Motile components in spermatids as related to transport of spermatids and spermatozoa

Two distinctly different components of motility were detected in living early spermatids of the rat using phase contrast microscopy and video-analysis: the primary flagellum (a 9 + 2 axonema) executes wave-like motion in three dimensions. At the same time the flagellum displays alternatively in clockwise and counter-clockwise directions partial torsion, whereas shortening and elongation can also be observed. The second component is based on rhythmical movements of the spermatid cytoplasm at identical stages. During differentiation the capacity for motion reduces progressively. For instance, late spermatids are only capable of bending their now thickened flagellum. Spermatozoa were found immotile. Germ cells during differentiation are thought to contribute themselves to their transfer through the germinal epithelium. Reduction of motility in the differentiating flagellum is due to growing accessory structures surrounding the axonema, whereas motility of the cytoplasm is reduced by its resorption. In man, some forms of hypofertility and sterility, such as the immotile-cilia syndrome, might already be caused by imperfect motile components present in spermatids.