THE NATURAL SUBCELLULAR SURFACE-STRUCTURE OF THE BOVINE SPERM CELL

We used atomic force microscopy (AFM), which utilizes a novel 3D image -contrast mechanism, to obtain nanometer-resolved, topographic data im ages of the natural surface structures of untreated bovine sperm cells . Freshly ejaculated, thawed, sonicated, and demembranated bovine sper m were adsorbed passively or by motility from suspension onto a coverg lass substrate and directly imaged in normal air and saline environmen ts without damaging the cells. Our AFM images of the surface structure s of unfixed sperm imaged in normal air were consistent with previous electron microscope results on frozen or fixed sperm, demonstrating th at the accurate preservation of small cellular structures is achievabl e using greatly simplified AFM sample preparation and imaging environm ents. Our AFM results also indicate that imaging sperm in physiologic buffer provides more native views of sperm due to the retention of cyt oplasmic structures easily disrupted by drying forces. In addition, th e AFM images show that numerous nanometer-sized subcellular structures of the sperm head and tail regions could be clearly visualized on rap idly prepared, unfixed, intact cells. Consequently, AFM should be cons idered a new tool for studying sperm structure abnormalities and monit oring the specific effects of, or damage caused by, various chemical r eactants or other treatments on the structures of metabolically active or partially demembranated sperm. AFM is now emerging as an important new structural technique for imaging hydrated cells and organelles an d, in addition, has the capabilities to physically ''interrogate'' the m with the local probe, (C) 1995 Academic Press, Inc.