FERTILIZATION IN MAMMALS

Process of Fertilization in Mammals

Process of Fertilization in Mammals

Introduction

The process of fertilization in mammals includes fusion and binding of sperms and eggs. Sperms are free swimming and egg can be ovulated. In recent years, accessible information is accumulating regarding the role and importance of carbohydrate residues during sperm egg interaction. This process is species specific and consists of defined events that occur in compulsory order . The process consists of loosing Attachment: A loose, unfocused connection between the zona pellucida (ZP) which is a cellular, glycoprotein coat surrounding the egg, and the spermatozoa. Primary binding is a firm binding between spermatozoa and the ZP that follows attachment. The binding is species precise and can be intervened by harmonizing receptors on the sperm head plasma membrane (ZP receptors); and ZP (sperm receptors). Acrosome reaction is the bound spermatozoa undergo the acrosome reaction (AR), an exocytotic process that involves fusion and vesiculation of the sperm plasma and outer acrosomal membranes.

This process results in release of the enzymatic acrosomai content and disclosure of the inner acrosomal membrane, thus exposing the ZP to the lytic enzymes of the acrosome that assists in ZP penetration. Secondary binding takes place when acrosome-reacted sperm remains bound to the ZP via secondary binding. This binding involves components of the sperm inner acrosomal membrane and secondary sperm receptors on the ZP. Penetration occurs when the spermatozoon penetrates through the ZP, probably by a combination of mechanical force created by the vigorous tail beatings, and enzymatic digestion of the ZP glycoproteins by proteinases. It is associated with the acrosomal content; Fusion takes place when the sperm reaches the perivitelline space (PVS) and fuses with the egg plasma membrane, thereby fertilizing the egg. Fusion can be followed by the cortical reaction (CR), an exocytotic process in which the cortical grandes release their enzymatic content into the PVS. Corticai reaction results in modification of the ZP glycoproteins, zona hardening and establishment of the block to polyspermy. This review will focus on the role of carbohydrate residues in the process of sperm-egg interaction, in mammals.

Zona Pellucida Structure and Function

The ZP is a porous, extracellular matrix composed of long, interconnected filaments. The ZP can be morphologicaily segregated, and there is an asymmetry between the inner or outer surface, as can be shown in the hamster, and in the house musk shrew. For most mammalian species studied, the ZP appears Carbohydrates in mammalian fertilization to comprise only three glycoproteins: ZP1, ZP2, ZP3. The glycoproteins can be synthesized and secreted to form the ZP during the process of oocyte growth.

Sperm Capacity

Sperm is able to fertilize oocytes through a maturation process of capacitation in the process can be accompanied by modifications of membrane biophysical characteristics, changes in protein phosphorylation state, elevations of Intracellular pH and calcium levels, and hyperpolarization of membrane potential. Cholesterol efflux from the sperm membranes induces the sperm membranes to be reorganized. Cholesterol removal leads to the elevation of calcium and bicarbonate Concentrations in the cytosol, which activates adenylyl cyclase8 to ...