mammalian fertilisation

MAMMALIAN FERTILIZATION

Stages of mammalian fertilization are as follows:

 Sperm preparation: Capacitation

 Induction of acrosome reaction by sperm

 Binding of sperm-egg

 Fusion of sperm and egg

Spermatogenesis and oogenesis are the process of synthesis of sperm and eggs respectively, for fertilization. During ovulation, fully matured oocytes released from graafian (antral) follicles undergoes meiotic division that transforms matured oocytes to unfertilized eggs to bind with sperm (Wassarman and Albertini 1994).

Sperm preparation: Capacitation

Sperm maturation also known as activation or sperm capacitation occurs in the genital tract of female and is preparatory step for acrosome reaction. Activation does not cause any morphological changes and is followed by hyperactivation of sperm which is strong and non-linear motion.

Capacitation includes number of processes like functional coupling of the signal transduction pathways that regulate the initiation of acrosome reactions by ZP3; alterations in flagellar motility that is required for penetration of ZP by sperm; and the development of the capacity to fuse the eggs. These events are accompanied by alterations in metabolism, membrane biophysical characteristics, changes in the protein phosphorylation state, elevations in intracellular pH and calcium levels, and hyperpolarization of membrane potential. Many factors mediate the activation of sperm in vivo such as sterol binding proteins (high density lipoprotein) are identified in the fallopian tubes and accelerate the efflux cholesterol from the sperm. Progesterone can also regulate some aspects of sperm activation. It is present in the environment of the fallopian tubes, derived both from follicular fluid and cells of the cumulus oophorus.Glucose is known to be essential for successful capacitation. It functions not only as an energy molecule allowing spermatozoa to swim, but it also enables the spermatozoa to fertilise eggs