MCB Lecture 26 Environmental and Genetic Interactions

Question 0

Describe the jump response

Answer 0

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

Question 1

Describe the nAChR’s role in relay of environmental signals in drosophila

Answer 1

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

Question 2

Describe the circuitry responsible for the jump response

Answer 2

Eyes
Giant fibre
Peripherally synapsing interneurons -> dorsal lateral muscle motor neurons -> Dorsal lateral muscle
Tergotrochanteral muscle neurons -> Tergotrochanteral muscle

Question 3

What is special about the nAChR across many different species?

Answer 3

Highly conserved DNA sequences, so the nAChR in different species are actually quite similar

Question 4

Describe the structure of the nAChR

Answer 4

5 subunits (pentamer)
Each subunit has 4 transmembrane helices

Question 5

Describe the function of the nAChR

Answer 5

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

Question 6

Describe nAChR expression in muscle cells

Answer 6

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

Question 7

Describe how we know that it is nAChR that is vital for the jump response

Answer 7

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

Question 8

Describe how insecticides and exogenous compounds affect insects

Answer 8

These compounds directly target the receptors on post synaptic neurons
They jam the nervous system of the flies

Question 9

Nicotine is …?

Answer 9

A plant defence molecule

Question 10

Neonicotinoids are …

Answer 10

Man made insecticides

Question 11

Spinosyns are …

Answer 11

Bacterial attack/defence molecules

Question 12

Venoms are …?

Answer 12

Snake/spider defence molecules

Question 13

Describe how some insects show resistance to insecticides

Answer 13

Mutations or deficits in some of the nAChR genes (Df2363) shows some resistance to insecticides

Question 14

What is the mutation that leads to insecticide resistance?

Answer 14

Df2363

Question 15

Insecticides target …

Answer 15

Signalling circuitry

Question 16

Mutagenesis increases …

Answer 16

Variation

Question 17

How are nAChRs involved in human disease?

Which diseases?

Answer 17

Epilepsy, Parkinson’s, Schizophrenia, Alzheimer’s

Channel dysfunction is involved in these diseases

Question 18

What is epilepsy?

How can these symptoms be explained?

Answer 18

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

Question 19

What is the pattern of inheritance of resistance to toxins?

Answer 19

It is recessive