Transcript Aucun titre de diapositive - Master 1 Biologie Sant&#233

The mushroom bodies (MBs) in the
adult Drosophila brain
Rein et al., 2002 Current Biology
from Martin Heisenberg
modified from
Armstong et al., Learning
& Memory 1998
A wild-type  neuron
 lobe
10mm
 vertical branch
 lobe
Srausfeld et al., MRT 2003
 horizontal branch
10mm
10mm
midline
Developmental Genetics
of mushroom bodies (MB)
• MB are involved in olfactory learning.
• MB are relatively well described structure
in the adult central brain.
• 4 neuroblasts in each hemisphere form one
MB.
• Flies without MB are viable and fertile.
• Good markers of MB (Gal4 lines,
antibodies)
• Clonal analysis (positive labelling : Gal 80)
Development of the Drosophila mushroom bodies: sequential generation of
three distinct types of neurons from a neuroblast
Lee et al., Development 1999
MARCM
Mosaic analysis with a repressible cell marker for studies of gene function
in neuronal morphogenesis
Lee and Luo Neuron 1999
Neuroblasts in the head and trunk
Noveen et al., Development 2000
Noveen et al., Development 2000
The MB primordia in the embryonic
brain (frontal view)
KCs, Kenyon cells (MB cells)
Development of the MBs. (A) Embryonic MB primordium (lateral view).
(B) Larval MB. (C) Late pupal and adult MBs.
The GAL4/UAS system
Brand & Perrimon, Development 1993
Gal4
UAS
+
white
mCD8-GFP
Visualise MBs
 neurons (cell bodies + dendrites + axons) of the MBs
in one particular GAL4 line

’ ’
  axons (and neurons) of the MBs some midline axons
are also labeled in another GAL4 line
MUSHROOM BODY SPECIFIC GAL4 LINES
GAL4-OK107
GAL4-201Y
GAL4-c739
AXONS
core AXONS
 AXONS
/'
'/

ALL AXONS

’

’


core
core


Marking mutant clones in a mosaic organism by the MARCM technique
Parental cell
Mitotic recombination
After DNA replication
Two distinct
mosaic progeny
x
Repressor
protein
Repressible
marker
x
x
FRT
x
Mutant
x
x
x
x
x
Centro
mere
Repressor
NB: one can make clones in wild-type background also!:
visualisation clones
x
A single photoreceptor can be traced from cell body in eye disc (arrow in left
panel) to the end of the extending axon in the optic lobe (arrow in right panel)
e: eye disc
b: brain
An adult MB neuroblast clone with five axonal bundles (3 medial and 2 dorsal).
This clone was generated by inducing mitotic recombination in newly hatched larva
Three models of the projection of the MB neuroblast progeny
(A) One neuroblast progeny project to a specific region, e.g. the  lobe( black cells)
(B) A MB neuroblast clone contributes to the entire cellular repertoire of the MB
(C) The progeny of the MB neuroblast are not confined to the MB. Some neurons
project to other region of the brain.
Summary of the structural organisation of the MB
(A) Each MB neuroblast generates a clonal unit that contains all the types of cells
(B) The intact MB is a fourthfold structure of these clonal units
Two mutually exclusive types of marked clones. Either all postmitotic neurons
generated subsequently in the same lineage will be labeled (upper), or only two
neurons derived from the GMC will be labeled in the whole lineage (lower).
N
G
Nb
N
FLP
A multi-cellular Nb clone
FLP
Two cell clones
In addition, mitotic recombination in a dividing GMC can generate a single
cell clone
FLP
Single-cell clone
A two cell clone
Three types of neurons:  , ’’ and 
The question is: how are they generated from a single neuroblast?
Lobe compositions of MB neuroblast clones generated at different stages
Sequential generation of three distinct types of MB neurons with characteristic
axonal projections
Morphological characterization of the three types of MB neurons
Different behaviors of and ’’ neurons during metamorphosis
Clones were generated at NHL for A and D, at early L3 for B and E,
at late L3 for C and F. Morphologies were examined just before PF (A-C) or 18 h
APF (D-F)
Axon reorganization of  neurons during metamorphosis. Clones were generated
in NHL and examined 12, 18 and 24 hours APF
Summary of the mushroom body development
brain = central brain + optic lobes = 200.000 neurons
central brain = central complex + MB
central complex = 20.000 neurons
2 X MB = 2 X 2.000 neurons = 4000 neurons
1 neuroblast
2 x 4 neuroblats
3 types of neurons
2 x 2000 neurons
- 
- ’’
-
2 x 1 MB