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Does Sperm Use Tiny Harpoons to Fertilize an Egg?


Image credit: The sperm “harpoon” shown on its side. Heping Zheng, PhD, University of Virginia School of Medicine.

It is reported that scientists have found very small “harpoons” on sperm that enable them to take onto eggs and other sperm in the course of fertilization. This discovery, resulting from fourteen-year research, is published in the journal Andrology.

According to the scientists from the University of Virginia (UVA), sperm are capable of creating spiky protein filaments on their head. Although it was widely known that the protein was believed to form the filaments, sperm lysozyme-like protein 1 (SLLP1), however the study indicates a new role. It is housed in the acrosomal matrix, which is a structure in the sperm head. While what the exact part the filaments plays in the course of fertilization is not crystal clear, scientists think that they are much helpful for the sperm to latch onto an egg.

As John Herr, reproduction researcher from the Department of Cell Biology of UVA said, this discovery had actually captured their imagination. One of the major proteins, which was rich in the acrosome, was crystallizing into filaments, and John Herr and his colleagues had assumed that they were engaged in  penetrating the egg.

According to John Herr, this was the new hypothesis resulting from the discovery, which would raise a lot of new questions and hypotheses in regard to the very fine structure of molecular events in the course of fertilization.

The finding was made by capturing the protein in a static crystal. Later this crystal was cooled to cryogenic temperatures to avoid degradation and then blasted with X-rays. From measurement of the refraction of the X-rays, John Herr and his colleagues could figure out the shape of the protein, which is cylinder-like and hollow in the middle when produced in the 3D models in the lab.

This new finding could help researchers better understand the process taking place in the course of fertilization. In Herr’s summery, he confirmed that at the very fundamental level, the good understanding of the fine molecular architecture would allow him to assume new functions for this family of proteins in the acrosome discovered in their laboratory