Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chapter 18.4 Expression of Genotype
Document related concepts
no text concepts found
Transcript
LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 18 Regulation of Gene Expression Lectures by Erin Barley Kathleen Fitzpatrick © 2011 Pearson Education, Inc. Concept 18.4: A program of differential gene expression leads to the different cell types in a multicellular organism • During embryonic development, a fertilized egg gives rise to many different cell types • Cell types are organized successively into tissues, organs, organ systems, and the whole organism • Gene expression orchestrates the developmental programs of animals © 2011 Pearson Education, Inc. A Genetic Program for Embryonic Development • The transformation from zygote to adult results from cell division, cell differentiation, and morphogenesis © 2011 Pearson Education, Inc. Figure 18.16 1 mm (a) Fertilized eggs of a frog 2 mm (b) Newly hatched tadpole Figure 18.16a 1 mm (a) Fertilized eggs of a frog Figure 18.16b 2 mm (b) Newly hatched tadpole • Cell differentiation is the process by which cells become specialized in structure and function • The physical processes that give an organism its shape constitute morphogenesis • Differential gene expression results from genes being regulated differently in each cell type • Materials in the egg can set up gene regulation that is carried out as cells divide © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. Figure 18.17 (a) Cytoplasmic determinants in the egg (b) Induction by nearby cells Unfertilized egg Sperm Fertilization Early embryo (32 cells) Nucleus Molecules of two different cytoplasmic determinants NUCLEUS Zygote (fertilized egg) Mitotic cell division Two-celled embryo Signal transduction pathway Signal receptor Signaling molecule (inducer) Figure 18.17a (a) Cytoplasmic determinants in the egg Unfertilized egg Sperm Fertilization Zygote (fertilized egg) Mitotic cell division Two-celled embryo Nucleus Molecules of two different cytoplasmic determinants • The other important source of developmental information is the environment around the cell, especially signals from nearby embryonic cells • In the process called induction, signal molecules from embryonic cells cause transcriptional changes in nearby target cells • Thus, interactions between cells induce differentiation of specialized cell types Animation: Cell Signaling © 2011 Pearson Education, Inc. Figure 18.17b (b) Induction by nearby cells Early embryo (32 cells) NUCLEUS Signal transduction pathway Signal receptor Signaling molecule (inducer) Sequential Regulation of Gene Expression During Cellular Differentiation • Determination commits a cell to its final fate • Determination precedes differentiation • Cell differentiation is marked by the production of tissue-specific proteins © 2011 Pearson Education, Inc. • 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 © 2011 Pearson Education, Inc. Figure 18.18-1 Nucleus Embryonic precursor cell Master regulatory gene myoD Other muscle-specific genes DNA OFF OFF Figure 18.18-2 Nucleus Embryonic precursor cell Myoblast (determined) Master regulatory gene myoD Other muscle-specific genes DNA OFF OFF mRNA OFF MyoD protein (transcription factor) Figure 18.18-3 Nucleus Embryonic precursor cell Master regulatory gene myoD Other muscle-specific genes DNA Myoblast (determined) OFF OFF mRNA OFF MyoD protein (transcription factor) mRNA MyoD Part of a muscle fiber (fully differentiated cell) mRNA Another transcription factor mRNA mRNA Myosin, other muscle proteins, and cell cycle– blocking proteins Pattern Formation: Setting Up the Body Plan • Pattern formation is the development of a spatial organization of tissues and organs • In animals, pattern formation begins with the establishment of the major axes • Positional information, the molecular cues that control pattern formation, tells a cell its location relative to the body axes and to neighboring cells © 2011 Pearson Education, Inc. • Pattern formation has been extensively studied in the fruit fly Drosophila melanogaster • Combining anatomical, genetic, and biochemical approaches, researchers have discovered developmental principles common to many other species, including humans © 2011 Pearson Education, Inc. The Life Cycle of Drosophila • In Drosophila, cytoplasmic determinants in the unfertilized egg determine the axes before fertilization • After fertilization, the embryo develops into a segmented larva with three larval stages © 2011 Pearson Education, Inc. Figure 18.19 Head Thorax Abdomen 1 Egg developing within ovarian follicle Follicle cell Nucleus Egg 0.5 mm Nurse cell Dorsal BODY AXES Anterior Left Right Posterior 2 Unfertilized egg Depleted nurse cells Ventral (a) Adult Egg shell Fertilization Laying of egg 3 Fertilized egg Embryonic development 4 Segmented embryo 0.1 mm Body segments 5 Larval stage (b) Development from egg to larva Hatching Figure 18.19a Head Thorax Abdomen 0.5 mm Dorsal BODY AXES Anterior Left Ventral (a) Adult Right Posterior Figure 18.19b Follicle cell 1 Egg Nucleus developing within ovarian follicle Egg Nurse cell 2 Unfertilized egg Depleted nurse cells Egg shell Fertilization Laying of egg 3 Fertilized egg Embryonic development 4 Segmented embryo Body segments 0.1 mm Hatching 5 Larval stage (b) Development from egg to larva Genetic Analysis of Early Development: Scientific Inquiry • Edward B. Lewis, Christiane Nüsslein-Volhard, and Eric Wieschaus won a Nobel Prize in 1995 for decoding pattern formation in Drosophila • Lewis discovered the homeotic genes, which control pattern formation in late embryo, larva, and adult stages © 2011 Pearson Education, Inc. Figure 18.20 Eye Leg Antenna Wild type Mutant Figure 18.20a Eye Antenna Wild type Figure 18.20b Leg Mutant • Nüsslein-Volhard and Wieschaus studied segment formation • They created mutants, conducted breeding experiments, and looked for corresponding genes • Many of the identified mutations were embryonic lethals, causing death during embryogenesis • They found 120 genes essential for normal segmentation © 2011 Pearson Education, Inc. Axis Establishment • Maternal effect genes encode for cytoplasmic determinants that initially establish the axes of the body of Drosophila • These maternal effect genes are also called eggpolarity genes because they control orientation of the egg and consequently the fly Animation: Development of Head-Tail Axis in Fruit Flies © 2011 Pearson Education, Inc. Bicoid: A Morphogen Determining Head Structures • One maternal effect gene, the bicoid gene, affects the front half of the body • An embryo whose mother has no functional bicoid gene lacks the front half of its body and has duplicate posterior structures at both ends © 2011 Pearson Education, Inc. Figure 18.21 Head Tail A8 T1 T2 T3 A1 A2 A3 A4 A5 A6 Wild-type larva A7 250 m Tail Tail A8 A8 A7 A6 A7 Mutant larva (bicoid) Figure 18.21a Head Tail A8 T1 T2 T3 A1 A2 A3 A4 A5 Wild-type larva A6 A7 250 m Figure 18.21b Tail Tail A8 A8 A7 A6 A7 Mutant larva (bicoid) • This phenotype suggests that the product of the mother’s bicoid gene is concentrated at the future anterior end • This hypothesis is an example of the morphogen gradient hypothesis, in which gradients of substances called morphogens establish an embryo’s axes and other features © 2011 Pearson Education, Inc. Figure 18.22 100 m RESULTS Anterior end Fertilization, translation of bicoid mRNA Bicoid mRNA in mature unfertilized egg Bicoid mRNA in mature unfertilized egg Bicoid protein in early embryo Bicoid protein in early embryo Figure 18.22a Bicoid mRNA in mature unfertilized egg Figure 18.22b 100 m Anterior end Bicoid protein in early embryo • The bicoid research is important for three reasons – It identified a specific protein required for some early steps in pattern formation – It increased understanding of the mother’s role in embryo development – It demonstrated a key developmental principle that a gradient of molecules can determine polarity and position in the embryo © 2011 Pearson Education, Inc.
