DAPC

Question 1

what is the DAPC?

Answer 1

a collection of proteins found on the muscle fiber (inside and outside)
- composed of sarcoplasmic, transmembrane and extracellular proteins

Question 2

important functions of DAPC

Answer 2

1. provide mechanical support for muscle fibre during stresses (ex. stretching)
2. signal transduction from extracellular space to nucleus

Question 3

can you name the proteins involved in the DAPC?

Answer 3

collagen, laminin, emerin
α-dystroglycan, β-dystroglycan
dystrophin
α-dystrobrevin
syncoilin
desmin
F-actin

Question 4

where is DAPC found?

Answer 4

all over the sarcolemma

Question 5

where is UAPC found?

Answer 5

where there’s a high concentration of AChRs - present in secondary folds of NMJ

Question 6

where is dystrophin abundant?

Answer 6

at the sarcolemma and at the troughs of the NMJ

Question 7

functions of the UAPC

Answer 7

• similar functions as the DAPC
• connect proteins on the exterior of the cell to proteins on the inside of the cell
• signal transduction

Question 8

mdx mice

Answer 8

• mice with muscular dystrophy that have a naturally occurring mutation in dystrophin gene
• often used as a model for muscular dystrophy

Question 9

immunoblotting/Western blot analyses

Answer 9

• used to assess DAPC or UAPC proteins expressed in muscle from a ground up sample
• gives us an idea of how much of each protein is present in a sample

Question 10

what are advantages of immunofluorescence technique

Answer 10

• allows for info about DAPC or UAPC localization AND amount present for each protein

Question 11

findings for DAPC/UAPC protein amounts present mdx mice vs healthy

Answer 11

• mdx mice have no dystrophin while healthy mice have lots
• dystrophic muscle has more utrophin produced - normally there isn’t very much but because there’s no dystrophin there’s more utrophin
• mdx mice have fewer of other DAPC related proteins

Question 12

human skeletal muscle biopsy technique

Answer 12

• uses Burgstrom needle where the other components fit inside
• 150 mg of muscle can be recovered per sample (usually sample twice so = 300 mg)
• suction allows to take a larger sample
• using Burgstrom needle results in smaller punctures and significantly less scarring compared to previous methods of muscle biopsy

Question 13

characteristics of a healthy muscle sample

Answer 13

• myonuclei are on the outside of muscle fibers

- most muscle fibres are about the same size

Question 14

characteristics of a young DMD patient muscle sample

Answer 14

• centrally located myonuclei - indicative of degeneration and regeneration
• very small fibers/variation in fibre size CSA
• buildup of CT and fatty tissue - result of damage since we see displacement of muscle with a diff type of tissue (not what we want)

Question 15

what happens to DAPC when there is no dystrophin?

Answer 15

it leads to a secondary decrease in other DAPC members

• no DAPC forms without dystrophin
• some fibers may mutate to have dystrophin (fluke but cool) and they will also have the DAPC proteins associated with dystrophin, but only those fibers

Question 16

what is the role of dystrophin?

how does it affect stiffness of muscle fibers?

Answer 16

• anchor sarcolemma to actin cytoskeleton (F-actin)

- muscle fibers without dystrophin are less stiff than healthy fibers