Acrosome
{{Short description|Organelle of sperm cells}}
File:Complete diagram of a human spermatozoa en.svg
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).{{cite web |url=http://encarta.msn.com/encnet/features/dictionary/DictionaryResults.aspx?refid=1861695331 |title=acrosome definition - Dictionary - MSN Encarta |access-date=2007-08-15 |archive-url=https://web.archive.org/web/20090214025038/http://encarta.msn.com/encnet/features/dictionary/DictionaryResults.aspx?refid=1861695331 |archive-date=2009-02-14 |url-status=dead }} These enzymes break down the outer membrane of the ovum,{{Cite journal|last1=Larson|first1=Jennine L.|last2=Miller|first2=David J.|date=1999|title=Simple histochemical stain for acrosomes on sperm from several species|journal=Molecular Reproduction and Development|language=en|volume=52|issue=4|pages=445–449|doi=10.1002/(SICI)1098-2795(199904)52:4<445::AID-MRD14>3.0.CO;2-6|pmid=10092125|s2cid=24542696 |issn=1098-2795}} 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, known as the acrosome reaction, can be stimulated in vitro by substances that a sperm cell may encounter naturally, such as progesterone{{Cite journal|last1=Lishko|first1=Polina V.|last2=Botchkina|first2=Inna L.|last3=Kirichok|first3=Yuriy|date=March 2011|title=Progesterone activates the principal Ca 2+ channel of human sperm|url=https://www.nature.com/articles/nature09767|journal=Nature|language=en|volume=471|issue=7338|pages=387–391|doi=10.1038/nature09767|pmid=21412339|bibcode=2011Natur.471..387L|s2cid=4340309|issn=1476-4687|url-access=subscription}} or follicular fluid, as well as the more commonly used calcium ionophore A23187.{{Cite journal|last1=Jamil|first1=K.|last2=White|first2=I. G.|date=December 1981|title=Induction of acrosomal reaction in sperm with ionophore A23187 and calcium|url=https://pubmed.ncbi.nlm.nih.gov/6797354/|journal=Archives of Andrology|volume=7|issue=4|pages=283–292|doi=10.3109/01485018108999319|issn=0148-5016|pmid=6797354}} This can be done to serve as a positive control when assessing the acrosome reaction of a sperm sample by flow cytometry{{cite journal |vauthors =Miyazaki R, Fukuda M, Takeuchi H, Itoh S, Takada M |title=Flow cytometry to evaluate acrosome-reacted sperm |journal=Arch. Androl. |volume=25 |issue=3 |pages=243–51 |year=1990 |pmid=2285347 |doi=10.3109/01485019008987613|doi-access=free }} 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.{{cite journal |vauthors =Carver-Ward JA, Moran-Verbeek IM, Hollanders JM |title=Comparative flow cytometric analysis of the human sperm acrosome reaction using CD46 antibody and lectins |journal=J. Assist. Reprod. Genet. |volume=14 |issue=2 |pages=111–9 |date=February 1997 |pmid=9048242 |pmc=3454831|doi=10.1007/bf02765780}}
In the case of globozoospermia (sperm with round heads), the Golgi apparatus is not transformed into the acrosome, causing male infertility.{{cite book |author =Hermann Behre |author2 =Eberhard Nieschlag |title=Andrology : Male Reproductive Health and Dysfunction |publisher=Springer |location=Berlin |year=2000 |page=155 |isbn=3-540-67224-9 }}