Evolutionary conservation of left/right asymmetry Flashcards
what is evolutionary conservation?
- Gene sequences similar in different organisms.
- Similar expression pattern of genes.
- Similar protein functions.
- Conserved protein-protein interactions or gene regulatory mechanisms.
- Process encoded and regulated by the same genes in different organisms.
What is outward bilateral symmetry?
Symmetrical on the outside but not inside: eyes, ears limbs.
What is meant by vertebrate asymmetry?
Inward asymmetry of the location, anatomy and physiology of internal organs.
What is situs solitus?
Normal pattern of asymmetry.
What is situs invertus?
Reversal of left/right axis
What is right isomerism?
No spleen
What is left isomerism?
Two spleens
What does iv (inversus viscerum) encode for?
A motor protein: left-right dynein
What does inv (situs invertus) encode for?
Inversin, a component of the cilia
What do the cilia do?
Cilia at the node direct gene expression in a directional manner.
How is L/R asymmetry established?
Leftward fluid flow generated by rotational movement of node cilia (beat in a clockwise manner).
What are the predictions for establishing if cilia at the node establish L/R asymmetry?
- Reversing the cilia flow will cause situs inversus.
- Re-establishing cilia flow in mutants with restore normal positioning of the organs.
The experiment actually worked.
What genes are expressed on the left side?
lefty, nodal and pitx2
What are some properties of the left-side genes?
Nodal signalling is asymmetric at the node.
Lefty is Nodal antagonist.
Pitx2 expression is Nodal-dependent.
L/R asymmetry in echinoderms (sea urchins). Where are the genes expressed?
Nodal is expressed on the right side of the sea urchin.
Nodal signalling in required for the establishment of the L/R axis.
Downstream genes network is conserved with expression of pitx2 and lefty on the right side of the embryo.
