morphogen gradient, cascade, signal transduction maternal effect genes zygotic genes syncytial...
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Morphogen gradient, cascade, signal transduction
Maternal effect genes
Zygotic genesSyncytial blastoderm
Cellular blastoderm
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Homeotic selector genesSimilar signal into different structures—
Different interpretation—controlled by Hox genes
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Metamorphosis
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Homeotic transformation of the wing and haltereHomeotic genes—mutated into homeosis transformation
As positional identity specifiers
Mutant-antennapedia—into legBithorax-haltere into wing
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Imaginal discs and adult thoracic appendages
Bithorax mutation—Ubx misexpressed T3 into T2 –anterior haltere into Anterior wing
Postbithorax muation (pbx)—Regulatory region of the Ubx—Posterior of the haltere into wing
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Homeotic selector genes
Each segment unique identity—master regulator genesHomeotic selector genes—control other genes-required throughout development
Spatial& temporal expression—mechanism of controlling of these genes
Fig. 5-37
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Regulatory elements
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The spatial pattern of expression of genes of the bithorax complex
Bithorax—Ultrabithorax –5-12 Abdominal-A—7-13 Abdominal-B—10-13
Bithorax mutant –PS 4 default state
Fig. 5-39
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Bithorax mutant –PS 4 default state+Ubx—5,6+Abd-A—7,8,9+Abd-B—10Combinatorial manner
Lack Ubx—5,6 to 4 also 7-14 thorax structure in the abdomen
Hox—gap, pair-rule for the first 4 hours, then polycomb (repression), and Trithorax (activation)
Fig. 5-39
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Segmental identity of imaginal disc
Antennapedia—expressed in legs, but not in antennaIf in head, antennae into legs
Hth (homothorax) and Dll (distal-less)—expressed in antennae and legIn antenna: as selector to specify antennaIn leg: antennapedia prevents Hth and Dll acting together
Dominant antennapedia mutant (gene on)—blocks Hth and Dll in antennae disc, so leg formsNo Hth, antenna into leg
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Gene expression in the visceral mesoderm patterns the underlying gut endodermPatterning of the endoderm
Labial—antennapedia complex
Fig. 5-40
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Fly and mouse/human genomes of homeotic genes
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Homeobox and homeodomain
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Expression pattern and the location on chromosome
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Mutation in HoxD13—synpolydactylyExtra digits & interphalangeal webbing (hetero)Similar but more severe & bony malformation of hands, wrists (Homo)
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Before fertilization ligand immobilized
Small quantities—bound to torso at the poleslittle left to diffuse
Anterior/posterior extremities
Terminal structure-acron., telson, most posterior abdominal segment
Torso---receptor tyrosine kinaseLigand---trunk
Fig. 5-7
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Torso signaling
Groucho: repressorHuckenbein, tailless are released from transcriptional suppression
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Egg chamber formation(oogenesis)
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Signals from older to younger egg chambers
Red arrow: Delta-Notch induces anterior polar follicle cellsJAK-STAT: form the stalk cellsYellow arrow: signals induce E-cadherins expression
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The oocyte move towards one end in contact with follicle cellsBoth the oocyte and the posterior follicle cells express high levels of the E-cadherin
If E-cadherin is removed, the oocyte is randomly positioned.Then the oocyte induces surrounding follicle cell to adopt posterior fate.
A/P Determination during oogenesis
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The EGFR signal establishes the A/P and D/V axial pattern
Red-actinGreen-gurken proteinAs well as mRNA
The expression of EGFR pathway target gene
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Torpedo--EGFR
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Specifying the Anterior-Posterior Axis of the
Drosophila Embryo During Oogenesishttp://www.youtube.com/watch?v=GntFBUa6nvs
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Specifying the Anterior-Posterior Axis of the
Drosophila Embryo During Oogenesis
Protein kinase A orients the microtubules
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mRNA localization in the oocyte
Dynein-gurken and bicoid to the plus endKinesin—oskar to the minus end
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The EGFR signal establishes the A/P and D/V axial pattern
Gurken—TGFTorpedo--- EGFR
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The localization of Gurken RNA
Cornichon, and Brainiac-Modification and Transportation of the protein
K10, Squid localize gurken mRNA (3’UTR&coding region)
Cappuccino and Spire –cytoskeleton ofthe oocyte
MAPK pathway
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The Key determinant in D/V polarity is pipe mRNA in follicle cells
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windbeutel—ER protein pipe—heparansulfate 2-o-sulfotransferase (Golgi) nudel—serine protease
The activation of Toll
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Perivitelline space
Fig. 31-16
The dorsal-ventral pathway
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Maternal genes—Fertilization to cellular blastodermDorsal system—for ventral structure(mesoderm, neurogenic ectoderm)
Toll gene product rescue the defectToll mutant – dorsalized (no ventral structure)
2. Transfer wt cytoplasm into Toll mutant specify a new dorsal-ventral axis (injection site =ventral side) spatzle (ligand) fragment diffuses throughout the space
Toll pathway
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Without Toll activationDorsal + cactusToll activation –tube (adaptor) and pelle (kinase)Phosphorylate cactus and promote its degradation
B cell gene expressionDorsal=NF-kBCactus=I-kB
The mechanism of localization of dorsal protein to the nucleus
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Dorsalization mutation
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The activation of NF-B by TNF-
NLS
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Fig. 31-17
The dorsal-ventral pathways
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Dorsal nuclear gradientActivates—twist, snail (ventral)Represses—dpp, zen (dorsal)
Fig. 31-19
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Toll protein activation results in a gradient of intranuclear dorsal protein
Spatzle is processed in the perivitelline space after fertilization
Fig. 5-8
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Zygotic genes pattern the early embryoDorsal protein activates twist and snail represses dpp, zen, tolloid
Rhomboid----neuroectodermRepressed by snail (not most ventral)
Binding sites for dorsal protein in their regulatory regions
Model for the subdivision of the dorso-ventral axis into different regions by the gradient in nuclear dorsal protein
Fig. 5-13
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Dorsalized embryo—Dorsal protein is not in nucleiDpp is everywhereTwist and snail are not expressed
Threshold effect—integrating Function of regulatory binding sites
Regulatory element=developmental switches
High affinity (more dorsal region-low conc.)
Low affinity (ventral side-high conc.)
Nuclear gradient in dorsal protein
Fig. 5-14
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Dpp protein gradient
Cellularization---signal through transmembrane proteinsDpp=BMP-4(TGF-)Dpp protein levels high, increase dorsal cellsshort of gastrulation (sog) prevent the dpp spreading into neuroectodermSog is degraded by Tolloid (most dorsal)
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Snail—(mesoderm)Reduce E-cadherin cell migration
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Microarray analysisfor gene expression profile
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Smad= Sma + MadSma-C. elegansMad-Fly
1. Antagonist2. Proteases
Fig. 31-24
The TGK-/BMP signaling pathway
dpp: decapentaplegic
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Fig. 31-23
The Wnt and BMP pathways are used in early development
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The self-renewal signal of the niche-Dpp signaling
EMBO reports, 12, 519-2011
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Biological responses to TGF-family signaling
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Type I, II receptor-Ser/Thr phosphorylation
The Smad-dependent pathway activated by TGF-
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Colorectal cancer: type II receptorPancreatic cancers: 50% Smad
One component between receptor and gene regulation
The Smad-dependent pathway activated by TGF-
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De-repression of target genes in Dpp signaling
groucho
Nature reviews genetics-8-663-2007
Activation
repression
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Structural and Functional Domains of Smad Family
TGFb , Activin: R-Smad 2,3BMPs: R-Smad 1, 5, 8Common Smad4-nucleocytoplasmic shuttling, DNA bindingInhibitory Smads: I-Smad 6, 7
bioscience.org
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Integration of two signal pathways at the
promoter
Cell,95,737, 1998SBE: Smad binding elementARE: activin-response elementTRE: TPA-response element (AP-1 binding)XBE: transcription X
Smad2 and FAST Smad3 and c-Jun/cFos
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Overview of TGF-b family signaling
Development, 136-3691-2009
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Post-translational modification of TGF- receptor
Trends in Cell Biology, 19, 385-2009
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The functions of the TGF- receptors are regulated by protein associations
Trends in Cell Biology, 19, 385-2009
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Different internalization pathwaysresulted in distinct cellular effects
Trends in Cell Biology, 19, 385-2009
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Models of morphogen gradient formation
Fig. 31-11, 12, 13sharpen
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Fig. 31-21
The axis determining systems