Download Lab 8: Chick 72 hours Lab 8: Chick, 72 hours

Lab 8: Chick
Chick, 72 hours
Nervous system
Cranial nerves
Digestive system
72 hour chick embryo
• Cranial nerves and ganglia are quickly
developing, with one new cranial ganglion
per neuromere.
p
• The organs of the digestive system are
forming.
• At this stage the embryo has a foregut,
hindgut, and the beginnings of organs
along the midgut.
Neural crest cells
• So versatile that they could be called a
fourth germ layer. They help form many
titissues:
– Melanocytes, adrenal glands, peripheral
system neurons including spinal ganglia, and
bones and cartilage of the head, and parts of
the cranial trigeminal and glossopharyngeal
and vagus ganglia
ganglia...
• They arise along the neural tube starting
around 27 hours and are migratory along
specific paths. Two movies show the
fluorescently labeled cells moving away
from the neural tube over 10-12 hrs.
Neural crest cells migrating
Neural crest cells migrating
Neural crest cells can be fluorescently
labeled with a specific antibody (HNK-1)
Immunocytochemistry for neural crest cells
HNK-1
HNK
1
expressing
cells in
color
Neural crest cell derivatives
Origin between ectoderm and neural tube
• Neural crest cells play a large role in
vertebrate evolution because they form so
many of the structures in the head and
pharyngeal arches that are characteristic
of a vertebrate body type.
• They are therefore the main cells
responsible for changes in craniofacial
evolution.
The avian bill is formed in part from the cranial
neural crest migrating from the fore and midbrain
region
i tto th
the b
branchial
hi l arches
h
(A): Migration of neural crest cells (shown in red)
(B) and (C): Maxillary (mx) and mandibular arches
(md)
(D): Beak bone (red) from NCC
NCC.
Trainor, P. ( Science 299: 523 2003).
The avian bill is not entirely made from NCCs – they
contribute but do they determine its pattern?
A grafting
experiment was
done to test this.
Chick neural crest
cells were put in the
quail embryo
((“quck”)
quck ) or quail
neural crest cells
were put in the duck
embryo (“duail”)
( duail ). The
results are on the
next slide.
The duck beak
of course is
longer. The
quail beak has
a maxillary
ill
bump near the
tip
p ((egg
gg tooth).
)
A. Quail NC
cells
transplanted in
a duck embryo
( quck)
(a
k) results
lt
in a stubby quail
type bill and
having the egg
tooth bump.
B. Duck NC cells
transplanted in a
quail embryo (a
duail)) results in a
longer duck type
bill.
• The results of the reciprocal transplants
indicate that it is the neural crest which
forms not only the cartilage and bone but
directs the overlying ectoderm and the
mesoderm as well in the formation of the
avian beak
beak.
Cranial nerves and ganglia
Sensory organs
• Most of the paired cranial nerves (bundled
collections of neurons) have a cell body
containing the nucleus and most of the
cytoplasm in ganglia (singular ganglion). The
thi d ffourth
third,
th and
d sixth
i th h
have no ganglia.
li
• Nerves are made up of neurons extending back
to the central nervous system or to some target
sensory organ or muscle.
• The next slide shows a typical migrating
embryonic neuron with a leading edge growth
cone which extends the axon from the cell body.
The migrating neuron as shown in
lecture.
Cranial nerves
• The sources of the neurons can be alongside
the neuromeres (rhombomeres), or from
ectoderm just under the epidermis (epibranchial
placodes) or growth from the developing
sensory organ (nose, eye, ear).
• The olfactory sensory nerve (I) forms axons
growing from the nasal pits toward the cerebral
hemispheres.
• The optic nerve (II) forms from the sensory
retina and later axons grow back to join to the
diencephalon.
diencephalon
• The oculomotor (III) nerves are motor and later
innervate the eye
y muscles (not
(
yet
y formed).
)
Cranial nerves of the hindbrain
• The trigeminal (V) is both sensory and motor
with the semilunar ganglion sending branches to
the eye (ophthalmic) and maxillary/mandibular
processes. Placode cells and neural crest form
p
this nerve.
• The facial nerve (VII with acousticofacialis
ganglion) is a mixed nerve for the face
face. Trace it
to the second mainly, but mandibular arch too.
Placode cells and neural crest contribute to this
nerve It is close to the auditory nerve (VIII)
nerve.
which innervates the nearby developing ear
(auditory vesicle).
• The glossopharyngeal (IX) and associated
superior ganglion is a sensory nerve can
be traced to the third arch. Epibranchial
placodes and neural crest form this nerve
nerve.
• The vagus (X) and associated jugular
ganglion is a mixed nerve for the fourth
arch. Epibranchial placodes contribute to
the neural crest forming these neurons
neurons.
Spinal cord
Spinal
p
accessory
nerve (XI)
Glossopharyngeal
ganglion (IX)
Otic vesicle
Acousticofacialis
ganglia (VII/VIII)
left
right
Neuromeres of
myelencephalon
Metencephalon
Yolk sac
anterior
Semilunar
ganglion
g
g
of
trigeminal nerve
Mesencephalon (V)
Spinal cord
Notochord
Facial nerve
Metencephalon
Semilunar
ganglion (V)
of trigeminal
nerve
Isthmus
Mesencephalon
Digestive system and endoderm derivatives
• At 72 hours the endodermal derivatives such as
the lung buds begin to rapidly expand into the
mesenchyme of mesoderm origin.
• The esophagus,
p g , stomach,, liver and duodenum
are just beginning to form. Try to trace the
connections between these tissues as they all
branch off the same original endodermal tube.
• Note the closeness of the ductus venosus to the
li
liver
rudiment;
di
t llater
t th
the liliver will
ill surround
d thi
this
vessel. Why would later much more vitelline
blood be directed to the liver?
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Pharyngeal region
• The four pharyngeal (branchial) arches are
characteristically found in all vertebrates
during development whether or not gills
are formed. This is an example of the
retention of common structures and
developmental pathways in vertebrate
evolution.
l ti
• The derivatives of the endoderm and
neurall crestt cells
ll vary th
the mostt iin
evolution.
Posterior endoderm derivatives
• The hindgut is the region posterior to the
caudal intestinal portal
portal. The hindgut ends
in the cloaca. Note how the allantois
branches off ventrally
ventrally. The cloaca is a
blind ending but will later form an opening
at the site of the cloacal membrane
(proctodeum). Try to find possible
functional openings of the mesonephric
ducts into the cloaca.
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Sagittal
g
section to show how allantois
branches off of the hindgut
Neural tube cell organization
• The dividing population of cells is closest to the
lumen in the ependymal (ventricular) layer as
mentioned in the lecture. At the early stages
seen in the next slide the division into three
layers (ependymal
(ependymal, mantle and marginal) is not
completed.
• Because all tube cells are attached at the
ependymal end and extend the full width, the
tube is considered to be a pseudostratified
epithelium Pseudo meaning that there is only
epithelium.
one cell layer but because cell bodies are at
various positions it looks like there are manyy
strata or layers.
Chick embryo neural tube cells before the formation of
the three neural layers.
Dividing cells can sometimes be seen close to the lumen
in the ventricular zone.
anaphase
•
In the spinal cord or brain of the 72 hour chick embryo the thin outer
marginal zone sometimes is seen (i.e rarely) as distinct from the two darker
and denser inner layers. Try to find it.
In viewing sections note how the
thi k
thickness
off the
th layers
l
varies
i between
b t
brain regions.
• In the next slide the adult spinal cord
structure is shown with the dorsal sensory
and ventral motor nerves.
• In the 72 hr chick the nerve axons are
growing toward the targets (such as the
limb bud which is very early in its
development) but the staining method
used for these sections does not allow
nerve fibers to be easily seen.
Adult neural tube structure
• The oculomotor nerves (cranial nerve III)
can sometimes be seen as thin usually
non-continuous streaks extending from the
mesencephalon floor toward the internal
carotid arteries. These nerves will
innervate the muscles of the eyes
eyes. (The
oculomotor nerves may not be seen in all
sets of sections
sections.
Body cavities
• The coelom is beginning to become
divided into the pericardial cavity
surrounding the heart, the pleural cavity
surrounding the lungs
lungs, and the peritoneal
cavity around the gut.