Maturation of mammalian spermatozoa: modifications of the acrosome and plasma membrane leading to fertilization

Abstract

The mammalian spermatozoon is a terminally differentiated cell. Its surface is covered by a continuous plasma membrane that is divided into distinct domains in which functional molecules are distributed. The acrosome is an internal organelle located at the anterior head and contains hydrolytic enzymes. The anterior acrosome participates in the acrosome reaction, which is an indispensable event during fertilization. These surface domains and the acrosome are formed during spermiogenesis, during which associated molecules are transported and organized. Many of the molecules thus arranged are functionally immature but gradually become mature during epididymal maturation. Some of them are further altered and redistributed during the fertilization process and play various roles. Here, the sequential changes in the acrosome and plasma membrane during spermatozoan maturation are reviewed, particular attention being paid to molecules derived from the testis.

Vezatin, a ubiquitous protein of adherens cell–cell junctions, is exclusively expressed in germ cells in mouse testis

“…At that stage, acrosomal specific proteins are usually transported from the endoplasmic reticulum to the developing acrosome, through the Golgi apparatus. However, other acrosomal proteins, like acrin 2, may be transported to the acrosome without transport through the Golgi (Toshimori 1998, Yoshinaga et al 2001. During the cap phase, the acrosomal vesicle starts to grow as a result of the progressive fusion of Golgiderived membranes and possibly of membranes derived from the lysozome-endosome system (West & Willison 1996).…”

The PATE gene is expressed in the accessory tissues of the human male genital tract and encodes a secreted sperm-associated protein

“…Their differentiation from round spermatids to highly polarized and fully motile cells is characterized by extensive biochemical, physiological and morphological events (Toshimori 1998, Ducheux et al 2003. These events start in the testis in the process called spermiogenesis.…”

Sperm Plasma Membrane Modifications Associated with Fertilization in Mammals

“…As sperm cells mature, some of their plasma membrane proteins appear to become redistributed laterally within the head or flagellum, or sometimes from the flagellum to the head as has been previously discussed [4,6]. Some of these interesting proteins are listed in Table 1 [3,5,7,[29][30][31][32][33], and typical cases are discussed below.…”

“…It has recently been shown that the surface domains of sperm cells, i.e., the plasm membrane proteins, are modified, as evidenced by changes in the immunostaining patterns, as the sperm undergo post-testicular functional maturation [2][3][4][5][6]. On the other hand, some reports have appeared which show that changes in immunostaining patterns are related to biochemical modification of the molecules rather than simple physical redistribution [7].…”