Embryonic vs Adult Stem Cells - Pros & Cons

• Unstable - difficult to controldifferentiation into specific cell type.• Immunogenic - potential immune-rejection when transplanted intopatients.• Teratomas - tumor composed oftissues from 3 embryonic germ layers.• Ethical Controversy - unethical forthose who believes that life begins atconception.

• Pluripotency - ability to differentiateinto any cell type.• Immortal - one cell can supply endlessamounts of cells.• Easily available - human embryosfrom fertility clinics.

DisadvantagesAdvantages

Embryonic Stem (ES) Cells

Embryonic vs Adult Stem Cells - Pros & Cons

• Minimal quantity - number ofisolatable cells may be small.• Finite life-span - may have limited life-span in culture.• Ageing - stem cells from agedindividuals may have higher chance ofgenetic damage due to ageing.• Immunogenic - potential immune-rejection if donor cells are derived fromanother individual.

• Already ‘specialised’ - induction ofdifferentiation into specific cell types willbe easier.• Plasticity - Recent evidences suggestwider than previously thought ranges oftissue types can be derived.• No Immune-rejection - if used inautologous transplantations.• No Teratomas - unlike ES cells.• No Ethical Controversy - sourcedfrom adult tissues.

DisadvantagesAdvantages

Adult Stem Cells

What is a Stem Cell? - Pluripotency

6,000,000,000 cells(230 different cell types)

1 Cell(Zygote - fertilised egg)

What makes Stem Cells “Stem Cells”?

Differentiation

Self-Renewal

Origin

Pluripotency

What makes Stem Cells, ‘Stem Cells’?

Differentiationvia Multipotent Progenitors

Self-Renewalthrough Asymmetric Cell Division

Self-Renewal vs Differentiation

DifferentiationSelf-Renewal

Skeletal Muscle Biology

Myogenic Lineage

Tajbakhsh Exp Cell Res 2005

bHLH transcription factorsMyogenic Regulatory Factors (MRFs)MyoD, Myf-5, myogenin

Paired-box transcription factorsPax3, Pax7

Stem CellPax3+ and/or Pax7+

Proliferation

Myogenic SpecificationMyf5+, MyoD+

DifferentiationMyoD+,Myogenin+

Terminal DifferentiationMyogenin+, MHC+

Modified from Tajbakhsh (2003)Current Opinion in Genetics & Development

GeneticGeneticHierarchyHierarchy

MyogenicLineage

Cryostat Section Isolated Cells

E15E18

Pax3Pax3++

Pax7Pax7++

MRFsMRFs++

Pax3Pax3+ + Pax7Pax7++

Pax3Pax3+ + MRFsMRFs++

Pax7Pax7+ + MRFsMRFs++

Pax3Pax3+ + Pax7Pax7+ + MRFsMRFs++

Triple Immuno-labeling;Pax3Pax3++

Pax7Pax7++

MRFsMRFs+ + ((MyoDMyoD+Myf-5++Myf-5+myogeninmyogenin))

Pax3 Pax7

MRFs

Developing Muscles from Rat Hindlimb

Adult Muscle Stem (Satellite) Cells

Symmetric vs Asymmetric Division

Stem Cell Stem Cell

DifferentiatedCell

Self-Renew

al

Symmetric Division Asymmetric Division

Symmetric vs Asymmetric Division

Stem CellPax3+

and/orPax7+1

ProliferationPax7+

Myogenic SpecificationMyf5+, MyoD+

DifferentiationMyoD+,Myogenin+

Terminal DifferentiationMyogenin+, MHC+

Symmetric vs Asymmetric Division

Asymmetric Cell Division - Stem Cell Hallmark

Environmental Asymmetry Divisional Asymmetry

DifferentiatedCell

DifferentiatedCell

Divisional Asymmetry

A. Extrinsic Regulation

B. Intrinsic Regulation

Engineering the ‘Niche’…

- adding growth factors &cytokines.- changing surface propertiesof the culture dish.- co-culture with ‘feeder’ cells.- co-culture with scaffolding ormatrix.

- activation of transcriptionfactors.

Yamashita Cold Spring Harb Perspect Biol 2010

Cancer Stem Cells?

Stem Cells - Therapeutic Applications1. Generation of cells/tissues for Cell-Based Therapies

Stem Cells - Therapeutic Applications2. Drug discovery/screening through safer and cheaper testing using

human cells.3. Study the mechanisms of human development, stem cell

differentiation and function.4. Study the mechanisms to understand and treat birth abnormalities.

Summary

• Stem Cell Definition?• Totipotency - Pluripotency - Multipotency

• Various sources of Stem Cells?• Advantages & Disadvantages

• Unique feature of “Stem Cells”?• Self-Renewal vs Differentiation and how this could be achieved

• Therapeutic applications of Stem Cells?• Find out examples that spark your interests from the news and media fordiscussion in Lab 12.

Lab 11 - Information & Overview

Please ensure that you read and bring the Laboratory Handout for theLaboratory Session tomorrow.

Questions?