Cellular Differentiation - Mol & Cell Biology MD105 PDF

Cell Differentiation Control Mol & Cell Biology MD105 Prof A. Stephanou  Objectives: Understand the process of cellular differentiation To know what determines and controls the differentiation process Understand Factors that determine haemopoiesis and muscle cell differe...

Cell Differentiation Control Mol & Cell Biology MD105 Prof A. Stephanou  Objectives: Understand the process of cellular differentiation To know what determines and controls the differentiation process Understand Factors that determine haemopoiesis and muscle cell differentiation  Cell Differentiation The process by which cells or parts of an organism become different from one and other and also from their previous state. The process by which cells or tissues of an organism acquire the ability to perform their special functions. A Genetic Program for Embryonic Development The transformation from zygote to adult results from cell division, cell differentiation, and morphogenesis  Cellular Differentiation 1 mm 2 mm (a) Fertilized eggs of a frog (b) Newly hatched tadpole  Cellular Differentiation so cells can interact with each other and with their environment this interaction turns specific signaling paths ON or OFF these pathways become important for mediating proliferation, differentiation and apoptosis all three are crucial to development Differentiation: Stem cells so fertilization of the egg takes place in the oviduct the fertilizes zygote travels to the uterus for implantation along the way – the zygote begins to divide (mitosis) 2-cell, 4-cell, 8-cell embryonic stages etc…. the embryo reaches a stage called the morula = ball of small cells (embryo has not enlargened) by the end of the first week the second embryonic stage – the blastocyst - forms  Differentiation: Embryonic Stem cells the blastocyst is a hollow ball of cells containing an outer rings of progenitor cells = trophoblast and an inner mass of cells at one end of the embryo = inner cell mass it is these ICM cells that are the source for the derivation of embryonic stem (ES) cells  Cytoplasmic Determinants and Inductive Signals An egg’s cytoplasm contains RNA, proteins, and other substances that are distributed unevenly in the unfertilized egg Cytoplasmic determinants are maternal substances in the egg that influence early development As the zygote divides by mitosis, cells contain different cytoplasmic determinants, which lead to different gene expression  Cellular interactions in development: Induction interactions between the cells of the germ layers influence the fate of the stem cells within these layers can affect their differentiation paths induction = mechanism where one cell population influences the development of neighbouring cells – e.g. mesoderm induces the overlying ectoderm to form neural tissue embryonic development is a series of inductive events – binary – have a choice between one fate or another (presence of one signal – development down one path, absence of signal – development down another path – gradient – multiple fates may result – dependent upon the level or threshold of the signaling molecule (these signaling molecules are called morphogens) – relay – a signal induces a cascade which determines the fate of cells in proximity – these cells than produce additional signals which affect the fate of their neighbours  (b) Induction by nearby cells Early embryo (a) Cellular Transduction Pathways (32 cells) NUCLEUS Signal transduction pathway Signal receptor Signaling molecule (inducer) 1 Genome 1 Cell >200 Cell Types Cell Type Specificity Cell uniqueness is determined by which portions of the genome are expressed Transcription mRNA Protein expression Unique function of cell Where does it begin differentiation?  How is this accomplished? Selective gene transcription In any given cell, only the genes necessary for basic metabolism and that cell’s special functions are active. muscle cells - actin, myosin pancreatic acinar cells - digestive enzymes neurons - tubulin, neurotransmitters Control of cell differentiation – Genomic level – Transcription/post – Transcription levels – Extracellular factors  Micro-RNAs Control of cell differentiation 1 2 3 One strand 4 The bound 5 Dicer cuts Prevents gene The micro- dsRNA into of miRNA miRNA can base- RNA (miRNA) short segments associates with pair with any expresion precursor folds protein. complementary back on itself mRNA Chromatin changes Transcription RNA processing mRNA Translation Protein degradation Protein processing complex and degradation Dicer Degradation of mRNA OR miRNA Target mRNA Hydrogen Blockage of translation bond Transcription Factors  Differentiation of blood cells Hematopoiesis: (hemat = blood, poien = to make), the blood of vertebrates contains many different types of cells with distinct functions. All mature blood cells are short lived and must be replaced continuously from stem cells. In humans, the hematopoietic stem cells produce billions of blood cells each hour to replace the aging cells. Hemangioblast: an embryonic stem cell that gives rise to blood vessels and universal blood stem cells. Universal blood stem cells: form myeloid and lymphoid precursors. Myeloid precursors form several types of differentiated cells including red blood cells which transport O2 and CO2. They also make platelets for coagulation of blood, and monocytes / granulocytes that serve a protective role. Lymphoid precursors make lymphocytes that are involved in B and T cell immunity. Hematopoiesis.  Hematopoiesis Regulated by cytokines and growth factors  Genetic control of muscle cell differentiation Myoblasts produce muscle-specific proteins and form skeletal muscle cells MyoD is one of several “master regulatory genes” that produce proteins that commit the cell to becoming skeletal muscle The MyoD protein is a transcription factor that binds to enhancers of various target genes Myo D is a master regulator of muscle cell differentiation. If you inject Myo D DNA into a fibroblast it turns into a muscle cell. It is a member of a myogenic family (Myo D, myogenin, myf-5, and MRF-4). These are transcription factors (basic helix-loop-helix) and activate genes that are needed for muscle cell differentiation.  Nucleus Master regulatory gene myoD Other muscle-specific genes DNA Embryonic precursor cell OFF OFF mRNA OFF MyoD protein Myoblast (transcription (determined) factor) mRNA mRNA mRNA mRNA Myosin, other muscle proteins, MyoD Another and cell cycle– Part of a muscle fiber transcription blocking proteins (fully differentiated cell) factor  Terminal Differentiation “A cell has progressed down a particular lineage to a point, that the cell cannot progress anymore” Examples: Neurons, Skeletal Muscle Cells, Keratinocyte Exclusion: Fibrocytes 1. produce extracellular matrix 2. express the hematopoietic cell surface markers (CD34+ & CD45+) and fibroblast marker (collagen) 3. migrate to wound sites (wound healing)  Cell Properties 1. Irreversible characteristic: e.g., mature keratinocyte -- cessation of DNA synthesis 2. Reversible characteristic: e.g., hepatocyte -- re-induction of albumin synthesis Reversible Stem cells Progenitor cells Differentiated cells irreversible irreversible Differentiation Process  Markers of Differentiation 1. Markers of the mature phenotype representing terminal differentiation 2. Examples: -- Epithelium: cytokeratins -- Astrocytes: glial fibrillary acidic protein -- Erythrocyte: hemoglobin -- Hepatocyte: albumin -- Keratinocytes: transglutaminase or involucrin -- Oligodendrocyte: glycerol phosphate dehydrogenase 3. Looking for the expression of differentiation marker proteins: -- RT-PCR -- Microarray  Regulation of Differentiation (4) (1) (3) (5) (2)  Induction of Differentiation 1. Heterotypic Cell Interaction: Cell Interaction --is responsible for initiating and promoting differentiation --mutual interaction between cells originating different germ layers promotes differentiation --Reciprocal Paracrine Interaction: for epidermal maturation Keratinocyte Fibroblasts Diseases associated with Differentiation: Pulmonary fibrosis Myofibroblast Fibroblast Deposit of collagen in lung Differentiation & Diseases  Differentiation & Malignancy 1. Cancer: a failure of cells to differentiate normally 2. With increasing progressing of cancer: -- histology of a cancer indicates poorer differentiation 3. Patients with poorly differentiated tumors: -- have a lower survival rate than patients with differentiated tumors 4. Many tumors grown in tissue culture can be induced to differentiate (phorbol myristate acetate) The clinical use of retinoids in cancer therapies and chemoprevention The nuclear receptor superfamily Mangelsdorf et al, (1995) Cell 83:835  The clinical use of retinoids in cancer therapies and chemoprevention Trade name Retinoid Activity Some Therapeutic applications Tretinoin ATRA Pan-RAR Promyelocytic leukemia, Leukoplakia (prevention), Actinic keratosis (prevention) Alitretinoin, 9-cis retinoic acid Pan-RAR Kaposi's sarcoma Panretin Pan-RXR Breast cancer Isotretinoin 13-cis retinoic acid Pan-RAR Oral leukoplakia, Skin cancer, Head and neck cancer (in combination with IFN), Neuroblastoma Bexarotene LDG1069 RXR Cutaneous T-cell lymphoma (stage IA- IB, IIA), NSCLC Fenretidine 4- HPR RAR Breast cancer 4-hydroxy Leukoplakia -phenylretinamide Ovarian cancer Acyclic retinoid polyprenoic acid RAR, RXR, Hepatocellular carcinoma (prevention) PPAR activities Abbreviations: ATRA, all trans retinoic acid4-HRP, 4-hydroxy-phenylretinamide; APL, promyelocytic leukemia; IFN, interferon; PPAR, peroxisome proliferator activated receptor; RAR, retinoic acid receptor; RXR, retinoid X receptor. (Adapted from:Altucci and Gronemeyer, Nat. Rev Cancer, 2001 1:181)