Immunofluorescence of sperm probed against anti-MFN2. Immunofluorescence using freshly collected caput epididymal sperm (A), freshly collected cauda epididymal sperm (B), cauda epididymal sperm incubated in non-capacitating medium (C), cauda epididymal sperm incubated in capacitating medium (D), or cauda epididymal sperm incubated in medium mimicking epididymal luminal fluid (E) and probed against anti-MFN2 was performed. MFN2 was localized to the sperm midpiece and post-acrosomal region in caput epididymal sperm, cauda epididymal sperm, and in sperm maintained in medium mimicking epididymal luminal fluid. In sperm incubated in non-capacitating or capacitating media the fluorescence was detected in the post-acrosomal region and throughout the flagellum. A 5 μm bar is indicated on all images. Nomarski differential interference contrast micrographs are located to the right of each fluorescent image.