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ANAT 381 > Ryan Lecture 2 > Flashcards

Ryan Lecture 2 Flashcards

1
Q

Fertilized egg —>

A

Blastula —> gastrula

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2
Q

What happens after fertilization - blastula formation

A

Cleavage occurs in almost all species
Extremely rapid mitotic divisions
Divides zygotic cytoplasm into numerous smaller cells = blastomeres
No increase in cytoplasmic vol

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3
Q

What is mid blastula transition

A

Slow down in rate of mitosis
All proteins/mRNA used = from oocyte/sperm
Onset of zygotic transcription - exception is mammals

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4
Q

When is blastula formed

A

End of cleavage
Variety of types = blastula, blastodisc, blastocyst (depends on Shape but all the same)

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5
Q

Describe xenopus blastula

A

Ectodermal = animal cap
Blastocoel = vegetal cap
Mesoderm, endoderm

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6
Q

Describe mouse blastula

A

Te = extraembryonic
Icm = embryo proper
Blastocoel = large, filled with fluid

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7
Q

Describe human (rabbit, chick) blastula

A

Flat blastodisc
Cavity becomes fluid filled
Epiblast = embryo
Hypoblast
Replaced by future cells of embryos, flat layered of cells

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8
Q

How many cells does human blastodisc/blastocyst have

A

70-100cells

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9
Q

When does human blastodisc formation begin

A

~5 days post fert

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10
Q

Describe early embryogenesis in drosophila- gen

A

Syncytial blastoderm - mitosis w/o cytokinesis
One nucleus, initial yolks cytoplasm (30 mins) —> 70 mins

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11
Q

Describe early embryogenesis in drosophila - first important thing

A

Nuclei move to periphery during 10th mitosis division
Cells surround yolks mass in early drosophila embryo

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12
Q

Describe early embryogenesis in drosophila - second important thing

A

After 13th division
Cell membranes form to create cellular blastoderm = single layer of cells around a yolky core
Mitotic divisions =synchronized, no longer at mid blastula transition, size of embryo stays the same
Dorsal, ventral and ant and post = many Nuclei important

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13
Q

Describe early embryogenesis in drosophila - third important thing

A

Cycle 14= mid blastula transition, zygotic transcription and asynchronous divisions, gastrulation begins
Cellularization = compartmentalize nucleus to single cell

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14
Q

Describe single cell to blastula In xenopus - gen

A

Fertilized egg —multiple rounds cell Division—> blastula, hollow sphere of cells (blastocoel)

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15
Q

Describe single cell to blastula In xenopus - features

A

Animal cap gives rise to embryo proper
Localization of proteins even at one cell stage
Important info that affects dev of cells, and axis of embryo

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16
Q

Describe single cell to blastula In zebrafish

A

Cleavage and blastoderm formation
Single cell - zygote to 512 cell, - now cell not that much bigger than single cell embryo

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17
Q

Describe single cell to blastula In mouse - gen

A

Totipotent stage =egg—>rotational cleavage—>4 cell stage —> morula
Pluripotent stage = compacted morula (tight junctions) —> blastocyst (te-extraembryonic, icm=embryonic relatively small compared to blastocoel cavity)

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18
Q

What is truly the most important time in your life

A

It is not birth, marriage, or death, but gastrulation

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19
Q

What is gastrulation

A

Series of cell movements and migration involving entire embryo
Extensive cell movements that establish final spatial relationship of the 3 germ layers = ectoderm, mesoderm, endoderm (also sometimes 4th=neural crest cells)
Species specific differences in pattern of gastrulation but only a few basic types movements

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20
Q

Describe the germ layers - gastrulation generally

A

Cells that wil form endoderm and mesoderm are brought to inside - MOUSE EXCEPTION
Ectoderm (skin and nervous system, surface and neuro ectoderm) spread over outside surface

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21
Q

Describe intercalaton - gastrulation cell movements

A

Rows of cells move between one another, creating an array of cells that is longer, in one or more directions (or another shape of cell)
Like zipper merge

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22
Q

Describe convergent extension - gastrulation cell movements

A

Cells intercalate in highly directional manner
Causes embryo to elongate
Lateral —> midline side in embryo
Longer, more directional group of cells
Correlated with planar cell polarity, now which direction is ant and post and where neighbours are

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23
Q

What does convergent extension depend on

A

Non canonical want/pcp (planar cell polarity) pathway

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24
Q

Describe model showing convergent extension

A

Bead model
Move in and spread out
Cluster of cells more likely to stick togetehr

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25
Q

Describe convergent extension in an Embryo

A

Happens during time of lots of mitosis
Dorsal side,rod like structure formed
Ball of cells = somites
Movement to middle gives embryo shape and structure

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26
Q

Describe invagination - gastrulation cell movements

A

Sheet of cells (epthelial sheet) bends inwards
Apically constrict, on one side
Get narrow and move into liumen = gives pop of cells = mesoderm or endoderm
Depends when they move in

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27
Q

Describe gastrulation in drosophila

A

Same outcome - 3 germ layers
Slightly diff process- happens through invagination

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28
Q

Describe gastrulation in drosophila - mesoderm

A

Derived from 1000 cells at Ventral midline that fold inwards to form ventral furrow

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29
Q

Describe gastrulation in drosophila - endoderm

A

Invaginates as 2 pockets at anterior and posterior ends of ventral furrow

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30
Q

Describe stage 4 drosophila embryo

A

Syncytial stage
Just before cellularization

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31
Q

Describe gastrulation in drosophila - invagination

A

Ventral view
Becomes mesoderm
2 pockets at ends = endoderm, ant and post
Overlying ectoderm will close up around

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32
Q

Describe invagination during drosophila gastrulation

A

Endoderm = more triangular in shape

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33
Q

Describe involution - gastrulation cell movements

A

Partially important in xenopus
Process by which an epithelial sheet rolls inwards to form an underlying layer
Dorsal lip of blastopore - cells involute, and move along surface of embryo, in opp dir

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34
Q

What is required for involution

A

Initial turn requires apical constriction
Dorsal leading edge - head-mesoderm = push in against cells that become later ectoderm = happens In dorsal blastopore lip
Bottle cells = change shape as involution happens

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35
Q

Describe process of involution - needed steps

A

Movement of nuclei - to basal side helps change shape - and apical actomyosin complex undergoes contraction to buckle epithelium- constriction, like hoodie

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36
Q

Describe amphibian gastrulation

A

Involution
Blastula —> gastrula —> neurula
Neurula = only future ectoderm on surface = surface ectoderm, neural plate ectoderm
Cells involute at dorsal blastopore lip

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37
Q

Describe xenopus cell movements during gastrulation - dorsal view of gastrulation

A

Cells move
Cells left on surface = forms start of neural tube and other cells will be the surface ectoderm

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38
Q

Describe xenopus cell movements during gastrulation - vegetal view of involuting cells

A

Surface ectoderm eventually covers neural tube - 15h elapsed time

39
Q

Describe xenopus cell movements during gastrulation - internal view of gastrulation

A

See movement and involution - as come through dorsal lip of blastopore and move up and around that surface

40
Q

Describe epiboly - gastrulation cell movements

A

Process in which a sheet of cells spreads by thinning movements of cells over another later of cells
Cells change shape
Especially important in zebra fish
Cell movement - by thinning
Can see in early xenopus

41
Q

What does epiboly do in zebrafish

A

Movement important = over surface of yolk - brings yolk yo indifferent of embryo so can nourish embryo

42
Q

Describe epiboly of zebrafish over time

A

30% epiboly, 4hr, embryo spreads over surface = c shape, epiboly cells gradually move down surface
—> 75% epiboly, 7.55 hr
—> 90% epiboly, 9hrs = stage embryo by how much these cells have moved down
1cell—>100% epiboly, as epiboly movement = cells contribute to grow on surface

43
Q

Describe ingression - gastrulation cell movements

A

Individual cells leave epithelial sheet and become freely migrating mesenchyme
Similar to epithelial to mesenchymal transition
In most blastodisc shaped embryos = humans, rabbits, chicken and mouse, but mouse do not form blastodisc at this point
Fall out and migrate down - but lose connections with neighbours = lose cell cell tight junctions

44
Q

Describe EMT (epithelial to mesenchymal transition) - stage 1

A

Initially = attached to neighbour via cell attachments =
Epithelial cell layer, epiblast = junctions complexes intact (tj, adherens, gap junctions)
Basement membrane intact

45
Q

Describe EMT (epithelial to mesenchymal transition) - stage 2

A

Junctional complexes begin to breakdown
Induced

46
Q

Describe EMT (epithelial to mesenchymal transition) - stage 3

A

Junctional complexes break down
Basement membrane breaks down
Ingresssing cell takes on mesenchymal phenotype - so cell can slip down

47
Q

Describe EMT (epithelial to mesenchymal transition) - stage 4

A

Cells leaves epithelial layer of epiblast
Becomes mesenchymal
Will contribute to mesoderm or endoderm
Migrate out, cells that remain in epithelial layer = become ectoderm

48
Q

Are all germ layers mesenchymal

A

NOOOOO
Any germ layer can be epithelial and any germ layer can be mesenchymal = refers to cell state

49
Q

Describe gastrulation in Chick embryos - ingression

A

Cells that fall out and moves towards midline embryo = primitive groove
Once cells reach primitive groove= eat go and they migrate into place
Result =ectoderm, mesoderm, endoderm

50
Q

Name important parts of chick embryo

A

Hesens node
Primitive groove
Epiblast
Blastocoel
Hypoblast
Migrating mesenchyme = will contribute to lateral plate mesoderm

51
Q

Describe gastrulation movements in chick embryos - formation of primitive streak, dorsal view

A

Formed post to ant

52
Q

Describe gastrulation movements in chick embryos -dorsal view

A

Cells stained with red dye
Get there and u turn = mostly on one side
Left and right patterning very early and carry info with them as they go forwards

53
Q

How do human embryos gastrulate - describe

A

Flat blastodiscs - most similar to chick and rabbit embryos
3rd week post fert
~14 days —> 21 days, now have definite germ layers

54
Q

Describe gastrulation in mouse

A

NOT FLAT Blastocyst
Icm forms structure - embryo proper
Endoderm and mesoderm come to outside of embryo - day 6.5
Different tho

55
Q

What is most mammalian embryos gastrulation similar to

A

Birds/reptiles

56
Q

Describe mouse and human - single cell thru gastrulation

A

Blastocyst stages similar, humans = more blastodisc shape
Early gastrula = diff
Late gastrula = MOUSE (tail end swings around and lateral parts ectoderm start to encompass embryo) HUMAN (tissues enclose yolk sac)

57
Q

What is at the end of gastrulation

A

3 germ layers
Tissues gain memory as go through all this
Germ layers = also patterned with respect to d-v and a-p axes

58
Q

Describe ectoderm

A

Outer cell layer
Epidermis, neural tissue, placodes (optic, optic, olfactory, hypophyseal)

59
Q

Describe mesoderm

A

Middle cell layer
Demis, muscle, bone, kidney, gonads

60
Q

Describe endoderm

A

Inner cell layer
Epithelial lining of gut, lung, liver, pancreas

61
Q

Describe 4th germ layer

A

Neural crest cells
Arise at boundary of neural and non neural ectoderm during neural tube closure - after gastrulation has happened
Cells in peripheral and enteric nervous systems, muscle, craniofacial bones and cartilage, melanocytes, VERY DIVERSE

62
Q

DESCRIbe neural crest cells and their derivatives

A

What is left after gastrulation = neural plate border
Will give rise to neural tube, brain and spinal cord - MEDIAL
Gives rise to surface ectoderm = LATERALLY
Cells migrate away = epi to mesenchymal transition, and migrates to diff parts of body as neural tube closes

63
Q

How do neural crest cells become what they do

A

Migratory path= where they end up determines what they become
From from ectodermal region originally
Smooth muscle cells, osteoblasts, osteoclasts, adipocytes, chondrocytes, melanocytes, Schwann cells, neurons
Bones in head = diencephalic
Heart and components, vasculature and neurons in brain

64
Q

What is an organizer

A

Group of cells capable of organizing neighbouring cells
Provide important info to surrounding cells

65
Q

What can organizer do

A

Can induce ectopic cell fates in host tissue following heterotopic transplantation
Important for endogenous structures but can also re pattern cells that are competent in other regions

66
Q

Describe Hilde mangold

A

Student, cut and paste experiment in amphibian embryos
Not awarded cause dead

67
Q

Describe hilde mangolds experiment

A

Take pieces of early blastula embryo and transplant them into other parts
Normal = primary endogenous axis, neural tube, notochord, sortie and ganglia form
Then she used tissue derived from transplanted dorsal blastopore lip = no pigment and could induce whole other axis, regions of embryo can induce axis
Secondary induced axis = new tissues, can tell since og structures pigmented

68
Q

What did hilde conclude basically

A

Dorsal blastopore lip = region where cells would pass by during gastrulation and get info
Transplantation of dorsal blastopore lip induces a secondary axis

69
Q

Is it a fate mapping exp - hilde

A

It didn’t become something else but it did induce other cells to

70
Q

Does this tell you about the potential of dorsal blastopore lip - hilde mangold

A

Inducing tissue
Then what will target become, or what will it induce =
WHAT IS POTENTIAL OF TISSUE WE ARE TRANSPLANTING
OR
WHAT IS POTENTIAL OF IT TO INDUCE SOMETHING ELSE

71
Q

WHAT Happens when transplant embryonic shield of zebrafish

A

Embryonic shield = specialized region embryo
In sit exp - looking at shh
= gives 2 diff embryos - similar effect of hilde exp

72
Q

What happens when transplant hensens node from chick embryos

A

Hensens node = ant end primitive streak
Can induce another embryo to dev
Can also induce a regionally structured a-p neural axis
Leads to = tissues from host being induced to start new ap structure

Spinal cord - donor
Forebrain
Forebrain
Spinal cord - host

73
Q

What is spemann mangold organizer

A

In amphibians
Sets up v early = at blastocyst stage
At dorsal blastopore lip

74
Q

Describe molecules required for induction of spemann mangold organizer

A

B cate + VegT, Vg1 (both needed to form organizer)—> nodal related high —> organizer
VegT, Vg1 —> nodal related low —> ventral mesoderm (lower nodal signal)

75
Q

Describe molecular signals required for patterning germ layers - ventral centre

A

Bmp4, bmp7
(Cv2, sizzled, Bambi, xlr, tsg)

76
Q

Describe molecular signals required for patterning germ layers - spemann mangold organizer

A

Antagonists inhibit activity fo signalling molecules, dampens signal at that place
Chordin, noggin, follistatin, frzb1, sfrp2, crescent, dickkopf-1, cerberus

77
Q

Describe the mutiple cell signalling inhibitors the organizer produces

A

Frzb1, dickkopf-1, crescent = inhibit wnts
Cerberus = inhibits xwnt-8, xnrs , bmps (Nodal related)
Chordin, noggin, follistatin = inhibit bmps
Inhibits of pathway = v imrpoatnt in organizers themselves

78
Q

Name the major axes in early embryo - 3

A

Dorsal - ventral, back to front
Anterior - posterior, top to bottom
Left - right (int vs ext human body = look symmetrical but not inside)

79
Q

What is an axis

A

Axis usually defines a direction or orientation
Asymmetrical - may be initially symmetrical

80
Q

Name additional axes in older embryos

A

Proximal -distal = close to far

81
Q

How does asymmetry - polarity happen

A

Unfertilized egg = single cell, usually radially symmetrical
Initial divisions after fert can generate functionally equivalent daughter cells
(Autonomous specification exception, bc first division asymmetric
Eventually cells must become different

82
Q

Name the 2 ways cells can become different - cell divisions

A

Asymmetric cell division = localization of cytoplasmic determinants followed by asymmetric cell division = recall, spindle parallel to determination gradient
Asymmetric patterning through inductive signals = cell cell signalling within fields of identical cells (closer = more signal info) or across boundaries (groups of cells that can stick together)

83
Q

Describe dorsal ventral axis in mammals

A

Forms from icm cells that are in contact with trophoblast
Icm = tells that undergo gastrulation
Dorsal axis, do not know much about it overall, but do know it form individual organs and spinal cord

84
Q

Describe d-v axis in chick - gen

A

Formation depends on pH
Occurs at blastodisc stage

85
Q

Describe d-v axis in chick - specificallly

A

Water and sodium ions transported from basic albumen (egg white above blastodisc) = basic through cells to acidic sub germinal cavity below in Hypoblast area
Creates a membrane potential diff
Side facing albumen becomes dorsal
Side facing yolk becomes ventral - got cells
RESULTS= in endodermal/future gut next to yolk, food source

86
Q

Where is d-v axis initiated in drosophila

A

Syncytial blastoderm = before cellularization in single cell

87
Q

Describe d-v axis formation in drosophila - gen protein

A

Depends on tf dorsal
Dorsal = product if maternal effect gene = mRNA deposited in egg from female/mom - around from beginning

88
Q

Describe d-v axis in chick -specifics

A

Dorsal initially found throughout syncytial blastoderm -so present throughout cytoplasm
Dorsal protein comes nuclear only on future ventral side of embryo, dorsal regulates ventral phenotypes

89
Q

How are many proteins named in drosophila

A

Based on phenotype caused when gene mutated
When dorsal mutated = causes dorsal phenotype

90
Q

What happens of absence of dorsal - in drosophila

A

Or if dorsal doesn’t enter nucleus = embryo becomes dorsalized
Has 2 dorsal sides of Emrbyo

91
Q

What happens if dorsal enters all the nuclei in drosophila

A

Embryo becomes centralized
2 ventral sides

92
Q

Describe dorsal entering nucleus

A

Dorsal triggered to enter nuclei in regions of embryo where spatzle ligand binds its receptor (toll)
Ligand present in ventral superficial surface (only on ventral side) = binds to receptors on surface of future cells
Toll activation = Triggers another series of events = casues dorsal enter nucleus

93
Q

Describe Nobel prize 1995 discovery

A

If mutate toll = no ventral phenotype

94
Q

When does d-v axis patterning start for all species - name

A

At blastula stage in mouse
At blastoderm stage in chick
At blastoderm stage in drosophila
At fertilization in xenopus

ANAT 381 (14 decks)

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