title: Multiple unconventional myosin domains of the intestinal brush border cytoskeleton.
abstract: Representatives of class V and class VI unconventional myosins are identified as components of the intestinal brush border cytoskeleton. With brush border myosin-I and myosin-II, this brings to four the number of myosin classes associated with this one subcellular domain and represents the first characterization of four classes of myosins expressed in a single metazoan cell type. The distribution and cytoskeletal association of each myosin is distinct as assessed by both biochemical fractionation and immunofluorescence localization. Myosin-VI exists in both the microvillus and terminal web although the terminal web is the predominant site of concentration. Myosin-V is present in the terminal web and, most notably, at the distal ends of the microvilli, thus becoming the first actin-binding protein to be localized to this domain as assessed by both immunohistochemical and biochemical methods. In the undifferentiated enterocytes of the intestinal crypts, myosin-VI is expressed but not yet localized to the brush border, in contrast to myosin-V, which does demonstrate an apical distribution in these cells. An assessment of myosin abundance indicates that while myosin-II is the most abundant in the cell and in the brush border, brush border myosin-I is only slightly less abundant in contrast to myosins-V and -VI, both of which are two orders of magnitude less abundant than the others. Extraction studies indicate that of these four myosins, myosin-V is the most tightly associated with the brush border membrane, as detergent, in addition to ATP, is required for efficient solubilization.
authors.affiliation: Department of Biology, Yale University, New Haven, CT 06511.
authors.forename: M B
authors.initials: MB
authors.lastname: Heintzelman
authors.forename: T
authors.initials: T
authors.lastname: Hasson
authors.forename: M S
authors.initials: MS
authors.lastname: Mooseker
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D002645:Chickens; D003599:Cytoskeleton / Q000737:chemistry*; D004847:Epithelial Cells; D004848:Epithelium / Q000737:chemistry; D005629:Frozen Sections; D015151:Immunoblotting; D007150:Immunohistochemistry; D007422:Intestines / Q000737:chemistry* / Q000166:cytology; D008856:Microscopy, Fluorescence; D008858:Microscopy, Phase-Contrast; D008871:Microvilli / Q000737:chemistry*; D009218:Myosins / Q000032:analysis* / Q000145:classification / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding; D013347:Subcellular Fractions / Q000737:chemistry
chemical_list: D000199:Actins; D009218:Myosins