This presentation is about gastrulation, formation of primitive streak and neurulation (i.e. formation of brain and spinal cord). Hope you like it. Thank You

1. Gastrulation
IN
MAMMALS
By : Swati Chahal

2. "It is not birth, marriage, or death,
but gastrulation, which is truly the most
important time in your life."
Lewis Wolpert (1986)
"It is not birth, marriage, or death,
but gastrulation, which is truly the most
important time in your life."
Lewis Wolpert (1986)

3. •
• The process in which a gastrula develops from a
blastula by the migration of cells is known as
gastrulation.
• Gastrulation produces a three-layered embryo
• Gastrulation Second major phase of embryonic
development; adds more cells to the embryo; sorts
the cells into distinct cell layers.
• The process in which a gastrula develops from a
blastula by the migration of cells is known as
gastrulation.
• Gastrulation produces a three-layered embryo
• Gastrulation Second major phase of embryonic
development; adds more cells to the embryo; sorts
the cells into distinct cell layers.

4. In this process, the bilaminar embryonic
disc, consisting of epiblast and hypoblast,
transforms into trilaminar embryonic disc
consisting of three primary germ layers :
- Ectoderm
- Mesoderm
- Endoderm.
In this process, the bilaminar embryonic
disc, consisting of epiblast and hypoblast,
transforms into trilaminar embryonic disc
consisting of three primary germ layers :
- Ectoderm
- Mesoderm
- Endoderm.

6. • Inner Cell Mass (ICM)
delaminates to form
hypoblast and epiblast
• Occurs just prior to
implantation &
gastrulation
• Epiblast (green cells) is
2-layered (i.e., it is
bilaminate) disc of
approximately cuboidal
cells & will form the
embryo proper
•Flatter hypoblast cells
lie below the epiblast
and will form yolk sac
• Inner Cell Mass (ICM)
delaminates to form
hypoblast and epiblast
• Occurs just prior to
implantation &
gastrulation
• Epiblast (green cells) is
2-layered (i.e., it is
bilaminate) disc of
approximately cuboidal
cells & will form the
embryo proper
•Flatter hypoblast cells
lie below the epiblast
and will form yolk sac

7. Human
Gastrulation
Human
Gastrulation

8. • Very little work has been done on human
gastrulation
• Most work on fixed and stained human embryos
• No experimental work is being done on human
gastrulation because it is not ethical or legal
• Therefore, difficulty getting specific stages
• Originally used knowledge from chick gastrulation:
general morphology looks similar
• Very little work has been done on human
gastrulation
• Most work on fixed and stained human embryos
• No experimental work is being done on human
gastrulation because it is not ethical or legal
• Therefore, difficulty getting specific stages
• Originally used knowledge from chick gastrulation:
general morphology looks similar

9. Gastrulation
in
Human Embryo
Gastrulation
in
Human Embryo

10. • Embryo is bilaminate
(i.e., epiblast and
hypoblast)
• Epiblast forms the
three germ layers
(ectoderm, mesoderm
and endoderm)
• Hypoblast forms the
extraembryonic
membranes
• Embryo is bilaminate
(i.e., epiblast and
hypoblast)
• Epiblast forms the
three germ layers
(ectoderm, mesoderm
and endoderm)
• Hypoblast forms the
extraembryonic
membranes

11. •Initially cells move along
surface (blue arrows) but
upon reaching the center
line (primitive streak) will
enter the embryo, turn the
corner and move internally
(red arrows).
• The moving surface cells
first pile up to form a
prominent bump known as
the primitive node (also
“node”). This occurs
because the cells move
along the top faster than
they can separate off and
move internally.
•Initially cells move along
surface (blue arrows) but
upon reaching the center
line (primitive streak) will
enter the embryo, turn the
corner and move internally
(red arrows).
• The moving surface cells
first pile up to form a
prominent bump known as
the primitive node (also
“node”). This occurs
because the cells move
along the top faster than
they can separate off and
move internally.

12. •
CELL movementsCELL movements

13. - Invagination: a sheet
of cells (called an
epithelial sheet) bends
inward.
- Ingression: individual
cells leave an epithelial
sheet and become
freely migrating
mesenchyme cells.
- Involution: an
epithelial sheet rolls
inward to form an
underlying layer.
- Invagination: a sheet
of cells (called an
epithelial sheet) bends
inward.
- Ingression: individual
cells leave an epithelial
sheet and become
freely migrating
mesenchyme cells.
- Involution: an
epithelial sheet rolls
inward to form an
underlying layer.

14. • Epiboly: a sheet of cells
spreads by thinning. The
movement of epithelial
sheets that spread as a unit,
rather than individually, to
enclose the deeper layers of
the embryo.
• Intercalation: rows of cells
move between one another,
creating an array of cells
that is longer (in one or more
dimensions) but thinner.
• Convergent Extension: rows
of cells intercalate, but the
intercalation is highly
directional.
• Epiboly: a sheet of cells
spreads by thinning. The
movement of epithelial
sheets that spread as a unit,
rather than individually, to
enclose the deeper layers of
the embryo.
• Intercalation: rows of cells
move between one another,
creating an array of cells
that is longer (in one or more
dimensions) but thinner.
• Convergent Extension: rows
of cells intercalate, but the
intercalation is highly
directional.

15. Formation
of
primitive node
Formation
of
primitive node

16. primitive streak is a
faint groove on the
dorsal surface of the
epiblast that
elongates from the
posterior to the
enterior part of the
embryo.
primitive streak is a
faint groove on the
dorsal surface of the
epiblast that
elongates from the
posterior to the
enterior part of the
embryo.

17. •The primitive streak
establishes the head
and tail ends of the
embryo as well as its
right and left sides.
•At the head end of
the primitive streak a
small group of
epiblastic cells forms
a rounded structure
called the primitive
node.
•The primitive streak
establishes the head
and tail ends of the
embryo as well as its
right and left sides.
•At the head end of
the primitive streak a
small group of
epiblastic cells forms
a rounded structure
called the primitive
node.

18. • The structure closer to the head end is called the
oropharyngeal membrane.
• The structure closer to the tail end is called the cloacal
membrane, which degenerates in the 7th week to form the
openings of the anus and the urinary and reproductive
tracts.
• About 16 days after fertilization, mesodermal cells from
the primitive node migrate towards the head end of the
embryo and form a hollow tube of cells in the middle called
the notochordal process.
• By 22-24 days, the notochordal process becomes a solid
cylinder of cells called the notochord.
• The structure closer to the head end is called the
oropharyngeal membrane.
• The structure closer to the tail end is called the cloacal
membrane, which degenerates in the 7th week to form the
openings of the anus and the urinary and reproductive
tracts.
• About 16 days after fertilization, mesodermal cells from
the primitive node migrate towards the head end of the
embryo and form a hollow tube of cells in the middle called
the notochordal process.
• By 22-24 days, the notochordal process becomes a solid
cylinder of cells called the notochord.

19. neurulationneurulation

20. • Notochord also induces ectodermal cells over it to form
the neural plate.
• By the end of the 3rd week, the lateral edges of the
neural plate become more elevated and form the neural
fold.
• The depressed mid region is called the neural groove.
Generally, the neural folds approach each other and
fuse, thus converting the neural plate into a neural
tube.
• Neural tube cells then develop into the brain and spinal
cord.
• The process by which the neural plate, neural folds, and
neural tube form is called neurulation.
• Notochord also induces ectodermal cells over it to form
the neural plate.
• By the end of the 3rd week, the lateral edges of the
neural plate become more elevated and form the neural
fold.
• The depressed mid region is called the neural groove.
Generally, the neural folds approach each other and
fuse, thus converting the neural plate into a neural
tube.
• Neural tube cells then develop into the brain and spinal
cord.
• The process by which the neural plate, neural folds, and
neural tube form is called neurulation.

22. • After 4 weeks of fertilization, the head and neural
tube develops into three enlarged areas of brain
called: the prosencephalon or forebrain,
mesencephalon or midbrain, and rhombencephalon
or hindbrain.
• After 5 weeks, the prosencephalon develops into
secondary brain vesicles called the telencephalon
and diencephalon; and the rhombencephalon
develops into secondary brain vesicles called the
metencephalon and myelencephalon.
• The areas of the neural tube adjacent to the
myelencephalon develop into the spinal cord.
• After 4 weeks of fertilization, the head and neural
tube develops into three enlarged areas of brain
called: the prosencephalon or forebrain,
mesencephalon or midbrain, and rhombencephalon
or hindbrain.
• After 5 weeks, the prosencephalon develops into
secondary brain vesicles called the telencephalon
and diencephalon; and the rhombencephalon
develops into secondary brain vesicles called the
metencephalon and myelencephalon.
• The areas of the neural tube adjacent to the
myelencephalon develop into the spinal cord.

23. Genes involved
in
gastulation
Genes involved
in
gastulation

24. • shh - Sonic Hedgehog plays a role in cell growth, cell
specialization, and the normal shaping of the body. This
protein is important for development of the brain and
spinal cord (central nervous system), eyes, limbs, and
many other parts of the body.
• Fgf8 - Fibroblast Growth Factor 8 plays an important
role in the regulation of embryonic development, cell
proliferation, cell
differentiation and cell migration. Required for normal
development of the gonadotropin-releasing hormone
(GnRH).
• Lrd - Left-right dynein protein selectively segregates
sister chromatids based on their replication history i.e.
determines the symmetry or left right axis of embryo.
• shh - Sonic Hedgehog plays a role in cell growth, cell
specialization, and the normal shaping of the body. This
protein is important for development of the brain and
spinal cord (central nervous system), eyes, limbs, and
many other parts of the body.
• Fgf8 - Fibroblast Growth Factor 8 plays an important
role in the regulation of embryonic development, cell
proliferation, cell
differentiation and cell migration. Required for normal
development of the gonadotropin-releasing hormone
(GnRH).
• Lrd - Left-right dynein protein selectively segregates
sister chromatids based on their replication history i.e.
determines the symmetry or left right axis of embryo.

25. • Kif2A - Kinesin Heavy Chain Member 2A required for
normal congress of chromosomes at the metaphase
plate.
• Lefty2 - This gene encodes for the TGF-beta family of
proteins. The encoded protein is secreted and plays a
role in left-right asymmetry determination of organ
systems during development.
- Mutations in this gene have been associated with left-
right axis malformations,
particularly in the heart and lungs.
• Kif2A - Kinesin Heavy Chain Member 2A required for
normal congress of chromosomes at the metaphase
plate.
• Lefty2 - This gene encodes for the TGF-beta family of
proteins. The encoded protein is secreted and plays a
role in left-right asymmetry determination of organ
systems during development.
- Mutations in this gene have been associated with left-
right axis malformations,
particularly in the heart and lungs.

26. Thank You