Download neural tube - Figure B

F ro g E m b r yo l o gy 2
Sirwan M. Mohammed
[email protected]
Learning objectives
By the end of this lecture students should be able to:
Understand the concept of blastulation in frog
embryo
Know Frog’s early and late gastrulation.
Describe neurilation & fate map of frog embryo
frog egg
frog sperm
Gamete Formation
Fertilization
Cleavage
Blastulation →Gastrulation
midsectional views
Organ Formation
top view
side view
Growth, Tissue
Specialization
Stages of
Embryonic
Development
The blastula leads
to the gastrula
through
gastrulation which
involves cell
divisions, cell
migrations and cell
rearrangements
Fertilized egg divides mitotically
fluid filled cavity - blastocoel- begins to form
Blastula - hollow ball of cells
- has between 25 and 27 cells
blastocoel
The Blastula - Polarity
Animal Pole
Blastomeres
Blastocoel
Vegetal Pole
Frog Blastula (section)
ectoderm
blastocoel
mesoderm
endoderm
vegetal pole
frog gastrulation mechanism
Gastrulation begins when a small indented crease,
1
the dorsal lip of the blastopore, appears on one
side of the blastula. The crease is formed by cells
changing shape and pushing inward from the
surface (invagination). Additional cells then roll
inward over the dorsal lip (involution) and move into
the interior, where they will form endoderm and
mesoderm. Meanwhile, cells of the animal pole, the
future ectoderm, change shape and begin spreading
over the outer surface.
SURFACE VIEW
Animal pole
CROSS SECTION
Blastocoel
Dorsal lip
Vegetal pole of blastopore Blastula
Blastocoel
shrinking
The blastopore lip grows on both sides of the
2
embryo, as more cells invaginate. When the sides
of the lip meet, the blastopore forms a circle that
becomes smaller as ectoderm spreads downward
over the surface. Internally, continued involution
expands the endoderm and mesoderm, and the
archenteron begins to form; as a result, the
blastocoel becomes smaller.
3 Late in gastrulation, the endoderm-lined archenteron
Blastocoel
remnant
has completely replaced the blastocoel and the
three germ layers are in place. The circular blastopore
surrounds a plug of yolk-filled cells.
Dorsal lip
of blastopore
Archenteron
Ectoderm
Mesoderm
Endoderm
Key
Future ectoderm
Future mesoderm
Future endoderm
Yolk plug
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Yolk plug
Gastrula
The developmental fate of cells depends on their
history and on inductive signals


Coupled with morphogenetic changes, development
requires timely differentiation of cells at specific
locations
Two general principles cause differentiation:
 During
early cleavage divisions, embryonic cells must
become different from one another
 After cell asymmetries are set up, interactions among
embryonic cells influence their fate, usually causing
changes in gene expression
Organ stages of development occur after tissue stages


Newly formed mesoderm cells lie along main longitudinal
axis of animal and combine to form a presumptive
notochord
Formation of the neural tube
Thickening of cells, neural plate, appears along the dorsal surface
of the embryo
 Neural folds develop on either side of neural groove
 Coelom appears and neural tube is complete


At this point, the embryo is called a neurula

Anterior end of the neural tube develops into the brain, and the
rest becomes the spinal cord
LE 47-14a
Early in vertebrate organogenesis, the
notochord forms from mesoderm, and the
neural plate forms from ectoderm
Neural folds
LM
1 mm
Neural
fold
Neural
plate
Notochord
Ectoderm
Mesoderm
Endoderm
Archenteron
Neural plate formation
Neural
fold
Neural plate
Neural crest
Outer layer
of ectoderm
Neural crest
Neural tube
Formation of the neural tube
The neural plate soon curves inward,
forming the neural tube
Development of neural tube and coelom in a frog embryo
Eye
SEM
Somites
Neural tube
Notochord
Coelom
Archenteron
(digestive cavity)
Somites
Tail bud
1 mm
Neural
crest
Somite
Mesoderm lateral to the
notochord forms blocks
called somites
Lateral to the somites, the
mesoderm splits to form the
coelom
Classic studies using frogs
– Gave indications that the lineage of cells
making up the three germ layers created by
gastrulation is traceable to cells in the blastula
Epidermis
Central
nervous
system
Epidermis
Notochord
Mesoderm
Endoderm
Neural tube stage
(transverse section)
(a) Fate map of a frog embryo. The fates of groups of cells in a frog blastula (left) were
determined in part by marking different regions of the blastula surface with nontoxic dyes
of various colors. The embryos were sectioned at later stages of development, such as
47.23a the neural tube stage shown on the right, and the locations of the dyed cells determined.
Blastula
Figure
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Later studies developed techniques
– That marked an individual blastomere during
cleavage and then followed it through
development
(b) Cell lineage analysis in a tunicate. In lineage analysis, an individual cell is injected with a
dye during cleavage, as indicated in the drawings of 64-cell embryos of a tunicate, an
invertebrate chordate. The dark regions in the light micrographs of larvae correspond to
the cells that developed from the two different blastomeres indicated in the drawings.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Derivatives of 3 Germ layers in adult vertebrates
ECTODERM
• Epidermis of skin and its
derivatives (including sweat
glands, hair follicles)
• Epithelial lining of mouth
and rectum
• Sense receptors in
epidermis
• Cornea and lens of eye
• Nervous system
• Adrenal medulla
• Tooth enamel
• Epithelium or pineal and
pituitary glands
MESODERM
• Notochord
• Skeletal system
• Muscular system
• Muscular layer of
stomach, intestine, etc.
• Excretory system
• Circulatory and lymphatic
systems
• Reproductive system
(except germ cells)
• Dermis of skin
• Lining of body cavity
• Adrenal cortex
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
ENDODERM
• Epithelial lining of
digestive tract
• Epithelial lining of
respiratory system
• Lining of urethra, urinary
bladder, and reproductive
system
• Liver
• Pancreas
• Thymus
• Thyroid and parathyroid
glands
References
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

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Campbell, N.A. and Reece,J.B.(2005)Biology.7th edition.Pearson Education,Inc.
Hickman C. P, L.S. Roberts, A.Larson ,H.I'Anson.(2004)Integrated principles of
zoology,12th edition,McGraw-Hill Companies, Inc.Chapter7&8
Slack, J.M.W.(2006)Essential developmental biology.Blackwell Publishing Ltd,Second
edition,Chap 7
Mader,S.S,(2009) . Concepts of Biology,McGraw-Hill Companies, Inc.,Chapter35