Light and electron microscopic study of mature spermatozoa from White Pekin duck (Anas platyrhynchos): An ultrastructural and molecular analysis

Summary: The morphology, ultrastructure, and functions of mature avian spermatozoa have been of immense commercial and scientific interest for several reasons. This is mainly important in case of birds in poultry production, conservation, and in the use of sperm morphometry as phylogenetic evidence. Avian spermatozoa share complex or no correlation of sperm morphometry with respect to testis and/or body size as described before. In this work, we have isolated mature spermatozoa from White Pekin duck (Anas platyrhynchos) by non-invasive methods and performed several immunostaining analysis as well as cytochemical analysis using electron and light microscopes. Here, we report the presence of different post-translationally modified tubulin such as tyrosinated-, detyrosinated-, acetylated-, polyglutamylated-, and glycylated-tubulin in specific regions of the mature spermatozoa. By using field-emission scanning electron microscope, we confirm the presence of acrosome-like structure at the tip of the sperm head. However, this structure remains non-reactive to common lectins such as Peanut Agglutinin (PNA) and cholesterol-sensitive dyes such as Filipin. We report that this acrosomal structure is primarily made of lipid-based structures and is resistant to 0.1% Triton X100. Confocal microscopy and super resolution structured illumination microscopy study indicates that the nucleus is bifurcated at the tip region. By using specific markers, we report that the perforatorium structure present at the tip of the spermatozoa head contains specialized organelles that is similar to atypical mitochondria. We propose that these ultrastructural and molecular parameters can be used as species-specific features. The bifurcated nucleus and presence of atypical mitochondria within this structure may be relevant for the complex mitochondrial inheritance and mitochondrial heteroplasmy observed in case of avian population.