Morphological characterisation of vesicular structures in the canine ejaculate.

Area of Science:

• Reproductive Biology
• Cell Biology
• Veterinary Science

Background:

• Membrane vesicles (MVs) in seminal plasma are crucial for semen quality and fertilization across species.
• While MVs are present in canine ejaculate, their detailed morphology and classification remain largely unknown.
• Understanding MV populations is essential for elucidating their distinct biochemical and functional roles.

Purpose of the Study:

• To comprehensively characterize the morphology of canine membrane vesicles (MVs) using light and transmission electron microscopy.
• To identify and classify different MV subpopulations based on size, structure, and content.
• To investigate the distribution frequency of MV types in relation to canine semen quality.

Main Methods:

• Preparation of MVs from canine ejaculates (normospermic, hypokinozoospermic, and azoospermic) for light microscopy (LM) and transmission electron microscopy (TEM).
• Utilized a novel TEM preparation protocol to enhance MV retrieval rates.
• Fractionation of semen samples to localize MVs, primarily to the sperm-rich fraction.

Main Results:

• LM identified three MV types, while TEM revealed 11 distinct MV types based on ultrastructural characteristics.
• Secondary vesicles (types i, H, K1/2) and primary vesicles (types A, B, C1/2, F, G, L) were differentiated by size, internal structure, and content density.
• Small primary vesicles were most common overall, but MV type distribution varied significantly between normospermic, pathospermic, and azoospermic dogs, with differences in mean and maximum diameters observed.

Conclusions:

• This study provides novel insights into the ultrastructure and distribution of canine MVs, particularly in normospermic males.
• The findings suggest potential differences in MV populations correlating with semen quality, paving the way for functional studies.
• The presence of MVs in a castrated azoospermic dog supports a partly prostatic origin for canine MVs.