Transcript Topic 12

BIOL 370 – Developmental Biology
Topic #12
The Emergence of the Ectoderm: Central
Nervous System and Epidermis
Lange
Major derivatives of the ectoderm germ layer
Three subdivisions of the ectoderm:
• Surface
• Neural Crest
• Neural Tube
Major derivatives of the ectoderm germ layer (Part 1)
Know that the surface
ectoderm will form an
organism’s eventual 
Major derivatives of the ectoderm germ layer (Part 3)
Know that the surface
ectoderm will form an
organism’s eventual 
Gastrulation and neurulation in a chick embryo
Gastrulation and neurulation in a chick embryo (Part 1)
Neural plate - a key
developmental structure that
serves as the basis for the
nervous system.
Notochord -a flexible rodshaped body found in embryos
of all chordates composed of
mesodermal cells. In most adult
organisms, the notochord
remains as the nucleus pulposus
of the intervertebral disc.
Gastrulation and neurulation in a chick embryo (Part 2)
Pharynx – a part
of both the
digestive system
and also the
respiratory system.
The pharynx is
considered the
conducting zone
for both systems.
Gastrulation and neurulation in a chick embryo (Part 3)
From the
gastrula
stage you
move into
the neural
stage….
Where the
nervous
system
develops.
Gastrulation and neurulation in a chick embryo (Part 4)
Gastrulation and neurulation in a chick embryo (Part 5)
Figure 9.3 Three views of neurulation in an amphibian embryo, showing early, middle, and late
neurulae in each case (Part 1)
Figure 9.4 Primary neurulation: neural tube formation in the chick embryo
For more
details, see
next two
slides. But
notice how we
are focusing
now
exclusively on
chick
endoderm.
Figure 9.4 Primary neurulation: neural tube formation in the chick embryo (Part 1)
MPH (medial hinge point) – the combined
Hensen's node and epiblast region that is
involved in the intial bending of the neural plate
during neurulation.
Figure 9.4 Primary neurulation: neural tube formation in the chick embryo (Part 2)
Anencephaly is the absence of a
major portion of the brain that
occurs during embryonic
development. This is a cephalic
disorder resulting from a neural
tube defect occurring when the
rostral end of the neural fails to
close. This typically happebs
between the 23rd and 26th day of
conception.
Spina Bifida is a similar
defect this time occurring at
the caudal end of the neural
tube.
Children with this condition
often times have locomotor
disorders.
Figure 9.5 Neurulation in the human embryo
Figure 9.6 Expression of N- and E-cadherin adhesion proteins during neurulation in Xenopus
In the experimental protocol (B) neurulation has
been altered by the injection of N-cadherin and Ecadherin. The alteration leads to the neural tube not
showing the normal stages of separation from the
presumptive epidermis.
Figure 9.7 Folate-binding protein in the neural folds as neural tube closure occurs
Women who are pregnant are often
advised to take supplements of folic acid.
The reason is due to the role that foliate
binding protein exerts on neural tube
closure.
Figure 9.8 Secondary neurulation in the caudal region of a 25-somite chick embryo
Mammalian Brain Development
• In development, the rostral neural tube will begin to
differentiate into more distinctive brain regions. The first
differentiation is into primary vesicles (there are three of
them).
• Following this vesicle development the brain continues
to differentiated into the secondary vesicles (there are five of
them).
Figure 9.9 Early human brain development (Part 1)
Figure 9.9 Early human brain development (Part 2)
Telencephalon
derived
Diencephalon
Derived
Mesencephalon
derived
Meten cephalon
derived
Mylencephalon
derived
Figure 9.10 Rhombomeres of the chick hindbrain
Rhombomeres - a transiently divided segment of the developing neural tube within the
hindbrain region (a neuromere) in the area that will eventually become the
rhombencephalon.
Rhombomeres appear as a series of slightly constricted swellings in the neural tube, caudal
to the cephalic flexure. In human embryonic development, the rhombomeres are present by
day 29.
Figure 9.11 Brain ventricle formation in zebrafish
Ventricles are a set of spaces within the brain containing
cerebrospinal fluid (CSF). The ventricles are continuous with the
central canal of the spinal cord. The ventricle lining consists of an
epithelial membrane called ependyma, made up of ependymal cells.
The red dye is
being injected
to show the
cavities where
the
Figure 9.11 Brain ventricle formation in zebrafish (Part 2)
The snakehead neural tube
undergoes normal ventricle
morphogenesis; however, the
ventricles do not inflate,
probably owing to impaired
ion transport.
Figure 9.12 Occlusion of the neural tube allows expansion of the future brain region
A programmed and
prescribed
occlusion of the
neural tube allows
normal expansion
of the brain
regions.
However….
Long term, non prescribed occlusion may lead to hydrocephaly.
Note that the
example here has
occurred post
parturition. In
cases where
hydrocephaly
occurs earlier in
development,
viability of the
fetus is doubtful.
Figure 9.14 Cascade of inductions initiated by the notochord in the ventral neural tube (Part 1)
Sonic Hedgehog protein concentrations
(produced by the notochord) will differ
depending upon distance away from
the notochord (due to paracrine
signaling)
Figure 9.14 Cascade of inductions initiated by the notochord in the ventral neural tube (Part 2)
Shh = Sonic Hedgehog
In “B” we see normal
development.
In “C” we see a donor
notochord placed in
an abnormal position
near the neural tube
and its guiding of a
second floor plate and
motor neuron region.
Figure 9.15 Diagram of a motor neuron
Axonal outgrowth occurs
in a neuron through the
production of microtubules
and F-actin at the axonal
endings.
Ross Harrison discovered this
basic process in 1907.
Figure 9.16 Axon growth cones
These projections form microspikes.
Figure 9.17 Myelination in the central and peripheral nervous systems
Figure 9.17 Myelination in the central and peripheral nervous systems (Part 1)
Figure 9.17 Myelination in the central and peripheral nervous systems (Part 2)
Stereotypical Human Cell Cycle
Figure 9.18 Neural stem cells in the germinal epithelium
Unlike later in life (at least for
mammals), the neural stem cells
display all stages of the cell cycle.
Figure 9.19 Differentiation of the walls of the neural tube
The neural tube will
further differentiate into a
wide array of structures
that are dependent upon
location.
Figure 9.20 Development of the human spinal cord
Figure 9.21 Cerebellar organization
Cerebellum - a region of the
brain that plays an important
role in motor control.
The cerebellum may also be
involved in some cognitive
functions such as attention and
language, and in regulating
fear and pleasure responses.
Bergmann glia - a type of glia also known as radial epithelial cells or
Golgi Epithelial Cells are astrocytes in the cerebellum.
Bergmann glia express high densities of glutamate transporters that
limit diffusion of the neurotransmitter glutamate during its release
from synaptic terminals.
In addition to their role in early development of the cerebellum,
Bergmann glia are also required for the pruning or addition of
synapses.
Some studies
have suggested
that over
pruning of
dendritic spines
may occur in
the prodromal
and early stages
of
schizophrenia.
Thymidine (T) is one of the four
nucleosides that form the bridges with
adenosine (A) in DNA. In the next
experimental data, ferret cortex
development is examined by using
tritiated thymidine to map where the cell
cycle is occurring in brain development.
Figure 9.23 Determination of cortical laminar identity in the ferret cerebrum (Part 1)
This study looks at the role of thymidine on determining cortical identity in the
cerebrum in ferrets. In “A” an early pulse of thymidine is administered late in
prenatal development, whereas “B” has a later pulse after parturition. The stem cells
in “A” become layer 6, whereas the same cells in “B” become layers 2&3.
Figure 9.23 Determination of cortical laminar identity in the ferret cerebrum (Part 2)
The blue represents “early” neuronal precursors that have formed and
been transplanted into an “old” host brain. If these cells have
completed synthesis prior to transplant, they move to region 6, but if
they undergo S, and G2 within the host, they will migrate to region
2&3.
Figure 9.25 Evidence of adult neural stem cells
Figure 9.27 Retention of fetal neuronal growth rate in humans
Compare the brain weights and body weights to see the
significance of differential (and continued) development in human
brains versus other primate brains.
Figure 9.28 Dorsal view of the human brain showing the progression of myelination (“white matter”)
over the cortical surface during adolescence
What would you anticipate the effects of the increased cortical
myelination be?
Figure 9.34 Retinal neurons sort out into functional layers during development
Marcello Malpighi (most work occurred in the 1660s)
was an Italian physician, who identified (and named after himself)
several anatomical structures. Examples include the Malpighian
tubule system in the kidney and the Malpighi layer in the skin.
Figure 9.37 Layers of the human epidermis
The Malpighian layer
of the skin is defined
as the combination of
both the stratum
basale and stratum
spinosum layers of
the epidermis.
The main structural features of the skin epidermis.
Keratinocytes
Stratum corneum
Most superficial layer; 20–30 layers of dead
cells represented only by flat membranous
sacs filled with keratin. Glycolipids in
extracellular space.
(a)
Dermis
Copyright © 2010 Pearson Education, Inc.
Stratum granulosum
Three to five layers of flattened cells, organelles
deteriorating; cytoplasm full of lamellated granules (release lipids) and keratohyaline granules.
Stratum spinosum
Several layers of keratinocytes unified by
desmosomes. Cells contain thick bundles of
intermediate filaments made of pre-keratin.
Stratum basale
Deepest epidermal layer; one row of actively
mitotic stem cells; some newly formed cells
become part of the more superficial layers.
See occasional melanocytes and epidermal
dendritic cells.
Desmosomes
(b)
Dermis
Melanocyte
Epidermal
dendritic
cell
Tactile
(Merkel)
cell
Sensory
nerve
ending
Melanin granule
Figure 9.38 Early development of the hair follicle and hair shaft
Figure 9.38 Early development of the hair follicle and hair shaft (Part 1)
Figure 9.38 Early development of the hair follicle and hair shaft (Part 2)
Figure 9.38 Early development of the hair follicle and hair shaft (Part 3)
Figure 9.41 Facial anomalies of anhidrotic ecotodermal dysplasia, caused by mutation of an EDA
gene
•
Anhidrotic Ectodermal Dysplasia (also called
"Christ-Siemens-Touraine Syndrome“) is a disorder
resulting in the abnormal development of a variety
of structures including the skin, hair, nails, teeth,
and sweat glands.
•
Individuals with this condition have a reduced
ability to sweat (hypohidrosis) because they have
fewer sweat glands than normal or their sweat
glands do not function properly potentially leading
to a dangerously high body temperature
(hyperthermia) in certain circumstances
•
Affected individuals tend to have sparse scalp and
body hair (hypotrichosis). The hair is often lightcoloured, brittle, and slow-growing.
•
This condition is also characterized by absent teeth
(hypodontia) or teeth that are malformed. The teeth
that are present are frequently small and pointed.
The most common cause of
Anhidrotic Ectodermal
Dysplasia is due to a mutation
in the EDA gene that provides
instructions for ectodermal
and mesodermal interaction
and development.
End.