Jayanti Tokas1, Puneet Tokas2, Shailini Jain3, Hariom Yadav3

1Department of Biotechnology, JMIT, Radaur, Haryana, India2KITM, Kurukshetra, Haryana, India

3NIDDK, National Institute of Health, Bethesda, MD 20892, USA

Stem Cells

Stem cells are master cells with two important characteristics Unspecialized cells capable of their own renewal Ability to differentiate into different cell types

The stem cells may have various differentiation potentials Totipotent Pluripotent Multipotent Unipotent

Stem Cells Fate

Replenish old/damaged Replenish old/damaged tissue by proliferation tissue by proliferation

and maturationand maturation

Differentiation - Differentiation - senescence and senescence and

apoptosisapoptosis

Fail to differentiate or undergo apoptosis -

Neoplasia

Stem Cell

Stem cell niche

Niche signals regulate stem cell Self-renewal Survival Maintenance

Niche cells adhere to stem cells by cell-cell adhesion

Stem/niche organization provides cues to organize spindles and self-renewal signals

Niches exist in many adult tissues: hematopoietic system, neural tissues, skin, gut epithelium, etc

Cytokines

Prime molecules modulating cellular growth and differentiation of embryonic, hematopoietic and other stem cell types

Act in low concentrations (10-4 -10-5 M) Complex molecules Two important characteristics

Redundancy Pleiotropism

STAT signaling

Principal mediator of the biological responses to ligands that activate gp130

Post-translationally regulated by tyrosine and serine phosphorylation

Structure: 1. Tetramer, a leucine zipper like domain located at

the amino terminus2. DNA binding domain3. Src homology domain 3- like region 4. Src homology domain 2 (SH2), a critical site of

tyrosine phosphorylation5. Carboxy-terminal transactivation domain

Y58

0

P Y

N-SH2

PTPase

C-

SH2

Y542

PTPaseN-SH2 C-SH2

BP

pY pYY

+PO4

PTPa

se

S

Y

+PO4

p Y542

pY580

C-SH2N-

SH2

Activation by External phosphotyrosines

Activation through binding of SH2 domains to C-terminal phosphotyrosines of SH2

Inactive Active

Abbreviations : S, substrate BP, bisphosphorylated SH2 domain binding protein

SH 2

Two alternate pathways SHP-2 signaling

PCytokine R

JAK

Cytokine

JAK PP

PP

STAT

SH2

P

P PSTAT

SH2

P

STAT

SH2 STAT

SH2P

P

Nucleus

Cell membrane

Cytoplasm

Gene expression

STATSTAT

SH2

P

PSH2

Cytokine Receptor Signaling

(Constantinescu, 2000)

Oct 3/4

Marker for undifferentiated cells Master regulator of initiation, maintenance

and differentiation of pluripotent cells Exerts effects via certain target genes like

genes encoding, the transcriptional co-factor UTf-1, Zfp42/Rex-1, PDGF, otx-2, etc

Requires several cofactors to execute its functions of maintaining pluripotency

Relationship between Oct-3/4 expression and stem cell fate

Embryonic Stem cells self renewal

LIF maintains ES cells self renewal Signal transduction by LIF and other IL-6 family

members occurs via a common signal transducer gp130

Dimerization of the receptor associated subunit activates receptor associated kinases like Src and the Janus family of kinases e.g. Jak1, Jak2 and Tyk2

Homo-dimerization (IL-6/IL-6R and IL-11/IL-11R) or hetero-dimerization (LIF/LIFR)

Embryonic stem cell renewal factor (ESRF) : a LIF independent signaling factor

IL-6 family cytokines

STAT3

Jak1/2/Tyk2

Self-renewal

- PERK1/2

-GTP

-PRaf

Ras

SHP2

Gab1

Grb2

-PMEK

Differentiation

-phosphorylation-dimerization

gp

130

Box3

Box2

Box1

P-Y126P-Y173P-Y265P-Y 275

Y118-P

STAT3-P

STAT3-P

Signaling pathways induced by IL-6 family cytokines

Essentials of Stem Cell Biology, pg no. 32

Hematopoietic stem cells (HSC) self renewal

Expression of cell surface molecules TpoR+Flk2+KIT HOXB4 EpoR and t EpoR (tEpoR EpoR ) SCF and IL-6 : expression of receptor

CXCR4 of stromal derived factor Self renewal blockade : IL-3 and TNF

Hematopoietic stem cells (HSC) self renewal

Keratinocyte Stem Cells

Present in hair follicle bulge area Cell adhesion, cell migration, and

clonogenicity Stem cells express more β1 integrin and

adhere more rapidly to collagen IV Misu :

Direct target gene of Myc Up-regulated in many cancers Depletion might result in increased self

renewal capacity

Role of Myc in regulating epidermal stem cell fate

Adhesion and cytoskeleton

Growth promoting target genes

New Players in Stem cell self renewal and Future directions

Nanog – marker for pluripotent cell lines Induced pluripotent stem cells from human

fibroblasts Maintenance of self renewal property in ES via

Nanog is independent of LIF/STAT3, and also Oct-3/4 Understanding the molecular mechanism of stem

cell renewal and commitment - unparalleled progress for tissue replacement, transplantation and other stem cell based therapies

Expression of genes AML1 or RUNX1 (human cord stem cells)

Stem cell research in livestock a long way to go……

Thank You