Haleh Ehtesham,1,*Iman Halvaei,2
1. PhD student of Tarbiat Modares University 2. Faculty of Medicine Faculty of Tarbiat Modares University
Introduction: Sexual reproduction occurs through fertilization during which two haploid gametes fuse to produce a genetically unique individual. Fertilization, the process by which the spermatozoon and the egg
unite, occurs in the ampulary region of the oviduct.In nature, fertilization occurs only after both the oocyte and the spermatozoon have completed their final stages of cytoplasmic maturation.
Sperm–oocyte interaction is a complex process of cell–cell interaction that requires species- specific recognition and binding of the two cells. Successful fertilization still requires controlled and correct activation of both sperm and oocyte.
Methods: Before spermatozoa can fertilize oocytes, they must first undergo biochemical and physiological modifications within the female reproductive tract. This process, referred to as capacitation, involves the removal of cholesterol and many glycoproteins from the surface of the spermatozoon, resulting in increased fluidity of the cell membrane. Capacitation, which commences in the uterus, is completed in the isthmus. The zona pellucida (ZP) is an extracellular matrix surrounding the oocyte and the early embryo that exerts several important functions during fertilization and early embryonic development
A number of different molecules regulate these pathways, including calcium, bicarbonate, GABA, progesterone, angiotensin and cytokines.
Phosphorylation of sperm proteins is an important part of capacitation, and this has been shown to be associated with the change in the pattern of sperm motility known as hyperactive motility, recognizable by an increase in lateral head displacement.
There is also some evidence that spermatozoa can translate some mRNA species during capacitation
Results: In the human, capacitation in vivo probably starts while the spermatozoa are passing through the cervix.
A low molecular weight motility factor found in follicular fluid, ovary, uterus and oviduct may increase sperm metabolism (and hence motility) by lowering ATP and increasing cyclic AMP levels within the sperm. Chemically defined media with appropriate concentrations of electrolytes, metabolic energy sources and a protein source (serum albumin) will also induce the acrosome reaction in a population of washed sperm. The removal or redistribution of glycoproteins on the sperm cell surface during capacitation exposes receptor sites that can respond to oocyte signals, leading to the acrosome reaction
Capacitation is temperature dependent and only occurs at 37–39°C. Sperm surface components are removed or altered during capacitation. In vitro, the acrosome reaction cannot occur until capacitation is complete.
Conclusion: Several important molecules that regulate avian fertilization have been discovered but this is mainly derived from experiments that referred to mammalian studies. Because there are no efficient methods yet that would allow us to produce gene-manipulated birds, knowledge of the avian fertilization mechanism is limited. Placentation across mammalian species is vastly different despite the similar goal of supporting the development of the offspring during gestation. Advances in technology such as single-nuclei RNA sequencing allow for further investigation of gene expression in distinct cell populations and how these change across developmental time.