development 31(12) 1793-1804 https://doi.org/10.1071/RD19230
Submitted: 18 June 2019  Accepted: 13 September 2019   Published: 21 October 2019

Abstract

Several studies report that a two-step culture where mammalian oocytes are first kept under meiosis-arresting conditions (prematuration) followed by IVM is beneficial to embryo development. The most promising results were obtained by stratifying the oocyte population using morphological criteria and allocating them to different culture conditions to best meet their metabolic needs. In this study, horse oocytes were characterised to identify subpopulations that may benefit from prematuration. We investigated gap-junction (GJ) coupling, large-scale chromatin configuration and meiotic competence in compact and expanded cumulus–oocyte complexes (COCs) according to follicle size (<1, 1–2, >2 cm) and season. Then we tested the effect of cilostamide-based prematuration in compact COCs collected from follicles <1 and 1–2 cm in diameter on embryo development. Meiotic competence was not affected by prematuration, whereas COCs from follicles 1–2 cm in diameter yielded embryos with a higher number of cells per blastocyst than oocytes that underwent direct IVM (P < 0.01, unpaired Mann–Whitney test), suggesting improved developmental competence. Oocytes collected from follicles <1 cm in diameter were not affected by prematuration. This study represents an extensive characterisation of the functional properties of immature horse oocytes and is the first report of the effects of cilostamide-based prematuration in horse oocyte IVM on embryo development.

Additional keywords: assisted reproduction, blastocyst, developmental competence, intracytoplasmic sperm injection (ICSI), oocyte maturation.


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