Role of the Acrosome in a Successful Pregnancy
The acrosome is a part of the sperm cell that assists in fertilization. The following article focuses on the importance of acrosome reaction (AR) in successful fertilization. Terms used to explain the process are defined below.
The Function of Cell Structures Described in this Article:
- Centriole – helps the cell to divide
- Mitochondria – provides energy to the sperm cell to move forward
- Golgi complex – develops into an acrosome in sperm cells
- Nucleus – contains DNA (genetic code)
Terms Related to the Acrosome Reaction (AR):
- Zona pellucida – Outer membrane of the oocyte
- Acrosome – a cap-like structure in the front portion of the head of the sperm cell
- Acrosomal vesicle – an enzyme-filled structure in the acrosome that has an acrosome granule
- Acrosome status – chemical and physical properties of the acrosome
The Acrosome and its Role in Fertilization
The acrosome develops from the Golgi complex. It lies between the sperm’s nuclear membrane and plasma membrane. Sometimes, the golgi complex fails to develop into the acrosome giving the sperm head a round shape. This condition results in a form of infertility called globozoospermia.
When the sperm first comes in contact with the egg, the acrosome goes through structural changes: capacitation and the acrosome reaction (AR). In capacitation, the sperm head is destabilized and cholesterol removed from its tail to promote motility. In the AR, the acrosomal vesicle ruptures. The membranes of the sperm and the acrosome vesicle fuse at the tip of the acrosome to form an opening. The acrosome granule dissolves to release enzymes such lysine. Enzymes break down the zona pellucida for the sperm to enter it for embryo formation.
Oxidative stress or DNA damage causes premature AR. Unsuccessful AR is also common in obese men or after exposure to metals. Further, DNA fragmentation lowers acrosome integrity and adversely influences reproduction outcomes. DNA damage has a higher chance of impaired AR when the fertility rate is lower than 60%.
Acrosome and ART Therapy
Other recent methods such as hyaluronic acid-binding sperm selection (PISCI), motile sperm organelle morphology examination (MSOME), and magnetic-activated cell sorting (MACS) are also gaining popularity. The success of all these methods depends on the assessment of the AR as a predictor of fertility.
Biology professionals induce AR using hormones (progesterone), calcium transporter (calcium ionophore), follicular fluid, and enzyme activator (phorbol myristate esters). This procedure can detect the presence or absence of proteins in the acrosome region that also determines the presence or loss of the acrosome. Evaluating AR in the laboratory predicts 30% – 50% fertilization for IVF couples.
Testing Acrosome Quantity and Function
Understanding fertilization requires not just knowledge of sperm structure and function but also premature acrosome reaction and AR deficiency. The AR test is an important determinant of male fertility since less than 5% of sperm undergoes a spontaneous AR.
The peanut-agglutinin assay for AR testing helps to determine fertilization potential. This technique involves inducing AR and checking acrosome status under a microscope or using flow cytometry with fluorescence labeling.
Even though ICSI may eliminate the need for AR testing, it is costly and invasive, making IVF the preferred technique. AR is also a prominent focus area in andrology research to assess the impact of food and drug toxicity on testicles and in the design of male contraceptives.