Spermatozoon and spermiogenesis in Mesocoelium monas (Platyhelminthes: Digenea): Ultrastructure and epifluorescence microscopy of labelling of tubulin and nucleus

Spermiogenesis and the spermatozoon were studied in the digenean Mesocoelium monas Rudolphi, 1819 (from the toad Bufo sp. in Gabon). An ultrastructural study revealed that spermiogenesis follows the usual pattern found in digeneans, i.e. proximo-distal fusion of axonemes with a median cytoplasmic process followed by elongation. The spermatozoon has two fully incorporated axonemes with the 9 +'1' trepaxonematan pattern. Indirect immunofluorescence localization of tubulin and fluorescent labelling of the nucleus were used to obtain additional information on the structure of the spermatozoon. It was thus shown that one of the axonemes is slightly shorter than the other (190 versus 220 μm) and that the filiform nucleus (65 μm in length) is located at the distal extremity of the spermatozoon (220 μm in length). Various monoclonal and polyclonal antibodies, specific to alpha, beta, acetylated-alpha, or general tubulin, were used and produced similar labelling.