Chapter%209%20-%20Axis%20specification%20in%20Drosophila

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Chapter 9 - Axis specification in Drosophila

• Drosophila genetics is the groundwork for
  _______________l genetics
• Cheap, easy to breed and maintain
• Drosophila geneticists take pride in being
  __________, in ___________ information and being
  Mac users.
• Problems- fairly complex, non-transparent

Fig. 8.1
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Drosophila
1. Cleavage

• Insects tend to undergo ________________-
  cleavage occurs at _____ of the egg
• In contrast to other creatures, insects form
  nuclei, then ____ ________

Termed a __________ _______

• Mitotic divisions
• 1-9 - duplicate _____ (8 min/division)

1
7

• Mitotic division
• 10 nuclei _______ to rim

• Mitotic division
• 11-14 progressively _________divisions

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Fig. 9.1
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Drosophila
1. Cleavage
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Note each nuclei has a _________ of
cytoskeletal proteins

• Mitotic divisions
• 14 cells created with each nuclei to create
  the _______ _____________

Nuclei staun
Tubulin stain
Egg plasma membrane _____ between nuclei to
create individual _____
Cycle 11-14- ______ ___________- nuclear division
slows and __________ increases
Fig. 9.3
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2. Gastrulation
Ventral
Dorsal
Ventral furrow (from mesoderm)
Fig. 9.6
Segments
Head
3 _____
8 _________
Fig. 9.7
It becomes the ventral tube
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2. Gastrulation
Establishment of anterior-posterior polarity-
Protein gradients rule the day
Gene family
Examples
a. _______________- in specific region of egg
bicoid ____ caudel
b. _____-among 1st gene transcribed in embryo
Kruppel _________
c. ______ result in 7 bands
fushi tarazu ______
d. ____________ result in 14 segments
_______ wingless
Fig. 9.8
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2. Gastrulation
a. Maternal effect genes
Active during creation of _________________
_______ mRNA injected, localize to posterior
_____ mRNA injected in anterior
Caudel (diffuse)
Hunchback (diffuse)
Fig. 9.10
Bicoid prevents ____ mRNA _____________ Nanos
prevents_________ mRNA ___________
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a. Maternal effect genes
Mechanism
Oocyte ________
Anterior
Caudel and hunchback mRNA
_____ mRNA
______mRNA
Syncytial Blastoderm _______
Posterior
Fig. 9.11
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a. Maternal effect genes
What if we mess up the ______gradient?
Inject bicoid into
Bicoid- mutant
Wild-type
Bicoid-/-
Bicoid-/-
Wild-type
Anterior
Middle
Posterior
Head in ____
Two ____
_________
Thus, bicoid specifies _______ development
Two ____
Fig. 9.14
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How does nanos specify __________?
Answer- By preventing _________ translation
Mechanism
In anterior, ________ binds 3UTR (untranslated
region) of hunchback mRNA, and mRNA is
polyadenylated and translated
Anterior (no nanos)
Posterior (with nanos)
In posterior, nanos prevents _____________, and
thus prevents ____________
Fig. 9.16
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2. Gastrulation
Segmentation genes
Two steps in Drosophila development
(Cell fate is flexible)
(Cell fate is determined)
Maternal effect genes activate ____ genes, which
activate _________ genes, which activate
________________ genes
Fig. 9.19
Segmentation genes establish ___________
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a. Gap Genes
Gap
hunchback

• Gap genes respond to ________ _______ proteins
• Gap proteins interact to define specific________
  of embryo
• Four major gap proteins- _______, ________,
  ________, _______
• These are all _____________ proteins- activate or
  repress ______________

giant
kruppel
knirps
Fig. 9.21
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b. Pair-rule genes

• Gap genes activate and repress ___________ genes
  in ________ stripe, resulting in ________ stripes
• Three major pair-rule proteins- ______,
  _____________, ______
• These are all ____________ proteins- activate or
  repress transcription
• Cells in each ______________contains
• a unique ______ of pair rule genes expression
  unlike any other parasegment

Fig. 9.21
Pair-rule
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Pair-rule
b. Pair-rule genes
Why do we observe expression of pair-rule
proteins in ______________ segment?
Answer- pair-rule genes use different ________
elements
Example- even-skipped (a pair-rule gene) has
several _______, but only one is _________ in a
given stripe
Different concentrations of ____ proteins
determine _________ gene expression
This ________ is only active in stripe 1
Fig. 9.22
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c. _________ __________ genes
Maternal, gap and pair-rule genes operate ______
cells are formed
Pair-rule
Segment polarity
_____________________
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Segment polarity genes act once cells are _______
Fig. 9.1
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c. Segment polarity genes
Segment polarity genes encode proteins that make
up ________ and __________ signal transduction
pathways
One cell produces ________
The adjacent cell produces ________
Fig. 9.25
Wingless and hedgehog activate expression of
_________ indirectly
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2. Gastrulation
_______ _______ genes
Responsible for directing structure formation of
each segment

• These genes are clustered on chromosome 3 in the
  ________
• ___________ (also called Hom-C) in two regions-
• The _______________ complex-
• The ________________ complex-

Two amazing features
1. The _____ of these genes on the chromosome
matches order of ______________ expression
Chromosome 3
2. _____________ are regulated by all gene
products expressed ___________ to it
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What about ______________ polarity??

• This occurs _______cells are created (post
  syncytial blastoderm)
• ______ ( a transcription factor) gradient is
  established
• Dorsal is found throughout syncytial blastoderm,
  but only in _______ of ______cells

How does this occur?
By a very complex pathway involving _____ and
__________ proteins ( and a host of other
proteins)
Organs form at the ___________ of dorsal-ventral
and ____________ regions of gene expression