Presentation on theme: "Developmental Genetics"— Presentation transcript:
1 Developmental Genetics How Selective Gene Expression Determines the Developmental Fate of Specific Cells-Chapter 16, pages Chapter 21, pages
2 DefinitionsDetermination = process of commitment of a cell to a particular fateDifferentiation = changes in cell shape and physiology associated with production of final cell typeDevelopmental field = a set of cells that together interact to form a developing structureMorphogen = substance that specifies cell identity as a function of its concentration
3 Gene ExpressionDifferentiation depends upon the expression of a specific subset of genes.Gene expression can be controlled at any level between transcription and activation of the protein product.
4 Control Points for Gene Expression in Eukaryotes DNAtranscriptionTranscriptional ControlRNAPost-Transcriptional ControlprocessingTranslational ControltranslationProteinPost-Translational Control
5 Developmental “Decisions” Binary decisionsSeparation of germ line from somaEstablishment of gender*Choosing one fate from multiple optionsAxis formation*Segmentation*Germ layer formationOrganogenesis
6 Ratio of Sex Chromosomes to Autosomes (X:A) A Cascade of Events Affects Expression of Sex-specific Traits in DrosophilaBalance of ActiveTranscription FactorsPresence or AbsenceOf Sxl ProteinSxl Protein Regulates Splicing of its own mRNASxl Protein Regulates Splicing of tra mRNATra Proteins Regulate Splicing of fru mRNAFru Proteins Control Sex-Specific BehaviorTra Protein Regulates Splicing of Dsx mRNADsx Proteins Activateor Repress Transcriptionof Sex-Specific Genes
8 Transcriptional Regulation As a Result of X:Autosome Ratio NUM:NUM dimers activate transcription of Sxl gene
9 Post-transcriptional Regulation of Sxl Protein Production
10 Post-transcriptional Regulation of Tra and Fru Protein Production Sxl Protein Regulates Splicing of tra mRNA
11 Post-transcriptional Regulation: Alternative Splicing of Tra pre-mRNA Sxl protein may block upstream 3’ splice site
12 Post-transcriptional Regulation of Fru Protein Production Sxl Protein Regulates Splicing of tra mRNATra Proteins Regulate Splicing of fru mRNAFru Proteins Control Sex-Specific Behavior as Transcriptional RegulatorsNervous system processing of information from antennaeCourtship Song Abdomen Movement
13 Post-Transcriptional Regulation of DSX Protein Production Tra Protein Regulates Splicing of Dsx mRNADsx Proteins Activateor Repress Transcriptionof Sex-Specific Genes
14 Summary of Protein Activities NUM:NUM HomodimersNUM = numeratorSxl = Sex LethalTra = TransformerDsx = Double sexFru = FruitlessTranscriptional ActivatorSplicing RegulatorSplicing RegulatorDsx-M = Transcriptional Repressor Dsx-F = Transcriptional ActivatorFru-M and Fru-F areTranscriptional Regulators
15 Applying Your Knowledge Transcriptional ControlPost-Transcriptional ControlWhich type of control is exerted toProduce Tra Protein in Female Fruit Flies?Keep the Sxl protein from being expressed in male fruit flies early in development?Produce male and female-specific versions of the Fru gene product?
16 Applying Your Knowledge Splicing RegulatorTranscription FactorWhich term best describes the action ofNUM:NUM homodimers?Tra protein?Sxl protein?
17 Development of Anterior-Posterior Body Axis in Drosophila
18 A Hierarchy of Gene Interactions Determines Segment Number and Identity Along the A-P Axis Egg-polarity genesEgg-polarity genes (Maternal)Gap genesHomeotic genesPair-rule genesZygotic genesSegment-polarity genes
20 Action of Egg-polarity Genes Bicoid and Nanos antpostTranscriptional activator of anterior-specific genes, including hunchback, a gene needed of head and thorax developmentNanospostantTranslational repressor of hunchback, preventing expression of anterior structures
21 Genes Influencing Segmentation along the A-P Axis
22 Action of Gap GenesGap gene products divide the body into broad zones for the formation of anteriorposterior segments.Mutations show a loss of specific adjacent segments from region where gap gene is transcribed.Krupple and Knirps encode transcription factors.
23 Action of Pair-Rule Genes Pair-rule genes divide the body into a series of two-segment units.Pair-rule gene mutations remove alternate segments, either odd or even.Alternating activity of the genes Ftz (stained gray) and Eve (stained brown) is shown.Fushi tarazu (Ftz) and Even-skipped (Eve) encode transcription factors.
24 Action of Segment-Polarity Genes Segment-polarity genes regulate the organization of subsets of cells within a segment.Segment-polarity mutations cause part of a segment to be deleted and replaced by a mirror image of a different part of the next segment.Engrailed (EN) encodes a transcription factor.Patched encodes a transmembrane protein.
25 Action of Homeotic Genes Homeotic genes influence the identity of specific segments, controlling the development of segment-specific structures.Mutations cause structures from one segment to develop in another.T3 develops as T2 in the Postbithorax mutation.Pbx is a cis-regulatory region controlling the action of Ubx on T3 development.
26 Clusters of Homeotic Genes Affects Structures Developing inGenesAntennapedia ComplexHead and Anterior Thoracic RegionsAntennapedia ScrBithorax ComplexAbdomen and Posterior Thoracic RegionsUltrabithorax Abdominal-A Abdominal-B
27 Order of homeotic genes is colinear with the order ScrAntpUbxAbd-BOrder of homeotic genes is colinear with the orderof expression along the anterior-posterior axis.
28 Evolutionary Conservation of Homeotic Gene Regions Homeotic genes share a 180 base pair region called the homeobox.The homeobox encodes a DNA-binding domain (homeodomain) with a helix-turn-helix structural motif.Homeobox regions are found in clustered genes in the mouse.
29 Homeotic gene mutation resulting in posterior location for anterior structures,i.e. ribs from lumbar vertebrae.
30 Applying Your Knowledge Splicing RegulatorTranscription FactorTranslation RegulatorWhich term best describes the action ofThe maternal product of the Nos gene?The zygotic product of the Even-skipped gene?The protein products of homeotic genes?