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Developmental Biology > 5: Cleavage: Becoming Multicellular and Development Consequences > Flashcards

5: Cleavage: Becoming Multicellular and Development Consequences Flashcards

1
Q

first few cellular divisions of a zygote

  1. zygote splits along a longitudinal plane
  2. also longitudinal, but at _ to the plane of the first
  3. _ to the first two and is equatorial in position
A

90 degrees
perpendicular

these early divisions produce separate cells called blastomeres

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2
Q

the rapid, multiple rounds of cell division are termed

A

cleavage

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3
Q

after the cleavage has produced over 100 cells, the embryo is called a

A

blastula

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4
Q

the blastula is usually a spherical layer of cells (_ )
surrounding a fluid-filled or yolk-filled cavity (the _ )

A

blastoderm
blastocoel

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5
Q

mammals at this stage form a structure called the _ ,
characterized by an inner cell mass that is distinct from the
surrounding blastula

A

blastocyst

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6
Q

each cell within the blastula is called a

A

blastomere

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7
Q

development proceeds at the rate of roughly one cleavage division per
day for the first _

A

2 days

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8
Q

when the embryo consists of approximately 16 cells, it is called a

A

morula

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9
Q

starting after the eight-cell stage, the embryos of placental mammals enter into
a phase called

A

compaction

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10
Q

during which the individual outer blastomeres tightly adhere through
gap and tight junctions and lose their individual identity when viewed
from the surface

A

compaction

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11
Q

compaction mediated by concentration of calcium (Ca++)-activated cell adhesion
molecules (such as _ ), in a ring around the apical surface of
the blastomeres

A

E-cadherin

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12
Q

through the activity of a sodium (Na+
), potassium (K+
)–adenosine
triphosphatase (ATPase)–based Na+
transport system, Na+
and water (H2O)
move across the epitheliumlike outer blastomeres and accumulate in spaces
among the inner blastomeres

A

cavitation

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13
Q

cavitation occurs about

A

4 days after fertilization

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14
Q

at the blastocyst stage, the embryo, which is still surrounded by the zona
pellucida, consists of two types of cells:

A

o Trophoblast – outer epithelial layer
o Inner cell mass – small inner group of cells

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15
Q

the end of the blastocyst that contains the inner cell mass is known as
the _ , and the opposite end is called the _

A

embryonic pole
abembryonic pole

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16
Q

cells of the inner cell mass give rise to the body of the _ itself in
addition to several _ , whereas cells of the trophoblast form only extraembryonic structures, including the _

A

embryo
extraembryonic structures
outer layers of the placenta

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17
Q

there is increasing evidence that _ (a growth factor secreted by cells of the inner cell mass), acts to maintain mitotic activity in the overlying trophoblast

A

fibroblast growth factor-4

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18
Q

The first cleavage of frog’s egg was observed by

A

Jan Swammerdam in 1738.

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19
Q

The entire process of cleavage in frog’s egg was studied by

A

Pierre Prevost
and Jean Baptiste André Dumas in 1824

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20
Q

planes of cleavage are named depending on the position of the

A

cleavage
furrow

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21
Q

the plane of the cleavage lies on the animal vegetal axis;
it bisects both the poles of the egg; the egg is divided into two equal halves

A

Meridional plane

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22
Q

the cleavage furrows may lie on either side of the meridional
plane; the furrows pass from animal to vegetal pole; the cleaved cells may be
unequal in size

A

Vertical plane

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23
Q

this cleavage plane bisects the egg at right angles to the
main axis; lies on the equatorial plane; divides the egg into two halves

A

Equatorial plane

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24
Q

similar to the equatorial plane, but it lies on either side of
the equator; also called as transverse or horizontal cleavage

A

Latitudinal plane

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25
Q

“yolk rich pole”

A

Vegetal Pole

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26
Q

yolk poor pole

A

Animal Pole

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27
Q

zygotic nucleus is generally displaced towards the _

A

animal pole

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28
Q

Types of Eggs

sparse evenly distributed yolk

A

Isolecithal

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29
Q

Types of Eggs

moderate amount of yolk and often unevenly distributed

A

Mesolecithal

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30
Q

Types of Eggs

dense yolk concentrated at one end

A

Telolecithal

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31
Q

Types of Eggs

yolk concentrated at the middle of the egg

A

Centrolecithal

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32
Q

Isolecithal example

A

sea urchin and mouse

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33
Q

Mesolecithal example

A

frog

34
Q

Telolecithal example

A

bird and reptile

35
Q

Centrolecithal example

A

fly

36
Q

Cleavage Patterns

A
  1. Total/ Holoblastic Cleavage
    a. equal holoblastic cleavage
    b. unequal holoblastic cleavage
  2. Meroblastic Cleavage
    a. discoidal clevage
    b. superficial cleavage
37
Q

the cleavage furrow bisects the entire egg;
such a cleavage may be either equal or unequal

A

Total or holoblastic cleavage

38
Q

in microlecithal and isolecithal eggs,
cleavage leads to the formation of blastomeres of equal size;

A

Equal holoblastic cleavage

39
Q

Equal holoblastic cleavage examples

A

amphioxus and placental mammals

40
Q

in mesolecithal and telolocithal eggs, cleavage leads to the formation of blastomeres of unequal size; among the
blastomeres there are many small sized micromeres and a few large sized macromeres

A

Unequal holoblastic cleavage

41
Q

the cleavage furrows are restricted to the active cytoplasm found either in the animal pole (macrolecithal egg) or superficially
surrounding the egg (centrolecithal egg)

A

Meroblastic cleavage

42
Q

since the macrolecithal eggs contain plenty of yolk,
the cytoplasm is restricted to the narrow region in the animal pole; hence
cleavage furrows can be formed only in 3 the disc-like animal pole region;
such a cleavage is called discoidal meroblastic cleavage;

A

Discoidal cleavage

43
Q

Discoidal cleavage examples

A

e.g. birds and
reptiles

44
Q

in centrolecithal eggs, the cleavage is restricted to
the peripheral cytoplasm of the egg;

A

Superficial cleavage

45
Q

Superficial cleavage example

A

insects

46
Q

Sachs’ Laws proposed by

A

Julius von Sachs in 1877

47
Q

states that “cells tend to divide into equal daughter cells” and “each new division plane tends to intersect the preceding plane at right angles” (acts to maintain the spheroidal shape of blastomeres)

A

Sachs’ Laws

48
Q

Balfour’s Law proposed by

A

Francis Maitland Balfour in 1885

49
Q

states that “the speed or rate of cleavage in any region of egg is inversely proportional to the amount of yolk it contains”

A

Balfour’s Law

50
Q

simplest pattern; in which successful division planes
are at 90 degree angles relative to each other; this results in the
blastomeres aligned directly over or to the side of one another

A

radial cleavage

51
Q
  • the division planes are not at 90-degree angles,
    resulting in blastomeres that are not aligned directly over or beside one another
A

spiral cleavage

52
Q

characteristic of deuterostomes

A

Radial Cleavage

53
Q

deuterostomes

A

(“mouth second”); e.g. human, starfish

54
Q

Radial Cleavage results in

A

indeterminant cells (cells that can individually give rise to a
complete embryo, and they don’t have a determined embryological fate early
on during the development of the embryo)

you can take a single cell from a developing embryo, and given the right condition, that single cell can give rise to a whole embryo; e.g. experiments done with frog embryo

55
Q

characteristic of protostomes

A

Spiral Cleavage

56
Q

Spiral Cleavage results in

A

determinant cells (cell that have a
determined embryological fate early on during the development of the
embryo)

determinant cells are programmed to become a specific type of cell, early on during the proces

57
Q

Classification of Cleavages based on the Potentiality of the Blastomeres for the
Future Development

A

a. Determinate
b. Indeterminate

58
Q

the developmental fate of each embryonic cell is established very early

A

Determinate

59
Q

Determinate: if a cell is isolated from the _ stage the embryo will not fully develop

A

4-cell

this is because the fate of each blastomere is predetermined in the early
embryonic stage itself

60
Q

examples of determinate

A

annelids, mollusks and ascidians (which produce mosaic type of eggs)

61
Q

early embryonic cells retain capacity to develop into a complete embryo if
isolated from other cells

A

Indeterminate

62
Q

Indeterminate: cleavage produces blastomeres which are qualitatively _

A

equipotential or
totipotent

63
Q

when they are isolated, they develop into complete embryos

A

Indeterminate

this is because the fates of blastomeres are not predetermined in the early embryonic period

64
Q

examples of indeterminate

A

vertebrates and certain invertebrates such as echinoderms (which produce
regulative type of eggs)

65
Q

types of eggs of holoblastic

A

isolecithal
mesolecithal

66
Q

types of eggs of meroblastic

A

telolecithal
centrolecithal

67
Q

patterns of cleavage of isolecithal

A
  1. radial - echinoderms, emphioxus
  2. spiral - annelids, molluscs, flatworms
  3. bilaterial - tunicates
  4. rotational - mammals, nematodes
68
Q

patterns of cleavage of mesolecithal

A

radial - amphibians

69
Q

patterns of cleavage of telolecithal

A
  1. bilateral - cephalopod molluscs
  2. discoidal - fish, reptiles, birds
70
Q

patterns of cleavage of centrolecithal

A

superficial - most insects

71
Q

occurs in centrolecithal eggs

A

Superficial Cleavage

72
Q

Superficial Cleavage: the early divisions occur in the surface layer of the egg and cleavage furrows
_ extend into the central yolk

A

do not

73
Q

Superficial Cleavage, the zygote nucleus lies in the _ of the egg

A

center

74
Q

Superficial Cleavage

it divides repeatedly without the division of the egg cytoplasm
o as a result, a large number of _ are formed

A

nuclei

75
Q

an invariant cleavage pattern divides the embryo into different cell
lines that differentiate according to the information they obtain from
differentially distributed cytoplasmic factors

A

cytoplasmic localization

76
Q

the organization of the cytoplasm of the egg before and after fertilization is
established by the redistribution of ooplasmic determinants

A

cytoplasmic localization

77
Q

helps seal the
developmental fate of each cell’s descendants

A

cytoplasmic localization

78
Q

acts as a trigger to initiate a program of events starting with
cleavage, and continuing with gastrulation and neurulation, etc

A

fertilization

79
Q

although fertilization results in union of maternal and paternal genomes, zygotic gene activity is _ until the blastula stage

A

not required

in fact, after fertilization and through cleavage, the maternal, paternal and
zygotic genomes are completely dispensible

80
Q

following the formation of the blastula, _ is activated, which carries the embryo through the rest of embryogenesis

A

zygotic gene transcription

81
Q

Evidence for maternal mRNA control of early development:

  1. maternal trait dominance in _ hybrids
  2. cleavage in _ embryos
  3. _ inhibition does not prevent cleavage
  4. _ inhibition prevents cleavage
A

interspecific
enucleate
transcriptional
translational

82
Q

roles of maternal factors

  1. processing of the _ , which is necessary for its participation in embryogenesis
  2. removal of _ (RNA and protein),
  3. robust activation of the _ , which is essential for the development of the embryo beyond two cells
A

male genome
maternal detritus
embryonic genome

Developmental Biology (6 decks)

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