Cell Communities 1

Cell CommunitiesChapter 20

Key topics

Structure & function of-- the extracellular matrix-- cell junctions

Tissue organization

Properties of -- Stem cells-- Cancer cells

Questions in this chapter you should be able to answer:

Chapter 20: all

Cell Communities 2

Extracellular Matrix – I Plant cell wall

Compositioncellulosehemicelluloselignin

OrganizationMiddle lamella1O wall2O wall

Plasmadesmata

Cell Communities 3

How are cellulose fibers synthesized and oriented?

Cellulose organizationCellulose synthase

-- pushed forwardMicrotubule tracts

– constrain movement

Cellulose fibers Microtubules

Cell Communities 4

Animal tissue organization

EpitheliaExtracellular matrix

-- Basal lamina-- Connective tissue

Epithelia have polarityTight junctions separate

apical vs basal surfaces

apical

Cell Communities 5

What are the 1O components of the ECM?

CollagensProteoglycans

Collagensstructure (Glc - X - Y)

X often prolineY often hydroxyproline

functionorganizationmany types

Gelatin

ScurvyVitamine-Cprolyl-hydroxylase hydroxyproline

Fibroblasts

Collagen

Cell Communities 6

What are proteoglycans?

Polysaccharide core (hyaluronate)+ Protein linkers+ GAG branches (glucoseaminoglycan)

GAGs-- Repeating disaccharides-- cationic-- e.g., Chondroitin

Functionshydroscopicswelling pressureinfluence cell migration

Cell Communities 7

How are cells linked together and to extracellular matrix?

May involveCytoskeleton

and componentsOf extracellular matrix

Cell Communities 8

What creates Cell-Cell linkages?

Cadherins mediate cell-cell linkage-- many types: C-, E-, P-, T- cadherins-- “homophillic” binding

Can be connected to cytoskeletonDesmosomes – intermediate filamentsAdherin junctions – actin filaments

Classic newt embryo experiment -- Townes and Holfreter (1955)

(simplified)

Cadherins

Cell Communities 9

Linkage to the ECM are also important

Integrins – mediate linkages between cytoskeleton and ECM

Also can be connected to cytoskeletonHemidesmosomes – intermediate filamentsContact Adhesions – actin filaments

linkages are ‘responsive’

Question 20-4Why are these linkages more common in fibroblasts, and desmosomes and adherin junctions more common in epithelial cells?

Cell Communities 10

How does tissue renewal occur?

Cell division vs stem cellse.g., Liver vs skin

What are the properties of stem cells?

Self renewal

Developmental commitment

Precursor terminally differentiated

Cell Communities 11

Somatic vs EmbryonicStem (ES) cells

Somatic – tissue specific-- degrees of commitment

-- multipotent vs unipotent

ES – any developmental fate-- must follow developmental pathway

-- else neoplasm

Cell Communities 12

How do somatic stem cells renew skin?

Skin structure-- stratified epithelium

Epidermal stem cells

Example of a stratified epithelium

Cell Communities 13

How do somatic stem cells renew intestine?

intestine structure

Epithelial stem cells

How is pattern of tissue regeneration different than for skin?

-- Is intestinal epithelium simple or stratified?

Cell Communities 14

Stem cell biotechnology

Tissue repair-- CNS injury-- burns-- disease (macular degeneration)

Organ replacement?-- in vitro regeneration

ES-cells

Cell Communities 15

Why do cells become tumorous?

Which type of cancer gene causes loss of cell division control?

Which type of cancer geneleads to genetic instability?

Which type of mutation requires two altered alleles to exert it’s effect?

-- How does LOH overcome this constraint Meningioma karyotypeLOH - #17 (Loss Of Heterogenecity)Aneuploidy - #s 9, 7, and 20Translocation/duplication - #s 2 and 6

Cell Communities 16

How does loss of genetic stability lead cells to become cancerous??

Benign tumor vs Malignant tumor vs Cancer

Evolutionary process

Lost dependence of extracellular regulation-- checkpoint failure

Loss of ‘mortality’ (e.g., telomere renewal)

Activation of genes for motility and invasiveness-- cell junction breakage-- cytoskeletal changes

Altered metabolism-- higher glycolysis, less Krebs – why?

Abnormal adhesion proteins-- cadherins, etc-- growth in new areas