Drosophila Axis Determination
DROSOPHILA AXIS DETERMINATION............................................................................................................. 1
SUMMARY OF GENES TO KNOW...............................................................................................................................3
WHY WAS DROSOPHILA CHOSEN TO STUDY EARLY EMBRYONIC DEVELOPMENT?.................................................................3
RELATIONSHIP OF DROSOPHILA TO REST OF ANIMAL KINGDOM.......................................................................................4
EARLY DEVELOPMENT IN DROSOPHILA.......................................................................................................................4
First 4 hours....................................................................................................................................................5
ESTABLISHMENT OF ANTERIOR/POSTERIOR & DORSAL/VENTRAL PATTERNING....................................................................5
IDENTIFICATION OF MUTANTS DEFECTIVE IN ANTERIOR/POSTERIOR PATTERNING: MATERNAL-EFFECT AND ZYGOTIC MUTANTS.....6
Maternal-effect genes:...................................................................................................................................6
Zygotically-active genes.................................................................................................................................6
SOME EXAMPLES OF ZYGOTICALLY-ACTIVE MUTANTS.....................................................................................................7
Gap Mutants:..................................................................................................................................................7
Pair-Rule Mutants:..........................................................................................................................................7
Segment-Polarity Mutants:............................................................................................................................7
RESEARCH..................................................................................................................................................... 9
IMMUNOCYTOCHEMISTRY (DETECTION OF PROTEIN).....................................................................................................9
MATERNAL EFFECT GENES........................................................................................................................... 10
3 CLASSES OF MATERNAL-EFFECT GENES..................................................................................................................10
BICOID MUTANTS PHENOTYPE...............................................................................................................................10
EXPRESSION PATTERNS OF HUNCHBACK, NANOS AND CAUDAL.......................................................................................11
Bicoid-Caudal interaction.............................................................................................................................12
Nanos-Hunchback interaction......................................................................................................................12
LOCALIZATION OF BICOID AND NANOS MRNA TRANSCRIPTS IN A/P REGIONS OF EMBRYO..................................................12
THE GAP GENES........................................................................................................................................... 13
GENETIC HIERARCHY LEADING TO SEGMENTATION......................................................................................................13
MUTANT PHENOTYPE...........................................................................................................................................13
PATTERN OF EXPRESSION OF GAP GENES IN WT EMBRYOS...........................................................................................14
WHAT REGULATES EXPRESSION OF THESE GENES?......................................................................................................14
How did scientists show that zygotic hunchback was dependant on bicoid?..............................................14
THE PAIR-RULE GENES................................................................................................................................. 15
MUTANT PHENOTYPE: MISSING ALTERNATE SEGMENTS..............................................................................................16
PATTERN OF EXPRESSION & PARASEGMENTS.............................................................................................................16
Parasegments:..............................................................................................................................................16
REGULATION OF EXPRESSION.................................................................................................................................16
Regulation of even-skipped Expression:.......................................................................................................17
Regulation of eve expression in stripe 2:.................................................................................................................18
Regulation of fushi-tarazu Expression:.........................................................................................................18
SEGMENT-POLARITY GENES........................................................................................................................ 19
PHENOTYPE OF SEGMENT-POLARITY MUTANTS..........................................................................................................19
PRODUCTS OF SEGMENT-POLARITY GENES................................................................................................................19
PATTERNS OF EXPRESSION OF SEGMENT-POLARITY GENES............................................................................................19
REGULATION OF EXPRESSION OF SEGMENT-POLARITY GENES........................................................................................20
Phase 1: Expression of engrailed (en) and wingless (wg) is initiated by pair-rule genes.............................20
Phase 2: Cell signaling between en expressing cells and wg expressing cells regulates the continued
expression of en and wg...............................................................................................................................21
Phase 3. En and Wg expression is independently maintained.....................................................................22
HOMEOTIC GENES....................................................................................................................................... 22
MUTANT PHENOTYPE IN DROSOPHILA.....................................................................................................................22
EXPRESSION PATTERNS & GENOME ORGANIZATION....................................................................................................22
WHAT IS CONSERVED COLLINEAR REGULATION OF HOX GENES?....................................................................................22
,Drosophila Axis Determination
, Drosophila Axis Determination
Summary of Genes to know
Group Gene Name Mutant phenotype Function
Head and thorax deleted, Codes transcription factor.
replaced by inverted Development, and identity of
bicoid
telson. anterior structures. Represses
caudal.
No abdomen. Codes translational repressor
nanos protein that represses maternal
hunchback. Posterior morphology.
Maternal-effect No abdomen. Codes RNA binding protein that
genes adds PolyA-tail to maternal
pumilio
hunchback – promoting its
translation
No abdomen. Probably codes transcriptional
caudal activator of knirps and giant.
Activates posterior terminal genes
Codes transcription factor. Activates
hunchback
anterior gap genes.
Codes protein that signals posterior
gurken follicle cells -> activation protein
kinase A
hunchback
Gap
Kruppel
genes
knirps
Zygotic- even-
Pair-rule skipped
effect
genes
genes fushi-tarazu
Segment engrailed Transcription Factor
polarity wingless Growth Factor
genes hedgehog
Maternal effect genes provide initial positional information required for zygote-effect genes
The first set of zygotic-effect genes to be activated along the anterior-posterior axis are the
gap genes, followed by the pair-rule genes, followed by the segment polarity genes
Why was Drosophila chosen to study early embryonic
development?
- Well-characterized genetically, there were established techniques for mutating and
mapping genome positions.
- Easy to culture + Short lifecycle
- Development mutants are easy to identify because the exoskeleton of Drosophila
larvae has several landmark features that can be used to identify mutants defective
in aspects of anterior/posterior and dorsal/ventral polarity
o Features such as the intricate patterns of hairs, indentations, and cuticle
structures, can be used to identify the anterior-posterior (A-P) axis, and the
dorsal-ventral axis (D-V).
- Once a mutation has been mapped in Drosophila, it is relatively easy to clone the
gene. The function of these genes can then be analyzed using the following genetic
and standard recombinant DNA techniques:
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