Transcript Gene regulation

Gene regulation
Ch 8
pp 280 -292
What will I learn?
THAT;
1. Gene regulation is at the heart of
development
2. The most important part of a gene is its
regulatory region, because;
1. It determines how, when, and by how much a
gene is activated
2. The combination of proteins which bind to this
region determine activation (or repression)
Definition of gene regulation
• Regulation of gene expression (gene
regulation) is the cellular control of the
amount and timing of the appearance of
the functional product of a gene.
The Story of ‘Eve’
• This example illustrates why gene regulation
is fundamental to development
• The Players
– Drosophila embryo
– Even-skipped gene
– Regulatory proteins
•
•
•
•
Bicoid
Hunchback
Giant
Kruppel
The setup
• In Drosophila, the fertilized egg initially
performs many rounds of mitosis without cell
division - resulting in a cell with many nuclei
• The embryo is 400 um long and 160 um wide
• It has anterior (that will eventually develop
into the head) and a posterior (that will
develop into the abdomen)
Act 1
• Removing the cytoplasm from the
anterior will result in the failure to
develop a head
• Replacing this cytoplasm with some
taken from the posterior of another
embryo will result in an embryo with two
tails
08_16_anterior_posteri.jpg
Act 2
• Labeling of the 4 proteins - Bicoid,
Hunchback, Giant, Kruppel with
fluorescent dyes reveals that they are
not randomly located inside the cell...
08_17_4.gene.reg.prot.jpg
Act 2 continued
• The nuclei are therefore bathed in
differing concentrations of these four
proteins - depending on their position in
the cell.
Act 3
• Even-skipped - ‘EVE’
• It is a master regulatory gene whose
product is a master regulatory protein
• This genes’ promoter region has the
ability to bind to all four of the regulatory
proteins
Act 4 The Reporter
• A reporter gene is an artificial DNA construct
used to reveal information
• Lac Z reporter gene is used extensively
• GAL (b-galactosidase) - Hydrolyzes colorless
galactosides to yield colored products.
• Attach different parts of the promoter region
of the ‘eve’ gene to LacZ to determine if that
region is bound and activated by proteins.
• Check the web on this please!
Isolate the different regions from the promoter and test in
embryo.
08_18_reporter.gene.jpg
The same STRIPE 2 region actually has binding sites for all
four of regulatory proteins - Bicoid and Hunchback are
activators of this region and Giant and Kruppel are repressors.
08_19_eve.stripe.2.jpg
Curtain
• The regulatory region of ‘Eve’ extends more
than 20,000 bp
• It is thought to bind more than 20 different
proteins
• It is very sensitive to the position of the gene
(nucleus) within the developing giant cell
• The different concentrations of the different
proteins impact on the expression of ‘Eve’
Gene Expression
• Regions huge distances from the gene
have an effect on the activation (or
repression) of that gene
• These regions bind proteins that then
interact, by DNA looping, with the local
promoter regions
• A combination effect is seen - and thus
the term combinatorial control is used
08_15_Reg. proteins.jpg
Combinatorial control
• Not just by how much are genes
regulated but also when.
• It is akin to an orchestra….
• It is fantastic coordination at each gene
locus
Maintaining the status quo
- with respect to gene
regulationthrough cell division
Inactive genes are kept inactive by regulatory proteins bound
to the DNA, and active genes are kept active! How, see below
08_24_chromatin.state.jpg
When things go wrong…
Activation of the wrong regulator can have devastating effects
08_25_eye.on.leg.jpg
One can move cells to new locations may lead to monsters!!
Other examples of
developmental issues.
Here either antenna, or
proboscis is growing on the
head,
Or dual thorax segments
with a pair of wings on
each!!