Drosophila melanogaster

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Drosophila melanogaster Genetic
studies Microsurgical manipulation One of the
best understood developmental systems 13,600
genes Axis determination Signaling
pathway Transcriptional regulation
P48-52
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4 stages embryo, larva, pupa, adult
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Rapid division 9 mins/division 9 divisions
13 divisions
Single cell
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Transgenic flies
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One single epithelial layer all
tissues Mesodermmuscle, connective
tissues Endoderm---midgut (foregut and
hidgut- Ectoderm) Ectoderm---nervous tissue and
epidermis
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gastrulation
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Larva hatch 24 hrs Acron associated with
head Telsonposterior terminal structure 3
thorcic and 8 abdominal segmentsspecialization
in cuticle (denticle belts and cuticular
structure)
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Genitalia Sex comb Pigmentation Small wing
p. 421-431
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Sex determining signal--- Sex-lethal (X
chromosome)
Transformer-spliced transformer 2
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Repression by autosome
2X higher numerator
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Dosage compensation
Barr body Xist-non-coding RNA
Male specific gene Repressed by Sxl
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Primordial germ cell -special cytoplasm Germ
plasm-polar granules, pole plasm
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Oskarorganization and assembly of
the pole plasm mRNA-posterior pole3
untranslated region
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Polarization of the body axes during oogenesis
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(No Transcript)
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Cyst formation 16 cell cyst enter a long S
phase only one (Oocyte) continues
meiosis Oocyte4 ring canals 15 cells become
nurse cells after germarium nurse cells left
meiotic cycle, grow rapidly without division, and
form polytene chromosomes
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A/P during oogenesis 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.
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Microtubule cytoskeleton reorganization is
essential for localization of bicoid and oskar
mRNA
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Maternal effect mutations---reguired for
pole plasm
assembly Lack polar granules grandchildless
mutation (homozygote female
Progenysterile) Central role Oskar, Vasa, and
Tudor Pole cell number amount of oskar
RNA Ectopic pole cells oskar RNA at the anterior
pole
MtlrRNA (mitochondrically encoded large
ribosomal RNA) gcl RNA for pole cell
formation antisense reduce pole cells mtlrRNA
rescue UV-irradation Vasa DEAD-box RNA
helicasetranslational regulator
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Germ cell migration
Germ cellextragonadal origin, migrate to
reach the somatic gonad a.
posterior end b. gastrulation c. migrate
dorsally through the wall of the posterior
midgut d. associate with the somatic gonadal
precursors e. GC align with somatic gonadal
mesoderm f. coalesce to form the embryonic gonad
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PGC migration----Genes and mechanisms Genetic
screensomatically expressed genes Guidance
(cues) Wunen repulsive signal (exclude
migrating pole cells from wrong
places) Misexpression wunen transform a tissue
permissive to PGC to repulsive one Phosphatidic
acid phosphatase 2 (transmembrane
protein)   Columbus factor (gonadal mesoderm)
attracts pole cells Misexpression
Columbusattract PGCs to tissues other than
gonadal mesoderm 3-hydroxy-3-methylglutaryl
coenzymeA reductase (cholesterol biosynthesis in
human, but fly does not make cholesterol)
  nanos, pumilio mutants stall at the outer gut
surface differentiate prematurely---act as
complete migration to the somatic gonads nanos
target RNA binding protein Sex lethal
(Sxl)---splicing and translational
regulation also depend on specific germ plasm
components, e.g polar granule component (Pgc)
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Patterning of the fly embryo
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Localized mRNA and Proteins Translated after
fertilization Positional information to
activate zygotic genes
Temporal sequence
parasegment Pattern in the segment Segment
identities
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p.350-358
Appendagesimaginal discspattern
formation Ectoderm invagination-epithelium(20-40
cellslarva 1000X) Specification occurs segment
being patterned-according to it
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A/P and D/V compartment
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Wing blade
Ventral fold under dorsal-double layers of
epithelium
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Signal region and the compartment
Maintain compartment boundariescommunication
between compartments Hh10 cells, induces
expression of Dpp through activation of Ci
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The hedgehog signaling pathway
Without signalCi is processed as a repressor
into nucleus With signal---full length Ci acts as
an activator in the nucleus
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Intercellular signaling set up PS boundary
Wg distributed asymmetricallyless in posterior
(endocytosis and degradation)
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TGFb , Activin R-Smad 2,3 BMPs R-Smad 1, 5,
8 Common Smad4 Inhibitory Smads I-Smad6,
7recruting Smurf
(ubiquitin ligase to
receptor)
Cell, 95,737,1998
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Smad Sma Mad Sma-C. elegans Mad-Fly
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Dpp-secreted into both compartment
Long range signalexpression of spalt
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Patterning the A/P axis of the wing disc

• Dpp-morphogen
• Low levelomb
• High levelspalt
• Clones cant respond to Dpp
• no spalt and omb
• 2. Ectopic hh-Dpplocalized
• activation of spalt and omb
• around the hh clones
• 3. Ts mutant of dppreduction in
• the region with expression of low
• Threshold genesomb
• 4. Clones expression low or high
• Dppdistinquish these two types
• of genes

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Ectopic expression of Hh and Dpp
L4compartment boundary L3 Hh L2 ---adjacent to
cells expressing spalt Ectopic Hh in
posteriorno effects In anteriormirrow-symmetric
repeated pattern Hh--Dpp
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Expression of Wingless (green) and vestigial
Homeotic selector gene apterous (Lmx-1) induces
fringe and Serrate, then Notch receptor
activation Leading to Wingless
expression Wgachaete, distal-less, vestigial
Wingless (green) Vestigial (red) D/V
boundary Dpp, Wg morphogen GFP-dpp active
transportation Endocytosis Regulate their
receptors Dpp inhibits receptorthick veins Dpp
high--receptor low, and dpp low Receptor high1,
prevent spreading 2,cells reach threshold at low
Dpp
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nervous system selection of a single neuroblast
(lateral inhibition)
Notch transmembrane protein DSL familyDelta,
Serrate, Lag-2
Kuzbaniancleave Notch ECD Presenilincleave
Notch ICD
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Leg disc extension
Jointed tubes of epidermissecrete the hard
cuticle (exoskeleton), inside Muscles, nerves
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Fate map of the leg imaginal disc
Proximo-distal segment Centerdistal end
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Signaling centers in A/P compartment
Dpp, wg meetsDll (distal end)
homothorax (proximal)
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Regional subdivision
Dpp, and Wg induce Dll and inhibit
homothorax Activates dachshund between Dll and hth
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Butterfly wing pattern
Eyespot centerdistal-less
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Segmental identity of imaginal disc
Homeotic selector genes Similar signal into
different structures Different
interpretation controlled by Hox
genes AntennapediaPS4 and 5 2 pairs of legs If
in head, antennae into legs (clones) which part
of the legdepends on their position along the
P/D axis (positional values are similar) Hth
(proximal) and Dll (distal)in antennae and
leg In combination as selector to specify
antenna No Hth, antenna into leg In leg
antennapedia prevents Hth and Dll acting
together Dominant antennapedia mutant (gene
on) blocks Hth and Dll in antennae disc, so leg
forms
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Imaginal discs and adult thoracic appendages
Bithorax mutationUbx misexpressed T3 into T2
anterior haltere into Anterior wing
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Postbithorax muation (pbx) Regulatory region of
the Ubx Posterior of the haltere into wing If
both mutationseffect is additive Four wings