Effect of Mare Age on Transcript Abundance of Connexins-37 and -43, Zona Pellucida Proteins, and Sperm Binding.

The research article investigates how the age of a mare can impact the expression of key proteins, and how this could in turn affect fertilization and sperm binding. The proteins in question are predominantly involved in cumulus-oocyte communication, with a special focus given to Zona Pellucida (ZP) proteins and connexins.

Research aims and methodology

• The goal of the research was to understand the effect of ageing on the abundance of key proteins, specifically Zona pellucida (ZP) proteins and connexins, in cells from ovarian follicles and ascertain its effect on fertilization and sperm binding.
• The study was conducted in two parts: The first experiment involved analyzing cells from young and old mares to assess protein changes; the second experiment used oocytes that failed to cleave after sperm injection, in order to study sperm binding differences..

Experiment 1: Transcript Abundance

• In the first part of the research, the team collected oocytes, corona radiata, cumulus, and granulosa cells from mares identified as either young (4-12 years) or old (> 20 years).
• The team then evaluated the transcript abundance of connexins -37 and -43, in addition to four types of zona pellucida glycoproteins and Tubulin.
• The results showed a decrease in transcript abundance for connexin -43 in oocytes, corona radiata, and granulosa cells, while Connexin -37 was decreased in cumulus cells in mares above 20 years old. This suggests potential age-related changes in cellular communication.
• A similar trend was observed in the abundance of ZP1 protein, where its level in corona radiata and cumulus cells from old mares showed a decrease. The researchers hypothesize this may impact the function of the Zona Pellucida, which has a significant role in sperm binding.

Experiment 2: Sperm Binding

• For the second part of the experiment, the researchers used oocytes that failed to divide after intracytoplasmic sperm injection (ICSI), analyzing them for up to 4 years.
• The researchers found that oocytes from older mares exhibited less sperm binding capability compared to those from younger mares. This finding may underline the declining fertility in older mares.
• The experiment also concluded that oocytes that fail to cleave after ICSI can be used for sperm binding studies for up to 2 years without impairing sperm binding capabilities. Such information can be valuable in fertility research.

In conclusion, this study provides evidence that ageing in mares influences the abundance of ZP proteins and connexins, potentially affecting cellular communication and ZP function, subsequently leading to reduced sperm binding. This forms an important piece of the puzzle in understanding the decline of fertility with ageing.