Transcript a pair-rule gene

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
1. Cleavage
Drosophila
• 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)
• Mitotic division
#10 – nuclei _______ to rim
• Mitotic division
#11-14 – progressively
_________divisions
Fig. 9.1
1
7
10
1. Cleavage
Drosophila
• Mitotic divisions
#14 – cells created with
each nuclei to create the
_______ _____________
14
Note – each nuclei has a _________
of cytoskeletal proteins
Nuclei
staun
Egg plasma membrane _____
between nuclei to create
individual _____
Cycle 11-14- ______ ___________nuclear division slows and
__________ increases
Fig. 9.3
Tubulin
stain
2. Gastrulation
Ventral
Dorsal
Ventral furrow
(from mesoderm)
Fig. 9.6
Segments
Head
3 _____
8 _________
It becomes the
ventral tube
Fig. 9.7
2. Gastrulation
Establishment of anterior-posterior polarity-
Gene family
Protein gradients rule the day
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
2. Gastrulation
a. Maternal effect genes
Active during creation of _________________
_____ mRNA
injected in anterior
Caudel (diffuse)
_______ mRNA
injected, localize
to posterior
Hunchback (diffuse)
Fig. 9.10
Bicoid prevents ____ mRNA _____________
Nanos prevents_________ mRNA ___________
a. Maternal effect genes
Oocyte ________
Caudel and hunchback mRNA
Mechanism
Anterior
_____
______ mRNA
mRNA
Syncytial Blastoderm _______
Posterior
Fig. 9.11
a. Maternal effect genes
What if we mess up the ______gradient?
Wildtype
Fig. 9.14
Bicoid
Inject bicoid into:
Bicoid-/-
Bicoid-/-
Wild-type
Anterior
Middle
Posterior
mutant
Two ____
Two
_________ Head in
____
____
Thus, bicoid specifies _______
development
How does nanos specify __________?
Answer- By preventing _________ translation
Mechanism
In anterior, ________ binds 3’UTR
(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
2. Gastrulation Segmentation genes
Two steps in Drosophila development
____________
genes
a. __________
________ genes
Egg
Specification
(Cell fate is flexible)
Bicoid, nanos,
hunchback, caudel, etc.
Determination
(Cell fate is determined)
b. Gap genes
c. ________ genes
d. Segment polarity genes
Maternal effect genes activate ____ genes, which activate
_________ genes, which activate ________________ genes
Segmentation
genes
establish
___________
Gap
Pair-rule
Fig. 9.19
Segment polarity
a. Gap Genes
Gap
• Gap genes respond to ________
_______ proteins
• Gap proteins interact to define
specific________ of embryo
• Four major gap proteins_______, ________, ________,
_______
•These are all _____________
proteins- activate or repress
______________
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 ____________ proteinsactivate or repress transcription
•Cells in each ______________contains
• a unique ______ of pair rule genes
expression unlike any other parasegment
Fig. 9.21
Pair-rule
b. Pair-rule genes
Why do we observe expression of pair-rule
proteins in ______________ segment?
Pair-rule
Answer- pair-rule genes use different ________ elements
Example- even-skipped (a pair-rule gene) has several
_______, but only one is _________ in a given stripe
This ________
is only active
in stripe #1
Different
concentrations
of ____
proteins
determine
_________
gene
expression
Fig. 9.22
c. _________ __________ genes
Maternal, gap and pair-rule
genes operate ______ cells
are formed
Pair-rule
_____________________
14
Fig. 9.1
Segment polarity
Segment
polarity
genes act
once cells
are _______
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
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-
1. The _____ of these
genes on the
chromosome matches
order of
______________
expression
2. _____________
are regulated by all
gene products
expressed
___________ to it
Chromosome 3
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