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CELL1001 > Development Lecture 2 > Flashcards

Development Lecture 2 Flashcards

1
Q

Describe gastrulation in sea urchin embryos?

A

FIRST PHASE OF GASTRULATION
1. some of the cells at the vegetal pole elongate to form the vegetal plate

  1. apical pole of some of these cells constricts so they form bottle cells
  2. bottle cells lose adhesion with hyaline membrane and other cells

SECOND PHASE OF GASTRUALTION = inward buckling of the monolayer at the vegetal plate

  1. constriction of the apical surface of vegetal plate cells due to action of actin and myosin filaments at the apical surface
  2. convergent-extension causes the elongation of the invaginating monolayer and the archenteron (tubular structure) is generated
  3. in order to elongate the archenteron further, secondary mesonchyme cells produce filopodia and make contact with them to the basal lamina of the animal pole
  4. the filopodia of the SMCs pull the the archenteron towards the animal pole
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2
Q

Describe the cleavage patterns of sea urchins

A
  • very stereotypical for the first eight divisions
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3
Q

What are the two main stages of gastrulation of sea urchins?

A
  1. Ingression of primary mesenchyme cells

2. invagination of the archenteron

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4
Q

What does the endoderm in sea urchins form?

A

The gut, mouth and anus

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5
Q

What three adhesion changes that primary mesenchyme cell smuts undergo in order to leave from the epithelium of the vegetal plate?

A
  1. lose affinity for neighbouring epithelial cells
  2. lose affinity fro the hyaline layer on the exterior of the embryo
  3. gain affinity for the basal lamina
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6
Q

The blastopore will form the _

A

anus of the sea urchin

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7
Q

How does the vegetal plate buckle?

A

Apical constriction:

  • the apical (the tip) ends of some cells in the vegetal plates would actively constrict due to myosin and actin movement
  • these cells become bottle cells
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8
Q

What do primary mesenchyme cells form?

A

the larva skeleton

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9
Q

What change occurs so that the bottle cells that form vegetal plate can lose adhesion with the hyaline membrane and becomes migratory loose clusters primary mesenchyme cells?

A

PMCs lack calcium dependent adhesion molecules, cadherins, from their epithelium

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10
Q

What is the site of invagination of the vegetal plate called?

A

the blastopore

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11
Q

What is convergent-extension?

A
  • cells become elongated perpendicular to the axis of elongation
    -at the other end the cells form lamellipodia, rich in actin and myosin
    -cells use the lamellipodia to exert traction on each other to force intercalation
    (they move closer together, like fingers being pushed into each other)
    the tube therefore becomes narrowed (convergence) and longer (elongation)
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12
Q

How is the archenteron pulled towards the ventral surface?

A
  • The SMCs filopodia have a greater affinity for the parts of the animal pole that will form the ventral surface
  • Filopodia remain in contact with this area for longer than other parts of the animal pole
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13
Q

How is GFP incorporated into a mouse genome?

A
  • introduce foreign genes into the mouse genome
  • e.g. Green Fluorescent Protein (GFP) first identified in jellyfish, and the resultant mice are known as transgenics
  • The gene for GFP is placed behind promoter/enhancer elements that allow transcription in either all or a subset of cells
  • then added to ES cells in culture
  • It is taken up by a small number of cells and incorporated into the mouse genome
  • Those expressing GFP, which give off green light under UV illuminescence, can be added to the blastocoel of a host blastocyst
  • becoming incorporated into the ICM
  • creating a chimeric mouse in which some of the cells produce GFP
  • If they are incorporated into the germ line (future gametes) then breeding experiments will produce a mouse line in which all cells express GFP
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14
Q

How are knockout mice created to test for genes involved in embryonic development?

A
  • a gene is isolated and mutated
  • e.g. replacing a exon with a foreign sequence
  • ES cells with the mutation are added to the blstocoel of a host blastocyst
  • ES cells are incorporated into the inner cell mass
  • mice with these mutations are inbred to produce homozygous offspring
  • offspring physiology is studied
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15
Q

How does the mammalian blastocyst form from a 16- to 32-cell embryo?

A
  1. compaction
    - forms an outer epithelium, the trophoblast
    - an internal inner cell mass
  2. trophoblast pumps sodium ions and water follows into the centre of the embryo to form the blastocoel
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16
Q

What does the trophoblast layer form in mammals?

A

chorionic layers of the placenta

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17
Q

What does the inner cell mass form?

A

The foetus tissues

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18
Q

What potency do inner cell mass cells have?

A

Pluripotent (form all metal tissue types)

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19
Q

What happens after compaction, once the blastocyst is formed?

A
  1. The ICM divides into the hypoblast (touching blastocoel) and the epiblast
  2. hypoblast cells spread around the trophoblast, lining the blastocoel to form an extra embryonic endoderm layer called Heuser’s membrane
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20
Q

What does hypoblast cells form?

A
  1. hesuer’s membrane - the extraemryonic layer between blastcoeol and trophoblasts
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21
Q

What is the cavity enclosed by Heuser’s membrane called?

A

The yolk sac

it is equivalent o the yolk sac of reptilian embryos, which helps to transport nutrients from the yolk to the embryo

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22
Q

What is Meckel’s diverticulum?

A

a remnant of the yolk sack which is a small bulge on the small intestine

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23
Q

What extra embryonic tissue does the epiblast form?

A

the amniotic membrane, extra embryonic ectoderm, this is a layer of flattened dpeithelial cells which line a fluid filled cavity called the amnion

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24
Q

What does the amniotic membrane do and what forms it?

A

Forms from the epiblast

- surrounds the entire embryo/fetus and provides it with a protective cushion

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25
Q

Which of these are amniotes and which are anamniotes?

birds, fish, reptiles, amphibians, mammals

A

amnitoes - reptiles, birds, mammals

anamniotes - fish amphibians

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26
Q

What does the epiblast layer form?

A

the three germ layers

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27
Q

What potency does epiblast cells have?

A

pluripotenet

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28
Q

What forms the vasculature of the placenta and the first cells of embryonic blood?

A

a layer of extra embryonic mesoderm which migrates from the epiblast between Heuser’s membrane and the trophoblast

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29
Q

How long can an embryo survive on nutrition from the egg only?

A

one week

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30
Q

How does a mammalian embryo establish a nutrition source?

A

implantation
1. in the uterus, the embryo ‘hatches’ from the zona pellucida

  1. the trophoblast attach to the uterine wall
  2. trophoblast in contact with the uterus undergo rapid proliferation and the cells fuse to form a cynctium composed of many nuclei, it is the SYNCTIOTROPHOBLAST
  3. the synctiotrophoblast penetrate the uterine cell wall
  4. lacunae (cavities) form in the sycntiotrophoblast
  5. the synctiotrophblast rupture maternal capillaries, so maternal blood fills the lacunae (maternal-placental circulation)
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31
Q

Who’s cell make up the placenta

A

maternal and embryonic

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32
Q

Where does implantation occur and why?

A

in the uterus

the zona pellucida stope the embryo egg implanting in the fallopian tubes

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33
Q

What is an ectopic pregnancy?

A

When the egg implants in the fallopian tubes (tubal pregnancy), cervix, ovary or abdominal cavity

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34
Q

Why are ectopic pregnancies terminated?

A
  • embryo does not implant properly
  • embryo still attracts a large blood supply
  • embryo may easily break away from implantation site
  • extensive bleeding is threat to mother
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35
Q

What is the synctiotrophoblast?

A

In implantation, when the embryo attaches to the uterus, the trophoblasts that are in contact with the uterine wall, rapidly proliferate and then all the cells fuse to form a synctium

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36
Q

What is the cytotrophoblast?

A

Single layer of epithelium cells which line the blastocoel and are in contact with the inner cell mass

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37
Q

How does the synctiotrophoblast penetrate the uterine wall?

A
  • secretes enzymes that digest the the extracellular matrix which usually surrounds and connects cells
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38
Q

What are lacunae?

A

cavities in the scyntiotrophoblatst that are filled with maternal blood

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39
Q

What does human chorionic gonadotrophin do?

A

Maintains progesterone level production by the corpeus luteum, without hCG endometrium breaks down

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40
Q

What do human pregnancy test identify?

A

hCG

41
Q

What induces the production of hCG?

A

implantation

42
Q

What cells produce hCG?

A

trophoblast cells

43
Q

What is progesterone needed for and what produces it?

A
  • maintain uterine endometrium

- luteal body and then placenta

44
Q

What other hormones do the trophoblasts product and what do they do?

A

Chorionic Somatomammotropin, Chorionic Thyrotropin, and Chorionic Corticotropin, which maintain placental growth, regulate the mother’s metabolism and the growth of mammary glands

45
Q

How do trophoblast cells ensure that an embryo has food supply before and after birth

A
  • secrete hormones that stimulate growth of mammary glands and maintain placental growth
  • forms the synctiotrophbolast which penetrate uterine wall
46
Q

What reaction does the trophoblast block?

A

trophoblast blocks maternal immune response to paternal antigens ont he embryo

47
Q

What is the first sign of gastrulation in mammals and birds?

A

the primitive streak = a ridge of cells forming at the posterior half of the epiblast layer

48
Q

What does the rostral end of the epiblast and hypoblast form?

A

buccopharyngeal membrane

later this forms the mouth

49
Q

What does the caudal end of the epiblast and hypoblast form?

A

cloacal membrane

this later forms the anus

50
Q

What is the primitive node called in gallus gallus?

A

Henson’s node

51
Q

what is the anaamniote equivalent of the primitive node and streak?

A

the blastopore

52
Q

What does the primitive node and streak do?

A

prefigure the the future rostral-caudal and left-right axes of the embryo

53
Q

What embryonic tissues do the endoderm form?

A

-epithelial lining of gut
-lungs, liver, pancreas
(germ layer closest to the blastocoel)

54
Q

What embryonic tissues do the mesoderm form?

A

muscle, bone, connective tissue, heart, kidney, gonads

55
Q

How are the notochord and prechordal plate formed?

A

Cells ingressing though the node, along the midline, in a rostral direction

56
Q

What is the prechordal plate?

A
  • loose population of mesoderm and endoderm cells
  • underlie the developing forebrain
  • contributes to the rostral endoderm
  • contributes to the mesodermal population of head and acts as important signalling centre for establishing different neuronal populations in the developing forebrain
57
Q

What is the notochord?

A

a flexible rod of cells that extends throughout most of the rostral-caudal axis of the embryo
it does NOT extend to to the rostral edge of the embryonic disc

58
Q

What adaptations does the notochord have in lower vertebrates (fish and amphibians)?

A

-large diameter because cells fill it with lipid filled vacuoles
- skeletal muscle is anchored to the notochord
and provides the right amount of flexibility required for swimming
- the notochord in amniotes is smaller because they don’t swim

59
Q

What is the function of the notochord?

A
  • source of signalling molecules that patterns the adjacent nervous system, mesoderm, endoderm
60
Q

What is the eventuality of the mammalian notochord?

A

The mammalian notochord will degenerate and be replaced by the vertebral column

61
Q

what part of the notochord is retained in mammals?

A

the nucleus pulposus of the inter- vertebral discs is the notochord retained

62
Q

How are somites formed?

A
  1. The paraxial mesoderm forms a compact rod of cells, the segmental plate
  2. At the rostral end of the segmental plate, balls of epithelial cells bud off, these are somite
  3. new cells are continually added to the caudal end of the segmental plate
63
Q

What is the rate of somite generation

A

3 -4 somites per day

64
Q

When are somites formed?

A

Day 20-30 of development

65
Q

How many somites are formed?

in humans, chicks, mice and snakes?

A

42 somites are formed, this is reduced to 38

Chicks produce 50 somites
mice produce 65 somites
snakes produce 500 somites

66
Q

What do mesodermal cells leaning against the notochord form?

A
  1. paraxial mesoderm (closest to notochord)
  2. intermediate mesoderm
  3. lateral plate mesoderm
67
Q

What do paraxial mesoderm cells form and in which direction?

A

somites

rostral to caudal

68
Q

Which organism is invagination clearly seen in?

A

seen in sea urchin embryos, involves the infolding of the surface epithelium of the blastula, usually occurs at the vegetal pole, forms an archenteron, occurs at the blastopore

69
Q

Which organism is involution clearly seen in?

A

seen in amphibians, forms an archenteron, extends towards the animal pole from the blastopore, involuting cells fold bac onto the inner surface of the blastula

70
Q

Which organism is ingression clearly seen in?

A

seen in chicks and mice (and humans), migration of individual cells from the surface epithelium into the interior of the embryo, cells ingress at the primitive streak

71
Q

A new somite is formed every _ in humans?

A

5 hours

72
Q

A new somite is formed every _ in chicks?

A

90minutes

73
Q

A new somite is formed every _ in zebrafish?

A

30 minutes

74
Q

What three populations of cells are formed by somites and what are their fates?

A

Sclerotome - forms axial skeleton (vertebrate + ribs), the base of the skull (occipital bone) to tail

Myotomes - forms all skeletal muscle

Dermatome - connective tissue of dermal layer of dorsal skin

75
Q

What does the intermediate mesoderm form?

A

blood cells, kidney, bladder, reproductive organs

76
Q

What does the lateral plate mesoderm form?

A

connective tissue
smooth muscle layers of digestive tract
connective tissue of the dermal layer of the ventral skin
membranes lining the body cavities
skeleton and connective tissue of the limbs
blood vessels
heart

77
Q

From what does the neural plate form?

A

The ectoderm anterior to node

78
Q

What is the neural plate?

A

Precursor to the nervous system

79
Q

cells of the neural plate elongate to form _

A

pseudostratified columnar epithelium

80
Q

Cells of the epidermis remain _

A

cuboidal

81
Q

What is regression?

A

As the embryo expands, through cell proliferation, the primitive streak becomes restricted to the posterior margin of the epiblast

82
Q

When does neural tube formation occur in humans?

A

fourth week of development

83
Q

What is the neural plate

A

A thickened region of ectoderm on the dorsal side of the embryo

84
Q

What neural specific genes are already transcribed at this stage?

A

Sox2 and Sox3

85
Q

What causes the elongation of neural plate cells?

A

changes in the structure of microtubules - they become polarised and elongated along the apical (external) – basal (internal) axis

86
Q

Neurulation:

A
  1. neural plate cells elongate into columnar cells
  2. lateral edges of the neural plate fold upwards due to changes in cell shape
  3. the neural plate folds around the midline of the neural plate (the median hinge point)
  4. neural plate cells at the hinge point contract their apical surfaces to create ‘wedge shaped cells’ due to myosin/actin action
  5. convergent extension - expansion of the rostral-caudal width, and convergence of the medial-lateral width
  6. apical constriction and convergent-extensions allow the lateral edges of the neural plate to fuse and form the neural tube
  7. the epidermis will also fuse to complete the surface layer
87
Q

What mechanisms cause neural tube closure?

A

convergent-extension

apical constriction

88
Q

What regions of the neural tube close first?

A

first in the hindbrain region and progresses in both directions until ti is fully closed

89
Q

Failure to close the anterior (rostral) neural tube causes

A

anencephaly - the brain degenerates and the cranium fails to form

90
Q

Failure to close the posterior (caudal) neural tube results in

A

spina bafida

- can cause severe paralysis

91
Q

Where does the ventral body wall and gut tube remain open in birds and humans?

A

at the umbilical cord

92
Q

At the end of neurulation, the embryo is a _ disc with _, _, and _ layers

A 
trilaminer disc
upper ectoderm
middle mesoderm
lower
endoderm
93
Q

The midline of the embryo is located at the _

A

lateral edges of the disc

94
Q

Define embryonic folding

A

when the lateral edges of the disc (its future midline) are brought together

95
Q

Embryonic folding is when

A
  1. folding closes of the gut tube
  2. gut tube is surrounded with splanchnic mesoderm (from the lateral plate)
    splanich mesoderm forms the dorsal and ventral mesentery
  3. The epidermis and somatic mesoderm (also from the lateral plate) close off the ventral body wall and form the body cavities (coelom)
96
Q

What is the umbilical cord?

A

The umbilcal cord contains the vasculature connecting the embryo to the placenta, as well as the yolk sac

97
Q

On what side of the embryo is the neural tube?

A

the dorsal (back)

98
Q

What divisions are present in the neural tube?

A

forebrain (prosencephalon), midbrain (mesencephalon), hindbrain (rhombencephalon), and spinal cord.

99
Q

ON either side of the notochord are _

A

somites

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