The Genetic Basis of Development

1. The Genetic Basis of Development 海洋大學生物科技研究所 何國牟

4. Comparative studies • help explain how the evolution of development leads to morphological diversity • Biologists in the field of evolutionary developmental biology, or “evo-devo,” as it is often called • Compare developmental processes of different multicellular organisms

5. Adult fruit fly Fruit fly embryo (10 hours) Fly chromosome Mouse chromosomes Mouse embryo (12 days) Adult mouse • An identical or very similar nucleotide sequence • Has been discovered in the homeotic genes of both vertebrates and invertebrates • Molecular analysis of the homeotic genes in Drosophila • Has shown that they all include a sequence called a homeobox

6. Comparison of Animal and Plant Development • In both plants and animals • Development relies on a cascade of transcriptional regulators turning genes on or off in a finely tuned series • But the genes that direct analogous developmental processes • Differ considerably in sequence in plants and animals, as a result of their remote ancestry

7. Model organisms • Researchers • Use mutations to deduce developmental pathways • Have applied the concepts and tools of molecular genetics to the study of developmental biology

8. DROSOPHILA MELANOGASTER (FRUIT FLY) CAENORHABDITIS ELEGANS (NEMATODE) 0.25 mm • When the primary research goal is to understand broad biological principles • The organism chosen for study is called a model organism

9. ARABIDOPSIS THAMANA (COMMON WALL CRESS) MUS MUSCULUS (MOUSE) DANIO RERIO (ZEBRAFISH) Good model systems?

10. Concept : Embryonic development involves cell division, cell differentiation, and morphogenesis • In the embryonic development of most organisms • A single-celled zygote gives rise to cells of many different types, each with a different structure and corresponding function

11. (b) Tadpole hatching from egg (a) Fertilized eggs of a frog • The transformation from a zygote into an organism • Results from three interrelated processes: cell division, cell differentiation, and morphogenesis

12. Through a succession of mitotic cell divisions • The zygote gives rise to a large number of cells • In cell differentiation • Cells become specialized in structure and function • Morphogenesis encompasses the processes • That give shape to the organism and its various parts

13. Concept :Different cell types result from differential gene expression in cells with the same DNA • Differences between cells in a multicellular organism • Evidence for Genomic Equivalence • Come almost entirely from differences in gene expression, not from differences in the cells’ genomes

14. Transcriptional Regulation of Gene Expression During Development • Cell determination • Precedes differentiation and involves the expression of genes for tissue-specific proteins • Tissue-specific proteins (organogenesis) • Enable differentiated cells to carry out their specific tasks

15. Cytoplasmic Determinants and Cell-Cell Signals in Cell Differentiation • Cytoplasmic determinants in the cytoplasm of the unfertilized egg • Regulate the expression of genes in the zygote that affect the developmental fate of embryonic cells Unfertilized egg cell Molecules of another cyto- plasmic deter- minant Sperm Sperm Molecules of a a cytoplasmic determinant Fertilization Nucleus Zygote (fertilized egg) Mitotic cell division Two-celled embryo (a) Cytoplasmic determinants in the egg.The unfertilized egg cell has molecules in its cytoplasm, encoded by the mother’s genes, that influence development. Many of these cytoplasmic determinants, like the two shown here, are unevenly distributed in the egg. After fertilization and mitotic division, the cell nuclei of the embryo are exposed to different sets of cytoplasmic determinants and, as a result, express different genes.

16. (b) Induction by nearby cells. The cells at the bottom of the early embryo depicted here are releasing chemicals that signal nearby cells to change their gene expression. • In the process called induction • Signal molecules from embryonic cells cause transcriptional changes in nearby target cells Early embryo (32 cells) Signal transduction pathway NUCLEUS Signal receptor Signal molecule (inducer)

17. 2 1 Nucleus Master control gene myoD Other muscle-specific genes DNA OFF OFF Embryonicprecursor cell Determination. Signals from othercells lead to activation of a masterregulatory gene called myoD, andthe cell makes MyoD protein, atranscription factor. The cell, nowcalled a myoblast, is irreversiblycommitted to becoming a skeletalmuscle cell. OFF mRNA MyoD protein(transcriptionfactor) Myoblast (determined) Differentiation. MyoD protein stimulatesthe myoD gene further, and activatesgenes encoding other muscle-specifictranscription factors, which in turn activate genes for muscle proteins. MyoD also turns on genes that block the cell cycle, thus stopping cell division. The nondividing myoblasts fuse to become mature multinucleate muscle cells, alsocalled muscle fibers. mRNA mRNA mRNA mRNA Myosin, othermuscle proteins,and cell-cycleblocking proteins MyoD Anothertranscriptionfactor Muscle cell(fully differentiated) Determination and differentiation of muscle cells

18. Eye Antenna Leg Wild type Mutant Genetic Analysis of Early Development: Scientific Inquiry • The study of developmental mutants • Laid the groundwork for understanding the mechanisms of development Figure 21.13

19. Follicle cell Nucleus Egg cell developing within ovarian follicle Egg cell Nurse cell Fertilization Laying of egg Fertilized egg Egg shell Nucleus Embryo Multinucleate single cell 3 4 6 7 1 5 2 Early blastoderm Plasma membrane formation Yolk Late blastoderm Cells of embryo Body segments Segmented embryo 0.1 mm Hatching Larval stages (3) Pupa Metamorphosis Head Abdomen Thorax Adult fly 0.5 mm Dorsal Anterior BODY AXES Posterior Figure 21.12 Ventral • Key developmental events in the life cycle of Drosophila

20. Zygote 0 First cell division Germ line (future gametes) Outer skin, nervous system Nervous system, outer skin, mus- culature Musculature, gonads Time after fertilization (hours) Musculature 10 Hatching Intestine Intestine Eggs Vulva ANTERIOR POSTERIOR 1.2 mm C. elegans: The Role of Cell Signaling • The complete cell lineage • Of each cell in the nematode roundworm C. elegans is known Figure 21.15

21. 2 Posterior 1 Anterior Signal protein 4 3 Receptor EMBRYO 3 4 Signal Anterior daughter cell of 3 Posterior daughter cell of 3 Will go on to form muscle and gonads Will go on to form adult intestine (a) Induction of the intestinal precursor cell at the four-cell stage. Induction • As early as the four-cell stage in C. elegans • Cell signaling helps direct daughter cells down the appropriate pathways, a process called induction Figure 21.16a

22. Epidermis Signal protein Gonad Anchor cell Vulval precursor cells Outer vulva ADULT Inner vulva Epidermis Figure 21.16b (b) Induction of vulval cell types during larval development. • Induction is also critical later in nematode development • As the embryo passes through three larval stages prior to becoming an adult • An inducing signal produced by one cell in the embryo • Can initiate a chain of inductions that results in the formation of a particular organ

23. 2 µm Figure 21.17 Programmed Cell Death (Apoptosis) • In apoptosis • Cell signaling is involved in programmed cell death

25. Interdigital tissue 1 mm Figure 21.19 • In vertebrates • Apoptosis is essential for normal morphogenesis of hands and feet in humans and paws in other animals

26. Human disease models • A.T. (87%) • G.C. (13%) ENU mutations Mutant proteins • - Missense (64%) • Splice site (26%) • Nonsense (10%) Mutant phenotypes Immunity & Hematopoiesis Musculoskeletal Dental Human disease models Cardiovascular Endocrine Metabolism Cancer & Development Neurological & Sensory

27. What is comparative genomics? • Comparative genomics - the study that compare two or more genomes to discover the similarities and differences

28. What is genome and genomics? • Genome : first used by H. Winkler in 1920, was created by elision of the words GENes and chromosONEs, and signifies: the complete set of chromosomes and their genes • Genomics : proposed by Thomas H. Roderick in 1986 for a new discipline and for a new journal Peter Goodfellow (1997) defines: Genomics as the study of genome

29. Structural and functional genomics • Structural genomics - mapping and sequencing the genome • Functional genomics Peter Goodfellow (1997) defines: Functional genomics is the attachment of information about function to knowledge of DNA sequence; paradoxically, genetics is a major tool for functional genomics

30. Comparative genomics Structural genomics • Genetic mapping • Cytogenetic mapping • Physical mapping • DNA sequencing • Biological databases Functional genomics • DNA microarray • Evolutionary analysis • Mouse genetics • Studying Human variation • Finding disease genes

31. Human genome project First formally proposed in 1985-1986, but the formal initiation of the HGP was in US on Oct 1, 1990. A draft of the human genome sequence was finished in 2001 and published in Nature & Science (IHGSC, 2001; Venter et al., 2001). Completed sequences were finished on April 25, 2003, exactly 50 years after the landmark paper of Watson & Crick on the structure of DNA The primary aim of this project is to determine the nucleotide sequence of the entire human nuclear genome.

32. Genome sizes (Adapted from Green & Waterston) Human & mouse genome ~3,000,000,000 bp (H.s.-IHGSC, 2001; Venter et al.,2001) Fruit Fly genome (D.m.) ~160,000,000 bp (Adams et al., 2000) Nematode genome (C.s) ~100,000,000 bp (CESC, 1998) Yeast genome ~15,000,000 bp (Goffeau et al., 1996) E. Coli genome ~5,000,000 bp