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BB20149 > Cleavage stages > Flashcards

Cleavage stages Flashcards

1
Q

What happens directly after fertilisation?

A

There are the first divisions of the embryo - mitotic cell cycles begin.

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2
Q

What is significant about the first divisions after fertilisation?

A

There is division with no/little increase in the overall volume of the embryo. There are short mitotic G1 and G2 phases (cell growth) and the daughter cells are smaller.

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3
Q

What is division after fertilisation driven by?

A

Maternal factors inherited from the egg such as protein and mRNA. The inheritance is not necessarily symmetrical e.g. the germ plasm.

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4
Q

What is a blastomere?

A

The name for a newly formed embryo cell.

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5
Q

What is cell specialisation?

A

When new cells have dedicated structures and functions.

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6
Q

What is lineage allocation?

A

Pathways of differentiation of the embryonic cells.

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7
Q

What is cell division called?

A

Cytokinesis.

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8
Q

What is the cleavage furrow?

A

The actomyosin ring that divides cells.

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9
Q

What is holoblastic cleavage?

A

Cleavage furrow that completely separates dividing blastomeres. This is complete cleavage. There is sparse, uniform yolk distribution.

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10
Q

What is meroblastic cleavage?

A

When only part of the blastomere is separated - incomplete cleavage. The yolk impedes membrane formation.

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11
Q

What is significant about the embryonic cleavage in sea urchin?

A

The divisions are holoblastic and the first 7 are stereotypic - the same in all sea urchin species.

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12
Q

What is significant about the first two divisions in the sea urchin?

A

They are meridional - they pass through the animal and vegetal poles.

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13
Q

What is significant about division 3 in the sea urchin?

A

It is equatorial.

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14
Q

What is significant about division 4 in the sea urchin?

A

The cells of animal tier divide meridionally.

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15
Q

What is significant about the blastula of sea urchins?

A

All the cells are the same size.

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16
Q

When are cell fates determined in the sea urchin?

A

The 60-cell stage.

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17
Q

What does the animal pole become at the 60 cell stage in the sea urchin?

A

Ectoderm - e.g. skin and neurons.

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18
Q

What is significant about drosophila cleavage?

A

It is meroblastic. and nucleus division (karyokinesis) occurs without cell division (cytokinesis).

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19
Q

WHat is karyokinesis?

A

Nucleus division.

20
Q

What does the drosophila cleavage result in?

A

Syncytium - many nuclei, one cytoplasm.

21
Q

What is a syncytium?

A

Many nuclei but only one cytoplasm - no cytokinesis.

22
Q

What is the mid-blastula transition in the drosophila cleavage stages and when does it occur?

A

Embryonic gene transcription begins - cycle 11 (the maternal mRNAs are degraded here too)

23
Q

What type of cleavage occurs in the zebrafish?

A

Meroblastic cleavage.

24
Q

What are the features of zebrafish eggs?

A

They are teleolecithal - they are mostly occupied by yolk.

25
Q

Where does cleavage occur in the zebrafish?

A

A thin region of animal pole - the blstodisc.

26
Q

When does the mid-blastula transition occur in the zebrafish?

A

Cell cycle 10 - this is hen the embryo gene expression begins.

27
Q

What are the germ layers in the late blastula fish embryo?

A

Ectoderm (large proportion), mesoderm (second largest) and endoderm (smallest).

28
Q

What type of cleavage does the zenopus undergo?

A

Holoblastic - the egg has radial animal-vegetal symmetry. The mesoleithal (moderate yolk) is displaced by radial cleavage ??

29
Q

What is significant about the animal pole in the xenopus?

A

It is more heavily pigmented - it is the region fertilised by sperm.

30
Q

What is the animal pole cleavage impeded by in the xenopus?

A

The yolk - the second division starts in the animal region before the first division is finished.

31
Q

Where is the first cleavage furrow onset?

A

In the animal pole.

32
Q

How is the first cleavage furrow initiated?

A

20 um wide contractile band made up of actin filaments and myosin ii. It is assembled just beneath the surface.

33
Q

What is the furrow rat of the first cleavage furrow?

A

4mm/h.

34
Q

How is the cleavage furrow initiated?

A

The surface initially forms periodic stress folds.

35
Q

How are filopodia involved in the first cleavage furrow?

A

They interact with opposing cell surfaces across cleavage furrow to mediate blastomere-blastomere adhesion.

36
Q

What does it mean that maternal factors are localised?

A

Different mRNAs and proteins are located in the animal and vegetal poles - separate in the ectoderm (animal pole) and endoderm/germ plasm (vegetal pole).

37
Q

What happens to maternal mRNA levels after fertilisation?

A

They decline as the maternal mRNA is degraded.

38
Q

When does embryonic gene activation occur in human and mouse?

A

4 cell stage at human, late 1 cell stage in the mouse.

39
Q

What does embryonic gene activation result in?

A

Embryo transcription initiated.

40
Q

What is lineage specification?

A

The first embryonic differentiation.

41
Q

How is mammalian lineage specific differentiation to other species?

A

In non-mammalian species, there is maternally dictated specification - it is pre determined.

42
Q

What are the two lineages established initially in mammals?

A

Trophectoderm and the inner cell mass.

43
Q

What does the trophectoderm give rise to?

A

Extra-embryonic tissue such as the placenta and chorion.

44
Q

What does the inner cell mass give rise to?

A

Embryonic tissue.

45
Q

What is lineage specification driven by?

A

Interplay between transcription factors.

46
Q

What transcription factors drive lineage specification in the trophectoderm?

A

Tead4, Cdx2.

47
Q

What transcription factors drive lineage specification in the ICM?

A

Nanog, Oct4, Esrrb and Sox2.

BB20149 (16 decks)

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