University:
Amherst College
Course:
BIOL 220 | Developmental Biology
Academic year:

2024
Views:

256

Pages:

26
Author:

negatyvus3px

Evo-Devo Developmental Mechanisms of Evolutionary Change Modern Phylogenetic Tree • Lines of evidence Chordata Deuterostomia – total DNA sequences – regulatory genes – new morphology • Computer programs to analyze % Urbilaterian ancestor Ecdyso/ oa / ^ Protostomia Vertebrata Cephalochordata Urochordata Hemichordata Echinodcrmata Arthropoda Tardigrada Onycophora Nematoda Priapulida Annelida Brachiopoda Lophotrochozoa Anccstral protists ^^ N Fhoronida Sipunculida Mollusca Platyhelminthes Rotifera Ctenophora Cnidaria (A) Porifera Modern Phylogenetic Tree Chordata Deuterostomia • Kingdoms – Porifera – Cniderians and Ctenophores – Bilateria • 0, 2 and 3 tissue layers respectively /“\ Urbi laterian ^ ancestor Ecdysozoa Protostomia ^ Arthropoda Tardigrada Onycophora Nematoda Priapulida Annelida Lophotrochozoa Ancestral x s protists Vertebrata Cephalochordata Urochordata Hemichordata Echinodcrmata Brachiopoda Phoronida Sipunculida Mollusca Platyhelminthes Rotifera Ctenophora Cnidaria (A) Porifera Bilateria • Deuterstomes – chordates (e.g. vertebrates) – echinoderms and hemichordates • Protostomes – ecdysozoa • exoskeletons, molt (e.g. nematodes and arthropods) – lophotrochozoa • soft (e.g. molluscs, flatworms, segmented worms) What Have We Learned? • Behind developmental change there are – transcription factors • differential gene expression patterns for differentiation • and gross changes in pattern – signaling pathways • integration of changes – physiological – morphological – transcriptional • intercellular and extracellular • = classical morphogens and inducers Historical Overview • New insights from – developmental genetics (gene regulation) – cell biology of signaling pathways • Idea – – – – interacting networks changes in a few things give major changes in pattern in lab sometimes lethal in nature? Common Regulatory Genes • Urbilaterian ancestor should have had genes still found in deuterostomes and protostomes – Pax6 in vertebrates and eyeless in fruit flies • eye formation – Nkx 2-5 in mouse and tinman in fruit flies • heart formation – Otx, Emx in frogs and mice, otd, emx in fruit flies • anterior head and nerve structures Mouse Pax 6 expressed in Drosophila leg TABLE 23.1 Developmental regulatory genes conserved between protostomes and deuterostomes (Part 2 ) Gene Function Distribution Otx- 1 , Otx -2/ Otd, Emx- 1 , Emx-2/ ems Pax6 / eyeless; Eyes Anterior patterning, Drosophila, vertebrates absentleya Polycomb group Netrins, Split proteins, and their receptors RAS sine occulus/ Six3 sog/ chordin , dpp/ BMP4 tinman / Nkx 2-5 vnd , msh cephalization Anterior CNS/ eye regulation Controls Hox expression / cell differentiation Axon guidance Signal transduction Anterior CNS/ eye pattern formation Dorsal-ventral patterning, neurogenesis Heart / blood vascular system Neural tube patterning Drosophila, vertebrates Drosophila, vertebrates Drosophila, vertebrates Drosophila, vertebrates Drosophila, vertebrates Drosophila, Xenopus Drosophila, mouse Drosophila , vertebrates Source: After Erwin 1999. DEVELOPMENTAL BIOLOGY, Seventh Edition, Table 23.1 (Part 2 ) Sinauer Associates. Inc. © 2003 All rights reserved Homologies and Deep Homologies Homology and Analogy • Homology – similarity derives from common ancestry – vertebrate limb bones • Analogy – similarity from performing similar function – butterfly and bird wings • Genes or processes can also be either Human arm Hand , wrist, and fingers Radius Humerus Seal limb Bird wing Bat wing © 2000 Sinatter Associates, Inc . Deep Homology of Hox Genes • Anterior-posterior specification • Homologs – – – – all animals same order on chromosomes same order of expression 3' = anterior human HOXB4 can substitute in flies for deformed A-P: Comparison of Regulatory Transcription Factors Anterior Posterior Brain B2 B1 — B3 r-* \ S \ S2 S3 Ventral nerve cord Thorax Abdomen 1 2 3 1 2 3 4 5 6 7 8 9 Drosophila Vertebrates Spinal cord Hindbrain ( rl - r8 ) Forebrain n 3 r o . £ o n 3 3“ O M 2 n n 3 n r a o -ST 3 ar a> o . 3 "3 £i otd, Otx lab/ Hoxb 1 Scr/ Hoxb-5 abd - Al Hoxb-8 U - tailless pb/ Hoxb-2 Antp/ Hoxb-6 Abd - B/ Hoxb- 9 U eras, Etrix Dfd / Hoxb-4 Ubx/ Hoxb 7 Hoxb-3 - 0 3 © 2000 Sinauer Associates, Inc . How Differ Between Phyla? • Transcription factors – gene could change – could have different targets downstream – could be expressed in different pattern • within or • between body portions – could change in number Changing Regulatory Circuits • Genes have many inputs and outputs – Genes have cis-regulatory elements which bind various transcription factors – Genes encode proteins (transcription factors) • These are arranged in large, interacting networks • Mutations – in cis elements potentially put the gene under new types of control by upstream regulators – in coding regions potentially allow the gene product to control new genes downstream How Can Hox Gene Changes Affect Morphology? ( A ) Changes in Hox gene number ( B ) Broad changes of Hox expression ( C ) Subtle changes within Hox domains ( D ) Changes in regulation or function of downstream genes raiii NiiMiii5* ’ © 2000 Smaller Associates, Inc . Downstream Responses (D) • Fruit fly – 2 wings, 2 halteres • Butterfly – 4 wings • Hox (Ubx) same expression pattern (in T3) – some genes down-regulated in Drosophila are not regulated by Ubx in butterflies – therefore escape (or acquire) (altered) regulation Changes Within a Body Portion (C) • Distal-less controls P-D axis of appendages – legs from each thoracic segment – not expressed in abdomen (AbdA and Ubx block) • But in butterfly and moth larvae (caterpillars), dll is expressed in prolegs along abdomen – Down-regulation of Ubx and abdA in regions where dll then gets expressed nunm> Distal-less Expression Dll (blue) in butterfly larva Dll (red) Ubx/AbdA (green) Change in Gene Sequence • Crustaceans (multiple legs) – all thoracic segments look the same – all express Antp, Ubx, abdA which don’t repress dll in crustaceans • Different in insects (6 legs) – Ubx gained a region that can repress dll New repressor region Homeodomain Insects Fly Mosquito A V UbdA peptide Polyalanine A A WFQNRRMKLKKEIQAIKELNEQEKQAQAQ rVQGGHLDQ* ILHEQN* WFQNRRMKLKKEIQAIKELNEQEKQAQAQ IQGHPEH* WFQNRRMKLKKEIQAIKELNEQEKQAQAQ Butterfly Moth WFQNRRMKLKKEIQAIKELNEQEKQAQRQ QGHPEH* Beetle WFQNRRMKLKKEIQAIKELNEQEKQAQAQ 'if *'IQVDPN* WFQNRRMKLKKEIQAIKELNEQEKQAQAAKAGLFINLGGLIANSF... Springtail WFQNRRMKLKKEIQAIKELNEQEKQAQNAKQANATAVTPGATTDSTPTP... Shrimp STSTVSSNSNSNN... WFQNRRMKLKKEIQAIKELNEQE QAQAAKTA Spider Centipede WFQNRRMKLKKEIQAIKELNEQ KRITPSKLHSNC-SSPTGILVTMKKM QRDTLSTV* Onycophoran WFQNRRMKLKKE Q IK LNEQEKK . . DEVELOPMENTAL BIOLOGY Seventh Edition Figure 23.6 (Part 2) Seiauer Associates Inc © 2003 AS lights reserved Result - - Antp Ubx abdA precursor AbdB Hox gene duplications I l Antp Ubx Antp Ubx Ubx + abdA AbdB j l i Crustacean evolution Abdomen — Insect evolution / Abdomen Thorax Thorax Genital segments \ rA“v — abdA AbdB Mouth parts ^ r \ Genital segments r'Sf —— Mouth parts v © 2000 Smaller Associates, Inc . legs repressed Changes Between Body Segments (B) • If both Ubx and abdA are ex pressed in thorax segment, crustacean m akes “legs” • If neither, makes maxilliped (feeding appendage) – e.g. brine shrimp have no m axillipeds – lobsters have maxillipeds in T1 and T2 Ubx and AbdA in Crustaceans green=Ubx/abdA Head segments Order Thorax Genus w T 1 T2 T3 T4 15 Anostraca [ i f Branch iopoda Ancestor Notostraca Maxillopoda Malacostraca [ [ Anemia Triops \ Cyclopodia, Calanoida Mesocyclopa Lepiostraca [ I f Paranebalia Decapoda [ [ ] [ Wfn nm maxilliped / Homaris Perielimenes \* leg © 2000 Smaller Associates, Inc . Vertebral Patterns Controlled by Hox Genes • Hox pattern determines type of vertebrae – cervical-thoracic (ribbed) -lumbarsacral-caudal • KO Hoxc-8 in mouse – L1 forms rib like T12 Hox Patterns Shifted in Chick and Mouse Long neck before forelimb Cervical Chick Hox Hox Hox Hox 9 10 5 6 Thoracic Lumbar Sacral Coccygeal Vertebrae BOB Somites Vertebrae Mouse Cervical Hox Hox 5 6 0 Occipital Q Cervical Lumbar Thoracic Sacral Caudal Hox Hox 9 10 Q Thoracic 0 Lumbar Q Sacral Q Caudal © 2000 Sinauer Associates, Inc . Loss of Forelimb in Snakes • Evolve from lizards, lose legs – forelimb forms anterior to most anterior expression of Hoxc-6 – then Hoxc-6 and Hoxc8 determine T (rib) segments – in snakes no segment has only Hoxc-6, all ribs Changes in Hox Number (A) • Sponges have only a few Hox genes • More complex invertebrates have a single cluster of ~ 7 • Invertebrate deuterostomes have one similar cluster • Two duplications in vertebrates 4 clusters – accompanied by neural crest, new cell types and spinal cord and brain – affect segmentation of nervous system and somite derivatives (bone and muscle) – hypothesis: divergence allows more functions

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