The acrosome is an
organelle that develops over the
anterior (front) half of the head in the
spermatozoa (sperm cells) of humans, and many other animals. It is a cap-like structure derived from the
Golgi apparatus. In
placental mammals, the acrosome contains degradative
enzymes (including
hyaluronidase and
acrosin).[1] These enzymes break down the outer membrane of the
ovum,[2] called the
zona pellucida, allowing the
haploidnucleus 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[3] or
follicular fluid, as well as the more commonly used calcium
ionophore A23187.[4] This can be done to serve as a positive control when assessing the acrosome reaction of a sperm sample by
flow cytometry[5] 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.[6]