Figure 2

Spatiotemporal progression of annulus during mouse spermiogenesis. The annulus (arrows) indicated by the SEPT4 antibody was first seen at the neck region of step 9 spermatids (b), not in step 8 spermatids (a). It stayed there until early step 15 (c-d), and after that it migrated to its distal position followed by the formation of mitochondrial sheath (e-h). It still existed in the mature spermatiozoon coonecting the midpiece and the principal piece of the tail (i). Green, SEPT4; Red, MitoTracker; Blue, DAPI. The scale bar represents 10 μm.