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limbs and back block > Muscle embryology > Flashcards

Muscle embryology Flashcards

1
Q

What is the role of the notochord ?

A

Signalling centre: it sends out signals to tell tissues what to become

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2
Q

What two regions don’t have mesoderm? What are these regions going to form?

A

At the top: oropharyngeal membrane
At the bottom: cloacal membrane

The go on to form the mouth and anus

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3
Q

Describe the differentiation of the mesoderm including days

A

Day 19: mesoderm enlarges and forms two triangular structures of mesoderm = paraxial mesoderm
Day 20: Mesoderm enlarges again. Ectoderm folds to form a groove = neural tube
Day 21: small population of cells outside the paraxial mesoderm = intermediate mesoderm. Lateral to that, there is the lateral plate mesoderm which goes onto line the whole embryo?

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4
Q

What does the neural tube go onto become?

A

Spinal cord

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5
Q

What does the intermediate mesoderm go onto form?

A

Genitourinary tract

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6
Q

What are the 3 groups the mesoderm divides into?

A

Paraxial
Intermediate
Lateral plate

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7
Q

What does the paraxial mesoderm form?

A

Somites

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8
Q

Define somites

A

Block of paraxial mesoderm that forms the axial skeleton

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9
Q

describe the differentiation of the lateral plate mesoderm

A

The intraembryonic coelom (cavities) enlarge and split the lateral plate mesoderm into 2 layers:
LPM around the amniotic cavity (upper): somatic/parietal zone
LPM around the yolk sac (lower): splanchnic/visceral zone

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10
Q

What is the origin of skeletal muscle?

A

Paraxial mesoderm

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11
Q

What is the origin of cardiac muscle?

A

visceral/splanchnic layer of lateral plate mesoderm

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12
Q

What is the origin of SMOOTH muscle?

A

Smooth: visceral/splanchnic lateral plate mesoderm

Pupil, sweat and mammary glands: ECTODERM

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13
Q

Describe the process of somitogenesis (somite formation) from paraxial mesoderm

A

Somites begin to form at DAY 20 in a cranio-caudal sequence.

It starts from where the head of the embryo will be and continues down the length of the embryo.

3 pairs form each day and it continues until end of week 5

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14
Q

Through what mechanism is somitogenesis controlled? What genes are involved in this mechanism and how does it work?

A

Clock and wave mechanism
Involves FGF family, Wnt and Notch.

Notch genes tell mesoderm cells to switch between a permissive (switched on) and non-permissive state.
A wave of FGF 8 then sweeps along the length of the embryo and interacts with the genes that are permissive at the right time and right area.
Wnt helps things move along.
This results in somite formation.

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15
Q

Describe somite differentiation

A

Somites are transformed into spheres = epithelium around a lumen.

2 different zones are formed:
Dermomyotome (cells in the dorsal half - TOP)
Sclerotome (cells in the ventral and medial half - BOTTOM)

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16
Q

What is the transition that somites make ?

A

Cells transition from mesenchymal to epithelial

17
Q

How do the cells arrangement in the dermomyotome and sclerotome differ?

A

Cells in dermomyotome are densely packed together

18
Q

What does the sclerotome go on to form?

A

Ribs and vertebrae

19
Q

what does the dermomyotome split to become? What do they go on to form?

A

Dermatome - forms dermis and connective tissue

Myotome - forms muscle

20
Q

What are MYOD and MYF5

A

myogenic regulatory (transcription) factors that activate muscle specific genes

21
Q

How do MYOD and MYF5 regulate muscle development

A

They enable the differentiation of myogenic precursor cells into myoblasts (muscle building cells)

22
Q

What are myoblasts and where do they come from?

A

Muscle building cells

Myotome

23
Q

How is MYOD activated and where is it found?

A

The neural tube produces Wnt (activating) and BMP (inhibitory) which combine to activate MYOD in the dermomyotome

24
Q

What does myogenin do?

A

Enables the differentiation of myoblasts into myotubes

25
Q

What cells express MYF5?

A

Muscle cell precursors (not sure if this is the same as myoblasts)

26
Q

What happens when MYOD and MYF5 are depleted?

A 
Stop dividing
Secrete Fibronectin (ECM is laid down) and bind to it via an integrin-crucial step
Cells align into chains and fuse together.
Cell membranes disappear and multinucleated myotubes form = PRIMARY MYOTUBES
27
Q

How is it ensured that there is enough signal for all the embryo?

A

The lateral plate mesoderm also produces Wnt and BMP

28
Q

What 2 signalling molecules does Notochord produce? What do they do?

A

Noggin and SHH

They induce sclerotome formation

29
Q

What is Wnt and what is its role?

A

Wnt is part of a major family of signalling molecules.

Involved in body axis pattering, cell proliferation, cell migration and cell fate specification

30
Q

What are BMPs and what is their role?

A

BMPs are family of growth factors

They induce cartilage/bone formation and control tissue architecture.

31
Q

What is sonic hedgehog and what is its role?

A

Belongs to hedgehog signalling family.
Acts as a morphogen (molecule that diffuses to form a concentration gradient) and has different effects on embryo cells according to concentration

32
Q

What does notch belong to and what is its role?

A

Family of transmembrane proteins.

Controls cell fate decisions

33
Q

What does FGF belong to and what is its role?

A

Family of signalling molecules.
Acts as a mitogen (encourages cells to initiate cell division). In development, they stimulate Wnt signalling, and are important in mesoderm induction and limb development

34
Q

what is responsible for smooth muscle differentiation?

A

Serum response factor

Myocardin enhances SRF activity

35
Q

What is skeletal muscle development under the control of?

A

MYOD
MYF5
Myogenin

36
Q

What directs the dermatome to become the dermis?

A

Neurotrophin-3 from dorsal neural tube (top bit)

37
Q

What two cell types does the myotome split into?

A

Dorsomedial muscle cells

Ventrolateral muscle cells

limbs and back block (28 decks)

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