The acrosome is a specialized organelle found on sperm cells. It wraps around the head of the sperm and contains enzymes designed to help the sperm penetrate the egg by breaking down the proteins in the egg's cell wall. In a process known as the acrosome reaction, the sperm cell fuses with the egg, releases the enzymes, and enters the egg to complete fertilization. This structure is of particular interest to fertility specialists, as problems with the acrosome reaction can cause fertility issues.
Viewed in cross-section, the acrosome looks like a thin cap covering the anterior section of the sperm. It forms during maturation of the sperm in the testes. As sperm approach the egg head first, they must fuse with the egg so the structure can break open, releasing the enzymes it contains. The enzymes soften the hard shell of the egg, making it possible for the sperm to penetrate by wriggling against the cell wall and slipping through the softened section.
Organisms that reproduce sexually rely on the acrosome to help their sperm enter the egg. Each sperm is slightly different, and success depends on the speed with which it reaches the egg, as well as the ability to successfully penetrate it. Once a sperm has managed to get beyond the shell of the egg, the tail drops off, as the sperm cell no longer needs to be motile. The fertilized egg can begin the process of multiplying and dividing, creating an embryo that will develop into a new organism with time.
In men with fertility issues, one test doctors may recommend is an assessment of the ability of the sperm to penetrate an egg. A sperm sample can be taken and exposed to chemicals that trigger the acrosome reaction in a specimen dish. If the sperm cell does not react as expected, this may explain why the man is having difficulty impregnating his partner. A doctor can discuss the options for the couple if they wish to continue trying to get pregnant.
It may be possible to get pregnant with the use of in vitro fertilization, where a care provider can assist the sperm with penetrating the egg and a viable fertilized embryo can later be implanted in the woman or a surrogate in a medical procedure. Couples may also consider the use of donor sperm that has been screened for viability in order to achieve a pregnancy.