The acrosome is an organelle that develops over the anterior half of the head in the spermatozoa (sperm cell) of many animals. It is a cap-like structure derived from the Golgi apparatus. Acrosome formation is completed during 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 nuclei in the sperm to join with the haploid nucleus found in the ova.

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]

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

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v • d • e Structures of the cell Endomembrane system Cell membrane - Nucleus (and Nucleolus) - Endoplasmic reticulum - Golgi apparatus - Peroxisome - Parenthesome Vesicles (Exosome - Lysosome - Endosome - Phagosome - Vacuole) Cytoplasmic granules (Melanosome - Microbody - Glyoxysome - Weibel-Palade body) Endosymbionts Mitochondrion - Plastids (Chloroplast - Chromoplast - Leucoplast) Cytoskeleton Microfilaments - Intermediate filaments - Microtubules - Prokaryotic cytoskeleton External Cell wall - Cilium/Flagellum - Acrosome Other Cytoplasm - Ribosome - MTOCs (Centrosome/Centriole - Basal body - Spindle pole body) - Vault - Proteasome