Red Blood Cells

 

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The red blood cell (RBC) membrane provides an excellent model system to study actin filament assembly and dynamics. Classic work from this lab and others have shown that the RBC membrane is supported by a spectrin-actin lattice termed the membrane skeleton, formed by short actin filament (F-actin) nodes interconnected by spectrin tetramers in a quasi-hexagonal lattice. The short F-actins are capped by tropomodulin (Tmod) at their pointed ends, adducin at their barbed ends, and coated with a tropomyosin (TM) molecule spanning their length. Spectrin-actin networks similar to the RBC membrane skeleton are essential for membrane morphology and mechanics in other cells, such as neuronal axons and polarized epithelial cells. Unlike many other cell types, a critical advantage to studying RBCs is that these cells can be easily isolated in large quantities and contain no transcellular or cytoplasmic cytoskeleton, allowing studies of the membrane skeleton in isolation from other populations of F-actin or myosin.

While much is known about the static geometry and arrangement of the membrane skeleton, key unsolved questions are how this regular lattice is assembled and the structural basis for hexagonal symmetry, including how F-actin lengths and numbers of spectrins at nodes are precisely regulated. Moreover, how the lattice nano-scale hexagonal architecture underpins the micron-scale biconcave shape of RBCs is unclear. We are tackling these questions by evaluating RBC shapes and membrane skeleton structure using confocal and super-resolution fluorescence microscopy and electron microscopy, membrane deformability using biomechanical assays, and physiology using hematological assays. By comparing RBCs from transgenic mice with mutations in Tmod, TM or adducin, we can test the roles of actin binding proteins in network symmetry, architecture, cell shapes and hematology. The data from these studies will be a crucial building block to model the forces exerted on cell membranes by the spectrin-actin network and how each component in that network contributes to overall cell shape and membrane curvature.

 

 

Relevant publications:

Gokhin DS, Fowler VM. Feisty filaments: actin dynamics in the red blood cell membrane skeleton. Curr Opin Hematol. 2016 May;23(3):206-214.

Gokhin DS, Nowak RB, Khoory JA, de la Piedra A, Ghiran IC, Fowler VM. Dynamic actin filaments control the mechanical behavior of the human red blood cell membrane. Mol Biol Cell. 2015 May 1;26(9):1699-710.