Section #8: An Introduction to Stem Cells Ward G. Walkup IV

Overview of Section #8 Slides Hi All, below is an overview of my section slides Slide #4: what a stem cell is Slides #5-6: adult vs. embryonic stem cells Slides #7-13: toti, multi and pluripotency of stem cells Slides #14-15: induced pluripotent stem cells Slides #16-30: different types of cloning #17-20: molecular cloning #21-26: reproductive cloning #27-30: therapeutic cloning Slides #31-37: Muotri Paper Slides #38 on: extra unused stuff on neural differentiation

Overview of Section Materials Todays section material will present an overview of stem cells, covering the following topics: What a stem cell is Adult versus embryonic stem cells Multi, pluri, totipotency and induced pluripotentcy of stem cells Different types of cloning (Molecular, Reproductive & Therapeutic) Generation of mice with chimeric brains

What is a Stem Cell? Cells that: Have the capacity for self-renewal and ability to divide for indefinite periods in culture Can give rise to two or more specialized cells (Unrestricted potential for differentiation) http://www.patentbaristas.com/wp/wp-content/uploads/2007/04/stem-cells.jpg & Biology 1, 2008 Lecture

Embryonic Stem Cells Embryonic stem cells Primitive (undifferentiated) cells derived from a 5-day preimplantation embryo that have the potential to become a wide variety of specialized cell types Adult (Somatic) stem cells An undifferentiated cell found in a differentiated tissue that can: Renew itself Differentiate to give rise to all the specialized cell types of tissue from which it originated Scientists do not agree about whether or not adult stem cells may give rise to cell types other than those of the tissue from which they originate

Types of Stem Cells (Adult & Embryonic) Embryonic stem cell has unrestricted potential for differentiation Adult stem cells are lineage restricted ADD SLOW SLIDE http://www.nature.com/ncb/journal/v3/n9/fig_tab/ncb0901-e205_F1.html

Toti, Pluri and Multipotency of Stem Cells Pluripotent A stem cell able to give rise to all cell types that make up the body, but not “extra embryonic” tissues such as amnion, chorion and other placental components An embryonic stem cell is an example of a pluripotent cell Pluripotency can be demonstrated by: Ability of the progeny from a single cell to form derivatives of all three embryonic germ layers (Endo-, Ecto- and Mesoderm) Ability to generate a teratoma after injection into an immunosuppressed mouse

Toti, Pluri and Multipotency of Stem Cells Pluripotent A stem cell able to give rise to all cell types that make up the body, but not “extra embryonic” tissues such as amnion, chorion and other placental components An embryonic stem cell is an example of a pluripotent cell Pluripotency can be demonstrated by: Ability of the progeny from a single cell to form derivatives of all three embryonic germ layers (Endo-, Ecto- and Mesoderm) Ability to generate a teratoma after injection into an immunosuppressed mouse

Toti, Pluri and Multipotency of Stem Cells Pluripotent A stem cell able to give rise to all cell types that make up the body, but not “extra embryonic” tissues such as amnion, chorion and other placental components An embryonic stem cell is an example of a pluripotent cell Pluripotency can be demonstrated by: Ability of the progeny from a single cell to form derivatives of all three embryonic germ layers (Endo-, Ecto- and Mesoderm) Ability to generate a teratoma after injection into an immunosuppressed mouse http://www.biology-online.org/articles/embryonic_stem_cells_prospects/figures.html

Toti, Pluri and Multipotency of Stem Cells Pluripotent A stem cell able to give rise to all cell types that make up the body, but not “extra embryonic” tissues such as amnion, chorion and other placental components An embryonic stem cell is an example of a pluripotent cell Pluripotency can be demonstrated by: Ability of the progeny from a single cell to form derivatives of all three embryonic germ layers (Endo-, Ecto- and Mesoderm) Ability to generate a teratoma after injection into an immunosuppressed mouse http://erl.pathology.iupui.edu/C604/GENE826.HTM

Toti, Pluri and Multipotency of Stem Cells Totipotent A stem cell able to give rise to all the cell types that make up the body, plus all of the cell types that make up extra embryonic tissues, such as the placenta A zygote is an example of a totipotent cell Multipotent A stem cell able to develop into more than one type of cell in the body An adult (Somatic) stem cell can be an example of a multipotent cell can is underlined because this is a conflicting area of research, a true example of a multipotent stem cell would be a tissue specific stem cell Biology 150 Development Lecture Slides, Fall 2006 Caltech (Multipotent)

Toti, Pluri and Multipotency of Stem Cells (Multipotent) Biology 150, Development Lecture Slides, Fall 2006, Caltech

Toti, Pluri and Multipotency of Stem Cells (Multipotent) Biology 150, Development Lecture Slides, Fall 2006, Caltech

induced Pluripotent Stem Cells (iPSCs) Adult cells (e.g. Fibroblasts) reprogrammed to an embryonic stem cell-like state by forced expression of specific genes Expression of the transcription factors Oct4, Sox2, c-Myc & Klf4, under lentiviral and retroviral promoters causes reprogramming Mouse and human iPSCs have been generated iPSCs have been shown to have important characteristics of pluripotent stem cells: Expression of stem cell markers Ability to form tumors containing cells from all 3 germ layers Ability to contribute to many different tissues when injected into mouse embryos at an early stage in dvelopment

Lentiviral & Retroviral Generating iPSCs Transfect Lentiviral & Retroviral Vectors Containing:

Molecular, Reproductive and Therapeutic Cloning Cloning is an umbrella term traditionally used by scientists to describe different processes for duplicating biological material A basic understanding of the different types of cloning is paramount for taking an informed stance on current public policy issues Three types of cloning will be discussed in the upcoming slides: Recombinant DNA Technology or DNA/Molecular Cloning Reproductive Cloning Therapeutic Cloning

Molecular Cloning Refers to the transfer of a DNA fragment of interest from one organism to a self-replicating genetic element The most common self-replicating genetic element is extra- chromosomal DNA known as a plasmid Typically a five part process: A DNA fragment containing the gene of interest is isolated from chromosomal DNA using restriction enzymes The gene of interest is united with a plasmid that has been cut using the same restriction enzymes The gene of interest and plasmid are covalently linked using DNA ligase, to yield a recombinant DNA molecule The recombinant DNA is moved into a host cell, to allow for propagation using the host cell’s enzymatic machinery Host cells containing the recombinant DNA are selected for and identified Plasmid alternatives: YACS (1 MB), BACS (100-300 kb inserts), , cosmids (45 kb), plasmids (20 kb)

Molecular Cloning 1. 2. & 3. Adapted From: Alberts et al. Molecular Biology of the Cell, 2002, Figure 8-30, p 501

Molecular Cloning In this example, #5 is a selection method if you incorporate an antibiotic into the media, when antibiotic resistance is only coded for on the extrachromosomal DNA 4. 5. Adapted From: Alberts et al. Molecular Biology of the Cell, 2002, Figure 8-31, p 501

Molecular Cloning Uses of Molecular Cloning: Deconvolution of complex biological and biochemical processes by studying components in isolation Examples: Metabolic pathways, Translation, Transcription Genetic engineering of organisms Examples: Bioremediation, crop engineering, heterologous production of pharmaceuticals Identification of evolutionary relationships Examples: DNA sequencing of genomes and individual genes

Reproductive Cloning Refers to technology used to generate an animal that has the same nuclear DNA (Somatic cell nucleus) as another currently, or previously existing animal Can use a technique known as Somatic Cell Nuclear Transfer (SCNT) to perform reproductive cloning* Genetic material from the nucleus of an adult egg is transfered to an egg whose nucleus, and thus its genetic material, has been removed (enucleated egg) The reconstructed egg containing DNA from the donor cell is treated with chemicals or electric current to stimulate cell division Once the embryo reaches a suitable stage, it is transferred to the uterus of a female host, where it continues to grow until birth Please mention the fact that the animal created using SCNT is not a truly identical clone (Mitochondrial DNA) * = Initial stage of SCNT (enucleated egg and somatic cell nucleus combination) is the same in both reproductive and therapeutic cloning

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Reproductive Cloning Animals created using nuclear transfer are not truly identical cones of the donor animal! Only the clone’s chromosomal DNA is the same as the donor Some of the clone’s genetic material comes from mitochondria located in the cytoplasm of the enucleated egg Interestingly, acquired mutations in mitochondrial DNA are believed to play a large role in the aging process

Reproductive Cloning Uses of Reproductive Cloning: Production of animals with special qualities Examples: Models for human disease, drug producing animals Repopulation of endangered species Examples: Guars, Sumatran Tigers, Great Pandas

Celebrities of Science: Cloned Animals The sheep is dolly (first cloned animal) The cat in the middle of the top row was not a clone, but its DNA and enucleated egg were used to clone the kitten below it (Arrow pointing to cloned cat) to the right is the world’s first cloned mule bottom left are the worlds first knockout pigs, that lack a gene product that causes a massive immune reaction in humans (first step towards pigs as sources of human organs) Pigs on right are first pigs cloned calves are first cows cloned http://www.guardian.co.uk/gall/0,8542,627251,00.html

Are Reproductively Cloned Animals Healthy? Cloning of animals is expensive and inefficient (>90% of attempts fail to produce viable offspring) While pigs, sheep, cattle, cats, mice, rabbits, goats and a guar have been cloned successfully, attempts to clone monkeys, chickens, horses and dogs have been unproductive Animals show a multitude of health defects, including: Compromised immune function Increased tumor growth and miscellaneous disorders Growth to abnormally large sizes Genetic instability (Aberrant gene expression patterns) Premature and unexplainable death genetic instability actually does not stem from gene mutation, it is actually due to alteration of normal gene expression profiles (determined by analysis of 10,000 gene expression levels by micro-array) unexplainable death = autopsy did not reveal any specific or identifiable cause of death

Therapeutic Cloning Refers to combining a patient’s somatic cell nucleus and an enucleated egg, and harvesting of embryonic stem cells from the resulting embryo for treatment of disease or injuries Therapeutic Cloning has some similarity with Reproductive Cloning The first step in Therapeutic Cloning is identical to the first step in SCNT (For generation of a blastocyst embryo) Following generation of the embryo, stem cells are extracted after 5 days of cell division The stem cell extraction process destroys the embryo, which raises a variety of ethical concerns

Therapeutic Cloning Uses of Therapeutic Cloning: Organ transplants without generating an immune response Tissue transplants Repopulation of damaged/apoptotic cells in degenerative diseases Examples: Parkinson’s, Alzheimer’s, Diabetes

Discussion of Muotri et al. In lecture, the potential for generation of chimeric animals using reproductive cloning was mentioned In 2005, it was unknown whether human embryonic stem cells (hESCs) could differentiate into authentic human neurons in vivo Muotri et al. showed that hESCs implanted into the brain ventricles of embryonic mice can differentiate into functional neural lineages and generate mature, active neurons that integrate into the mouse brain In other words, they generated a mouse with a chimeric brain

Experimental Roadmap The authors first showed in vitro, that their hESCs could differentiate into neurons when given appropriate cues from surrounding cells The authors then wanted to test if their hESCs could differentiate into functional neurons in vivo hESC’s were infected with a lentiviral vector designed to express GFP hESC’s were injected into the lateral ventricle of embryos removed from pregnant mice After pups were born, they were sacrificed, and their brains were sectioned and examined for the presence of neural and stem cell specific markers, cell morphology, and neural activity for the in vitro work: the cells are at least neuron like (they just test for morphology and presence or absence of nerual and undifferentiated cell markers, respectively. note on the last bullet point, specific EGFP neurons were assayed electrophysiologically for activity

In Vitro Neruonal Differentiation of hESCs hESC = human embryonic stem cells NESTIN = a neuronal precursor marker (e.g. stem cell marker) MAP2(a+b) = microtubule associated protein, an immature neuronal marker the main point of this figure is that they used several different neural specific and stem cell specific markers and stains to show that the stem cells can indeed differentiate into neurons by cell co-culture with PA6 cells (cells positive for neuralmarkers, negative for stem cell specific markers) Muotri AR et al. PNAS (2005) 102, 51: 18644-8

Chimerism of hESC in the Mouse Developing Brain (Visualized by EGFP Fluorescence) Shows that hESC can differentiate into different cell types in vivo. Ki67 = proliferative markers (stem cell markers) S100-Beta = astrocyte marker (Glial cell marker) GST-Pi = oligodendrocyte marker TUJ-1 = neuronal marker b) 200 laser captured EGFP cells, when PCR’d were positive for only human specific TBP (TATA binding protein gene) sequence, whereas 200 non-EGFP cells were positive only for mouse TBP sequence (Shows no weird fusion events are going on) c & d) Shows neurons in different areas of the brain, illustrating that the hESCs migrated out of the ventricle and into many different host brain regions e) EGFP cells are negative for proliferative markers (ki67) f) EGFP cells express astrocyte specific markers g) EGFP cells express oligoendrocyte specific markers h) EGFP celsl express neuron specific markers Muotri AR et al. PNAS (2005) 102, 51: 18644-8

Results and Conclusions The Muotri et al. experiment produced several very interesting results: No teratomas or tumors were observed in any of the cloned mice No immunological rejection of the hESCs occurred < 0.1% of the total mouse brain cells were of human origin hESC derived neural cells showed widespread incorporation into the brain (hippocampus, thalamus, cerebellum, etc.), indicating transplanted cells migrated out from the ventricle and into various brain regions

Results and Conclusions (Contd) hESC derived neurons, oligodendrocytes and astrocytes were the same size, and exhibited the same connectivity patterns as the respective mouse cells, indicating that the hESC derived cells have the ability to adjust their size and connectivity in relation to adjacent cells hESC derived pyramidal neurons were fully functional in response to electrophysiological stimulation These two pieces of data point to conserved neural differentiation signals from mouse to man

Future Applications Extend the approach used in the paper to other tissues of the embryo, to evaluate the funcitonal differentiation of hESCs in specific fetal environments Introduction of hESC-derived neurons into the developing nervous system provides a new approach for the study of neurological disorders Mainly in cases where animal model does not recapitulate the neurodegenerative process observed in humans Also applicable in cases where affected individual dies before development of a functional nervous system

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Neural differentiation Reference

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next two slides are on noto-cord development they just could be used as an example of how turning on a single (or in some cases several) transcription factor(s) can have a huge effect on cell proliferation and differentiation

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