chapter 9 - axis specification in drosophila drosophila genetics is the groundwork for...
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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
• Insects tend to undergo ________________- cleavage occurs at _____ of the egg
• In contrast to other creatures, insects form nuclei, then ____ ________
Fig. 9.1
Drosophila1. Cleavage
1 7
10
• Mitotic divisions #1-#9 - duplicate _____ (8 min/division)
• Mitotic division #10 – nuclei _______ to rim
Termed a __________ _______
• Mitotic division #11-14 – progressively
_________divisions
Fig. 9.3
Drosophila1. Cleavage
14• Mitotic divisions #14 – cells created with each nuclei to create the _______ _____________
Note – each nuclei has a _________ of cytoskeletal proteins
Nucleistaun
Tubulinstain
Egg plasma membrane _____ between nuclei to create individual _____
Cycle 11-14- ______ ___________- nuclear division slows and __________ increases
2. Gastrulation Ventral Dorsal
Ventral furrow(from mesoderm)
It becomes the ventral tube
Segments
3 _____
8 _________
Head
Fig. 9.6
Fig. 9.7
2. Gastrulation
Establishment of anterior-posterior polarity-
a. _______________- in specific region of
egg
b. _____-among 1st gene transcribed in embryo
c. ______ – result in 7 bands
d. ____________ – result in 14 segments
Gene family
Fig. 9.8
Examples
bicoid____
caudel
fushi tarazu______
Kruppel_________
_______wingless
Protein gradients rule the day
2. Gastrulation
Active during creation of _________________
Fig. 9.10
_____ mRNA injected in anterior
_______ mRNA injected, localize to posterior
Hunchback (diffuse)Caudel (diffuse)
Bicoid prevents ____ mRNA _____________Nanos prevents_________ mRNA ___________
a. Maternal effect genes
Oocyte ________
Syncytial Blastoderm _______
Mechanism
Anterior
Posterior
a. Maternal effect genes
Fig. 9.11
______mRNA
_____ mRNA
Caudel and hunchback mRNA
What if we mess up the ______gradient?
Bicoid- mutant
Wild-type
Two ____
Inject bicoid into:
Anterior
Wild-typeBicoid-/- Bicoid-/-
Middle Posterior
_________ Head in ____
Two ____
Thus, bicoid specifies _______ development
a. Maternal effect genes
Fig. 9.14
How does nanos specify __________?Answer- By preventing _________ translation
Anterior (no nanos)
MechanismIn anterior, ________ binds 3’UTR (untranslated region) of hunchback mRNA, and mRNA is polyadenylated and translated
In posterior, nanos prevents _____________, and thus prevents ____________
Posterior (with nanos)
Fig. 9.16
2. Gastrulation Segmentation genes
Two steps in Drosophila development
Bicoid, nanos, hunchback, caudel, etc.
a. __________ ________ genes
____________ genes
b. Gap genes c. ________ genes
d. Segment polarity genes
Specification DeterminationEgg(Cell fate is flexible) (Cell fate is determined)
Maternal effect genes activate ____ genes, which activate _________ genes, which activate ________________ genes
Segmentation genes
establish ___________ Gap Pair-rule Segment polarity
Fig. 9.19
a. Gap Genes
• Gap genes respond to ________ _______ proteins
• Gap proteins interact to define specific________ of embryo
• Four major gap proteins- _______, ________, ________, _______
•These are all _____________ proteins- activate or repress ______________
Fig. 9.21
Gap
hunchback
giant
kruppel
knirps
Fig. 9.21
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
Pair-rule
Pair-rule
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
Fig. 9.22
This ________ is only active in stripe #1
b. Pair-rule genes
Different concentrations of ____ proteins determine _________ gene expression
c. _________ __________ genes
Pair-rule Segment polarity
Segment polarity genes act once cells are _______
_____________________
Maternal, gap and pair-rule genes operate ______ cells
are formed
14
Fig. 9.1
c. Segment polarity genes
Segment polarity genes encode proteins that make up ________ and __________ signal transduction pathways
One cell produces ________
The adjacent cell produces ________
Wingless and hedgehog activate expression of _________ indirectly
Fig. 9.25
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-
Chromosome 3
1. The _____ of these genes on the chromosome matches order of ______________ expression2. _____________ are regulated by all gene products expressed ___________ to it
Two amazing features
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