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n. A structure forming the end of the head of a spermatozoon.


n. a process at the anterior end of a sperm cell that produces enzymes to facilitate penetration of the egg


The acrosome is an organelle that develops over the anterior half of the head in the spermatozoa (sperm cells) of many animals. It is a cap-like structure derived from the Golgi apparatus. Acrosome formation is fully completed 5–10 years after testicular maturation. In Eutherian mammals the acrosome contains digestive enzymes (including hyaluronidase and acrosin). These enzymes break down the outer membrane of the ovum, called the zona pellucida, allowing the haploid nucleus in the sperm cell to join with the haploid nucleus in the ovum.

This shedding of the acrosome, or acrosome reaction, can be stimulated in vitro by substances a sperm cell may encounter naturally such as progesterone or follicular fluid, as well as the more commonly used calcium ionophore A23187. This can be done to serve as a positive control when assessing the acrosome reaction of a sperm sample by flow cytometry or fluorescence microscopy. This is usually done after staining with a fluoresceinated lectin such as FITC-PNA, FITC-PSA, FITC-ConA, or fluoresceinated antibody such as FITC-CD46.

In the case of globozoospermia (sperm with round heads), the Golgi apparatus is not transformed into the acrosome, causing male infertility.

Usage examples of "acrosome".

At first it was thought that the enzyme on the acrosome was being inhibited in some fashion and thus the spermatozoon was being prevented from penetrating the zona pellucida—the protective layer of the ovum— but a series of beautiful demonstrations by Russell and Austin at Cambridge proved beyond all doubt that not only could fertilization still take place outside the uterus, but that non-parthogenic cell division could still be induced in vitro at least as far as the morula stage.