A Step Toward Understanding Direct Impacts of a Higher Estrus-Associated Temperature (HEAT): Transcript Level Changes...

Area of Science:

• Reproductive Biology
• Molecular Endocrinology
• Oocyte Biology

Background:

• Elevated body temperature (HEAT) is a normal physiological condition in sexually receptive female bovines during the periovulatory period.
• Understanding the molecular impact of HEAT on oocyte quality and maturation is crucial for reproductive success.

Purpose of the Study:

• To investigate the direct and delayed effects of acute heat exposure (41 °C) during in vitro maturation (IVM) on gene expression in bovine oocytes.
• To identify specific transcripts involved in steroidogenesis, oocyte maturation, and heat response.

Main Methods:

• Targeted RNA-sequencing was employed to analyze transcriptomic changes in cumulus-oocyte complexes (COCs).
• Oocytes were exposed to 41 °C during IVM, with analysis at different time points (0-6 hours) and during recovery (4-18 hours).
• Multidimensional scaling plots were used for sample visualization and analysis.

Main Results:

• A significant majority of transcripts (72.3%) were affected within the first 2-4 hours of IVM exposure to 41 °C.
• Direct heat exposure altered transcripts related to progesterone production, germinal vesicle breakdown, meiotic progression, cell cycle, and ovulation.
• Three transcripts showed delayed effects, with changes only apparent after 4 hours of recovery.

Conclusions:

• Acute heat stress during IVM rapidly alters the molecular profile of bovine oocytes, suggesting accelerated maturation.
• These findings provide novel insights into the dynamic physiological responses of COCs to thermal stress in female bovines.
• Understanding these molecular dynamics is vital for improving assisted reproductive technologies and managing heat stress in livestock.