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.