an integrated view

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