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Axis Specification I. Nusslein-Volhard, 2004 The Maternal-Effect Mutants (also found the D/V Group)

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Presentation on theme: "Axis Specification I. Nusslein-Volhard, 2004 The Maternal-Effect Mutants (also found the D/V Group)"— Presentation transcript:

1 Axis Specification I

2 Nusslein-Volhard, 2004 The Maternal-Effect Mutants (also found the D/V Group)

3 A-P polarity set up in egg chamber bicoid mRNA oskar mRNA protein + nanos RNA microtubule-based - +

4 maternal The Maternal A/P Information BCDNANOS The Terminal System BCD is a transcription factor and a translation factor (represses Caudal translation) NANOS is a translation factor (represses Hunchback translation)

5 Nusslein-Volhard and Wieschaus, Nature 1980 Wieschaus Nobel Lecture, 1995 The Zygotic Genes

6 maternal zygotic Creating Complex Patterns From Simple Ones BCD Gradient GAP Genes HB = Red, KR = Green Pair Rule Gene (fushi tarazu) Segment Polarity (engrailed)

7 BCD GiantKruppel Complex Patterns From Simple Ones: Gap Genes

8 maternal zygotic 3 Maternal “Systems” for A/P ≈11 Gap Gene Domains Creating Complex Patterns From Simple Ones 8 Pair-rule genes x 7 stripes = 56 domains eve ftz

9 Dave Kosman Generating Precise Positional Information Along Axes

10 S. Small eve Stripe 2 enhancer--lacZ eve Stripe 3/7 enhancer--lacZ Understanding Transcriptional Control of Patterning: The Story of eve Levine and colleagues eve is a pair rule gene-- expressed in 7 “stripes” How is this pattern created? Step 1: “Promoter bashing” to identify relevant enhancers eve ftz

11 eve stripe 2 Eve Gt Kr Step 1: “Promoter bashing” to identify relevant enhancers Step 2: Use expression patterns and genetics to identify candidate regulators Step 3: Use biochemistry to identify direct regulators Step 4: In vivo proof: mutating cis binding sites should cause same change in expression as mutating trans regulators Studying Transcriptional Control of Development Small, Blair and Levine EMBO 1992

12 Sepsidae (scavenger flies) PMID: 18584029 Eisen Lab ≈100 mya

13 PMID: 18584029 Eisen Lab

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15 PMID: 18584029 Eisen Lab

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17 Positional Information in the Embryo Controls: Segmentation and Pattern Within a Segment Segment Identity (Making Segments Different From One Another)

18 Hh Wg Segment Polarity Genes -wg and hh Signaling Pathways -Establish 14 Segmental Boundaries -Act as morphogens to pattern within each segment

19 Positional Information in the Embryo Controls: Segmentation and Pattern Within a Segment Segment Identity (Making Segments Different From One Another)

20 Homoeosis (Bateson 1894): alteration of one organ of a segmental or homologous series from its own characteristic form to that of another member of the series “homoeotic mutants ” Fun with Flies! Antenae to Leg Leg to Antenae Proboscis to Leg Haltere to Wing Wing to Haltere Genitalia to Leg Ultrabithorax Ed Lewis

21 Homeotic (Hox) genes are expressed differentially along the A/P Axis Specify segment identity

22 Drosophila Mouse

23 Drosophila Hypothetical common ancestor Amphioxus Mouse

24 UBX Expression WingHaltere Regulation of Segment Identity by a “Hox Code” Wild Type T2 T3 Antp ONAntp OFF Ubx OFFUbx ON WingHaltere Ubx mutant T2 T3Antp ONUbx OFFWing Ultrabithorax

25 Mammals Are Segmented Too Cervical Thoracic Lumbar Sacral

26 Wellik and Capecchi, 2003 Hox Genes Specify A/P Identity in Vertebrates 5/6 mutant Triple homozygote A/a C/c D/c X 1/64 pups = aaccdd

27 Patterning the Dorsal-Ventral Axis wt V D A P Dorsalized Ventralized Maternal-Effect Mutants: The D/V Group

28 A. Courey D/V Patterning Establishes the Mesodermal Identity Determined by twist and snail Toll pathway: on on ventral side

29 It is not birth, marriage or death, but gastrulation, which is truly the most important time in your life. - Lewis Wolpert (1986) Gastrulation

30 Drosophila gastrulation The mesoderm and endoderm invaginate separately (a bit unusual) Ventral View

31 Cell Adhesion and Cell Sorting Cell IdentityMorphogenesis ? Cell Biology Cell Division/Death Cell Adhesion Cell Movement Cell Shape

32 Apical constrictionInvagination Epithelial-mesenchymal transition (EMT) Migration/spreading The Cell Biology of Fly Mesoderm Gastrulation

33 twist and snail folded gastrulation (ligand) Concertina (G alpha) GPCR? RhoGEF fog expression in mesoderm is dependent on twist and snail folded gastrulation and concertina Effect Apical Constriction Apical constriction

34 twist and snail folded gastrulation (ligand) Concertina (G alpha) GPCR? RhoGEF folded gastrulation and concertina Affect Gastrulation T48 fog Rho Kinase myosin Apical constriction Myosin relocalizes from basal to apical at the time of apical constriction

35 Epithelial-mesenchymal transition (EMT) DE-cadherin May Regulate EMT in the Drosophila Mesoderm snail DE-cadherin EMT

36 FGF Signaling Promotes Mesoderm Migration (FGFR)

37 Apical constriction Epithelial-mesenchymal transition (EMT) Migration How Cell Identity Controls Morphogenesis of Gastrulation Cell Identity (twist, snail) fog, T48 Cell Adhesion E-Cadherin? FGF-R


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