title: The extrusion of membraneous threads by avian and mammalian spermatozoa, in vitro.
abstract: Extremely fine threads have been seen, under dark-field illumination, extending from the tips of the sperm flagella of four avian and two mammalian species. They occur after a variable period of incubation in balanced salt solutions. The threads, never more than one per flagellum, can be as long as the flagellum itself. Often they are attached to the substrate by their remote end, tethering the cell and showing elastic deformation. When not stressed, they remain threadlike and undergo the Brownian motion characteristic of fine filaments. Shedding of the threads has been seen, as has their apparent retraction. When cockerel sperm are broken into proximal and distal segments which are respectively motile and immotile, the threads develop at the tips of only the proximal segments. This proves that the formation of the thread is not dependent on structures normally present at the natural tip of the flagellum. Each thread is a regular tubule of membrane, with a standard minimum diameter of 28 nm, and having blebs of membrane, containing vesicles, at irregular intervals. The tubular membrane is assumed to be plasmalemma and is equivalent, maximally, to less than 10% of the cell's calculated surface area. It is most likely that the thread is formed by extrusion, as a stalk bearing fluid-filled pinocytotic vesicles. Thread formation is prevented by adding bovine serum albumin to the diluent. The phenomenon may be relevant to understanding how spermatozoa are impaired by the 'dilution effect'.
authors.affiliation: Department of Physiology, School of Medical Sciences, University of Bristol, U.K.
authors.forename: D M
authors.initials: DM
authors.lastname: Woolley
mesh_terms: D000818:Animals; D001717:Birds; D002462:Cell Membrane / Q000648:ultrastructure; D066298:In Vitro Techniques; D008297:Male; D008322:Mammals; D051379:Mice; D008853:Microscopy / Q000379:methods; D008854:Microscopy, Electron; D010873:Pinocytosis; D051381:Rats; D013082:Sperm Tail / Q000502:physiology / Q000648:ultrastructure*