Download 1 Biology 4361 Name:______KEY__________ Exam 4 ID

Biology 4361
Exam 4
August 1, 2008
Name:______KEY__________
ID#: ____________________
Multiple choice (one point each; indicate the best answer)
1. Neural tube closure is accomplished by movement of the
a. medial hinge point cells.
b. medial and dorsolateral hinge point cells.
c. medial and dorsolateral hinge point cells, and surface ectoderm.
d. medial and dorsolateral hinge point cells, surface ectoderm, and somite
mesoderm.
2. Neurons in the central nervous system are myelinated by
a. glial cells.
b. Schwann cells.
c. oligodendrocytes.
d. myelinocytes.
3. Spina bifida is a medical condition caused by failure of
a. the anterior neuropore to close.
b. the posterior neuropore to close.
c. cerebrospinal fluid production by the central canal.
d. none of the above.
4. Neural tube cells are specified by opposing dorsal-ventral gradients of
a. Wnts and Nodal.
b. FGF and Shh.
c. BMPs and Wnts.
d. BMPs and Shh.
5. In human skin, replacement cells are first formed in the
a. cornified layer.
b. granular layer.
c. germinal layer.
d. all of the above.
6. Neurons are produced in the __________________ of the neural tube.
a. ventricular zone
b. intermediate zone
c. marginal zone
d. sulcus limitans
7. Cranial neural crest cells contribute to which structures?
a. inner ear bones, cranial nerves
b. thymus cells, jaw
c. facial cartilage, facial bone
d. all of the above
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8. Trunk neural crest cells are specified
a. prior to migration.
b. during migration.
c. by paracrine factors after arrival at their destination.
d. none of the above.
9. Vagal neural crest cells contribute to formation of
a. melanocytes.
b. adrenal medulla.
c. parasympathetic ganglia of the gut.
d. none of the above.
10. Trunk neural crest cells migrate
a. exclusively around the somites.
b. exclusively through the somites.
c. around and through the somites.
d. into the pharyngeal pouches.
11. Subdivisions of mesodermal lineages are specified by BMP gradients which are
a. high anterior, low posterior.
b. high dorsal, low ventral.
c. high ventral, low dorsal.
d. high lateral, low proximal.
12. The Notch receptor is thought to play a key role in which part of somitogenesis?
a. The clock and wave mechanism.
b. Periodicity.
c. Fissure formation.
d. all of the above.
13. Recent evidence suggests that differences in somite numbers between vertebrate species may
be the result of
a. differences in the length of the pre-somitic mesoderm.
b. use of mechanisms other than the “clock and wave"
c. faster cycling of the “clock” mechanism.
d. none of the above.
14. Specification of somites
a. occurs early, in the pre-somitic mesoderm.
b. occurs early, as the individual somites are being formed.
c. occurs midway through the formation of individual somites.
d. occurs late, after formation of individual somites.
15. Tongue muscle is derived from the
a. sclerotome.
b. primaxial myotome.
c. abaxial myotome.
d. none of the above.
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16. What tissue is associated with MyoD?
a. Intramembranous bone.
b. Endochondral bone.
c. Muscle.
d. Ligament.
17. The presence of the transcription factor _______ is diagnostic of the ________ .
a. BMP, sclerotome.
b. Nodal, myotome.
c. Shh, dermatome.
d. scleraxis, syndetome.
18. In male mammals, the mesonephric tubules and duct become
a. ureters.
b. metanephrogenic mesenchyme.
c. efferent ducts, epididymus, and vas deferens.
d. nothing; they disappear through apoptosis.
19. Cardiogenenic mesoderm forms
a. early in gastrulation.
b. late in gastrulation.
c. in the neurula stage.
d. in the organogenesis stage.
20. Cardiogenic mesoderm is induced by signals from the
a. primitive streak.
b. notochord.
c. neurectoderm.
d. endoderm.
21. Cushion cells, which form the heart valves, arise from
a. ventricular myocytes.
b. epidermal ectoderm.
c. endoderm.
d. endocardial endothelial cells.
22. The heart is specified in a rostral-caudal axis by
a. Shh.
b. BMPs.
c. Wnts.
d. retinoic acid.
23. During human development, the aortic arches
a. are all retained.
b. either disappear or form various arteries.
c. eventually disappear.
d. none of the above.
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24. Primary capillary networks are remodeled during
a. extraembryonic vasculogenesis.
b. intraembryonic vasculogenesis.
c. angiogenesis.
d. capillogenesis.
25. Venous and arterial capillaries join via which ligand/receptor combination?
a. Delta/Notch
b. Shh/Patched
c. Fgf2/FGFR
d. none of the above.
26. Human gut formation involves
a. somatic mesoderm.
b. splanchnic mesoderm.
c. somatic ectoderm.
d. splanchnic ectoderm.
True / False (1 point each)
27. Neural crest cells travel exclusively along pathways delineated by extracellular matrix
molecules.
True / False
28. Trunk neural crest cells migrating via the dorsolateral pathway contact the
ectoderm.
True / False
29. The ventricular zone of the neural tube consists of multiple layers of germinal
epithelium.
True / False
30. The initial expansion of the anterior neural tube is caused by cell proliferation in the
ependymal layer. True / False
31. Newly formed neurons migrate through layers of neurons that preceded them. True / False
32. Myelination of human brain neurons is completed during the third trimester of
pregnancy.
True / False
33. Blood vessels generally start forming after the heart starts beating. True / False
34. Proliferating chondrocytes are induced to become hypertrophic by the transcription factor
Runx2 (Andy’s question). True / False
35. Hematopoietic stem cells form red blood cells; lymphoid stem cells form white
blood cells.
True / False
36. The tonsil is derived from the lateral plate mesoderm of the pharyngeal pouch. True / False
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Fill in. Indicate the location of each of the following structures, cells, or tissues. Label each with
a line, arrow, or circle. (½ point each)
37 – 50.
neural tube neural crest cells
intermediate
mesoderm
primaxial
myotome
dermamyotome
abaxial
myotome
epidermal ectoderm
somatopleure
lateral plate mesoderm
sclerotome
spalnchnopleure
somite
endoderm
notochord
Indicate where each of the following cells, structure or organs originate. Label each with a line,
arrow, or circle. (½ point each)
51 – 64.
dermal layer of skin
hindbrain
dorsal root ganglion
melanocytes
limb muscle
kidney
ovarian tissue (excluding oocytes)
amnion
heart
allantois
vascular
endothelium
shoulder cartilage
rib cartilage
vertebrae
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Define. Write a brief definition of any five of the terms or phrases. (2 points each)
65. primary neurulation
Folding of the neural plate via medial and dorsolateral hinge point cells to form a hollow tube.
66. myelination
Wrapping or covering central and peripheral nervous system neuronal axons with a myelin
sheath consisting of lipid membranes from oligodendrocytes or Schwann cells, respectively.
67. somite epithelialization
Early somites consist of loose mesenchyme. The outer portion of these cells form tight junctions
and convert into an epithelial layer.
68. myotube
Myocytes proliferate, polarize, and organize themselves into linear sets. The connections between
the sets eventually fuse, forming a long, syncitial tube out of the precursor cells.
69. cardiogenic mesoderm
Lateral plate mesoderm in the anterior portion of the early gastrulating chick or mammalian
embryo that will form blood cells, blood vessels, and the heart.
70. angiogenesis
A process of pruning and connecting the capillary plexus generated through vasculogenesis to
form capillary beds.
71. hemangioblast
Progenitor cells that will produce blood cells and blood vessels.
72. surfactant
A molecule produced by the embryonic lung that lubricates lung tissue (e.g. alveoli) that allows
the lungs to expand and contract against neighboring tissues without friction.
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Short Answer. Answer any four (5 points each). Be certain to address all parts of
the questions.
73. Describe the “re-segmentation” of the sclerotome. What is the significance of the resegmentation process to the organism in terms of bone, muscle and nerves?
Each segmented block of sclerotome tissue becomes divides itself into rostral (head) and caudal
(tail) portions; the rostral portion then fuses anteriorly with the caudal portion of the sclerotome
adjacent to it, while the caudal portion fuses posteriorly with the adjacent rostral portion.
Meanwhile, the muscles and nerves that move the spine develop according to the original somite
segmentation.
The re-segmentation of the sclerotome results in the vertebrae being one-half segment out of
phase with the muscles and nerves that move them, and consequently allow compression or
bending between vertebrae.
74. Describe how tendons are formed exactly in place between bones and muscles.
Tendons form between the muscle-forming myotome and the bone-forming sclerotome. Fgf
signals from the developing myotome induce sclerotome cells to produce the transcription factor
scleraxis, which specifies the cells to become tendon.
Sclerotome cells inhibit scleraxis transcription in areas beyond the cell layer adjacent to the
myotome cells; thereby limiting tendon specification to a narrow band between the incipient
muscle and cartilage/bone.
75. Describe in general terms the “clock and wave” mechanism for creating somites. List the
necessary components and their functions.
In the clock and wave model, somites are formed by inducing gene activity so that it moves
progressively through a tissue and forms a somite border at its terminus (the wave peak), where it
interacts with proteins or growth factors to produce a phenotypic change.
The wave can be made to cycle if the activation of the gene also activates the production of its
own inhibitor, which eventually builds to concentrations that will stop the process, and repeated
cycles can be produced by making the inhibitor is unstable. As its titer eventually drops, starting
the wave is activated again.
Components:
1) Trigger – to start the wave
2) Effector genes – to produce the phenotype and produce the unstable effector inhibitor
3) Inhibitor – to block effector activity
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76. During the formation of the circulatory system, venous and arterial capillaries connect
exclusively to each other. How is this accomplished?
Arterial endothelial cells contain eprhin-B2+ ligands on their membranes; venous endothelial
cells contain ephrin-receptors (EphB4+) on their outer membranes. Interaction of this ligandreceptor pair is essential for the fusion of capillaries in tissues and organs.
77. Amniote eggs demonstrate a variety of adaptations to development on land or inside the
mother’s body. For any two of these adaptations, describe the structure, how it is produced,
and what environmental challenge it addresses.
Amnion – is the membrane which encloses and protects the embryo in a fluid matrix; it is
produced by the somatopleure (somatic mesoderm and ectoderm).
Chorion – forms the embryonic portion of the placenta, which provides nutrition, gas, and waste
exchange for the embryo; it is produced by the somatopleure (somatic mesoderm and ectoderm)
and trophoblast.
Allantois – is the nitrogenous waste repository or passageway for amniotes; it is produced by the
splanchnopleure (splanchnic mesoderm and endoderm).
Yolk sac – provides nutrition in telolecithal organisms and is a source of blood cells for
mammals; it is produced by the splanchnopleure (splanchnic mesoderm and endoderm).
78. Describe formation of the chick heart from the cardiogenic mesoderm through the heart
looping stage. (Formation of structures only; no gene activities).
The heart originates as two tubes (vessels) which are formed from the lateral plate mesoderm via
blood islands. These vessels move proximally via movement of the splanchnic mesoderm, meet,
and eventually fuse into one tube, which splits at the caudal end into the vitelline veins and at the
rostral end into the conotruncus. The tube then performs a “loop” movement, in which the caudal
(atrial) end moves anterior and dorsal to the rostral (ventricular) end.
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Short Essay. Answer 79 and either 80 or 81 (10 points each). Be certain to address all parts of
the questions and provide complete answers.
79. Listed below are a set of molecules (paracrine factors, growth factors, morphogens, receptors,
and transcription factors) that we have repeatedly seen throughout our study of developing
organisms. For any three molecules on the list: A) declare what class of molecule it is using
the classifications above; some may belong to more than one class, but one is sufficient; B)
list one developmental event associated with that particular molecule and describe its role in
that event; C) list one other paracrine factor, etc. that is somehow associated with the
molecule of choice (e.g. one stimulates production of the other; one antagonizes the other,
etc.). For part C, you may use any associated paracrine factor, etc., not just those on the list.
Note – you are not limited to examples from the most recent set of lectures; use anything we
have covered throughout the semester.
BMP (any)
Shh
Nodal
Fgf (any)
retinoic acid
Notch
Wnt (any)
VEGF
Hox (any)
TGF-β (or TGF-β superfamily)
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80. Describe the basic steps in endochondral ossification.
Mesenchymal cells (scleroderm/somite) commit to become cartilage (chondrocytes).
Committed mesenchyme cells (chondrocytes) condense to nodules.
Chondrocytes proliferate; secrete cartilage-specific ECM.
Chondrocytes stop dividing; become hypertrophic; secrete specific ECM; secrete VEGF.
Hypertrophic chondrocytes die (apoptosis); replaced by osteoblasts (sclerotome mesenchyme).
Osteoblasts become osteocytes; ECM mineralizes (adds CaPO4).
Osteoclasts enter via blood stream; resorb bone; form marrow cavity
81. Describe the dorsolateral and ventrolateral migration of trunk neural crest cells. Provide
details as to the timing of the migration, pathways taken, eventual fate, and location of the
neural crest cells that follow each pathway or portion of the pathways.
Early-migrating trunk neural crest cells travel through the ventrolateral pathway. The NC cells
migrate ventrally between the neural tube the anterior portion of the somite. A portion of the NC
cells move into the anterior somite and stay, forming dorsal root ganglia, and a portion move
through the somite mesenchyme to form sympathetic ganglia, adrenal medulla, and aortic nerve
clusters.
Later-migrating trunk neural crest cells move through the dorsolateral pathway between the
somite and epidermal ectoderm. These NC cells become melanocytes.
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