Need to be done cautiously within the context of PM compositional

Need to be done cautiously within the context of PM compositional heterogeneity and membrane anchorage to the cytoskeleton.Author Manuscript Author Manuscript Author Manuscript Author Manuscript4. Direct evidence for submicrometric lipid domains in living cellsIn 1987, Yechiel and Edidin suggested the existence of submicrometric domains [19]. Their discussion arose from FRAP analysis at various sizes of photobleached spots on human skin fibroblasts, using a fluorescent PC analog. The morphological evidence was less convincing due to the imaging capacity available at the time. In 1991, Rodgers and Glaser visualized submicrometric domains on erythrocyte ghosts after insertion of fluorescent phospholipid analogs, without clear equivalents found in living RBCs [20]. In 2002, Kusumi and coll. hypothesized that phospholipids are confined within compartments delineated by transmembrane proteins anchored to the underlying cytoskeleton and acting as pickets, before undergoing hop diffusion to adjacent compartments ([21]; see also Section 5.2). In the past decade, several groups have presented evidence of submicrometric domains in a variety of living cells, including prokaryotes (Section 4.1), yeast (4.2) and animal cells (4.3), although some generalizations appear still premature. 4.1. Prokaryotes The existence of nanometric lipid domains has been for a long time restricted to eukaryotes simply because their formation and/or maintenance require sterols, which are absent from the membranes of most bacteria (see membrane composition of E. coli at Table 3). However, it has been recently shown that bacteria organize many signal transduction, protein secretion and transport processes in functional membrane microdomains, which seem equivalent to eukaryotic lipid rafts (reviewed in [161]). The formation of these functional membrane microdomains seems to require flotillin-like proteins. Interestingly, heterogeneous distribution in domains of a flotillin-like protein from B. Subtilis has been directly visualized by fluorescence microscopy [162]. The importance of GSK343 web flotillins was further highlighted by the observation that domains exhibiting high GP value in Laurdan-labeled B. subtilis (Fig. 5a) could coalesce into larger domains upon loss of flotillins [31]. However, lipid composition of these flotillin-enriched structures is not clear. Since sterols are absent from most bacterial membranes, domain organization should depend on sterol surrogates and, hence, the involvement of PD150606 site polyisoprenoid lipids has been proposed (reviewed in [161]). A recent study using nanoSIMS has suggested hopanoid (pentacyclic triterpenoids structurally similar to steroids)-enriched domains in cyanobacterium Nostoc punctiforme [163]. Using the fluorescent dye 10-N-nonylacridine orange (NAO) that decorates cardiolipin, other groups have shown the presence of cardiolipin-enriched domains at the cell poles and at the division septum in E. coli [164] and B. subtilis [165], suggesting the presence in bacterial membranes of domains that could be involved in cell division. Whether functionalProg Lipid Res. Author manuscript; available in PMC 2017 April 01.Carquin et al.Pagemembrane microdomains and cardiolipin-enriched domains are spatially and functionally related remains to be explored. Importantly, it is also still unclear if bacterial and eukaryotic membrane domains share similarities. Taking into account the resolution limits of available microscopy techniques, this question is part.Need to be done cautiously within the context of PM compositional heterogeneity and membrane anchorage to the cytoskeleton.Author Manuscript Author Manuscript Author Manuscript Author Manuscript4. Direct evidence for submicrometric lipid domains in living cellsIn 1987, Yechiel and Edidin suggested the existence of submicrometric domains [19]. Their discussion arose from FRAP analysis at various sizes of photobleached spots on human skin fibroblasts, using a fluorescent PC analog. The morphological evidence was less convincing due to the imaging capacity available at the time. In 1991, Rodgers and Glaser visualized submicrometric domains on erythrocyte ghosts after insertion of fluorescent phospholipid analogs, without clear equivalents found in living RBCs [20]. In 2002, Kusumi and coll. hypothesized that phospholipids are confined within compartments delineated by transmembrane proteins anchored to the underlying cytoskeleton and acting as pickets, before undergoing hop diffusion to adjacent compartments ([21]; see also Section 5.2). In the past decade, several groups have presented evidence of submicrometric domains in a variety of living cells, including prokaryotes (Section 4.1), yeast (4.2) and animal cells (4.3), although some generalizations appear still premature. 4.1. Prokaryotes The existence of nanometric lipid domains has been for a long time restricted to eukaryotes simply because their formation and/or maintenance require sterols, which are absent from the membranes of most bacteria (see membrane composition of E. coli at Table 3). However, it has been recently shown that bacteria organize many signal transduction, protein secretion and transport processes in functional membrane microdomains, which seem equivalent to eukaryotic lipid rafts (reviewed in [161]). The formation of these functional membrane microdomains seems to require flotillin-like proteins. Interestingly, heterogeneous distribution in domains of a flotillin-like protein from B. Subtilis has been directly visualized by fluorescence microscopy [162]. The importance of flotillins was further highlighted by the observation that domains exhibiting high GP value in Laurdan-labeled B. subtilis (Fig. 5a) could coalesce into larger domains upon loss of flotillins [31]. However, lipid composition of these flotillin-enriched structures is not clear. Since sterols are absent from most bacterial membranes, domain organization should depend on sterol surrogates and, hence, the involvement of polyisoprenoid lipids has been proposed (reviewed in [161]). A recent study using nanoSIMS has suggested hopanoid (pentacyclic triterpenoids structurally similar to steroids)-enriched domains in cyanobacterium Nostoc punctiforme [163]. Using the fluorescent dye 10-N-nonylacridine orange (NAO) that decorates cardiolipin, other groups have shown the presence of cardiolipin-enriched domains at the cell poles and at the division septum in E. coli [164] and B. subtilis [165], suggesting the presence in bacterial membranes of domains that could be involved in cell division. Whether functionalProg Lipid Res. Author manuscript; available in PMC 2017 April 01.Carquin et al.Pagemembrane microdomains and cardiolipin-enriched domains are spatially and functionally related remains to be explored. Importantly, it is also still unclear if bacterial and eukaryotic membrane domains share similarities. Taking into account the resolution limits of available microscopy techniques, this question is part.