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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. 4 stages: embryo, larva, pupa, adult . Rapid division 9 mins/division 9 divisions.

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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



Rapid division

9 mins/division

9 divisions

13 divisions

Single cell


One single epithelial layer –all tissues

Mesoderm—muscle, connective tissues

Endoderm---midgut (foregut and hidgut-


Ectoderm---nervous tissue and epidermis


Larva hatch 24 hrs

Acron: associated with head

Telson:posterior terminal structure

3 thorcic and 8 abdominal segments—specialization in cuticle

(denticle belts and cuticular structure)



Sex comb


Small wing

p. 421-431


Sex determining signal--- Sex-lethal (X chromosome)

Transformer-spliced + transformer 2


Repression by autosome

2X higher numerator


Dosage compensation

Barr body

Xist-non-coding RNA

Male specific gene

Repressed by Sxl


Primordial germ cell -special cytoplasm

Germ plasm-polar granules, pole plasm


Oskar—organization and assembly of

the pole plasm

mRNA-posterior pole—3’ untranslated region


Cyst formation:

16 cell cyst enter a long S phase

only one (Oocyte) continues meiosis

Oocyte—4 ring canals

15 cells become nurse cells

after germarium nurse cells left meiotic cycle, grow rapidly without division, and form polytene chromosomes


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.


Microtubule cytoskeleton reorganization

is essential for localization of

bicoid and oskar mRNA


Maternal effect mutations---reguired for

pole plasm assembly

Lack polar granules: grandchildless mutation (homozygote female—


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 helicase—translational regulator


Germ cell migration

Germ cell—extragonadal 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


PGC migration----Genes and mechanisms

Genetic screen—somatically 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 Columbus—attract 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)


Localized mRNA and Proteins

Translated after fertilization—

Positional information to activate zygotic genes

Temporal sequence


Pattern in the segment

Segment identities



Appendages:imaginal discs—pattern formation

Ectoderm invagination-epithelium(20-40 cells—larva 1000X)

Specification occurs –segment being patterned-according to it

wing blade
Wing blade

Ventral fold under dorsal-double layers of epithelium

signal region and the compartment
Signal region and the compartment

Maintain compartment boundaries—communication between compartments

Hh—10 cells, induces expression of Dpp through activation of Ci

the hedgehog signaling pathway
The hedgehog signaling pathway

Without signal—Ci is processed as a repressor

into nucleus

With signal---full length Ci acts as an activator in

the nucleus


Intercellular signaling set up PS boundary

Wg distributed asymmetrically—less in posterior (endocytosis and degradation)


TGFb , Activin: R-Smad 2,3

BMPs: R-Smad 1, 5, 8

Common Smad4

Inhibitory Smads: I-Smad6, 7—recruting

Smurf (ubiquitin ligase to


Cell, 95,737,1998


Smad= Sma + Mad

Sma-C. elegans



Dpp-secreted into both compartment

Long range signal—expression of spalt

patterning the a p axis of the wing disc
Patterning the A/P axis of the wing disc
  • Dpp-morphogen
  • Low level—omb
  • High level—spalt
  • Clones can’t respond to Dpp—
  • no spalt and omb
  • 2. Ectopic hh-Dpp—localized
  • activation of spalt and omb
  • around the hh clones
  • 3. Ts mutant of dpp—reduction in
  • the region with expression of low
  • Threshold genes—omb
  • 4. Clones expression low or high
  • Dpp—distinquish these two types
  • of genes
ectopic expression of hh and dpp
Ectopic expression of Hh and Dpp

L4—compartment boundary

L3– Hh

L2 ---adjacent to cells expressing spalt

Ectopic Hh in posterior—no effects

In anterior—mirrow-symmetric repeated pattern


expression of wingless green and vestigial
Expression of Wingless (green) and vestigial

Homeotic selector gene—

apterous (Lmx-1)

induces fringe and Serrate,

then Notch receptor activation –

Leading to Wingless expression

Wg—achaete, distal-less, vestigial

Wingless (green)

Vestigial (red)

D/V boundary

Dpp, Wg morphogen

GFP-dpp active transportation—


Regulate their receptors

Dpp inhibits receptor—thick veins

Dpp high--receptor low, and dpp low

Receptor high—1, prevent spreading

2,cells reach threshold at low Dpp


nervous system: selection of a single neuroblast (lateral inhibition)

Notch –transmembrane protein

DSL family—Delta, Serrate, Lag-2

Kuzbanian—cleave Notch ECD

Presenilin—cleave Notch ICD

leg disc extension
Leg disc extension

Jointed tubes of epidermis—secrete the hard cuticle (exoskeleton), inside:

Muscles, nerves

fate map of the leg imaginal disc
Fate map of the leg imaginal disc

Proximo-distal segment

Center—distal end

signaling centers in a p compartment
Signaling centers in A/P compartment

Dpp, wg meets—Dll (distal end)

homothorax (proximal)

regional subdivision
Regional subdivision

Dpp, and Wg induce Dll and

inhibit homothorax

Activates dachshund between Dll and hth

butterfly wing pattern
Butterfly wing pattern

Eyespot center—distal-less

segmental identity of imaginal disc
Segmental identity of imaginal disc

Homeotic selector genes

Similar signal into different structures—

Different interpretation—

controlled by Hox genes

Antennapedia—PS4 and 5– 2 pairs of legs

If in head, antennae into legs (clones) –

which part of the leg—depends 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

imaginal discs and adult thoracic appendages
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

If both mutations—effect is additive—

Four wings