CMMB 403 Final Exam Questions With
Correct Answers
What are the origins of the optic vesicle and the lens? - answeroptic vesicle = forebrain (neural
ectoderm)
lens = surface epidermis --> placode
Describe the process of lens induction - answer1. the optic vesicle (forebrain) induces
thicke...
CMMB 403 Final Exam Questions With
Correct Answers
What are the origins of the optic vesicle and the lens? - answer✔optic vesicle = forebrain (neural
ectoderm)
lens = surface epidermis --> placode
Describe the process of lens induction - answer✔1. the optic vesicle (forebrain) induces
thickening of the surface epidermis (prospective lens placode)
2. the optic vesicle pinches in to form the optic cup and the lens invaginate as well (lens placode
comes into contact w/ the optic vesicle)
3. the optic cup forms two layers: neural retina and the pigmented retina
4. the lens pinches off
What is a placode? - answer✔epithelial thickening of ectoderm that develops into neurons or
other parts of the sensory organs
What is the function of jervine? - answer✔Its a SHH inhibitor, preventing the repression of Pax6
at the midline, causing cyclopia
What is the function of Pax6? - answer✔Eye development
Where is Shh expressed along the midline? - answer✔- the prechordal plate (floor plate of the
neural tube) and the notochord
How does the signalling in Mexican cave-dwelling fish differ for eye development? - answer✔-
they sent need to see because they live in caves
- so they have evolved to over express Shh and down regulated Pax6 everywhere = no eye
development
What is the function of the Rx gene? - answer✔retinal development --> functions to maintain the
expression of Pax6 (AMPLIFY PAX6)
Where do neural crest cells form? - answer✔The entire length of the neural tube
How do neural crest cells migrate? When in development does migration occur? - answer✔They
undergo an EMT
- migrate in the 4th week of development
What transcription factors are necessary to cause the release of E-cadherin and allow the neural
crest cells to undergo an EMT and migrate - answer✔Snail/Slug --> neural crest cells lose E-
cadherin and become mesenchymal and can migrate through the body
What are the four main regions of neural crest and what do they form? - answer✔1. Vagal/
Sacral: forms the parasympathetic neurons that innervate the gut
2. trunk: forms the sensory neurons and dorsal root ganglia (and the melanocytes)
3. cranial: forms the bones and cartilage of the face
4. cardiac: forms the outflow tracts of the heart
What chemotaxis elements are responsible for the migration of the vagal/sacral neural crest cells
into the gut? - answer✔gut produces GDNF signal which binds to the RET receptors on the
neural crest cells --> chemoattraction that drives the movement of neural crest cells into the gut
What causes Hirschprungs disease? - answer✔mutation in GDNF or the RET receptor to prevent
chemoattraction driving the movement of neural crest cells to the gut
- dont get proper peristalsis in the gut anymore
What are the two pathways that trunk neural crest cells can migrate down? Which one forms
what and which happens first? - answer✔First - the ventral pathway: neural crest cells migrate to
the anterior sclerotome where they either become the sympathetic ganglia or the dorsal root
ganglia
Second - the more dorsolateral pathway: future melanocytes migrate between the dermis and
epidermis
Where are the cell bodies of the sensory neurons found? - answer✔- found in the dorsal root
ganglia, not right in the central nervous system
What drives the migration of trunk neural crest through the anterior sclerotome instead of the
posterior? - answer✔- the neural crest cells express Eph receptors
- the posterior sclerotome expresses ephrins
- these repel eachother
What do the neural crest cells who stay in the anterior sclerotome become? - answer✔if they stay
in the anterior sclerotome --> become more dorsal cell types DRG
What do the neural crest cells who are repulsed and migrate out of the anterior sclerotome
become? - answer✔cells that migrate out of the anterior sclerotome migrate back more ventrally
--> become the sympathetic ganglion
How does the migration of the axons of the motor neurons resemble the neural crest cells? -
answer✔motor neuron axons also express Eph receptors and are driven to migrate through the
anterior sclerotome too
What is the cell signalling pathway required for the trunk neural crest cells to migrate through
the dermis/epidermis and become melanocytes? - answer✔- melanocytes express the Kit receptor
tyrosine kinase
- the dermis expresses the SCF (stem cell factor) ligand which activates the Kit receptor on the
neural crest cells
- causes phosphorylation and activation of the transcription factor, MITF
- and causes melanocytes to proliferate and migrate
What mutations would be present in people who have skin pigmentation problems? - answer✔-
problem would be in the migration of their melanocytes through the body --> driven by the Ras
pathways (via Kit repceptors and SCF ligand)
- could have a mutation in the Kit receptor on the neural crest cell
- or could have a mutation in the SCF ligand from the dermis
What is the role of the MITF transcription factor? - answer✔- MITF is a transcription factor that
activates melanoblast specific genes... it is produced when the Ras pathway is active --> SCF is
released from the dermis which activates the Kit receptor on the melanocyte neural crest cells
- get melanocyte proliferation
What would you see in someone w/ a Kit mutation? - answer✔lack of pigmentation --> lack of
melanocyte proliferation
Why are MITF mutations in dalmations and painted horses associated with pigmentation
problems and with deafness? - answer✔- melanocytes also play a role in migration to the inner
ear to promote blood vessel formation in the cochlea
What do cranial neural crest cells that migrate through pharyngeal arches 1 and 2 become? -
answer✔- become the middle ear: incus, malleus, and stapes
What do the cranial neural crest cells that migrate through pharyngeal arches 3, 4, and 6 become?
- answer✔- become the bones are cartilage of the throat and face
What are the bones of the middle ear derived from? (incus, malleus, and stapes) -
answer✔middle ear bones are derived from cranial neural crest the migrated through the first 2
pharyngeal arches
What population of neural crest cells can form bone? - answer✔Only cranial
Where do the cardiac neural crest cells migrate through? - answer✔arches 3, 4, and 6
What do the cardiac neural crest cells differentiate into? - answer✔- the septum that separates the
truncus arteriosis (single outflow tract that has mixed oxygenated and unoxygenated blood) into
the aorta and the pulmonary artery
How do we know that cardiac neural crest cells contribute to heart development? - answer✔-
quail grafting into chick embryos
- can also use a conditional LacZ reporter gene that is only expressed using a neural crest-
specific Cre recombinase
Describe how to make a transgenic LacZ reporter mouse that will have permanent lineage tracing
of neural crest cells - answer✔- make a gene construct w/ LacZ on a ROSA26 gene locus that is
constitutively expressed but you put a LoxP flanked stop cassette prior to the lacZ gene so that it
is not expressed
- breed w/ mice who have a Wnt1Cre recombinase that is specific to neural crest cells
- mice will be Cre+loxpROSA and in neural crest cells, the Cre recombinase will cleave out the
stop codon and LacZ will be expressed, staining the cell
- all subsequent cells will also be stained, making a permanent lineage of all neural crest
derivatives
Which of the three main ectoderm derivatives can go on to form neurons? - answer✔All of them
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