Tetrahymena thermophila mating results in lipid heterogeneity at membrane fusion sites. (A) SIMS image for m/z 184, representative of the phosphocholine headgroup, demonstrating the absence of phosphatidylcholine at the conjugation junction. (B) SIMS image for m/z 126, representative of the phosphoethanolamine headgroup, demonstrating the presence of phosphatidylethanolamine at the conjugation junction. SIMS images were acquired using a 200 nm beam spot size (B250 nm lateral resolution). Scale bar = 50 µm. From Science 2004, 305, 71. Reprinted with permission from AAAS.