Lecture A7, A8 Flashcards
Muscles are formed from this type of cell?
myoblasts
Myoblasts (def.)
embryonic precursors of myocytes
myocytes (a.k.a ____ )
muscle cells
Differentiation of myoblasts into muscle cells is called ______
-myogenesis
During myogenesis of skeletal muscle, myoblasts do what?
-fuse into multinucleated myotubes, which are combined into muscle fibers
Myoblasts arise from ______ called _____
-blocks of mesodermal cells
-somites
Somites are found where?
-lateral to the neural tube in the embryo that is derived from the neural crest.
Somites also give rise to tissues other than muscle like: ______
-skeletal tissue and CT in skin
where myoblasts will form in developing somite is determined by ______
specific signals from surrounding tissue including neural tube and the lateral ectoderm
early somite differentiates into ______
dermomyotosome & sclerotome
dermomyotosome differentiates into ______
dermotome & myotome
sclerotome gives rise to ____
skeletal structure
dermotome gives rise to ______
connective tissue of skin
____ induce myogenesis
Wnt, Hh and BMP
In myogenesis, there are multiple types of ______
Wnt proteins and Frizzled receptors
BMPs act similarly to _____ and act as _____
-TGFB proteins
-morphogens
BMPs organize what?
several parts of human body including bones
In myogenesis, Wnt 1/3a from ____ , Wnt6/7a from _____ , BMP4 from _____ and HH act on early somite
-neural tube
-surface ectoderm
-lateral mesoderm plates
Like other progenitor cells, myoblasts ______ to increase cell number.
-proliferate
In the correct environment, (signalling proteins), myoblasts will further ______
differentiate into muscles
Myoblasts also migrate via cell movement through ______ to the sites where muscles will form (aka _____)
-the developing embryo
-premuscle masses
_____ are transcription factors that direct myoblast
differentiation
-MEFs and MRFs
MRF stands for _____
muscle regulator factor proteins
MRF is expressed where?
-only in muscle
Types of MRF: _____
MyoD, Myf5, Myogenin (MyoG) and Mrf4 (in order of activation)
MRF is ____ (type of TF) that does what? (2)
-a bHLH TF
-binds a DNA motif called the E-box, interacts with MEFs
MRF binds to ____ as co-factors
E-proteins
MEF stands for _____
muscle enhancer factor proteins
MEF is expressed where?
-in several cell linages
MEF does what?
-interacts with MRFs
-binds DNA motif called MADS box (MEF-box)
MEF often binds DNA as _____
a dimer
The myogenic program is split into two parts: _____
-determination
-differentiation
Determination of myogenic program has two parts: ____
-induction
-maintenance
Maintenance of myogenic program involves _____
steady state of MRFs and MEFs
Differentiation of myogenic program involves _____
muscle differentiation genes
Expressing MyoD (a MRF) does what in cell?
-turns cell into a myoblast cell
MyoD expression induces muscle cell fate in this lineage?
-mesodermal
MyoD expression does not induce muscle cell fate in these lineages?
-endodermal + ectodermal
MRFs are required at ______ of the myogenic lineage
-multiple stages
MRF transcription factors directly regulate _____ in myoblasts and are degraded after _____
-the cell cycle
-associated phase
MRF associated with G1
-MyoD
MRF associated with M
-Myf5
Myocytic stem cell (aka ____)
satellite cell
Myoblasts fusion (uninucleated) form ___ which differentiate to form _____
-myotubes (multinucleated)
-muscle fiber/myofiber (multinucleated)
committed satellite cell does this to contribute to muscle regeneration and repair?
symmetric division (horizontal plane)
satellite stem cell does this to contribute to muscle regeneration and repair?
symmetric division (horizontal plane)
asymmetric division (vertical plane)
3 types of muscle cells
1) Skeletal muscle
2) Cardiac muscle
3) Smooth muscle
Multiple myoblasts fuse together to form _______
skeletal muscle
The dermomyotome (DM) is derived from the ______
-dorsal part of the somite
A myotome is ____ (def.)
- the group of muscles innervated by a single spinal nerve
Primary myogenesis (def.) + happens at what stage?
-cell fusion (somitic stem cell -> fetal stem cell)
-embryonic
Secondary myogenesis (def.) + happens at what stage?
-basal lamina assembly + innervation/NMJ formation (fetal stem cell -> myocytes)
-fetal
General structure of skeletal muscle
- myofiber (muscle cell) has multiple myofibrils which has sarcomere units
Sarcomere: I band
thin filaments
Sarcomere: A band
-thin and thick filaments
-doesn’t change length during contraction
Sarcomere: H zone
-thick filaments only
-shortens during contraction
Sarcomere: Z disk
-border between two sacromeres
General structure of smooth muscle cells
-thick and thin filaments
-dense bodies + attachment plaques
dense bodies + attachment plaques in smooth muscle cells are analogous to _____ of skeletal and cardiac muscle fibers
Z-discs
Parts of skeletal myofibrils + function
-actin (filamentous and globular)- thin filament
-myosin - thick filament
-tropomyosin - covers myosin-binding site on actin
-troponin - attaches to tropomyosin with Ca++ binding site
Sliding-filament Contraction is dependent on ____
ATP, Ca++
The sarcoplasmic reticulum does what?
-release Ca++ upon depolarization with nerve signals through Ca++ release channel
Ca++ recovery in sarcoplasmic reticulum
-Ca++ renters SR through Ca++ ATPase
T tubules are found in what type of cells?
striated muscle cells (cardiac and skeletal )
Transverse tubules do what?
permit rapid transmission of the action potential into the cell
Nerve that synapses on neuromuscular junction releases _____
acetylcholine (ach)
neuromuscular junction (def.)
chemical synapse between a motor neuron and a muscle fiber
ACh (def.)
neurotransmitter secreted from parasympathetic neurons
Skeletal muscle contraction steps
1) nerve triggers release of ach from synaptic knob into cleft
2) ach binds to ach receptors on NMJ (starts impulse in sarcolemma of muscle fiber)
3)impulse spread through T tubules
4) Ca++ ions released from terminal cisternae into sarcoplasm
5) Ca binds to troponin which changes shape, moving tropomyosin = open active sites
6)myosin heads of thick filament attaches to open sites = crossbridges
7) myosin moves thin fila. toward center then ATP binds myosin heads
8) ATP broken into ADP & P
9) repeating movement until Ca++ removed (active transport)
10) tropomyosin covers active sites = relaxation of filaments
smooth muscle cells have this characteristics: ____
single nuclei (mononuclear), not organized myofibrils
adjacent smooth muscle cells were physically couplied at ____
dense bodies
caveolae function
regulate cell signaling and uptake and release of Ca2+ from sarcoplasmic reticulum
characteristics of cardiac muscle
-mononuclear
-gap junctions + desmosomes
-intercalated discs
Cardiomyocyte lineage from ____
cardiac mesoderm (further differentiation activates/repressed by Wnt)
Myoepithelial cells are _____ to muscle cells
-similar
Myoepithelium are part of secretory glands: _____
- Sweat
- Mammary
- Lacrimal (tear)
- Salivary
Myoepithelial cells lineage
stem cell -> luminal progenitor + basal progenitor
luminal progenitor -> ductal luminal + alveolar
basal progenitor -> myoepithelial
Mammary gland epithelium cell lineages
ectoderm => mesenchymal stem cell => endothelial precursor cell => ductal precursor cells (puberty) + alveolar precursors cells (pregnancy) => (both produce) myoepithelial cells + luminal cell
