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Drosophila timescales (at
25°C):
3 hrs: cellular blastoderm with 5000 cells
with all cells’ identities specified
24 hrs: embryo hatches as feeding larva
Movies: •
QT Drosophila Development -different views: embryogenesis –SEM morph –
QT Drosophila embryogenesis –
QT Drosophila Cleavage: following Histone-GFP –
QT Drosophila Gastrulation: following Histone-GFP –
Drosophila – 2 lectures
(½ – 1- ½ )
• Cleavage
• View -gastrulation, organogen. frame metamorph.
• Once we know the embryo, meet the molecules
• Because this is a largely ‘solved’ system
• Because these genes have key roles in all metazoans
• EVERY one of 5000 cleavage state cell has a D/V and A/P
‘molecular address’, and is therefore specified.
First to AnteriorPosterior Axis (A-P)
Both axes defined
in Drosophila
A-P:
-Termini
-Segmented body
Acron and Telson are ‘TERMINAL’ structures
To overview
Movie:
“Embryo genesis”
Bicoid
mRNA
Bicoid mRNA-binding protein
1. Bicoid RNA ‘caught’ at the ‘entrance’
2. Unanchored Bicoid RNA returned
to the anterior side by dynein on MTs
Show:
Bcd-gastrulation
Gastrulation-dorsal
In syncitium
For control of Hunchback protein – Bicoid is a transcription factor, but Nanos . . .
Nanos is an RNA binding protein that PREVENTS Hunchback Translation
Gap genes are turned on in broad stripes
by maternal genes, each other. ALL TFs.
Hunchback
Gt
Kr
kn
hb
(later)
Gt
Kr
kn
hb
(later)
Gap genes are turned on in broad stripes
by maternal genes, each other
Pair rule genes are turned on in
7 stripes each, harder to conceptualize
Each stripe of the
P-R gene has its
Own enhancer.
Even-skipped
gene – 7 stripes.
Each stripe has its own enhancer, responding to a
different combinatorial of Gap and Maternal proteins
Gap genes are turned on in broad stripes
by maternal genes, each other
Pair rule genes are all Trascription Factors too
– turn on Segment Polarity gene expression
hh
hh
hh
hh
Two morphogens/ligands/organizers in adjacent cells
Active
No
The embryo
Now has two
Adjacent organizers
Which release a
Morphogen
From syncitium with
Gradient of 1 (or 2)
Morphogens, to
series
Of segments, each
With 2 morphogens
2 Apposing DEVELOPMENTAL ORGANIZERS
http://bcs.whfreeman.com/thelifewire/content/chp19/1902003.html
Both axes defined
in Drosophila,
every cell of 5000.
Now to D/V
After the activity of four different pathways, the D/V patterning of the ectoderm Is controlled by a
conserved Ser/Thr receptor that is dependent on the gradient of its ligand dpp and dpp’s interactors
D/V: An evolutionarily
Conserved mechanism
dpp/BMP-4
Figure 23.14 Homologous Pathways Specifying Neural Ectoderm in Protostomes
(Drosophila) and Deuterostomes (Xenopus) D/V
Gastrulation - Drosophila
http://www.flybase.org/data/images/Animation/
AND Course Site (Movies)
4 STAGES OF ESTABLISHING DORSAL/VENTRAL – 4 SEQUENTIAL PATHWAYS +
STAGE
PATHWAY PATHWAY OUTCOME
I.
RTK pathway
Sets follicle cell D/V state
II.
Proteolytic cascade
Sets embryos’ cell D/V state
III.
Toll/Cactus/Doral
Sets nuclear D/V state
IV.
Dorsal TF thresholds
Diff. pathway per D/V address
4 STAGES OF ESTABLISHING DORSAL/VENTRAL – 4 SEQUENTIAL PATHWAYS +
STAGE
PATHWAY PATHWAY OUTCOME
I.
RTK pathway
Sets follicle cell D/V state
II.
Proteolytic cascade
Sets embryos’ cell D/V state
III.
Toll/Cactus/Doral
Sets nuclear D/V state
IV.
Dorsal TF thresholds
Diff. pathway per D/V address
Dorsal fate determined in oocyte, through signaling
between oocyte and somatic follicle cells
Gurken protein on future dorsal side of oocyte, facing cells which become dorsal
Human blood
clotting cascade –
Also a series of
(extracellular)
proteolytic cleavages
Ventral fates dictated by NUCLEAR presence of the protein Dorsal
Dorsalized
Ventralized
Gradient of Nuclear Dorsal protein imparts D-V IDs to cells
Twist Protein specifies mesoderm
Lateral inhibition in neurectoderm to specify neruogenesis: Notch mediated
All Rhomboid expressing cells express Notch, then undergo
a stochastic process for ¼ cells to become neuronal
Lateral inhibition in neurectoderm to specify neruogenesis: Notch mediated
TGF-Beta family
Key factor for
D-V identities in
Vertebrates
Key factor for
Dorsal identities in
Drosophila
After the activity of four different pathways, the D/V patterning of the ectoderm Is controlled by a
conserved Ser/Thr receptor that is dependent on the gradient of its ligand dpp and dpp’s interactors
D/V: An evolutionarily
Conserved mechanism
dpp/BMP-4
Figure 23.14 Homologous Pathways Specifying Neural Ectoderm in Protostomes
(Drosophila) and Deuterostomes (Xenopus) D/V
The course primarily addresses development of urbilaterian
descendents. All reflect on the ancestor-differences are details.
msh, ind, and sog
mark specific D/V
cells/coordinates
So now we’ve
defined both axes
in Drosophila, including
every cell of 5000.
Subsequent to A/P specification through segmentation gene action,
the Homeotic genes then allow unique functions for each segment.
Stopped here
All animals have related developmental histories
out in
evert
Figure 6.16 Scanning Electron Micrograph of a Compound Eye in Drosophila
Eye disc patterning controlled by ‘reuse’ of the pathways seen in general axis specification
Figure 6.17 Differentiation of Photoreceptors in the Drosophila Compound Eye
Figure 6.18 Major Genes Known to be Involved in the Induction of Drosophila Photoreceptors