The Establishment of Left and Right. Flashcards
What kind of gene pairs establish the dorsal/ventral axis of the body?
Antagonistic gene pairs.
What genes establish the anterior/posterior axis?
FGF and the HOX genes.
At what stage of embryonic development is the left/right axis established?
During gastrulation.
Which is established first, the anterior/posterior axis or the left/right axis?
Anterior posterior.
The left/right axis is established last.
Where is the asymmetry in humans?
On the inside of the body.
What is the normal condition of humans?
2 lobes on the left lung and 3 on the right.
The heart points to the left.
The liver is on the right side.
The stomach and spleen are on the left.
What is right isomerism in humans?
Each lung has 3 lobes. (2 right lungs).
There will be no spleen.
What is left isomerism in humans?
Each lung has 2 lobes. (2 left lungs).
There will be 2 spleens.
What is situs inversus in humans?
2 lobes on the right lung and 3 on the left.
The heart points right.
The liver is on the left.
The stomach and spleen are on the right.
When does left/right development start?
At around 4-5 weeks.
Where are the internal organs initially found in the embryo?
In the centre of the embryo.
What happens to form left/right asymmetry at around 7 weeks?
There is a rotation by the internal organs which displaces the liver to the left and the stomach and spleen to the right.
At what stage of embryonic development are the organs in their proper places?
At around 11 weeks.
Where does the heart develop in the body?
In the centre.
How does the heart develop in the embryo?
The heart will rotate so that it is pointing to the left hand side of the body.
At what stage will the heart begin to rotate?
At around 6 weeks.
How do the lungs develop in the developing embryo?
The lungs will develop as an outgrowth of the digestive tube.
At what stage will the lungs develop?
At around 4 weeks.
Where are the mono cilia found in mice and humans?
At Hensons node of the primitive streak.
How do the mono cilia influence the left/right axis?
They will be bent by extra embryonic fluid.
How does the extra embryonic fluid cause the mono cilia to bend?
The extra embryonic fluid produces a left hand flow, causing a vortical motion that bends the cilia.
What does the bending of the cilia lead to?
It is thought to lead to the changes in gene expression that lead to the establishment of the left/right axis.
What are the changes in gene expression caused by the left hand flow of the extra embryonic fluid and the bending of the cilia?
There is an asymmetric expression of genes where FGF-8 and SHH are expressed in different gradients.
Where is FGF-8 expressed in the embryo?
On the left side of the embryo.
What does the expression of FGF-8 cause?
FGF-8 turns on the genes NODAL and LEFTY-2.
What does the gene LEFTY-2 cause?
The expression of the gene PIT-X2.
What does the gene PIT-X2 cause?
It will initiate the formation of left side structure.
What genes are expressed on the right side of the embryo?
The SNAIL gene.
Why SNAIL not expressed on the left side of the embryo?
NODAL and LEFTY-2 will inhibit it.
Which gene will determine the structures on the right side of the embryo?
The SNAIL gene.
Problems in what will disrupt the formation of the left/right axis?
Problems in the mono-cilia.
What is one of the problems that causes a defect in cilia?
Primary cilia dyskinesia.
What happens to people who are affected by primary cilia dyskinesia?
They will have an accumulation of mucus in the lungs as cilia are responsible for removing particles such as dust.
They will also not be able to hear very well as cilia are involved with hearing.
Women who have this disease will be infertile as the cilia carry the fertilised egg to the uterus.
What causes primary cilia dyskinesia?
A mutation in the dynein proteins.
How does the mutation in the dynein proteins affect the determination of the left/right axis?
There is no mechanism to determine right/left asymmetry.
A fertile female will produce offspring with cytus inversus what percentage of the time?
50%.
In a chicken embryo, what gene is expressed on the left?
SHH.
In a chicken embryo, what gene is expressed on the right?
Activin.
What does SHH cause in the chicken?
An identical cascade to the one in humans and mice.
Where NODAL and LEFTY-2 are expressed and PIT-X2 is turned on by LEFTY-2.
What gene determines the right structures of the chicken embryo?
SNAIL.
What happens if SHH is inhibited from functioning?
It will inhibit NODAL expression.
SNAIL will be expressed on both sides of the embryo.
What induces the expression of NODAL?
SHH.
Why is SNAIL expressed on both sides of the embryo if SHH is inhibited?
Because SHH induces the expression of NODAL which will inhibit SNAIL.
If there is no NODAL then snail will not be inhibited on the left side and will be expressed.
If a bead is covered with SHH and implanted on the right side of the embryo, what will happen?
The left right axis will be disrupted and NODAL will be expressed on both sides which means there are 2 left sides.
If SHH is not expressed, how will this affect the PIT-X gene?
No PIT-X2 will be expressed.
If no PIT-X2 is expressed, what will happen?
No PIT-X2 will be expressed and 2 right sides will develop.
Why will 2 left sides develop if a bead is covered with SHH and implanted on the right side of the embryo?
Because SHH is expressed on both sides.
This means that PIT-X2 will be expressed on both sides.
And 2 left sides will develop.
What does VEG-1 do to express the left/right axis in frogs?
It is involved in the dorsal ventral axis but, may also be involved in defining left/right asymmetry.
When the frog embryo is developing, what will the heart and gut do in a normal situation?
The gut will rotate to the left and the heart to rotate to the right.
If VEG-1 is expressed in a developing frog embryo, what will happen with the heart and the gut?
There will be an opposite rotation of the gut and the heart.
The heart will rotate to the left and the gut to the right.
If there is a mis expression on PIT-X2 in the developing frog embryo, what will occur?
It has the same effect as VEG-1.
The heart will rotate to the left and the gut to the right.
How is the posterior temporal lobe in the brain asymmetric?
It is larger on the left side than on the right side.
How is the right frontal lobe of the brain asymmetric?
It protrudes more than the left frontal lobe.
Are there differences in cognition between the 2 sides of the brain?
Yes.
The right side of the brain is responsible for analytical thought and language and the left side is responsible for creativity.
What is the pineal gland responsible for?
For establishing circadian rhythms.
What is the pineal gland attached to?
The pineal stalk.
What side of the brain is the pineal stalk on?
The left.
Where is the parapineal located?
On the left side of the brain.
Where do the habenular nuclei have their highest density?
On the left side of the brain.
How do mutations in NODAL affect the pineal?
It will be expressed on both sides of the brain or in the middle.
What is thought to be responsible for causing the asymmetry of the pineal and habenular nuclei?
The pineal gland.
What happens when the parapineal glad is removed?
The density of the habenular nuclei will become equal which forms 2 right habenular nuclei.
The pineal gland will become centrally located.
