1
Q
Epiblast
A
- disc-like structure
- sheet of cells (epithelium) that will undergo gastrulation
- in mouse and chick embryos, a group of cells within the blastocyst or blastoderm, respectively, that gives rise to the embryo proper
- in the mouse, it develops from cells of the inner cell mass
- not spherical or hollow like the blastula in frogs/amphibian embryos
- there is initially no distinct regions of ectoderm, mesoderm or endoderm
- Cells of the epiblast converge and ingress towards and into the primitive streak
- part of the blastodisc in the chick
- lies on top of a fluid filled space called the subgerminal space
2
Q
Primitive streak
A
- region where gastrulation occurs
- extends to the centre of the embryo as gastrulation proceeds
- the streak starts in the future posterior and reaches the furthest anterior part of the embryo
- the earlier primitive streak is when the germ layers are specified and internalized
- lays down the anterior-posterior axis
- this is similar in mouse and chick and called streak elongation
- equivalent of the blastopore seen in amphibians
- the site of gastrulation in avian and mammalian embryos and the forerunner of the antero-posterior axis
- it is a strip of ingressing cells that extends into the epiblast from the posterior margin
- epiblast cells move through the streak into the interior of the embryo to form mesoderm and endoderm
- is highly regulative
3
Q
Ventral closure
A
- the coming together and closing of the lateral edges/sides of the chick or mammalian embryo on the ventral side of the body to form the gut
- lateral edges fold to create a gut tube (endoderm) surrounded by mesoderm and ectoderm
- brings together ventral tissues to the ventral aspect of the embryo
4
Q
Blastodisc / Blastoderm (also called epiblast)
A
- a sheet of cells that give rise to the three germ layers of the embryo
- in the chick, the blastodisc consists of the epiblast and hypoblast
- alternative name for the blastoderm in the chick
- blastoderm: a post-cleavage embryo composed of a solid layer of cells rather than a spherical blastula, as found in early chick, zebrafish, and Drosophila embryos
- arises through cleavage of the early embryo
- analogous to the frog blastula
- surrounded by albumin and protective membranes
- If blastodisc is sectioned into many pieces, each will form a primitive streak, this is how twins are formed
5
Q
Area pellucida
A
-the central clear area of the chick blastoderm
6
Q
Subgerminal space
A
- the cavity that develops under the area pellucida in the early chick blastoderm
- the epiblast lies on top of this fluid filled space
7
Q
Area opaca
A
-the outer dark ring on the outer edge of the chick blastoderm
8
Q
Hypoblast
A
- a sheet of cells in the early chick embryo that covers the yolk under the blastoderm and gives rise to extra-embryonic structures such as the stalk of the yolk sac
- part of the blastodisc in the chick
- lies on top of the yolk and is replaced by the endoblast (extra-embryonic tissues that aid in nutrition and development of epiblast)
- The hypoblast provides an inhibitory signal to streak elongation, as this is replaced by endoblast this inhibition is lost and streak elongation proceeds
9
Q
Embryo proper
A
-are the cells that are going to contribute to tissues in the embryo at birth
10
Q
Koller’s sickle
A
- important structure in chick
- a crescent shaped ridge of small cells lying at the front of the posterior marginal zone in the chick blastoderm
- defines the position of the primitive streak
11
Q
Posterior marginal zone (PMZ)
A
- major signalling center
- breaks the radial symmetry of the epiblast (also called blastodisc or blastoderm)
- where primitive streak will form
- is sufficient for streak formation
- The position of the PMZ is determined by gravity and also defines the dorsal-ventral axis
- is similar to the Nieuwkoop Centre
- forms at the junction of the area pellucida and area opaca
- this area specifies the dorsal and posterior side of the embryo
- region where gastrulation will initiate
- a dense region of cells at the edge of the blastoderm of the chick embryo that will give rise to the primitive streak
- transplantation of posterior marginal zone cells from one chick blastoderm to another can result in an additional primitive streak
12
Q
Ingression
A
- during gastrulation, cells are dividing and migrating, and pass through the streak as individual cells
- the movement of individual cells from the outside of the embryo into the interior during gastrulation
- cells are specified toward mesoderm and endoderm as they enter and migrate through the streak
- The first cells to move through the primitive streak are endoderm, these replace the endoblast that covers the yolk
- Later cells that migrate through the streak are mesodermal, the first to enter are most posterior, as the streak elongates more anterior identity is apparent
- cells of the epiblast move and converge upon the streak, pass through the streak and move into the inside of the embryo
- in mammalian and avian embryosm cells detach from the epiblast surface and ingress through the primitive streak
13
Q
Mesenchyme
A
- migratory cells
- loosely packed cells of mesodermal origin (in contrast to cells part of the epithelium)
- loose connective tissue, usually of mesodermal origin, whose cells are capable of migration
- some epithelia of ectodermal origin such as the neural crest undergo an epithelial to mesenchymal transition
14
Q
Endoblast
A
- in chick embryo, the layer of cells that grows out from the posterior marginal zone prior to the primitive streak formation and replaces the hypoblast underlying the epiblast
- extra-embryonic tissues that aid in nutrition and development of the epiblast
- replaces the hypoblast
15
Q
Hensen’s node
A
- major signalling center
- a condensation of cells at the anterior end of the primitive streak in chick embryos
- it corresponds to the Spemann-Mangold organizer in amphibians
- the equivalent region in mammals is just called the node
- cells of the node give rise to the prechordal plate and the notochord in chick embryos and to the notochord in mammals
- forms once the primitive streak has fully elongated (streak starts in the future posterior and reaches the furthest anterior part of the embryo)
- at the most anterior point the node forms and the node and streak regress back to the posterior = node regression
- thought to be a major organizing centre similar to the Spemann-Mangold organizer
- patterns the germ layers as it regresses
- anterior structures are patterned first
16
Q
Prechordal plate (mesoderm)
A
- cells that migrate anterior to the node during regression of the Henson’s node become the prechordal plate
- The mesoderm that migrates anterior to the Node to contribute to the head process (anterior to the notochord)
- the anterior-most mesoderm in the vertebrate embryo
- located anterior to the notochord
- gives rise to various ventral tissues of the head
17
Q
Head process
A
- forms anterior to the notochord during regression of Henson’s node
- the anterior end of the notochord that projects into the head of mammalian and avian embryos
18
Q
Lateral plate mesoderm
A
- mesoderm on the flanks of the embryo
- as the node regresses, the mesoderm lateral to the somites become lateral plate mesoderm
- mesoderm in vertebrate embryos that lies lateral and ventral to the somites and gives rise to the tissues of the heart, kidney, gonads, blood and the limb connective tissues
19
Q
Tailbud
A
- forms when the node reaches the posterior after regression
- this is a stem cell population that generates tail structures
- the structure at the posterior end of vertebrate embryos containing stem-like cells that give rise to the post-anal tail
20
Q
Neural plate
A
- ectoderm forms neural plates which fold to form the neural tube
- an area of thickened dorsal ectodermal epithelium at the anterior of a vertebrate embryo that gives rise to the nervous system through the process of neuruation
21
Q
Neural tube
A
ectoderm forms neural plates which fold to form the neural tube
-the ectodermally derived tubular structure that forms along the dorsal midline of a vertebrate embryo and gives rise to the nervous system
22
Q
Head fold
A
-an infolding of the three germ layers in the head region of the gastrula in chick and mammalian embryos that indicates the start of the development of the pharynx and the foregut
23
Q
Embryonic membranes
A
- membranes external to the embryo proper that are involved in its protection, nutrition, and oxygen exchange in avians (birds)
- in mammals, they include the amnion, chorion, allantois (placental tissues) and yolk sac
- Allantois analogous to structure that makes placenta, extends to edge of sac for gas exchange
24
Q
Primitive streak elongation failure and how to rescue it?
A
- Failure of streak elongation results in a ventralized embryo (blood tissue and some muscle)
- addition of activin (Vg-1 and Wnt-8c are the chick versions) activate Nodal in the posterior marginal zone and primitive streak to rescue dorsal structures (such as the notochord)
- Nodal (a signal) initiates mesoderm induction and formation in the primitive streak
- The hypoblast provides an inhibitory signal to streak elongation
- As this is replaced by endoblast this inhibition is lost and streak elongation proceeds
- Initiation of the streak is associated with Fgf expression
- Nodal and Fgf together induce streak formation and elongation
- BMP is expressed outside the streak and inhibits dorsal structures (e.g. axial notochord mesoderm)
- BMP in turn is inhibited by chordin expressed at the tip of the streak
25
Vg-1
- is the activin version of the chick to rescue the dorsal structures during failure of streak elongation (results in ventralized embryo)
- with Wnt-8c, activate Nodal in the posterior marginal zone and primitive streak
26
Wnt-8c
- is the activin version of the chick to rescue the dorsal structures during failure of streak elongation (results in ventralized embryo)
- with Vg-1, activate Nodal in the posterior marginal zone and primitive streak
- induce organizer and dorsal fate
27
Nodal
- activated by Vg-1 and Wnt-8c
- low Nodal=ventral structure
- in the posterior marginal zone and primitive streak
- Nodal initiates mesoderm induction in the primitive streak (with BMPR1, Wnt-3, and Brachyury in the mouse)
- Nodal is a signal that induces mesodermal formation
- Nodal and Fgf together to induce streak formation and elongation
- induces organizer and dorsal fate
- in the mouse, Nodal and Wnt at their highest activate goosecoid (Gsc), this induces node formation and Nodal patterns mesoderm and endoderm during gastrulation
28
Fibroblast Growth Factor (FGF)
- Initiation of the streak is associated with Fgf expression
- Nodal and Fgf together to induce streak formation and elongation
29
BMP
- ventralizes the embryo
- BMP is expressed outside the streak and inhibits dorsal structures (e.g. axial notochord mesoderm)
- BMP in turn is inhibited by chordin expressed at the tip of the streak
30
Chordin
- expressed at the tip of the streak
| - inhibits BMP
31
Distal visceral endoderm (DVE)
- in mouse gastrulation, the epiblast is adjacent to Distal Visceral endoderm
- formation of the DVE (distal visceral endoderm ) breaks the radial symmetry of the epiblast
- Distal since it is furthest from the extra embryonic ectoderm
- The DVE transitions to the AVE (anterior visceral endoderm) to mark the location of the head formation
- the endoderm located at the distal end of the cup-shaped mouse epiblast, which moves and extends away from the posterior side of the embryo, upon which it becomes the anterior visceral endoderm
32
Anterior visceral endoderm (AVE)
- During gastrulation in the mouse, The DVE transitions to the AVE (anterior visceral endoderm) to mark the location of the head formation
- streak forms opposite of the AVE
- an extra-embryonic tissue in the early mouse embryo that is involved in inducing anterior regions of the embryo
33
Extra-embryonic ectoderm
- in mammals, embryonic tissue that contributes to the formation of the placenta
- involved in implantation
34
BMP-4
- seen in Xenopus embryo
- BMP in chick
- ventralizes the embryo and is inhibited by Noggin (Chordin in the chick)
- extra embryonic ectoderm
- induces streak formation in the mouse
35
Wnt-3
-inducing mesoderm in the streak with BMPR1, Nodal and Brachyury during axes formation in the mouse
36
BMP receptor type 1 (BMPR1)
-inducing mesoderm in the streak with Wnt-3, Nodal and Brachyury during axes formation in the mouse
37
Brachyury
-inducing mesoderm in the streak with BMPR1, Nodal and Wnt-3 during axes formation in the mouse
38
Node
- in avian and mammalian embryos, the embryonic organizing center analogous to the Spemann-Mangold organizer of amphibians
- it is also known as Henson's node in birds
- in plants, that part of the stem at which leaves and lateral buds form
39
Goosecoid
-in the mouse, Nodal and Wnt at their highest activate goosecoid (Gsc), this induces node formation
40
Cerberus-like 1
-During mouse gastrulation, Cerberus and Lefly inhibits Nodal signalling in the primitive streak
41
Dickkopf (Wnt inhibitor)
-in the mouse, is a Wnt signalling inhibitor
42
Chick lifecylce
1) egg(development within oviduct)
2) blastoderm (embryo, development within oviduct)
3) cleavage (development within oviduct)
4) area opaca, area pellucida and posterior marginal zone forms (development within oviduct)
5) gastrulation
6) Stage 4- Henson's node and primitive streak form
7) Stage 14- 22 somites
8) organogenesis
9) Stage 30
10) hatching
11) chick
12) adult
43
How is the primitive streak formed by mesoderm induction and patterning?
1) signalling by epiblast cells at the posterior marginal zone
2) Nodal function antagonized by Cerberus produced by hypoblast
3) Hypoblast replaced by endoblast, Nodal and FGF induce formation of the primitive streak
44
How is axes formation in the mouse accomplished?
1) specification of the distal visceral endoderm (DVE, 5.5 days)
2) Proliferation and movement of anterior visceral endoderm (AVE, 6 days)
3) Specification of anterior ectoderm and beginning of primitive streak (6.5 days)
45
Why was the chick used as a model?
- Easy to manipulate by cutting a small incision in the egg and observe the development of the embryo inside
- Easy to culture
- Flat embryo
- Problem: genome is not good to manipulate
46
What are some major deviations seen in chick (bird) development compared with frog (amphibian) development?
-Epiblast: The embryo is initially a layer of cells called an epithelium, Not spherical hollow blastula, In the epiblast there are initially no distinct regions of ectoderm, mesoderm or endoderm
-The timing of germ-layer specification is occurring before and during gastrulation
-There is considerable cell proliferation and migration = cell mixing
-Fate map does not exist since germ layers are all mixed up
-During gastrulation: The primitive streak becomes the equivalent of the blastopore, Cells of the epiblast converge and ingress towards and into the primitive streak
-Ventral closure is another defining feature: The gut cavity is created as the lateral edges of the embryo,
Fold to create a gut tube (endoderm) surrounded by mesoderm and ectoderm
47
Epithelium
chick embryo starts off initially as this layer of cells
48
What creates the first differences of cells in the embryo?
- position in the embryo (outside vs inside) creates the first differences
- will create the trophectoderm and inner cell mass
49
In the chick, there are three important structures/signalling centres. What are they?
1) Koller sickle: crescent-shaped ridge, define the position of the primitive streak
2) Posterior marginal zone (PMZ): forms at the junction of the area pellucida and area opaca, this area specifies the dorsal and posterior side of the embryo, the region where gastrulation will initiate
3) Henson's Node: the node in mammals, forms once the primitive streak has fully elongated (streak starts in the future posterior and reaches the furthest anterior part of the embryo), at the most anterior point the node forms and the node and streak regress back to the posterior = node regression, thought to be a major organizing centre similar to the Spemann-Mangold organizer, patterns the germ layers as it regresses, anterior structures are patterned first
50
Node regression
- the node and streak regress back to the posterior, this is known as node regression
- the Henson's node patterns the germ layers as it regresses (anterior structures are patterned first)
- the primitive streak lays down the anterior-posterior axis
- cells that migrate anterior to the node become the prechordal plate
- the head process forms anterior to the notochord
- the node as it regresses patterns and lays down the notochord and somites on either side
- mesoderm lateral to somites becomes lateral plate mesoderm
- when the node reaches the posterior, it stops and forms the tail bud (stem cell population that generates the tail structures)
* node regression patterns the tissues in an anterior to posterior direction
51
Ingression in the chick vs involution in the frog
Ingression: during gastrulation of chick embryo, cells are dividing and migrating, then pass through the streak as individual cells
Involution: in the frog embryo, cells migrate as a coherent sheet through the streak
52
During ingression, cells of the epiblast move and converge upon the streak, pass through the streak and move into the inside of the embryo. What happens to the cells based on their new position?
- the first cells to move through the primitive streak and are the furthest cells become specified towards endoderm (these replace the endoblast that covers the yolk)
- the later cells that migrate through the streak and are found in the middle become specified towards mesoderm (the first to enter are most posterior, as the streak elongates more anterior identity is apparent)
- remaining epithelial cells become ectoderm
- the endoblast is eventually replaced by endoderm
53
Mesenchyme vs epithelium
mesenchyme=migratory mesodermal cells that are loosely packed
epithelium=a sheet of tightly packed cells bound to each other by adhesive cell junctions
54
Gastrulation
- head to tail axis is patterned
- cells move as sheets
- put germ layers in the cell in the right position
55
Axial mesoderm
mesoderm that forms along the main axis of the body, such as the notochord, vertebral column, somites and neural tube in vertebrates
56
Paraxial mesoderm
mesoderm lying on either side of the dorsal midline and which gives rise to the somites
57
Somite staged embryo
- Somite number is used to stage the development of tissues
| - Organ development and tissue development during this time
58
Maternal determinants
not as relevant in chick embryo
59
Where does mesoderm induction and patterning happen in the chick embryo?
-occurs in the primitive streak
60
What are the similarities between the chick embryo and the Xenopus embryo?
- The Posterior Marginal Zone is probably similar to the Xenopus Nieuwkoop Centre
- Hensen’s Node is analogous to Spemann-Mangold organizer
- Mesoderm patterning is similar
- XWnt-8/Wnt-8c and Nodal induce organizer and dorsal fate
- Low Nodal=ventral structure
- BMP/BMP-4 ventralizes the embryo and this is inhibited by Noggin/Chordin
61
What are the differences between the chick embryo and the Xenopus embryo?
- Organizer is moving in the chick
| - Cells are specialized as they migrate through the streak to become mesoderm and endoderm
62
What happens during gastrulation in the mouse?
- The epiblast is adjacent to Distal Visceral endoderm
- Formation of the DVE (distal visceral endoderm ) breaks the radial symmetry of the epiblast
- Distal as it is furthest from the extra embryonic ectoderm (Involved in implantation)
- The DVE transitions to the AVE (anterior visceral endoderm) to mark the location of the head formation
- Cerberus and Lefly inhibits Nodal signalling in the primitive streak
- Streak forms opposite of the AVE
63
How is mouse gastrulation different from chick?
- Translation of the primitive streak induces a second axis but without head formation
- In mouse, head development is separated from patterning of the rest of the body
64
How is axes formation done in the mouse?
- Extra embryonic ectoderm BMP-4 to induce streak formation
- Primitive streak: BMP receptor 1 (BMPR1), Wnt-3, Nodal and Brachyury, This is inducing mesoderm in the streak
- Nodal and Wnt at their highest activate goosecoid (Gsc)
- This induces node formation
- Nodal patterns mesoderm and endoderm during gastrulation
- ThuVE prohibits mesoderm formation
- Cerberus-like 1 = Nodal inhibitor
- Dickkopf=Wnt inhibitor
- Prospective mesoderm with migration displaces ectoderm to initiate streak elongation
65
ThuVE (in mouse axes formation)
prohibits mesoderm formation
66
Late embryogenesis of the mouse
- The mouse embryo undergoes embryo turning, an exaggerated ventral closure
- Extra embryonic tissue assist in embryo nutrition and protection
- Allantois migrates out to the make contact with the placenta (the umbilical cord)
BIOL 3542
flashcards
Decks in class (10)
# Cards
-
Midterm 1235
-
Midterm Exam Answers39
-
Assignments48
-
Final exam - Xenopus Development129
-
Final Exam - Mouse Development31
-
Final Exam - Chick Development66
-
Final Exam - Somite development34
-
Final Exam - Limb Development26
-
Final Exam - Cell Differentiation and Stem Cells22
-
Final Exam - Plant Development34
