Cell fusion requires the reorganization of cellular envelopes, which is a challenging process that must be tightly controlled. The involvement of Schizosaccaromyces pombe fusion-promoting proteins Dni1p and Dni2p has been addressed. When any or both of them are missing, cells fail to fuse at medium-high temperature due to an abnormal organization of plasma membrane and cell wall at the area of cell-cell contact. At low temperature, mutants are able to fuse, suggesting that Dni1p and Dni2p facilitate fusion under conditions of elevated membrane fluidity. Dni1p and Dni2p have four transmembrane domains and the structural properties of claudins. Structure-function analyses demonstrate that in Dni2p, but not in Dni1p, these functional properties are required for function. While Dni2p is localized at the endoplasmic reticulum (ER) before cell fusion, Dni1p is only detected in the plasma membrane (PM). At the moment of cell fusion both proteins co-localize at a PM microdomain at the point of cell-cell contact. Both proteins form a complex where each one seems to exert a specific function; while Dni1 is the functional component, Dni2 is required to establish/ maintain the microdomain where Dni1p needs to locate to play its role. We are investigating the connection between ER and PM during cell fusion.

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