Flashcards in MCB Lecture 26 Environmental and Genetic Interactions Deck (20)
Describe the nAChR's role in relay of environmental signals in drosophila
The environment is detected by nAChR. These caused changes in cells, and thus bring about a response in Drosophila.
Specifically, nAChR play a big role in the Jump Response, which allows Drosophila to escape from predators.
The jump response involves the eye detecting a shadow. This message is sent through neurons to muscles to cause them to contract. The chemical synapse requires nAChR to detect the Acetylcholine released at the synapse
Describe the jump response
A drosophila detects a shadow with there eyes
This message gets transduced and the Giant fibre is stimulated
The impulses travel down the giant fibre
nAChRs on Peripherally stimulating interneurons and Tergotrochanterol Muscle neurons detect the acetylcholine released by the giant fibre.
Tertrochanteral muscle and Dorsal lateral muscle are innervated and contract
The fly jumps and is removed from danger
Describe the circuitry responsible for the jump response
Peripherally synapsing interneurons -> dorsal lateral muscle motor neurons -> Dorsal lateral muscle
Tergotrochanteral muscle neurons -> Tergotrochanteral muscle
What is special about the nAChR across many different species?
Highly conserved DNA sequences, so the nAChR in different species are actually quite similar
Describe the structure of the nAChR
5 subunits (pentamer)
Each subunit has 4 transmembrane helices
Describe the function of the nAChR
Binds the ligand acetylcholine, which causes a conformational change
The conformational change is the channel opening
Sodium and calcium pass through the channel into the cell
Describe nAChR expression in muscle cells
Neuro-muscular junctions want even faster nAChRs.
In muscle cells, there is increased transcription of a gene coding for the epsilon subunit
This subunit out competes the gamma subunit in the nAChR
The receptor now has the epsilon subunit which causes the whole receptor to act more quickly
Describe how we know that it is nAChR that is vital for the jump response
When there is a mutation in Dalpha7, the flies do not show the jump response when put through the flight and olfactory test
When the nAChR transgender is put back into these flies, they show these responses
Describe how insecticides and exogenous compounds affect insects
These compounds directly target the receptors on post synaptic neurons
They jam the nervous system of the flies
Nicotine is ...?
A plant defence molecule
Neonicotinoids are ...
Man made insecticides
Spinosyns are ...
Bacterial attack/defence molecules
Venoms are ...?
Snake/spider defence molecules
Describe how some insects show resistance to insecticides
Mutations or deficits in some of the nAChR genes (Df2363) shows some resistance to insecticides
What is the mutation that leads to insecticide resistance?
Insecticides target ...
Mutagenesis increases ...
How are nAChRs involved in human disease?
Epilepsy, Parkinson's, Schizophrenia, Alzheimer's
Channel dysfunction is involved in these diseases
What is epilepsy?
How can these symptoms be explained?
Epilepsy is sleep and awake seizures
There are mutations in the nAChRs (3 have been found)
This leads to increased excitability of the neurons and increased sensitivity to ACh