Acrosome

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).^[1] 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^[2] 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.^[3]

Human spermatozoön

In the case of globozoospermia (sperm with round heads), the Golgi apparatus is not transformed into the acrosome, causing male infertility.^[4]

References

1. "acrosome definition - Dictionary - MSN Encarta". Archived from the original on 2009-10-31. Retrieved 2007-08-15.
2. Miyazaki R, Fukuda M, Takeuchi H, Itoh S, Takada M (1990). "Flow cytometry to evaluate acrosome-reacted sperm". Arch. Androl. 25 (3): 243–51. doi:10.3109/01485019008987613. PMID 2285347.
3. Carver-Ward JA, Moran-Verbeek IM, Hollanders JM (February 1997). "Comparative flow cytometric analysis of the human sperm acrosome reaction using CD46 antibody and lectins". J. Assist. Reprod. Genet. 14 (2): 111–9. doi:10.1007/bf02765780. PMC 3454831. PMID 9048242.
4. Hermann Behre; Eberhard Nieschlag (2000). Andrology : Male Reproductive Health and Dysfunction. Berlin: Springer. p. 155. ISBN 3-540-67224-9.