Cytoskeleton

cytoskeleton functions

maintain cell shape/structure

cellular motion

cellular adhesion

intracellular transport

cell division

some cells have specialized cytoskeleton - muscle, cilia

cytoskeletal components

microfilaments - smallest

intermediate filaments

microtubules - largest

actin microfilaments

dynamic

made of many small globular subunits (g-actin)

polymerize into filaments (f-actin), bonds not strong, add actin to +end

ATP/ADP binding acts as a molecular switch by changing conformation

Filaments in constant flux (polymerization/depolymerization)

accessory actin binding proteins control diverse arrangement of microfilaments (nucleate polymerization, crosslink, branch, and cap polymers)

microfilament function - structure

different types of filaments with structural roles to support and shape the plasma membrane at the cell periphery

microfilament function - adhesion

actin cytoskeleton attached to the extracellular matrix

microfilament function - movement

directly through actin polymerization (leading edge of cell moves out into environment)

through myosin motor proteins

microfilament function - cell division

cleavage furrow

actin - cancer

actin based motility is critical to cancer metastasis

dystrophin

a large scaffolding protein that supports muscle structure and function by linking actin filaments with the membrane and ECM of muscle cells (adhesion)

Muscular Dystrophy (MD)

mutations in dystrophin - splicing error causing exon 50 to be cut out, leading to a premature stop codon

x-linked - females are symptomless carriers

complex events lead to muscle cell death

animals waste leading to premature death

canine MD ia analogous to Duchenne in humans

genome editing with CRISPR/Cas9

RNA guided DNA nuclease programmed for precision targeting

viral delivery

microtubule (MT) polymerization

dynamic instability

• constant polymerizing/depolymerizing

• rapid alteration allows for aupport of dynamic cellular processes

microtubule organizing centers (MTOCs) nucleate

• centrosomes/centrioles near center of cell

• plus ends face out

microtubule functions

structure - resist compressive forces

cell division - mitotic spindle separates replicated chromosomes into each daughter cell (blocking polymerization or stabilizing polymers can inhibit mitosis [cancer chemotherapies])

microtubule based movement

motor protein classes

• kinesin - generally +end directed

• dynein - always -end directed

intracellular transport to move cargo around the cell

flagella/cilia

• sperm motility

• movement of mucus in upper respiratory system

• movement of egg through oviduct to uterus

• fluid flow in developing embryo - body symmetry

non-motile “primary cilia” are key signaling sites for olfaction and vision

intermediate filaments function

large and diverse groups of proteins - keratins, desmins, laminins, etc

many are cell type specific

• ~50 distinct keratins in mammals

• can indicate tissue of origin or epithelial cancers (cacinomas)

tension bearing element in cell

laminins support nuclear envelope

keratins

provide cells with mechanical stability

intracellular keratins interact with

• hemidesmosomes for cell-ECM adhesion

• desmosomes for cell-cell adhesion

epidermolytic hyperkeratosis

splice site mutation in keratin 10 gene (frame shift leading to truncation)

norfolk terrier

skin is fragile and prone to blister

• skin thickening (hyperkeratosis)

• increased pigmentation