Jayanti Tokas 1 Puneet Tokas 2 Shailini Jain

Jayanti Tokas 1, Puneet Tokas 2, Shailini Jain 3, Hariom Yadav 3 1 Department of Biotechnology, JMIT, Radaur, Haryana, India 2 KITM, Kurukshetra, Haryana, India 3 NIDDK, National Institute of Health, Bethesda, MD 20892, USA

Stem Cells n Stem cells are master cells with two important characteristics q q n Unspecialized cells capable of their own renewal Ability to differentiate into different cell types The stem cells may have various differentiation potentials q q Totipotent Pluripotent Multipotent Unipotent

Stem Cells Fate Stem Cell Fail to differentiate or undergo apoptosis Neoplasia Replenish old/damaged tissue by proliferation and maturation Differentiation senescence and apoptosis

Stem cell niche n Niche signals regulate stem cell q q q n n n 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 n n 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 q Pleiotropism q

STAT signaling n n n Principal mediator of the biological responses to ligands that activate gp 130 Post-translationally regulated by tyrosine and serine phosphorylation Structure: 1. 2. 3. 4. 5. Tetramer, a leucine zipper like domain located at the amino terminus DNA binding domain Src homology domain 3 - like region Src homology domain 2 (SH 2), a critical site of tyrosine phosphorylation Carboxy-terminal transactivation domain

Two alternate pathways SHP-2 signaling Active Inactive S BP S CSH 2 P Y NSH 2 PTPase SH 2 Y 5 4 Y 5 2 0 8 Activation by External phosphotyrosines Abbreviations : S, substrate BP, bisphorylated SH 2 domain binding protein NSH 2 p Y 542 Y p. Y C-SH 2 PTPase C-SH 2 p. Y 580 se P a TP Y Activation through binding of SH 2 domains to C-terminal phosphotyrosines of SH 2 p. Y N-SH 2 +PO 4 S +PO 4

Cytokine Receptor Signaling Cytokin e Cell membrane P Cytokine R JAK SH 2 2 Gene expression P SH ST T A P 2 SH P STA T JAK P P GAS like site SH 2 STAT Nucleus P SH 2 STA T P P P Cytoplasm STAT P SH 2 (Constantinescu, 2000)

Oct 3/4 n n 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, Zfp 42/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 n n n LIF maintains ES cells self renewal Signal transduction by LIF and other IL-6 family members occurs via a common signal transducer gp 130 Dimerization of the receptor associated subunit activates receptor associated kinases like Src and the Janus family of kinases e. g. Jak 1, Jak 2 and Tyk 2 Homo-dimerization (IL-6/IL-6 R and IL-11/IL-11 R) or hetero-dimerization (LIF/LIFR) Embryonic stem cell renewal factor (ESRF) : a LIF independent signaling factor

Signaling pathways induced by IL-6 family cytokines Jak 1/2/Tyk 2 -phosphorylation -dimerization P-Y 126 P-Y 173 P-Y 265 P-Y 275 Gab 1 Box 2 gp 130 STAT 3 Box 1 SHP 2 Y 118 -P Ras -GTP -P Raf Grb 2 Box 3 MEK -P STAT 3 -P Self-renewal ERK 1/2 -P Differentiation Essentials of Stem Cell Biology, pg no. 32

Hematopoietic stem cells (HSC) self renewal n n n Expression of cell surface molecules Tpo. R+Flk 2+KIT HOXB 4 Epo. R and t Epo. R (t. Epo. R ) SCF and IL-6 : expression of receptor CXCR 4 of stromal derived factor Self renewal blockade : IL-3 and TNF

Hematopoietic stem cells (HSC) self renewal

Keratinocyte Stem Cells n n Present in hair follicle bulge area Cell adhesion, cell migration, and clonogenicity Stem cells express more β 1 integrin and adhere more rapidly to collagen IV Misu : q q q 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 n n n 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/STAT 3, 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 AML 1 or RUNX 1 (human cord stem cells) Stem cell research in livestock a long way to go……

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