This image, produced by the freeze-fracture technique, shows regional specialization in the structure of mammalian sperm. The P-face of the plasma membrane of a guinea pig sperm tail can be divided into three zones, each with different distributions of intramembranous particles (reflecting integral membrane proteins). This image was first published in Friend and Fawcett (1974) J. Cell Biol. 63:641-64, and reprinted as Figure 5 from Chapter 1 (The Cell Surface) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. A PDF copy of the accompanying chapter is available on the ASCB's BioEDUCATE website.
With freeze-fracture, tissue is rapidly frozen and cracked to shear along zones of weakness. Cleavage of membranes occurs along the hydrophobic interior of the lipid bilayer to reveal views of a "p-face" (the outwardly-facing inner half of the membrane) and an "e-face" (the inwardly-facing outer half of the membrane), and a metallic replica is made of the fractured surface.
