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.

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1 Biology 4361 Name: KEY Exam 4 ID#: August 1, 2008 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. 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 1

2 8. Trunk neural crest cells are specified a. prior to migration. b. during migration. c. by paracrine factors after arrival at their destination. 9. Vagal neural crest cells contribute to formation of a. melanocytes. b. adrenal medulla. c. parasympathetic ganglia of the gut. 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. 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. 2

3 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. 3

4 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 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 4

5 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) neural tube neural crest cells intermediate mesoderm dermamyotome primaxial myotome abaxial myotome epidermal ectoderm somatopleure spalnchnopleure sclerotome somite lateral plate mesoderm endoderm notochord Indicate where each of the following cells, structure or organs originate. Label each with a line, arrow, or circle. (½ point each) dermal layer of skin hindbrain dorsal root ganglion melanocytes limb muscle kidney ovarian tissue (excluding oocytes) amnion allantois shoulder cartilage rib cartilage vertebrae heart vascular endothelium 5

6 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. 6

7 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 7

8 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. 8

9 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) 9

10 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 CaPO 4 ). 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. 10