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Limbs And Back - Week 3 > Muscle Embryology > Flashcards

Muscle Embryology Flashcards

1
Q

How does mesoderm form during gastrulation?

A

Cells of the epiblast invaginate via the primitive streak and fibroblast growth factor 8. The push down at the primitive streak and then out. The cells which end up between the ectoderm and endoderm become the mesoderm.

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2
Q

What is the notochord?

A

A signalling centre in the mesoderm, made up of a solid rod of cells, which controls specification of surrounding cells.

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3
Q

All but two regions of the embryo contain all three germ layers. Which regions do not contain mesoderm?

A

Oropharyngeal membrane and cloacal membrane.

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4
Q

What are the distinct regions of mesoderm?

A
  • notochord
  • paraxial mesoderm
  • intermediate mesoderm
  • lateral plate mesoderm
  • extra embryonic mesoderm
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5
Q

When does mesoderm differentiation occur?

A

Day 17-21

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6
Q

In which direction do cells move to form the paraxial mesoderm?

A

Bilaterally and cranially from primitive streak

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7
Q

Where is paraxial mesoderm found?

A

Adjacent to notochord and neural tube

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8
Q

What does paraxial mesoderm go on to form?

A

Somites

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9
Q

What does intermediate mesoderm go on to form?

A

The genitourinary system.

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10
Q

Which cavity splits the lateral plate mesoderm in to two layers?

A

The intraembryonic coelom

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11
Q

What are the two layers of the lateral plate mesoderm?

A
  1. Somatic/parietal layer

2. Splanchnic/visceral layer

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12
Q

Where do skeletal muscles originate from?

A

Paraxial mesoderm

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13
Q

Where does smooth muscle of the gut and its derivates originate from?

A

Visceral layer of lateral plate mesoderm

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14
Q

Where does cardiac muscle originate from?

A

Visceral layer of lateral plate mesoderm

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15
Q

Which muscles do not originate from mesoderm but ectoderm?

A

Smooth muscles of the pupil, mammary and sweat glands

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16
Q

What is somitogenesis?

A

The formation of somites from paraxial mesoderm.

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17
Q

Where do somites form?

A

Alongside the developing neural tube in a craniocaudal sequence.

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18
Q

When do somites form?

A

From day 20 to the end of week 5 - approximately 3 pairs a day.

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19
Q

How might the age of an embryo be accurately determined?

A

By counting pairs of somites.

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20
Q

How is somitogenesis controlled?

A
  • mesenchymal-epithelial transition so cells are closely packed
  • notochord influences somite formation
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21
Q

What is presomitic mesoderm?

A

Unsegmented mesoderm

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22
Q

List some of the molecules involved in somitogenesis.

A

FGF, Wnt and Notch

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23
Q

Describe the sclerotome.

A
  • formed through somite differentiation
  • cells in the ventral and medial area undergo epithelial - mesenchymal transition
  • form vertebrae and ribs
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24
Q

Describe the dermomyotome.

A
  • formed through somite differentiation
  • made up of cells in the dorsal half
  • splits to form dermatome and myotome
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25
Q

What does the dermatome go on to form?

A

The dermis of the back

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26
Q

What does the myotome go on to form?

A

Muscles

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27
Q

What is a somite?

A

A block of paraxial mesoderm which gives rise to skeletal muscles.

28
Q

What produces factors MYOD and MYF5?

A

The notochord and neural tube

29
Q

What are myocytes?

A

Mature muscle cells

30
Q

What are myoblasts?

A

Muscle cell precursors

31
Q

How are primary myotubes formed?

A

Myoblasts align into chains and fuse, the cell membranes disappear and a multinucleated myotube or primary myotube is formed.

32
Q

Which molecule mediates the differentiation of myoblasts in to primary myotubes?

A

Myogenin

33
Q

How do myoblasts undergo cell division?

A

Under the influence of growth factors.

34
Q

What happens to myoblasts when growth factors are depleted?

A

They stop dividing

35
Q

State two molecules which regulate muscle development.

A

MYOD and MYF5

36
Q

What do MYOD and MYF5 have in common?

A
  • both are transcription factors
  • both activate muscle specific genes
  • both enable the differentiation of myogenic precursor cells in the dermomyotome into myoblasts
37
Q

What do myogenic precursor cells differentiate in to?

A

Myoblasts

38
Q

What non muscle cells can MYOD and MYF5 convert in to muscle cells?

A

Fibroblasts, adipocytes, chondrocytes and retinal pigment cells

39
Q

Are WNT proteins activating or inhibitory?

A

Activating

40
Q

Are BMP proteins activating or inhibitory?

A

Inhibitory

41
Q

Which structures in the embryo secrete WNT and BMP?

A

The neural tube and lateral plate mesoderm

42
Q

When combined, what do WNT and BMP activate?

A

MYOD in the dermomyotome

43
Q

What happens when MYOD is activated in the dermomyotome?

A

A group of muscle cell precursors is created which then express MYF5

44
Q

Which molecules induce sclerotome formation?

A

Sonic hedgehog and noggin

45
Q

Where are sonic hedgehog and noggin secreted from?

A

The notochord

46
Q

What are some of the developmental processes controlled by the WNT family of molecules?

A

Body axis patterning, cell fate specification, cell proliferation and migration.

47
Q

What type of molecules arise from the Wnt family?

A

Signalling molecules

48
Q

What type of molecules arise from the BMP family?

A

Growth factors/cytokines

49
Q

What do BMP molecules do?

A
  • control tissue architecture throughout the body

- induce formation of bone/cartilage in development

50
Q

What does dysregulated BMP signalling lead to?

A

Many pathological processes including cancer

51
Q

What is a morphogen?

A

A molecule that diffuses to form a concentration gradient and has different effects on the cells of the embryo depending on its concentration.

52
Q

Describe sonic hedgehog molecule.

A

Part of the hedgehog signalling family and acts as a morphogen.

53
Q

Describe notch molecules.

A

Family of transmembrane proteins that control cell fate decisions.

54
Q

What type of molecules are FGFs?

A

Signalling molecules which activate cell surface receptors, often act as mitogens. In development they often stimulate Wnt signalling.

55
Q

What are mitogens?

A

Molecules which encourage cells to commence cell division.

56
Q

What did gain and loss of function experiments with MYOD1 show?

A

Gain - they can turn non muscle cells in to muscle cells
Loss - loss of MYOD1 alone is not enough to inhibit skeletal muscle development. Skeletal muscle development will not occur when both MYOD1 and MYF5 are tampered with.

57
Q

Where does (most) smooth muscle originate from?

A

Splanchnic layer of lateral plate of mesoderm.

58
Q

What factor is responsible for smooth muscle differentiation?

A

Serum response factor

59
Q

What pathways upregulate serum response factor?

A

Kinase phosphorylation pathways

60
Q

What factors can enhance serum response factor?

A

Myocardin and myocardin related transcription factors.

61
Q

Where does skeletal muscle originate from?

A

The dermomyotome of a somite

62
Q

Where are tendons derived from?

A

Sclerotome

63
Q

What transcription factor controls the formation of tendons?

A

Scleraxis

64
Q

Where does cardiac muscle originate from?

A

Splanchnic layer of lateral plate mesoderm

65
Q

A lack of or mutations in which molecule may cause congenital heart defects?

A

NKX2.5

66
Q

Is MYOD involved in early cardiac muscle development?

A

No

Limbs And Back - Week 3 (6 decks)

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