Post-testicular development of a novel membrane substructure within the equatorial segment of ram, bull, boar, and goat spermatozoa as viewed by atomic force microscopy

Area of Science:

• Reproductive biology
• Cell biology
• Biophysics

Background:

• Mammalian spermatozoa undergo significant morphological and functional changes during post-testicular development and after ejaculation.
• The plasma membrane of spermatozoa plays a crucial role in fertilization, particularly during sperm-oocyte interaction.

Purpose of the Study:

• To investigate changes in the plasma membrane of mammalian spermatozoa during post-testicular development, after ejaculation, and following acrosome reaction.
• To characterize a specific substructure within the equatorial segment of spermatozoa.

Main Methods:

• Atomic force microscopy was employed to examine the surface topography of spermatozoa from various mammalian species.
• Immunological techniques using a monoclonal antibody were used to probe the nature of the equatorial subsegment.

Main Results:

• The postacrosomal plasma membrane showed greater irregularity than the acrosomal membrane in ejaculated spermatozoa.
• A distinct, semicircular equatorial subsegment with a coarse appearance was identified in Artiodactyla species but not in others.
• This subsegment's topography altered from finely ridged to truncated papillae post-acrosome reaction.
• The equatorial subsegment binds a specific antibody only in permeabilized sperm, indicating association with the perinuclear theca.

Conclusions:

• The equatorial subsegment is a species-specific feature that develops during epididymal maturation.
• Its topographical changes post-acrosome reaction suggest a dynamic role in fertilization.
• The equatorial subsegment's association with the perinuclear theca implies a function in mediating sperm-oolemma fusion.