[Tuition Notes - Overmugged] Chapter 4 Stem Cells

Chapter 4: Stem Cells H2 Biology

TABLE OF CONTENTS Introduction01 Types of Stem Cells02 Applications of Stem Cells03 Bioethics04

Introduction For a multicellular organism to function properly, it must diversify cell types, control their production, and eliminate aged/damaged cells. Differentiation is a process by which a less specialised cell develops tissue-specific adaptation that enables it to become a more specialised cell type. Many differentiated cell types have limited life spans. Disease can also lead to their loss. Since differentiated cells do not usually divide, their supply must be replenished and this is achieved through stem cells.

Introduction All stem-cells have three unique features: 1. Stem cells are a group of undifferentiated and unspecialised cells. 2. Stem cells can undergo extensive proliferation and are capable of self-renewal through mitosis. 3. Stem cells can differentiate into various specialised cell types upon stimulation by the appropriate molecular signals.

Introduction Stem cells are a group of undifferentiated and unspecialised cells: • Specialised cells in tissues are differentiated and have tissue-specific structures that allow them to be adapted to perform unique roles. e.g. of specialised cells include red blood cells, muscle cells and nerve cells. • Stem cells, however, do not have any tissue-specific structures and cannot perform tissue specific functions.

Introduction Stem cells can undergo extensive proliferation and are capable of self-renewal through mitosis: There are 2 possible types of cell division a stem cell can undergo: i) Symmetrical Division – the stem cell divides to produce 2 daughter stem cells that have the same characteristics as parent cell – i.e, same developmental and differentiation potential as the parent cell. ii) Asymmetrical Division – the stem cell divides to produce 1 daughter stem cell that is identical to the parent cell and 1 progenitor daughter cell which is able to increase or renew population of specialized cells in a specific tissue.

Introduction Stem cells can differentiate into various specialized cell types upon stimulation by the appropriate molecular signals: i) These molecular signals switch some genes on and others off ii) E.g., Molecular Signals: Transcription factors, growth factors, hormones, cell-cell signals, properties of neighboring cells.

Types of Stem Cells In mammals, stem cells are commonly categorised according to their ability to differentiate/differentiation potential, i.e. totipotent, pluripotent or multipotent. Totipotent Stem Cells: Has the ability to differentiate into all of the cell types that make up an entire organism including extra-embryonic tissue such as placenta, which nourishes the embryo. Via multiple cellular divisions, totipotent stem cells have the ability to give rise to an entire organism. Totipotent cells are said to be also pluripotent and multipotent. E.g., Zygotic stem cell that is derived from a fertilised egg, zygote, as well as cells that are produced within the first 3 mitotic divisions (i.e. up to 8 cell stage) after the egg is fertilized.

Types of Stem Cells In mammals, stem cells are commonly categorised according to their ability to differentiate/differentiation potential, i.e. totipotent, pluripotent or multipotent. Pluripotent Stem Cells: Has the ability to differentiate into all of the cell types that make up an organism except extraembryonic tissue such as the placenta. Pluripotent stem cells alone cannot form the entire organism as extraembryonic tissues such as the placenta is required for foetal nourishment and development. Pluripotent cells are also said to be multipotent. E.g., Embryonic stem cells (ESCs) are derived from cells of inner cell mass of blastocyst (200-300 cells), which forms at about 4 to 5 days post fertilisation

Types of Stem Cells In mammals, stem cells are commonly categorised according to their ability to differentiate/differentiation potential, i.e. totipotent, pluripotent or multipotent. Multipotent Stem Cells: Has the ability to differentiate into several related specialised cell types but far fewer types than the pluripotent embryonic stem cell. The main purpose of multipotent adult stem cells is to produce specialized cells for growth and development, and for replacement of cells that are lost due to cell death and injury. E.g., Stem cells found in a juvenile or adult animal is usually multipotent adult stem cells. These stem cells are found in different tissues of an organism after embryonic development. They are found in small numbers in diverse tissues such as bone marrow, blood, cornea and retina, teeth, intestine, liver, muscles, nervous system and brain, pancreas and skin. Examples are blood/hematopoietic stem cells