drosophila melanogaster development
DESCRIPTION
Drosophila melanogaster development. How do Drosophila embryos develop? How can one use genetics to find genes that regulate embryo development?. Life cycle of Drosophila . egg. 4 days. female. embryogenesis. pupa. DROSOPHILA LIFE CYCLE. 1 day. larva. 1st instar. 1 day. 4 days. - PowerPoint PPT PresentationTRANSCRIPT
Drosophila melanogaster development
How do Drosophila embryos develop?
How can one use genetics to find genes that regulate embryo development?
DROSOPHILA
LIFE CYCLE
4 days
4 days
1 day
1 day
2 days
Life cycle of Drosophila
egg
larva1st instar
larva2nd instarlarva
3rd instar
pupaembryogenesis
female
OOGENESIS IN DROSOPHILA
Germarium
ring canal
Germline Cyst Formation
Cystoblast
Pro-Oocyte(undergoes meiosis)
germline stem cells follicle
stem cells
germline: stem cell > cystoblast > 1 oocyte + 15 nurse cells
OOGENESIS IN DROSOPHILA
Germarium Vitellariumnurse cell oocyte
stalk
follicle cells
border cells
germline stem cells follicle
stem cells
oocyte
oocyte + nurse cells surrounded by (somatic) follicle cells
Drosophila oocyte and supporting cells
Nurse cells Ring canals Oocyte Follicle cells
(from Gonzalez-Reyes and St Johnston (1994) Science 266: 639-642.)
Drosophila oocyte and supporting cells
Nurse cell nuclei Follicle cell nuclei
(from Gonzalez-Reyes and St Johnston (1994) Science 266: 639-642.)
Nuclear divisions start without cell division in Drosophila (superficial cleavage)
Fig. 9.1Zygotic gene expression begins
egg blastoderm fate map larva
T
A
Larvae already have substantial patterning
acron
head
thorax
abdomen
telson
T1
T2T3A1A2A3
A4A5A6A7A8
(cuticle)
“stripy” expressionof segmentation gene
fushi tarazu (ftz)
anterior
posterior
ventral dorsal
epithelium(6,000 cells)
The fruit fly body plan is assembled in 24 hours: How?
Christiane Nüsslein-Volhard and Eric Wieschaus used genetics to identify proteins that
set up the embryonic body plan
Wieschaus and Nüsslein-Volhard
looked for mutants that affect the fly body plan
wildtype
Genes identified in a famous screen for Drosophila mutants with embryo patterning defects
Screen for developmental mutants (Drosophila)Lethal hits = 100% (essential genes - ca. 5.000)
(efficiency of mutagenesis = number of hits per gene)
embryonal-lethal mutantszygotic mutants
25 %with morphological defects 3 %- segmentation defects (AP) 0.5 %- tissue types defective (DV) 0.5 %
female-sterile mutants 8 %
100 %
with effects on embryogenesis 2 %(= maternal-effect mutants)
- antero-posterior pattern 0.4 %- dorso-ventral pattern 0.3 %
ca. 2% of all genes involved in embryo pattern formation(male-sterile mutants)
(ca. 100 of >15.000 protein-encoding genes, only 5.000 essential genes)
Maternal-effect mutationsGenes expressed during oogenesis (= before fertilization)
or genes expressed in maternal cells (follicle) All progeny of heterozygous mother are normal.All progeny are affected only if mother is homozygous mutant
Zygotic mutationsGenes expressed during embryogenesis (= after fertilization)Only genetically mutant embryos are affected.(25% of progeny of heterozygous mother are affected.)
Drosophila axis detemination; dorsal/ventral polarity
How does the embryonic dorsal-ventral axis get translated into differentiation of different tissue
types?
amnio-serosa dorsal
ectoderm
neuro-ectoderm
mesoderm
Cell fate specification at the blastoderm stage
mesoderm formationfate map
dorsal
ventral
Dorsal-Ventral fate map
Gurken protein specifies the Anterior-Posterior axis of the Drosophila embryo during oogenesis
(Similar to EGF)
Localized maternal mRNA sets up anterior and posterior poles
Gurken also signals dorsal pole formation during oogenesis
follicle cellsanterior posterior
A P
V
D D
V
-+-
microtubules
71-6 810A
gurken expression in the oocyte
10A
gurken expression in the
oocyte
1-6
migration of nucleus
+-
-
8
oocyte nucleus
Expression of the Gurken Message and Protein Between the Oocyte Nucleus and the Dorsal Anterior Cell Membrane
DORSO-VENTRAL PATTERN FORMATIONfollicle cells
Oocyte
pipe expression
Ventral follicle cell
Pipe (Golgi?)
X
NucleusWind (ER?)
X
X
mod. from van Eeden & St.Johnston
Gurken = Epidermal Growth Factor (EGF)
Torpedo = EGF receptor(in follicle cells)
Toll Tl - membrane receptor
cactus cact - cytoplasmic inhibitor of Dorsal nuclear translocation
dorsal dl - transcription factor (morphogen)
Zygotic mutations tube - cytoplasmic proteinpelle - ser/thr protein kinase
Maternal effect mutations
ndl, pipe, wblgd, snk, ea - serine proteasesspz - ligand
Dorsal protein
dorsal RNA
Toll proteinSpätzle proteinDorsal protein
nudel, pipe, wbl
amnio serosa
dorsal ectoderm
neuro-ectoderm
mesodermDl
nuclear protein
Dorso-ventral pattern formation
dorsal
Wild type
ventralized
dorsal mutant
cactus mutant
dorsalized T1 T2 T3 A1 A2 A3 A4 A5 A6 A7 A8
Dorso-ventral pattern formation
dorsal
ventral
Wild type toll mutant cactus mutant
Translocation of Dorsal protein into ventral nuclei but not lateral or dorsal nuclei
Generation of Dorsal-Ventral Polarity in Drosophila
Generation of Dorsal-Ventral Polarity in Drosophila
Wild type
toll mutant
Inject wild-type cytoplasm
mesodermneuro-ectoderm
(denticle belts)
dorsal ectoderm
Dorso-ventral pattern formation pivotal role of Toll pathway
into toll mutant eggs
dorsalized
local rescue
ventral
dorsal
polarity reversal
Conserved pathway for regulating nuclear transport of transcription factors in Drosophila and mammals
Cells with highest nuclear Dorsal levels become mesoderm
Zygotically expressed genes
Action of Dorsal protein in ventral cells
Action of Dorsal protein in ventral cellsHigh affinity for promoter,Not much Dorsal needed to activate
Action of Dorsal protein in ventral cellsLower affinity for promoter,More Dorsal needed to activate
twist
dpp
Dorsal protein
dorsal RNA
Toll proteinSpätzle protein
Dorsal protein
nudel, pipe, windbeutel
Dorso-ventral pattern formation: summaryoocyte nucleus dorsal> repression of ventral fate
in dorsal follicle cells
ventral production of ligand> activation of Toll receptor
> graded nuclear uptakeof Dorsal morphogen
> regulation of zygotictarget gene expression
> cell fates along DV axis
Use of a similar regulatory system to pattern insects and vertebrates
Patterns mesoderm in vertebrates
Patterns ectoderm in Drosophila
Gastrulation in Drosophila
Schematic representation of gastrulation in
Drosophila