On the presence of bridges linking the inner and outer acrosomal membranes of boar spermatozoa

Abstract

The presence of structures bridging the inner and outer acrosomal membranes of the equatorial segment of boar spermatozoa was clearly demonstrated in cells that have undergone a variety of treatment procedures to displace the electron-dense contents of the acrosome. En-face sections show bridges to be punctate and not linearly extensive as might be suggested by sections perpendicular to the flat plane of the head. About 4.5 x 10(5) bridges, each measuring 7 nm across and spaced 7 nm apart, are arrayed hexagonally in the equatorial segment, but bridges are not present within the principal segment of the acrosome. Short-term treatment with trypsin partially digests the bridges, but does not disrupt the spacing or strict parallel configuration of equatorial segment membranes. However, short-term treatment with pronase digests most bridges and effectively disrupts the typical configuration of the equatorial segment. Freeze-fracture of the cytoplasmic face of the acrosomal membranes of the equatorial segment reveals a pattern throughout the phospholipid layer of the membrane which is similar to the pattern of bridges present in en-face thin sections of the equatorial segments. The data suggest that numerous bridges link the inner and outer acrosomal membranes of the equatorial segment of the acrosome and they play a major, if not an exclusive, role in maintaining the close spacing and parallel arrangement of the membranes in this portion of the acrosome.

Human SP-10: Acrosomal Distribution, Processing, and Fate after the Acrosome Reaction1

“…In any case, the anterior equatorial segment of the acrosome in human sperm shows little SP-10 in comparison to other acrosomal domains. Interestingly, the acrosomal membranes in the equatorial segment of boar sperm are closely apposed and are connected by electron-dense cross bridges [17]. A structure in human sperm analogous to the cross-bridges observed in boar sperm could exclude SP-10 and other acrosomal proteins from this portion of the equatorial segment.…”

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

“…The OAM and IAM are connected by periodic crossbridges that are resistant to detergent treatment (Russell et al 1980;Olson and Winfrey 1991), suggesting that membrane fluidity is limited (Arts et al 1994). The equatorial segment is formed in the late spermatid stage (Lalli and Clermont 1981).…”

Sperm surface changes during the acrosome reaction as observed by freeze‐fracture

“…Fusion in the equatorial segment appears inhibited by the ordered structure of the acrosomal material in the equatorial segment (Russell et al, 1980). In fact, the fusion pathways follow the directions of the hexagonal lattice observed on the P face of the outer acrosomal membrane, reflecting such an order in the equatorial segment contents (Fig.…”

“…The hybrid membrane reticulum of the acrosomal cap forms a continuum sufficient to explain its cohesiveness; moreover, the outer acrosomal membrane is lined with an adherent acrosomal material (Barros et al, 1967;Russell et al, 1980;Shams-Borhan and Harrison, 1981;Huneau et al, 1984;Yanagimachi and Phillips, 1984) that may reinforce the cap . It is not clear at all if some true vesicles of mixed membranes exist, although they may occur at the posterior margin of the acrosomal cap.…”