Morphogen gradient, cascade, signal transduction Maternal effect genes Zygotic genes Syncytial blastoderm Cellular blastoderm

Homeotic selector genes Similar signal into different structures— Different interpretation—controlled by Hox genes

Metamorphosis

Homeotic transformation of the wing and haltere Homeotic genes—mutated into homeosis transformation As positional identity specifiers Mutant-antennapedia—into leg Bithorax-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 genes Homeotic 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—10 Combinatorial 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 antenna If in head, antennae into legs Hth (homothorax) and Dll (distal-less)—expressed in antennae and leg In antenna: as selector to specify antenna In leg: antennapedia prevents Hth and Dll acting together Dominant antennapedia mutant (gene on)— blocks Hth and Dll in antennae disc, so leg forms No Hth, antenna into leg

Gene expression in the visceral mesoderm patterns the underlying gut endoderm Patterning 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—synpolydactyly Extra 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 poles little left to diffuse Anterior/posterior extremities Terminal structure- acron., telson, most posterior abdominal segment Torso---receptor tyrosine kinase Ligand---trunk Fig. 5-7

Torso signaling Groucho: repressor Huckenbein, 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 cells JAK-STAT: form the stalk cells Yellow arrow: signals induce E-cadherins expression

The oocyte move towards one end in contact with follicle cells Both 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-actin Green-gurken protein As well as mRNA The expression of EGFR pathway target gene

Torpedo--EGFR

Specifying the Anterior-Posterior Axis of the Drosophila Embryo During Oogenesis

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 end Kinesin—oskar to the minus end

The EGFR signal establishes the A/P and D/V axial pattern Gurken—TGF  Torpedo--- 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 of the 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 The dorsal-ventral pathway

Maternal genes— Fertilization to cellular blastoderm Dorsal system—for ventral structure (mesoderm, neurogenic ectoderm) Toll gene product rescue the defect Toll 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 activation Dorsal + cactus Toll activation – tube (adaptor) and pelle (kinase) Phosphorylate cactus and promote its degradation B cell gene expression Dorsal=NF-kB Cactus=I-kB The mechanism of localization of dorsal protein to the nucleus

Dorsalization mutation

The activation of NF-  B by TNF-  NLS

Fig The dorsal-ventral pathways

Dorsal nuclear gradient Activates—twist, snail (ventral) Represses—dpp, zen (dorsal) Fig

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 embryo Dorsal protein activates twist and snail represses dpp, zen, tolloid Rhomboid----neuroectoderm Repressed 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 nuclei Dpp is everywhere Twist 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 proteins Dpp=BMP-4(TGF-  ) Dpp protein levels high, increase dorsal cells short of gastrulation (sog) prevent the dpp spreading into neuroectoderm Sog is degraded by Tolloid (most dorsal)

Snail—(mesoderm) Reduce E-cadherin cell migration

Microarray analysis for gene expression profile

Smad= Sma + Mad Sma-C. elegans Mad-Fly 1.Antagonist 2.Proteases Fig The TGK-  /BMP signaling pathway dpp: decapentaplegic

Fig The Wnt and BMP pathways are used in early development

The self-renewal signal of the niche-Dpp signaling EMBO reports, 12,

Biological responses to TGF-  family signaling

Type I, II receptor-Ser/Thr phosphorylation The Smad-dependent pathway activated by TGF- 

Colorectal cancer: type II receptor Pancreatic 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 Activation repression

Structural and Functional Domains of Smad Family TGFb, Activin: R-Smad 2,3 BMPs: R-Smad 1, 5, 8 Common Smad4-nucleocytoplasmic shuttling, DNA binding Inhibitory Smads: I-Smad 6, 7 bioscience.org

Integration of two signal pathways at the promoter Cell,95,737, 1998 SBE: Smad binding element ARE: activin-response element TRE: TPA-response element (AP-1 binding) XBE: transcription X Smad2 and FAST Smad3 and c-Jun/cFos

Overview of TGF-b family signaling Development,

Post-translational modification of TGF-  receptor Trends in Cell Biology, 19,

The functions of the TGF-  receptors are regulated by protein associations Trends in Cell Biology, 19,

Different internalization pathways resulted in distinct cellular effects Trends in Cell Biology, 19,

Models of morphogen gradient formation Fig , 12, 13 sharpen

Fig The axis determining systems