Discovery of zinc flux or zinc spark during mammalian fertilization helps better understand the role of zinc in egg (oocyte) activation and embryo development.

The zona pellucida (ZP), a glycoprotein matrix around the oocyte plays an important role in preventing multiple sperms fertilizing an egg, known as polyspermy
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Zinc sparks induce physiochemical changes in the egg zona pellucida that prevent polyspermy

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).

The study published in the journal Canadian Medical Association gives a detailed understanding about zinc’s role in zona pellucida hardening.

Role of Zona Pellucida

Zona pellucida surrounding the oocyte plays an important role during various stages of oocyte development.

• During oogenesis, the zona pellucida facilitates a bi-directional communication between oocyte and surrounding somatic cells.
• Following ovulation of the egg from the ovary, the zona pellucida acts as a barrier that allows sperm binding through interaction with zona pellucida glycoprotein.
• After fertilization, the zona pellucida hardens preventing polyspermy which can cause birth defects, miscarriages, etc,.
• When the zygote undergoes cell division, during the pre-implantation stage the zona pellucida helps to keep the dividing embryo in a fixed space so that the size of embryo does not increase.

Zinc Sparks in Zona Pellucida Hardening

Zinc is released from the vesicles of the egg’s cortex after fertilization or egg activation plays an important role in zona pellucida hardening. Zinc spark is a calcium coordinated event that results in 20% reduction of intercellular zinc levels, that triggers the egg to resume its cell cycle.

During zinc spark, the zona pellucida is exposed to a higher concentration of zinc which initiates structural changes. The changes in the zona pellucida density and cross linking prevent multiple sperms from fertilizing the egg.

Zinc induced structural changes in zona pellucida are
Increased zona pellucida density with reduced gaps between the fibrils.
Zinc facilitate protein crosslinking within zona pellucida which increases the resistance for sperm penetration.

Concentraction of zinc as low as 50 µm can initiate the structural changes in zona pellucida. This suggest that zinc directly alters the zona pellucida properties.

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However, zinc alone doesn’t account for all changes occurring in zona pellucida after fertilization. It suggests that zinc along with other enzymatic changes mediate zona pellucida hardening.

This discovery emphasizes a new role of zinc in extracellular processes involved in reproduction. Zinc has emerged as an important regulator during fertilization and early embryonic development. Zinc also influence the activity of zona pellucida.

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By investigating the molecular interactions between zinc and zona pellucida proteins, scientists can uncover the specific ways zinc can help fertilization processes in infertility treatments.

Reference:

1. Zinc sparks induce physiochemical changes in the egg zona pellucida that prevent polyspermy – (https://pmc.ncbi.nlm.nih.gov/articles/PMC5439353/)

Source-Medindia