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UVic BIOL 309 - Spring 2019 > Early Vertebrate Development > Flashcards

Early Vertebrate Development Flashcards

1
Q

What is the primary role of Pitx2 in biological development? Is there a specific function in humans?

A

Influencing left-right asymmetry. In humans: Pitx2 > leftness.

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2
Q

What are the characteristic symptoms of Reiger symptoms?

A

No left-right defects, but mild skull dysmorphism, eye socket and dental anomalies.

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3
Q

What is the relevance of Nodal signalling in asymmetry?

A

Loss of function leads to left-right patterning defects originating at the node.

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4
Q

What 2 theories have been used to try to decribe the asymmetrical mechanism of nodal flow?

A
  1. Leftward current carries “parcels” of signalling molecules
  2. Leftward current “mechanically” stimulates peripheral cilia
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5
Q

What 2 important things are present in the proposed nodal vesicular parcels responsible for left/ right asymmetry?

A
  1. Calcium ++

2. Sonic Hedgehog

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6
Q

How is left/right assymmetry affected when direction of nodal flow is reversed?

A

Left and right are then reversed during development.

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7
Q

How are nodal cilia involved in the development of left/right asymmetry in vertebrates?

A

They rotate clockwise to cause the flow of nearby molecules to travel from right to left.

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8
Q

What is KIF3B?

A

A microtubule motor protein in the same family as kinesin, responsible for development of cilia in the node.

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9
Q

What is meant by situs ambiguous?

A

Any deviation from normal internal organ orientation.

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10
Q

What is meant by situs inversus? What about situs inversus thoracalis and situs inversus abdominalis?

A

The inversion of internal organ orientation.
Thoracalis: inversion of thoracic organs
Abdominalis: inversion of abdominal organs

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11
Q

What is a morphogen?

A

A signalling molecule which organizes surrounding cells into a pattern/gradient. Acts on cells in a concentration-dependent manner.

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12
Q

How does a morphogen determine the fate of surrounding cells?

A

By arranging them according to differing concentrations of the morphogen.

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13
Q

Which TGF-beta family signalling molecule is active in the endoderm? What does this produce?

A

Xnr, active in the endoderm as a concentration gradient with the highest concentration at the dorsal side and the lowest at the ventral side.

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14
Q

Which TGF-beta family signalling molecule is active in the mesoderm? What does this produce?

A

BMP4, active in the mesoderm as a concentration gradient with the highest concentration at the ventral side and the lowest at the dorsal side.

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15
Q

What is the significance of Cerl and Lefty in biological development? What does it inhibit to accomplish this?

A

Both expressed in the AVE (anterior visceral endoderm), critical for correct anterior-posterior positioning. Acts as an antagonist for Nodal.

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16
Q

What important role does Nodal play in early vertebrate development?

A

Specifies the primitive streak formation.

BONUS: inhibited by Cerl and Lefty so it doesn’t just activate anywhere.

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17
Q

What does “Cerl” mean?

A

Cerberus-like.

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18
Q

Even if Cerl and Lefty are inhibited (activating Nodal), primitive streaks don’t pop up everywhere, why?

A

Because signalling from both Nodal and the Wnt pathway (Wnt3) are needed to induce formation of the primitive streak (redundancy).

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19
Q

What is the function of Gsc (Goosecoid)

A

Specifies the Spemann organizer fate.

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20
Q

What is the AVE? How does it form?

A

Anterior visceral endoderm. Extraembryonic, forms from the migration of cells from medial regions.

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21
Q

What structure in the mammal embryo is functionally equivalent to the Spemann organizer in frogs?

A

(Henson’s) node.

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22
Q

Cerl and Lefty inhibit Nodal (important for primitive streak formation alongside Wnt), but what signalling molecules inhibit Wnt?

A

Cerberus, Frzb and Dickkopf.

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23
Q

What structure in the mammal embryo is functionally equivalent to the anterior endomesoderm in frogs?

A

The anterior visceral endoderm (AVE).

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24
Q

Where in the mammalian embryo does involution occur?

A

Along the primitive groove.

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25
Q

What structure in the mammal embryo is functionally equivalent to the dorsal lip in frogs?

A

The node.

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26
Q

How do expression of Frzb and Dickkopf influence development?

A

Both inhibit Wnt
Frzb: increase head size
Dickkopf: decrease head size

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27
Q

Besides acting as an “off switch”, how can microRNA affect development?

A

By fine-tuning and stabilizing gene expression (dealing with concentration gradients).

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28
Q

What gradient is used for specializing the dorsal-ventral mesoderm?

A

The BMP gradient.

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29
Q

What gradient is used for specializing the anterior-posterior neural ectoderm?

A

The Wnt gradient.

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30
Q

Where is Wnt3 expressed in the mammalian embryo prior to gastrulation?

A

The posterior visceral embryo (PVE) and the posterior epiblast.

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31
Q

Where does gastrulation initiate in the embryo of amniotes?

A

At the posterior region of the epiblast.

32
Q

Wnt signalling is required for _________ development and is inhibited during _________.

A

Required for posterior development, inhibited during anterior development.

33
Q

When Cerberus functionality is lost why does head development still occur?

A

Because Frzb and Dickkopf have similar function as Cerberus in mediating head development (redundancy).

34
Q

What 5 signalling molecules inhibit BMP?

A
  1. Chordin
  2. Noggin
  3. Follistatin
  4. Cerberus
  5. Xnr3
35
Q

How does transplantation of a young frog gastrula dorsal lip influence the final tadpole form?

A

Tadpole develops with a second axis (TWO HEADS).

36
Q

What is the function of siamois protein? What does it act alongside?

A

Acts with Smad 2/4 as a transcription factor for goosecoid protein (not strong enough alone).

37
Q

What is the function of goosecoid protein?

A

Specifies the Spemann organizer.

38
Q

Where is the Nieuwkoop center? What is it’s function?

A

Located in the dorsal endoderm, activates siamois protein to initiate transcription of goosecoid which specifies the Spemann organizer.

39
Q

How is the dorsal-ventral axis defined in an embryo? What causes the uniform surface of the egg to differentiate?

A

The site of sperm entry defines the dorsal-ventral axis.

40
Q

Where is dishevelled protein (+GBP+Wnt11 mRNA) located before sperm entry? What about after?

A

Located at the bottom of the vegetal pole, but migrates to the dorsal side upon sperm entry.

41
Q

How is dishevelled protein able to migrate following sperm entry to the egg?

A

Microtubules form from the sperm and spread around the membrane to the opposite side of the embryo. Dishevelled is transported along these microtubules.

42
Q

What is know to block microtubule formation in a fertilized egg, resulting in a ventralized embryo?

A

Blocked by UV.

43
Q

Where in the fertilized embryo are Dsh and GBP enriched following cortical rotation?

A

Dsh and GBP are dorsally enriched.

44
Q

Where is beta-catenin degraded in the embryo following cortical rotation? Where is it stable?

A

Degraded on the ventral side but dorsally stabilized.

45
Q

What 6 steps outline the Wnt signalling pathway? Which of these components functions as an inhibitor?

A
  1. Wnt
  2. Frizzled
  3. Disheveled (inhibitor)
  4. GSK-3 (inhibitor)
  5. Beta-catenin
  6. Transcription
46
Q

VegT is required for the formation of ______ and _______.

A

Endoderm and mesoderm.

47
Q

The results of the animal/vegetal sandwich experiments show that ______ is able to induce _______,

A

Endoderm is able to induce mesoderm.

48
Q

How can UV ventralized embryos be rescued?

A

By using the dorsal endoderm (Nieuwkoop center) to induce the dorsal mesoderm (Spemann’s organizer).

49
Q

What is know to cause development of a dorsalized embryo?

A

Exposure to LiCl at the one-cell stage.

50
Q

What is the default fate of the ectoderm? Why does it not become this when separated from the mesoderm?

A

Neural tissue. The mesoderm secretes BMP (induces epidermis) inhibitors (ex: Noggin) which cause ectoderm to become neural tissue.

51
Q

What part of the BMP signalling pathway is inhibited by Noggin (or chordin, or follistatin)?

A

The inhibitors act on the BMP ligand to inhibit.

52
Q

What developed structures arise from the dorsal mesoderm?

A

Notochord and neural tube.

53
Q

What developed structures arise from the endoderm?

A

Pharynx, tongue, trachea, gall bladder, pancreas, bile duct, oesphagus, stomach, small intestine, proctodaeum.

54
Q

What developed structures arise from the ventral mesoderm?

A

Blood and mesenchyme.

55
Q

What developed structures arise from the somite?

A

Back muscles, vertebrae, dermis.

56
Q

During what developmental stage do events occur which lead to neural fate determination?

A

Gastrulation.

57
Q

What occurs when cells are translocated prior to determination?

A

Embryo develops according to the fate map.

58
Q

What occurs when cells are translocated following determination.

A

Tissues develop into their determined fates regardless of where they have been moved to?

59
Q

At what stage of development will cleavage no longer yield viable organisms?

A

After the 4-cell stage, cleavage does not result in viable organisms (b/c of asymmetry).

60
Q

What is meant by “regulative” development?

A

Internal adjustment allows the embryo to maintain normal development despite disturbances.

61
Q

What is meant by “mosaic” development?

A

All body regions spatially compartmentalized in the early embryo.

62
Q

What 3 mechanisms are there for monozygous twinning?

A
  1. (25%) Each have own chorion and amnion
  2. (60-70%) Each have own amnion but share chorion
  3. (1-2%) Share chorion and amnion
63
Q

What is meant by “polyembryony”?

A

The formation of more than one embryo from a single fertilized egg (ex: armadillos have identical quadruplets).

64
Q

How does a chimeric organism arise?

A

A rare event (kinda the opposite of twinning) where 2 fertilized eggs fuse to become a single organism with 2 different sets of chromosomes depending on tissue.

65
Q

What is the chorion? What about the amnion?

A

Chorion: outermost embryo membrane for exchange (mammals = placenta)
Amnion: secretes fluid

66
Q

What occurs during the “compaction” event in early cleavage? What is important for this?

A

Flattening and joining of cell ball at 8-cell stage. E-caderin mediates formation of cell junctions.

67
Q

What is the purpose of the yolk sac? What types of organisms have this?

A

Nourishes the developing organism, present in birds and reptiles.

68
Q

What is discoidal cleavage? What organisms do this?

A

Only the upper cells divide, leaving large yolk sac below. Exhibited in fish, bird, and reptile development.

69
Q

Which of the embryonic tissues arise from the embryo itself? Which are supplied by the mother?

A

Embryo: chorion (placenta), amnion, yolk sac
Mother: uterine epithelium, decidua (placenta)

70
Q

What is the allantois?

A

One of the tissues supporting the developing embryo which does gas exchange and stores waste.

71
Q

Localization of ___ establishes the future posterior in amphibians.

A

Par2

72
Q

What is displaced radial cleavage? What organisms do this?

A

Initial 2 cleavages are vertical before the first horizontal cleavage. Occurs in amphibians.

73
Q

What is the function of Par6?

A

Implicated in cytoskeletal rearrangement (particularly in humans).

74
Q

Why are Par proteins important for animal early development?

A

Establishes asymmetry.

75
Q

_______ localization specifies germ cell formation. What is essential for their specification?

A

P-granule. Ribonucleoprotein complexes are essential for specification.

76
Q

What is the function of macho-1?

A

Specifies muscle development.

77
Q

What differentiates meroblastic cleavage from holoblastic cleavage?

A

Meroblastic: partial cleavage of the embryo
Holoblastic: complete cleavage of the embryo

UVic BIOL 309 - Spring 2019 (9 decks)

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