Morphogen gradient, cascade, signal transduction

Maternal effect genes

Zygotic genesSyncytial blastoderm

Cellular blastoderm

Homeotic selector genesSimilar signal into different structures—

Different interpretation—controlled by Hox genes

Metamorphosis

Homeotic transformation of the wing and haltereHomeotic genes—mutated into homeosis transformation

As positional identity specifiers

Mutant-antennapedia—into legBithorax-haltere into wing

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

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

Regulatory elements

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

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

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

Gene expression in the visceral mesoderm patterns the underlying gut endodermPatterning of the endoderm

Labial—antennapedia complex

Fig. 5-40

Fly and mouse/human genomes of homeotic genes

Homeobox and homeodomain

Expression pattern and the location on chromosome

Mutation in HoxD13—synpolydactylyExtra digits & interphalangeal webbing (hetero)Similar but more severe & bony malformation of hands, wrists (Homo)

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

Torso signaling

Groucho: repressorHuckenbein, tailless are released from transcriptional suppression

Egg chamber formation(oogenesis)

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

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

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

Torpedo--EGFR

Specifying the Anterior-Posterior Axis of the

Drosophila Embryo During Oogenesishttp://www.youtube.com/watch?v=GntFBUa6nvs

Specifying the Anterior-Posterior Axis of the

Drosophila Embryo During Oogenesis

Protein kinase A orients the microtubules

mRNA localization in the oocyte

Dynein-gurken and bicoid to the plus endKinesin—oskar to the minus end

The EGFR signal establishes the A/P and D/V axial pattern

Gurken—TGFTorpedo--- EGFR

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

The Key determinant in D/V polarity is pipe mRNA in follicle cells

windbeutel—ER protein pipe—heparansulfate 2-o-sulfotransferase (Golgi) nudel—serine protease

The activation of Toll

Perivitelline space

Fig. 31-16

The dorsal-ventral pathway

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

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

Dorsalization mutation

The activation of NF-B by TNF-

NLS

Fig. 31-17

The dorsal-ventral pathways

Dorsal nuclear gradientActivates—twist, snail (ventral)Represses—dpp, zen (dorsal)

Fig. 31-19

Toll protein activation results in a gradient of intranuclear dorsal protein

Spatzle is processed in the perivitelline space after fertilization

Fig. 5-8

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

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

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)

Snail—(mesoderm)Reduce E-cadherin cell migration

Microarray analysisfor gene expression profile

Smad= Sma + MadSma-C. elegansMad-Fly

1. Antagonist2. Proteases

Fig. 31-24

The TGK-/BMP signaling pathway

dpp: decapentaplegic

Fig. 31-23

The Wnt and BMP pathways are used in early development

The self-renewal signal of the niche-Dpp signaling

EMBO reports, 12, 519-2011

Biological responses to TGF-family signaling

Type I, II receptor-Ser/Thr phosphorylation

The Smad-dependent pathway activated by TGF-

Colorectal cancer: type II receptorPancreatic cancers: 50% Smad

One component between receptor and gene regulation

The Smad-dependent pathway activated by TGF-

De-repression of target genes in Dpp signaling

groucho

Nature reviews genetics-8-663-2007

Activation

repression

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

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

Overview of TGF-b family signaling

Development, 136-3691-2009

Post-translational modification of TGF- receptor

Trends in Cell Biology, 19, 385-2009

The functions of the TGF- receptors are regulated by protein associations

Trends in Cell Biology, 19, 385-2009

Different internalization pathwaysresulted in distinct cellular effects

Trends in Cell Biology, 19, 385-2009

Models of morphogen gradient formation

Fig. 31-11, 12, 13sharpen

Fig. 31-21

The axis determining systems