Post on 06-Jan-2016
description
An Integrated view
Nerve Muscle and Movement
Assessment SA Q totalling 70 Specimen paper
http://biolpc22.york.ac.uk/404
Practical worth 30 marks, deadline 18 Dec Submit 1 practical report
To join together…Nerve conductionSynaptic physiologyMuscle contractionMechanics of MotionAxon guidance
what could be better than ……fly jumping?
with a little help from our genetics friends
Aim How a fly is built to get away
Key reference Allen, MJ et al (2006) Making an
escape: Development and function of the Drosophila giant fibre system Sem Cell & Devel Biol. 17: 31-41
Genetic tools EMS-induced
mutations Sequenced genome UAS GAL4 system
tissue specific knockouts
tissue specific GFP tissue may be a
few cells
How does a fly jump?
Jump using middle leg
Trimarchi & Schneiderman
How far do they go?
Wild type flies go 30 mm
1 2 3 4 5 6 7
CS female fly #
0
10
20
30
ma
x d
ista
nce
jum
pe
d (m
m)
me
an
± S
E
How much work/force? Work
KE = ½ m g d = ½ 10-6 x 10 x 0.03 = 150 nJ
Power output = 40 µW or 300 W / kg at the top end of insect muscle output
Force measure contraction isometrically peak force 25 x weight of fly
Which muscles? zap head and record muscle potentials
here given one small and one large stimulus
Summary thoracic muscles, very energetically
demanding
Now onto: what neuromuscular systems does the fly use?(What’s in a fly???)
TDT
VNCCNS
tc
femurtibia
tarsus
foregut
GDN
mn
IFM
What’s in a fly?
tc - trochantermn - motor neuron GDN - Giant descending neuron [= GF] IFM – Indirect flight musclesTDT – tergal depressor of the trochanter [= TTM]VNC - ventral nerve cord
What's in the fly CNS ?
brain
thoracic ganglion
Plan start with
muscle motoneuron giant descending interneuron sensory input
development
TDT muscle
Koenig & Ikeda, 2005
this end pulls • the leg straight
this end pulls • the wing, • thorax, • stretching the IFMs
TDT has a double whammy
TDT in section
TDT is… Striated muscle Tubular muscle Fast twitch
Innervation
innervated by 3 motoneurons
1 large – very extensive endings
2 small
Neuromodulation by octopamine –
containing neuron
TDT motoneuron thoracic
nervous system
lateral cell body
dorsal neuropil
Summary thoracic muscles, very energetically
demanding muscle and motoneuron designed for
speed
PSI Relay between GDN and
? drives 5 DLM
motoneurons failure occurs
separately
Amplifier ?
GDN (=GF) GDN PSI
TDTmn
GDN → TDTmn synapse electrical ↑ chemical ▼
ACh
GDN → TDTmn synapse shakingB2
no electrical synapses an innexin mutant asymmetry in
innexins
shakingB2 and chats2 neither electrical nor
cholinergic synapses
Axonal conduction in GDN AP with para Na+ channels and K
channels identified shaker potassium channels differentiate sh from slo
sh – voltage activated K channel slo - Ca activated K channel
Excitation of GDN Visual
zap head
flash light
+benzaldehyde
Fly eye
Visual input to GDN Cobalt fill of GDN in Muscalobular cells
probably electricallycoupled to GDN
Mechanosensory input
GDN (PDB segment)
antennal endings
Summary thoracic muscles, very energetically
demanding muscle and motoneuron designed for
speed GDN circuit designed for speed and
robustness
Now onto: how does the circuit grow?
Development GDN & TDTmn
born during embryogenesis
Connect during pupation
Key steps GDN neurite outgrowth Axon pathfinding (larval stages—24 h
APF) Target recognition and initial synapse
formation (24–55 h APF) meet TDTmn bend
Synapse stabilization and maintenance (55–100 h APF)
So what are the Molecular regulators of growth
bendless
Giant axon stops and does not bend
Part of ubiqutination system for degrading proteins
This degrades signal saying “go”
Semaphorin-1a Regulates neurite
outgrowth No sema-1a GDN
axon goes to retina (50%)
Regulates bend No sema-1a GDN
axon does not bend (50%)
May be the protein bendless degrades
Target of sema-1a Plexins ?
Which signal via Rac, a GTPase
rac blocked
Too much rac
Summary thoracic muscles, very energetically
demanding muscle and motoneuron designed for
speed GDN circuit designed for speed and
robustness Identification of signalling molecules
controlling neuronal growth & synapses
Habituation of jump response
dunce (phosphodiesterase) & rutabaga (adenyl cyclase)
Jumping as a test for disease
Epilepsy
+/+
easprior
afterbang
eas
Mutants hyperexcitable followed by paralysis
Flies as genetic models Parkinsonism, Alzheimer, Fragile X…
Behaviour, anatomy, physiology, cell biology well known
Screen for modifiers
Summary thoracic muscles, very energetically
demanding muscle and motoneuron designed for
speed GDN circuit designed for speed and
robustness Identification of signalling molecules
controlling neuronal growth & synapses System for physiological mutant
analysis