Coverslips, trace insertion in the outer PM leaflet of fluorescent lipid analogs has revealed submicrometric domains of 0.5m in diameter. Similar domains have been observed upon direct labeling of endogenous SM and cholesterol using toxin derivatives (Fig. 6, 7 Table 1) [26, 27, 29, 30, 146]. Importantly, double labeling of RBCs with the SM-specific lysenin fragment (see above), then with BODIPY-SM, reveals perfect colocalization, suggesting the relevance of BODIPY-SM to study its native counterpart [26]. Submicrometric lipid domains have been confirmed on RBCs suspended in a 3D-gel, thus without artificial stretching, suggesting a genuine feature of RBCs in vivo. Mechanistically, lipid domains are governed by temperature, membrane lipid composition and membrane:cytoskeleton anchorage, thus by membrane tension (Fig. 7; see also Section 5) [26, 29]. In addition to RBCs, oligodendrocytes are also a useful model to study PM organization, based on differential relative abundance of specific lipids during differentiation (Section 3.1.3; for a review, see [132]) and a high global lipid content ( 75 of their total dry weight, with a protein:lipid ratio of 0.3 vs 1 in most cells [174]). In fact, several reports have contributed with seminal findings in this regard. First, PIP2 is a major regulator of myelin compaction by its close interaction with myelin basic proteins [175]. Second, galactosylceramide and sulfatides form submicrometric domains [176], mutually interacting at the apposed membranes of wrapped myelin (for a review, see [177]), regulating PM organization and lateral diffusion of myelin proteins [178]. Third, GM1 submicrometric domains are essential for oligodendrocyte precursor survival by providing signaling platforms for growth factor-mediated integrin purchase PD0325901 activation [179]. Fourth, sulfatide submicrometric domains are necessary for neuron-dependent oligodendrocyte maturation by contact with laminin, a molecule that is UNC0642 web present at the axolemma [180] (Table 1). Lipid domains can also be generated by the hydrolysis of specific lipids. As an example, one can cite the Cer-rich domains with diameters of 200nm up to several micrometers that can be formed upon degradation by acid SMase of sphingomyelin into Cer in response to stress [33-35]. Such domains, also called platforms, can be visualized by a variety of techniques, including fluorescence and confocal microscopy, and exhibit a gel like phase. They can play a role in transmembrane signaling and can be involved in the physiopathology of various diseases, including cancer [34].Author Manuscript Author Manuscript Author Manuscript Author Manuscript5. BiogenesisIt is not clear how submicrometric lipid domains are formed, but various mechanisms have been proposed. These include: (i) lipid:lipid interactions (Section 5.1); (ii) protein:lipid interactions, including with the cytoskeleton or the cell wall (5.2); (iii) membrane turnover (5.3); and (iv) extrinsic factors such as temperature, pH and osmolarity (5.4). Interplay/ balance between these different mechanisms likely varies from one cell to another, impacting on domain abundance, size (Section 4) and function (Section 6).Prog Lipid Res. Author manuscript; available in PMC 2017 April 01.Carquin et al.Page5.1. Lipid-based mechanismsAuthor Manuscript Author Manuscript Author Manuscript Author ManuscriptArtificial models are convenient to analyze biophysical parameters of lipid domains and have been at the cornerstone of identifying ke.Coverslips, trace insertion in the outer PM leaflet of fluorescent lipid analogs has revealed submicrometric domains of 0.5m in diameter. Similar domains have been observed upon direct labeling of endogenous SM and cholesterol using toxin derivatives (Fig. 6, 7 Table 1) [26, 27, 29, 30, 146]. Importantly, double labeling of RBCs with the SM-specific lysenin fragment (see above), then with BODIPY-SM, reveals perfect colocalization, suggesting the relevance of BODIPY-SM to study its native counterpart [26]. Submicrometric lipid domains have been confirmed on RBCs suspended in a 3D-gel, thus without artificial stretching, suggesting a genuine feature of RBCs in vivo. Mechanistically, lipid domains are governed by temperature, membrane lipid composition and membrane:cytoskeleton anchorage, thus by membrane tension (Fig. 7; see also Section 5) [26, 29]. In addition to RBCs, oligodendrocytes are also a useful model to study PM organization, based on differential relative abundance of specific lipids during differentiation (Section 3.1.3; for a review, see [132]) and a high global lipid content ( 75 of their total dry weight, with a protein:lipid ratio of 0.3 vs 1 in most cells [174]). In fact, several reports have contributed with seminal findings in this regard. First, PIP2 is a major regulator of myelin compaction by its close interaction with myelin basic proteins [175]. Second, galactosylceramide and sulfatides form submicrometric domains [176], mutually interacting at the apposed membranes of wrapped myelin (for a review, see [177]), regulating PM organization and lateral diffusion of myelin proteins [178]. Third, GM1 submicrometric domains are essential for oligodendrocyte precursor survival by providing signaling platforms for growth factor-mediated integrin activation [179]. Fourth, sulfatide submicrometric domains are necessary for neuron-dependent oligodendrocyte maturation by contact with laminin, a molecule that is present at the axolemma [180] (Table 1). Lipid domains can also be generated by the hydrolysis of specific lipids. As an example, one can cite the Cer-rich domains with diameters of 200nm up to several micrometers that can be formed upon degradation by acid SMase of sphingomyelin into Cer in response to stress [33-35]. Such domains, also called platforms, can be visualized by a variety of techniques, including fluorescence and confocal microscopy, and exhibit a gel like phase. They can play a role in transmembrane signaling and can be involved in the physiopathology of various diseases, including cancer [34].Author Manuscript Author Manuscript Author Manuscript Author Manuscript5. BiogenesisIt is not clear how submicrometric lipid domains are formed, but various mechanisms have been proposed. These include: (i) lipid:lipid interactions (Section 5.1); (ii) protein:lipid interactions, including with the cytoskeleton or the cell wall (5.2); (iii) membrane turnover (5.3); and (iv) extrinsic factors such as temperature, pH and osmolarity (5.4). Interplay/ balance between these different mechanisms likely varies from one cell to another, impacting on domain abundance, size (Section 4) and function (Section 6).Prog Lipid Res. Author manuscript; available in PMC 2017 April 01.Carquin et al.Page5.1. Lipid-based mechanismsAuthor Manuscript Author Manuscript Author Manuscript Author ManuscriptArtificial models are convenient to analyze biophysical parameters of lipid domains and have been at the cornerstone of identifying ke.
