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Animal Developmental Biology > Frogs > Flashcards

Frogs Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Which frog species are model organisms for development?

A

Rana pipens and Xenopus

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2
Q

Why are frogs good model organisms?

A

Large broods, rapid development and good for transplantation studies

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3
Q

What types of studies are frogs not good for?

A

Genetic studies, polyploidy is a problem

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4
Q

What type of yolk distribution is found in frog eggs?

A

Mesolecithal, vast majority is in the vegetal pole

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5
Q

Where on the egg does fertilization occur?

A

Animal pole. The sperm can’t get through the yolk

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6
Q

What two things come from the sperm?

A

Nucleus and centrioles that set the first plane of division

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7
Q

What is a cortical rotation?

A

The cytoplasm next to the membrane spins within the egg. The spin is caused by microtubules from the centrioles

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8
Q

What part of the egg forms from the cortical rotation?

A

Grey crescent

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9
Q

What happens in the first cleavage?

A

Meridional, bisects grey crescent

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10
Q

What happens in the second cleavage?

A

Meridional, perpendicular to the first cleavage

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11
Q

What happens in the third cleavage?

A

Equatorial, displaced due to the yolk

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12
Q

What type of cleavage is seen in frogs?

A

Holoblastic, radial, unequal

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13
Q

Why is unequal cleavage seen in frogs?

A

The vegetal pole cells divide more slowly than the animal pole cells because the yolk resists cytokinesis

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14
Q

What happens in the 12th division?

A

Mid-blastula transition

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15
Q

What is the mid-blastula transition?

A

The transition from maternal signals to the zygotic genome

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16
Q

What changes in the embryo after the mid-blastula transition?

A

Transcription and translation get increased and the cell cycle is slowed down. Each cell division takes longer

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17
Q

Why is the blastocoel displaced in a frog blastula?

A

It can’t form in the vegetal pole because of the yolk and slow division, so it can only form in the animal pole

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18
Q

What is the fate of the epidermal ectoderm?

A

Skin

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19
Q

What is the fate of the neural plate ectoderm?

A

Brain and nervous tissue

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20
Q

What is the fate of the axial mesoderm?

A

Notochord

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21
Q

What is the fate of the paraxial mesoderm?

A

Somites

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22
Q

What are somites?

A

Regular mesoderm divisions on either side of the developing nervous system and notochord

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23
Q

What is the fate of lateral plate mesoderm?

A

Liver, spleen, body cavity

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24
Q

What is the fate of the endoderm?

A

Gut and lungs

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25
Q

What 5 morphogenetic events happen during gastrulation in frogs?

A

Epiboly, vegetal rotation, invagination, involution, intercalation

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26
Q

Which cells will undergo the epiboly during gastrulation?

A

Animal pole cells

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27
Q

What happens during the epiboly in gastrulation?

A

The animal pole cell layers intercalate and become narrower, which forces the cells to expand down over the vegetal pole

28
Q

What happens during the vegetal rotation in gastrulation?

A

The vegetal cells are forced upwards and starting buckling in the blastocoel

29
Q

Where is the invagination during gastrulation occurring?

A

Blastopore

30
Q

What structure results from the invagination of the blastopore cells?

A

The dorsal blastopore lip

31
Q

Which two structures are formed by the involution during gastrulation?

A

Archenteron and yolk plug

32
Q

How is the archenteron created?

A

Involution of the cells over the blastopore lips causes the new cavity to be formed and spreads endoderm and mesoderm cells through the animal pole

33
Q

What happens to the blastocoel during gastrulation?

A

It gets displaced by the archenteron and eventually replaced. The fluid inside squeezes in between the loosely packed cells between the blastocoel and archenteron

34
Q

What drives the involution of cells and lets them recognize and follow a path?

A

Integrin-fibronectin communication

35
Q

How do involuting cells use fibronectin to recognize and follow a path?

A

The lead cells reach out with lamellipodia and contact the fibronectin, then follow that signal while dragging other cells behind them

36
Q

What are lamellipodia?

A

Sheet-like extension of plasma membrane for communication

37
Q

Which cells undergo intercalation during gastrulation?

A

Mesoderm

38
Q

What are the 3 mechanisms that drive the intercalation during gastrulation?

A

Polarized cell adhesion and the recognition of fibronectin, differential expression of protocadherins in the axial and paraxial mesoderm, actin contraction caused by calcium

39
Q

Why is the grey crescent important?

A

Contains a maternal signal that specifies the organizer

40
Q

Why does transplanting cells from the dorsal blastopore lip onto another embryo create a new body axis?

A

They signal and organize the surrounding cells to become specified

41
Q

What did Barth and Holtfreter observe when they cultured amphibian tissue on glass?

A

It differentiated into ectodermal structures even though no inducing tissues were present

42
Q

What did de Robertis show was occurring when amphibian tissue cultured on glass differentiated?

A

The glass was stimulating the MAPK/Erk pathway, which inhibits Smad1

43
Q

How do the findings of de Robertis work with the idea of a chemical inducing agent?

A

The glass is stopping the signal that is normally there in the embryo, so the pathway inhibits Smad1 and causes differentiation into brain instead of skin

44
Q

Which signal needs to be blocked in order for cells to become neural tissue?

A

BMP

45
Q

Where is goosecoid expressed?

A

Brain cells

46
Q

Where is brachyury expressed?

A

Notochord

47
Q

What class of signals do chordin, follistatin, and noggin belong to?

A

Neural inducer genes and BMP inhibitors

48
Q

What does chordin do?

A

Establishes the neural chord and competes with BMP for its receptor

49
Q

What does noggin do?

A

Establishes the placement of the brain and competes with BMP for its receptor

50
Q

Which side of the embryo expresses BMP?

A

Ventral

51
Q

Which side of the embryo expresses chordin, follistatin and noggin?

A

Dorsal

52
Q

How does BMP determine the fate of ectoderm cells?

A

An absence of BMP leads to specification of neural ectoderm, its presence leads to specification of epidermal ectoderm

53
Q

What is the organizer in frogs?

A

Dorsal blastopore lip

54
Q

What is the Nieuwkoop centre?

A

A set of maternal signals in the dorsal side of the vegetal cells of the embryo that specifies overlying cells to become the organizer

55
Q

What are VegT and Vg1? Are they maternal or zygotic signals?

A

Maternal transcription factors that activate TGF-beta family paracrine signals by working through the Smad2 pathway

56
Q

Where is beta-catenin in the vegetal cells of the embryo?

A

Dorsal side

57
Q

How does the cortical rotation from fertilization affect the placement of beta-catenin?

A

The rotation carries maternal signals to the dorsal side of the vegetal cells. The signals brought include Wnt II, dishevelled, and GBP which inhibit GSK-3 and prevent beta-catenin breakdown

58
Q

What is Tcf3?

A

A transcription factor that is suppressing transcription of siamois and twin

59
Q

What happens to Tcf3 when beta-catenin is present?

A

Beta catenin binds to Tcf3 and it becomes an activator instead of a suppressor

60
Q

What do siamois and twin do?

A

Activate transcription of neural inducer and organizer genes by working with Smad2 (i.e. noggin, chordin, goosecoid)

61
Q

How are Nodal concentrations related to VegT and Vg1?

A

High VegT and Vg1 concentrations means low Nodal

62
Q

How are Nodal concentrations related to beta-catenin?

A

High beta-catenin means high Nodal

63
Q

High beta-catenin and high Nodal specifies what?

A

The organizer

64
Q

High VegT and Vg1 and low Nodal specifies what?

A

Ventral mesoderm

65
Q

What are the 4 functions of the organizer?

A
  • self-differentiation of dorsal mesoderm
  • dorsalizes surrounding mesoderm into paraxial mesoderm
  • dorsalizes ectoderm into the neural tube
  • initiates gastrulation

Animal Developmental Biology (26 decks)

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