Membrane Structure Changes Before Lipid Domains Form

The chemical composition of lipid membranes is tightly linked to localized lipid-domain structure. But such lipid membranes have their own version of the chicken and egg problem: Which comes first, structural changes or the formation of lipid domains? The structural changes do, according to Andrew G. Ewing of the University of Gothenburg, Sweden; Nicholas Winograd of Pennsylvania State University; and coworkers (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.0908101107). The researchers came to that conclusion by using time-of-flight secondary ion mass spectrometry imaging of cell membranes from the single-celled protozoan Tetrahymena during the mating process. They used a physical perturbation called trituration to distinguish between cells in different stages of mating. In the later stages of mating, Tetrahymena cells form pores to exchange genetic material. These pores require a curved local architecture that favors certain lipids in the membranes. The researchers find that the pores form first and then the lipid composition changes, characterized by a decrease in phosphatidylcholine, instead of the other way around.