Filipin‐sterol complexes in the plasma membrane of zebrafish spermatozoa

Abstract

The presence and distribution of filipin-sterol complexes in the plasma membrane of zebrafish (Brachydanio rerio) sperm was investigated. The zebrafish sperm plasma membrane, treated with freeze-fracture techniques, is seen to contain a multitude of intramembranous particles that, in a specific region of the posterior part of the sperm head, are organized into unusual particle arrays that appear as simple hexagons or parallelograms. The polyene antibiotic filipin forms complexes with 3-beta-OH sterols to produce characteristic protrusions and pits in membranes that are readily observable in freeze-fracture replicas. Numerous filipin-sterol complexes were found to populate the sperm plasma membrane, and the complexes exhibited variability in their distribution in different sperm. This appears to be the first illustrated example of an acrosomeless sperm that exhibits a high concentration of filipin-sterol complexes. In contrast, the unique grating formed by the intramembranous particles as well as variable amounts of membrane surrounding the unusual particle arrays were always free of the filipin-sterol complexes. Thus, while cholesterol appears to be present in the plasma membrane of the zebrafish sperm, it is not apparent in the highly differentiated region of the membrane based on the observed distribution of the filipin-sterol complexes.

Distribution of intramembranous particles and filipin‐sterol complexes in the spermatid and spermatozoon of Culex quinquefasciatus (Culicidae)

“…Its presence tends to decrease the viscosity and to restrict the mobility of phospholipids and proteins. The regional differences observed in the distribution of cholesterol in the mosquito sperm membrane probably are due to specific functions played by some membrane domains, as already suggested for vertebrate spermatozoa [21,23,36].…”

“…The establishment of surface domains during differentiation of the spermatid may also involve changes in the distribution of phospholipids and sterols. Previous studies have shown that cholesterol plays an important role in the regulation of membrane permeability, fluidity and enzymatic activity [21,23,36].…”

“…Also the sterol and sterol sulfate contents change during epididymal sperm maturation [22]. The distribution of plasma membrane cholesterol during the maturation and capacitation processes of the vertebrates sperm has been analysed using polyenic antibiotics, including filipin [11,21,23,28,36,38]. However, few studies analysed the alterations that occur on the cell surface during insect spermatid differentiation and the capacitation process, which take place in the spermatheca [5,9].…”

Distribution of filipin‐sterol complexes in the plasma membrane of stallion spermatozoa during the epididymal maturation process

“…Binding of filipin to membrane sterols is very specific, requiring a planar steroid nucleus, an unesterified 3-hydroxyl group and an apolar side chain at C-17 (Kinsky, 1970;De Kruijff et al, 1974;Norman et al, 1976;Miller, 1984). The interaction results in the formation of a multimolecular filipin-sterol complex that is relatively insoluble in organic solvents and can be recognized in thin sections and in freeze-fracture replicas (Tillack and Kinsky, 1973;Elias et al, 1978Elias et al, , 1979Kessel et al, 1985).…”