Fig. 3.

Murine sperm are highly compartmentalized in terms of structure and function. A: the head and the 2 major pieces of the flagellum, the midpiece, and principal piece. Oxidative respiration is restricted to the midpiece, whereas glycolysis is organized down the length of the principal piece. B: GLUT3 is shown as expressed throughout the flagellum. It is likely that the pentose phosphate pathway is active in the midpiece, which also has high abundance of the germ cell-specific hexokinase, but not other glycolytic enzymes, such as glyceraldehyde-3-phosphate dehydrogenase. Arrowhead points to faint staining in the apical acrosome of one cell to show the location of the head in this sperm. But, as this figure shows, even faint signal in the head is relatively uncommon among murine sperm.