Effects of progesterone on transzonal projection dynamics during IVM following a pre-IVM in bovine cumulus-oocyte complexes

• Grant number: 25/13140-2
• Support Opportunities: Scholarships abroad - Research Internship - Master's degree
• Start date: September 30, 2025
• End date: March 29, 2026
• Field of knowledge: Agronomical Sciences - Veterinary Medicine - Animal Reproduction
• Principal Investigator: Juliano Coelho da Silveira
• Grantee: Luca Angi Souza
• Supervisor: Valentina Lodde
• Host Institution: Faculdade de Zootecnia e Engenharia de Alimentos (FZEA). Universidade de São Paulo (USP). Pirassununga , SP, Brazil
• Institution abroad: Università degli Studi di Milano, Italy
• Associated to the scholarship: 24/03052-6 - Extracellular Vesicles Containing NPR2 and EGFr Supplemented During Oocyte Maturation: Effects on Transzonal Projection Communication, Meiotic Resumption, and Oocyte Quality, BP.MS

Abstract

In bovine species, the acquisition of oocyte developmental competence depends on proper cytoplasmic maturation, which is supported by continuous communication between the oocyte and the surrounding cumulus cells through transzonal projections (TZPs). These actin-based structures allow the transfer of essential molecules into the oocyte, helping to maintain meiotic arrest and prepare the cytoplasm. However, when cumulus-oocyte complexes (COCs) from small antral follicles (~3 mm) are subjected to conventional in vitro maturation (IVM), meiosis often resumes prematurely, leading to TZP retraction and disrupted oocyte-cumulus communication. This disruption impairs cytoplasmic maturation and contributes to lower blastocyst rates in in vitro embryo production (IVP). To address this, pre-IVM protocols that better mimic in vivo conditions have been developed, such as the CNP-based approach, which aims to maintain meiotic arrest and preserve TZPs. This is typically followed by an IVM step that includes, among other factors, EGF-like ligands and elevated progesterone (P4) supplementation to induce the resumption of meiosis. However, recent studies indicate that higher progesterone levels during IVM are associated with reduced TZP density, which correlates with lower meiotic maturation rates and poorer developmental competence. This project aims to evaluate the effects of omitting progesterone supplementation during the IVM step following a pre-IVM on TZP density, gap junction functionality, and subsequent blastocyst development and quality. The results will help refine pre-IVM protocols and clarify the role of progesterone during folliculogenesis.