Session 14 - Transdifferentiation

Session 14 - Transdifferentiation - Transdifferentiation...

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Unformatted text preview: Transdifferentiation Session XIV- 3/7/07 Dogma: Stem cells are tissue specific and cannot cross the germ layer barrier Gastrulation Ectoderm Blastocyst y Embryonic stem cells Nervous tissue Neural stem cells N TA G Skin Skin stem cells Bone marrow and blood Mesoderm Mesenchymal/hematopoietic SCs Muscle, bone, and fat M l b df t Tissue SCs Lung, liver Lung liver, pancreas Endoderm Primordial germ cells Organ specific SCs Esophagus, stomach, g intestine/Intestinal SCs Adapted from "Handbook of Stem Cells" Whole bone marrow or HSC enriched populations contribute to other tissues (mouse) Clinical settings and "transdifferentiation" g Other SC differentiating into blood Neural derived SC make blood (irradiation) Muscle derived SC make blood (irradiation) ( ) Model I: Tissue stem cells are "plastic" - they can transdiffer any type of tissue when placed in the right environment Gastrulation Ectoderm Blastocyst y Embryonic stem cells Nervous tissue Neural stem cells Skin Skin stem cells Bone marrow and blood Mesoderm Mesenchymal/hematopoietic SCs Muscle, bone, and fat M l b df t Tissue SCs Lung, liver Lung liver, pancreas Endoderm Primordial germ cells Organ specific SCs Esophagus, stomach, g intestine/Intestinal SCs Model II: There is common population of tissue stem cells set aside during development and maintained in the body in adulthood that can make any kin Gastrulation Ectoderm Skin Skin stem cells Nervous tissue Neural stem cells Blastocyst Embryonic stem cells Mesoderm Bone marrow and blood Mesenchymal/hematopoietic SCs y p Muscle, bone, and fat Tissue SCs Lung, liver, pancreas L li Organ specific SCs Endoderm Esophagus, stomach, intestine/Intestinal SCs intestine/Intestinal i t ti /I t ti l SC /I Primordial germ cells NSC/SkinSC HSC/MSC Organ SCs/intestinat SCs Common tissue cells What is the mechanism leading to the "switch of cell fate"? (model 1) Existence of common primitive (un-committed) stem cell among all the tissue stem cell populations Transdifferentiation - turning on specific lineage inducers (ie, transcription factors), and turning off other specific inducers; this would be triggered by th ifi i d thi ld b t i db various environmental clues Cell fusion event in which the migratory HSCs identity would be lost into a particular lineage with which the HSC has converged (like muscle) Contamination of one stem cell population with another (mainly contamination of all SC population with circulating HSC) Why is the " transdifferentiation" transdifferentiation of stem cell important? Clinical application - you can inject HSCs (or the primitive common progenitor) and help cure genetic diseases that are spread around the body, like muscular distrophy Basic science: the developmental programs, and cell fate commitment are not as tightly regulated ll f t it t t ti htl l t d as we thought and they are reversible (not only in nuclear transfer) What is the mechanism leading to this switch of cell fate? Transdifferentiation - turning on specific lineage inducers (ie, transcription factors), and turning off other specific inducers; this would be triggered by various environmental i d thi ld b t i db i i t l clues Existence of common primitive (un-committed) stem cell among all the tissue stem cell populations Cell fusion event in which the migratory HSCs identity would be lost into a particular lineage with which the HSC p g has converged (like muscle) Contamination of one stem cell population with another Muscle into blood: contamination not transdifferentiation Repeat the muscle cell transplantation studies, but also separate cells by FACS , p y based on specific cell surface markers C45+ (blood) Sca-1 (HSC) cells in the mix Sca 1 contribute to hematopoiesis, while other cells from muscle could not What is the mechanism leading to this switch of cell fate? Transdifferentiation - turning on specific lineage inducers (ie, transcription factors), and turning off other specific inducers; this would be triggered by various environmental i d thi ld b t i db i i t l clues Existence of common primitive (un-committed) stem cell among all the tissue stem cell populations Cell fusion event in which the migratory HSCs (or its p g y) progeny) fuse with other committed cell types yp Contamination of one stem cell population with another How can one demonstrate that cell fusion occurs? HSC Beta-Actin-GFP Rosa26 fl-stop-fl Muscle injury Exercise Muscle-specific-Cre or Beta-Actin-Cre ( (for engraftment anywhere) g y ) All the green cells outside the blood (descending from the original HSC), HSC) were also blue (so they come from cell fusion) There is no contribution to the muscle stem cell compartment Mechanism of bone-marrow derived muscle If you inject macrophages you get the same result Why is the " transdifferentiation" transdifferentiation of stem cell important? Clinical application - you can inject HSCs and help cure diseases that are spread p p around the body, like muscular distrophy Basic science: the developmental programs, programs and cell fate commitment are not tightly regulated and are reversible (??) Clinical application - you can inject HSCs and help cure diseases that are spread around the body, like muscular distrophy Can we use this cell fusion phenomenon as a means of delivering genes to gg injured/diseased tissues? Problem: inefficiency Can we improve on this? QUESTIONS? Transdifferentiation is an induced phenomenon tha between "embryologically" related cells Gastrulation Ectoderm Blastocyst Embryonic stem cells Nervous tissue Neural stem cells N TA G Skin Skin stem cells Bone marrow and bl d B d blood Mesoderm Mesenchymal/hematopoietic SCs Muscle, bone, Muscle bone and fat Tissue SCs Lung, liver, pancreas Endoderm Primordial germ cells g Organ specific SCs Esophagus, stomach, intestine/I t ti l SCs Intestinal SC Adapted from "Handbook of Stem Cells" Metaplasia - a phenomenon known to pathologist for 20 years Metaplasia: The replacement of one differentiated cell type with another differentiated cell type. Examples found in clinical setting: An example is the condition synovial chondromatosis where cells of the synovial membrane undergo metaplasia to become cartilageproducing chondrocytes chondrocytes. Cervical metaplasia, where glandular epithelium becomes squamous epithelium Switch of gastric to intestinal stem cells can cause patches of intestinal epithelium to appear in the stomach Pancreas patches into liver (or vice-versa) in preneoplastic alterations Model of metaplasia (transdifferentiation) "master" gene master Somatic mutation or environmental stress Examples of fate switches is driven by master gene regulators of embryonic cell fate MESODERMAL DERIVED -Fibroblast to skeletal m scle TC (M D promotes skeletal muscle fate) Fibroblast muscle, TC, (MyoD t k l t l l f t ) - Myoblast (muscle precursor) to adipocytes, TC, (C/EBPalpha inhibits muscle fate) ENDODERMAL DERIVED - Pancreas to liver, in vivo; - metaplasia induced by carcinogens (clones) - overexpression of KGF (a liver fate inducer) under insulin (pancreatic beta cell specific) promoter - Pancreatic cells to hepatocytes, TC, (C/EBP beta) - Hepatic cells to pancreatic like cells: (Pdx1 Ngn3 PTF1 p48 Hes1) pancreatic-like (Pdx1, Ngn3, PTF1-p48, - Intestine in the lung, in vivo -over-activate wnt pathway(important for lung vs intestine fate during embryogenesis) from a lung promoter FIBROBLAST INTO ESCs (Oct3/4; Sox2, c-Myc, Klf4) In vitro transdifferentiation pancreas <--> liver C/EBP beta In vivo induction of liver to pancreas differentiation liver p pancreas The hope is that eventually we might convert any cell type into anything provided that we have the right combination anything, of transcription factors that would cause the switch The challenges: -find the master switches -erase the appropritae methylation marks (remember the OCT3/4 promoter was not completely demethylated) QUESTIONS? ...
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This note was uploaded on 09/28/2008 for the course BIO 4400 taught by Professor Tumbar,td during the Spring '07 term at Cornell University (Engineering School).

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