Acrosome reaction

The acrosome reaction is the step in procreation that enables the sperm to penetrate the egg cell's plasma membrane . It begins with the release of the contents ( exocytosis ) of the acrosome, a special lysosome that lies in the head of the sperm immediately below its plasma membrane.

Primary binding of the sperm cell

schematic representation of the acrosome reaction in sea ​​urchins

With the zona pellucida , the egg cell has a protective covering, which also plays an important role in fertilization. The "first contact" of a capacitive sperm cell with this protective cover is called the primary or initial bond between egg and sperm cell. Proteins on the surface of the sperm cell and the Zona pellucida protein ZP3 come into contact , which triggers the acrosome reaction.

Here, the cell membrane of the sperm fuses in its head area with the membrane of the acrosome , a component of the sperm cell. The hydrolyzing enzymes contained in the acrosome are thus released, and as a direct consequence of this the zona pellucida is dissolved ( lysed ) at this point . The cell membrane at the tip of the sperm head is lost. Only the inner (rear) membrane of the acrosome now lies in front of the nucleus of the sperm.

Secondary binding of the sperm cell

The secondary binding of the sperm cell now takes place at the protein ZP2 of the zona pellucida, which enables both the maintenance and the strengthening of the binding.

An acrosome reaction is only possible with completely capacitive sperm cells. Thus, the acrosome reaction can be used as the most important summary parameter for male fertility : If the motility of the sperm cells is disturbed, they do not reach the fallopian tube . If they reach it, but there are problems with capacitation , the acrosome reaction is prevented. Accordingly, the acrosome reaction is a test that can also be used in the laboratory to assess the fertilization capacity of the sperm cells.

Individual evidence

1. ^ P. Vigil, RF Orellana, ME Cortés: Modulation of spermatozoon acrosome reaction. In: Biological research. Volume 44, Number 2, 2011, pp. 151-159, ISSN  0717-6287 . doi : 10.4067 / S0716-97602011000200007 . PMID 22513418 .
2. ↑ D. Ickowicz, M. Finkelstein, H. Breitbart: Mechanism of sperm capacitation and the acrosome reaction: role of protein kinases. In: Asian journal of andrology. Volume 14, Number 6, November 2012, pp. 816-821, ISSN  1745-7262 . doi : 10.1038 / aja.2012.81 . PMID 23001443 . PMC 3720105 (free full text).

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