The follicular system: a new protocol for oocyte in vitro maturation in cattle

Abstract

In vitro production of bovine embryos (IVP) has been applied to increase fertility and enhance genetic improvement in beef and dairy herds, despite its recognized low efficiency. In vitro maturation (IVM) is considered to be the main technical bottleneck of IVP in cattle. Current IVM protocols do not reflect the physiological conditions and determine a mismatch between oocyte nuclear and cytoplasmic maturation. Oocytes subjected to IVM are derived from follicles at different developmental stages and are heterogeneous with regard to degree of chromatin condensation and stocks of transcripts important for early embryo development. This project aims to develop a new IVM system, the Follicular System, which includes a strategy to harvest a homogeneous population of oocytes, as well as a sequential culture system adjusted to the oocyte developmental stage, mimicking the intrafollicular environment before (pre-IVM phase) and after ovulation (IVM phase). The central hypothesis of this project is that the Follicular System can increase the number and quality of bovine embryos produced in vitro, in comparison with conventional protocols with just one culture step and supra-physiological concentrations of FSH. The experiments proposed herein aim to validate a protocol for the recovery of homogeneous oocytes from Nelore and Holstein donors, as well as to assess the impact of the Follicular System on embryo in vitro production from Holstein cows. The impact of the Follicular System on IVP will be assessed through IVP, freezability and conception rates. I addition, aiming to shed light onto the mechanisms by which the Follicular System may benefit developmental competence, we will assess the effects of the Follicular System on gene expression patterns of cumulus cells. (AU)