Cell Bio Week 10

Interphase microtubules

maintain cell shape/polarity, serve as tracks for intracellular transport, guide cell migration, form cilia and flagella, signaling

tubulin heterodimers

alpha/beta tubulin

microtubule nucleation

unfavorable, harder than actin. more favorable with pre-formed nucleus

microtubules nucleated by microtubule organizing center (MTOC)

centriole (mother/daughter) + pericentriolar material = nucleate microtubules, uses Y-TuRC (seed)

Microtubule polymerization

GTP cap- changes size based on growth speed, depolymerization occurs when growth catches up to cap/hydrolysis catches up to addition, growth occurs when addition is faster than hydrolysis

Catastrophe

rapid switch from growth to shrinking (depolymerization)

Rescue

rapid switch from depolymerization to growth

dynamic instability

allows microtubules to probe the cytoplasm- twitching behavior- switching between growth and depolymerization, caused by local differences in amount of GTP tubulin

kymography

measure fluorescence intensity along microtubule over time, measure rate of polymerization, frequency of catastrophe, frequency of rescue

plus-end tracking proteins are an important group of…

MAPs (microtubule associated proteins)

polymerization factors

xMAPZ15, EB1

depolymerization factors

MCAK

Rescue factors

Clip, Clasp

Catastrophe factors

MCAK, KLPs

Stabilization factors

APC, MACF, Clasp

EB1 recognizes a microdomain (GTP cap) on microtubules

binds GTP-tubulin, recognizes vertices between two alpha and beta subunits, prefers GTP tubulin (GTP cap), only binds to growing MTs, is a critical hub of microtubule plus end, “marks” GTP- cap

C-terminal tails of alpha and beta are subject to…

post-translational modifications (PTMs)- label distinct populations of microtubules

tubulin isoforms

Beta 2 (more stable) and Beta 3 (less stable)

tubulin tyrosination and glutamylation…

regulates MAP association

microtubule arrays take on…

different geometries

MAPs

microtubule associated proteins

+ TIPS - subset of MAPs

proteins that track along plus end of microtubules, bind to SXIP or EEY motifs, become major hub

post-translational modifications

phosphorylation, acetylation, etc.

blebbing

driven by plasma membrane protrusions (blebs), tumor cells/lymphocytes, faster, i.e. squeezing toothpaste

mesenchymal

adhesion-dependent, fibroblasts/endothelia, sending out protrusions, slower

substrate compliance increases with…

blebbing

size and strength of adhesions increase with…

mesenchymal

blebbing and mesenchymal are a…

spectrum- can convert between

periphery

lamellipodia (Arp2/3) and filopodia (formins/Ena VASP)

interior

lamella, stress fibers (myosin/bundling proteins)

initial actin polymerization establishes…

cell-matrix adhesions and myosin contractility leads to their maturation

non-muscle myosin II forms…

contractile cables- bring different ends of actin together

cell-matrix adhesions

connect outside of cell to inside of cell using extracellular matrix

interns

receptors- bind extracellular matrix, made of alpha/beta pair, low affinity until they bind ligand, then become high affinity/active, bidirectional signaling receptors: outside-in and inside-out activation- depends on cellular context - talin

extra-cellular matrix (ECM)

non-cellular component within all tissues and organs, composed of water + proteins + polysaccharides, provides physical scaffolding, biochemical and biomechanics cues needed for morphogenesis, tissues + organ specific, collagen, vitronectin, laminin, fibronectin, elastin

cells secrete extracellular matrix as they…

migrate

fibroblasts are professional…

ECM secretors

Integrin a-B heterodimers are…

ECM receptors- pairs dictate what they actually bind

Integrins are force receptors

can detect how stiff a substrate is

substrate compliance →

less stiff

size and strength of adhesions →

more stiff

adhesions are born in the…

lamellipodia, mature in the lamella

Nascent adhesions formed in the…

lamellipodia- Arp2/3

actin dynamics are coupled to…

adhesion maturation

molecular clutch hypothesis

integrins act as a clutch turning actin retrograde flow into protrusion

epithelia segregate inside from out

form sheets of uniform polarized cells, maintained by adhesion molecules (cadherins), asymmetrical with apical + basal domains, carry out polarized functions- secretion, nutrient absorption, fluid transport, epithelia become building blocks for various tissues

interns help to establish…

cell polarity

epithelial cells express…

B1 integrin

epithelia cells function in a…

polarized manner

tight junctions

prevent things from going in between cells

adherens junctions

tissue integrity, signaling, development

epithelial cells maintain adhesions as they…

migrate