VJC H2 Bio Chpt 09 Stem Cells Notes 2024

1 VICTORIA JUNIOR COLLEGE BIOLOGY DEPARTMENT YEAR ONE LECTURE 2024 (H2 9744 & H1 8876) CORE IDEA 1: THE CELL AND BIOMOLECULES OF LIFE Stem Cells Learning Outcomes: Candidates should be able to: (t) describe the unique features of stem cells, including zygotic stem cells, embryonic stem cells and blood stem cells (lymphoid and myeloid), correctly using the terms: i. totipotency (e.g. zygotic stem cells) ii. pluripotency (e.g. embryonic stem cells) iii. multipotency (e.g. lymphoid and myeloid stem cells) (u) explain the normal functions of stem cells in a living organism, including embryonic stem cells and blood stem cells (lymphoid and myeloid) (v) discuss the ethical implications of the application of stem cells in research and medical applications and how human induced pluripotent stem cells (iPSCs) overcome some of these issues (procedural details of how iPSCs are formed are not required). Note: LO (p) – (r) in H1 syllabus Contents: Section Page Learning Outcome 1. Features of Stem Cells 2-4 LO (t) (p) in H1 8876 (a) Introduction to stem cells 2 (b) Features of Stem Cells 2 2. Types of Stem Cells and their Normal Functions 4-8 LO (u) (q) in H1 8876 (a) Zygotic stem cells 4 (b) Embryonic stem cells (Pluripotent stem cells) 5 (c) Adult Stem Cell 6 3. Ethical Implications of Stem Cells in Research and Medical Applications 9-12 LO (v) (r) in H1 8876 (a) Potential Uses of Stem Cells 9 (b) What are ethical Implications? 11 (c) Ethical implications in stem cell research 11 (d) Induced Pluripotent Stem Cells (iPSCs) 12

2 1. FEATURES AND POTENCY OF STEM CELLS LO: Describe the unique features of stem cells, including zygotic stem cells, embryonic stem cells and blood stem cells (lymphoid and myeloid), correctly using the terms: i. totipotency (e.g. zygotic stem cells) ii. pluripotency (e.g. embryonic stem cells) iii. multipotency (e.g. lymphoid and myeloid stem cells) (a) Introduction to stem cells • A stem cell is a cell from an embryo, foetus or adult that is unspecialised, and has the ability to divide for long periods ( self- renewal) or, in the case of adult stem cells, throughout the life of the organism. • It can, under certain conditions, differentiate to give rise to the tissues and organs of the body. (b) Features of Stem Cells • Stem cells differ from other kinds of cells in the body. All stem cells, regardless of their source, have the following features: (i) They are capable of dividing (mitotic cell division) and renewing themselves for long periods (long term self-renewal). (ii) They are unspecialised and are able to give rise to specialised cell types under appropriate conditions (differentiation). (i) Long term self-renewal • Stem cells are capable of making identical copies of themselves via mitotic cell divisions for the lifetime of the organism. This characteristic is referred to as self-renewal. o Stem cells may replicate many times. When cells replicate themselves many times over, it is called proliferation. o A population of stem cells that proliferates for many months in the laboratory can yield millions of cells. If the resulting cells continue to be unspecialised, like the parent stem cells, the cells are said to be capable of long-term self-renewal. • Stem cells can either undergo symmetric division to give rise to 2 identical daughter cells, or they can undergo asymmetric division to form 2 different daughter cells, in which 1 remain as a stem cell and the other differentiates into a specialised cell. Fig. 2 Symmetric and asymmetric divisions. Fig. 1. Differentiation of stem cell

3 • When a stem cell divides by mitosis, one of two possible outcomes occur: o By symmetric division, both daughter cells retain the property of self-renewal to ensure that a pool of stem cells is constantly replenished in the adult organ. o By asymmetric division, one daughter cell remains a stem cell capable of self-renewal while the other daughter cell undergoes differentiation to become a specialized cell (such as a muscle cell, a red blood cell, or a brain cell). (ii) Differentiation • One of the fundamental properties of a stem cell is that it does not have any tissue-specific structures that allow it to perform specialised functions. o Tissue-specific structures refer to specific proteins found in certain types of cells that give them their specific functions. • Without tissue-specific structures, a stem cell cannot perform specialised functions such as to pump blood through the body (like a heart muscle cell), carry oxygen through the bloodstream (like a red blood cell), or relay electrochemical signals (like a nerve cell). • However, unspecialised stem cells can give rise to specialised cells, including heart muscle cells, blood cells, or nerve cells. • When unspecialised stem cells give rise to specialised cells, the process is called differentiation. • Once a cell becomes specialised, it has a very limited capacity to produce new cells. • These new cells and tissues are used to repair or replace damaged or diseased cells in the body. • Scientists are just beginning to understand the cell signalling that trigger stem cell differentiation. o The signals for differentiation include chemicals secreted by other cells, physical contact with neighbouring cells, and certain molecules in the environment. o These signals may lead to expression of specific genes to form tissue specific structures on the specialized cells. Fig. 3. Expression of different types of genes lead to differentiation of stem cell

4 (iii) Potency of Stem cells • Potency specifies the differentiation potential (the potential to differentiate into different cell types) of the stem cell. Stem cells can be classified under different levels of potency: Totipotency ability of the cell to differentiate into any cell type to form the whole organism. Pluripotency ability of the cell to differentiate into almost any cell type to form any organ or type of cell (except the placenta or other extra-embryonic membranes) Multipotency ability of the cell to give rise to a limited range of cells and tissues appropriate to their location. Unipotency ability of the cell to give rise to only one type of cells 2. TYPES OF STEM CELLS AND THEIR NORMAL FUNCTIONS LO: Explain the normal functions of stem cells in a living organism, including embryonic stem cells and blood stem cells (lymphoid and myeloid) (a) Zygotic stem cells • These are totipotent stem cells derived from the morula during the zygotic stage of development. They are also pluripotent and multipotent. • Totipotency refers to the ability of a cell to differentiate into any cell type to form a whole organism. Fig. 4. Development of the human embryo - Embryogenesis

5 (b) Embryonic stem cells (Pluripotent stem cells) • Embryonic stem cells are pluripotent stem cells derived the inner cell mass, which is part of the early (5 – 6 day) embryo called the blastocyst. They are also multipotent, but not totipotent. • Pluripotency refers to the ability of a cell to differentiate into almost any cell type to form any organ or type of cell. • Under normal conditions in the uterus, these cells would go on to form the entire foetus. The embryonic stem cells are unable to form the placenta or other extra-embryonic membranes (e.g. chorion). Thus, they cannot be used to form a whole organism. Fig. 5. Development of embryonic stem cells. (FYI) During a developmental process known as gastrulation, the inner cell mass can differentiate into three primary layers: ectoderm, endoderm, and mesoderm. Cells in each the three germ layers can eventually differentiate to form specialized cell types that make up the various organs or tissues of the foetus . • In the laboratory, cells from the inner cell mass can be removed from the blastocyst and cultured