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34 Cards in this Set
- Front
- Back
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Neurulation
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1) notochord -- > overlying ectoderm -- > neuroectoderm -- > neural plate
2) neural plate folds -- > neural tubes (neuralpores at both ends connect tube to amniotic cavity), some cells form neural crest cells |
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Notochord
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Solid cylinder of mesoderm extending in midline of trilaminar disk from primitive node to prochordal plate
Functions: 1) induction of ectoderm to form neruoectoderm which forms neural plate 2) induces formation of vertebral body 3) forms nucleus pulposus of intervertebral disk |
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Anterior Neuropore
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Anterior opening of neural tube
Closes day 25 Becomes Lamina Terminalis Failure to close: upper neural tube defects ex. anencephaly |
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Posterior Neuropore
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Posterior opening of neural tube
Closes day 27 Failure to close: spina bifida, myeloschisis |
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Neural Crest Cells
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From lateral border of neural plate
Mediated by BMP-4 and BMP-7 Differentiation by expression of slug (zinc-finger transcription factor) Break away from neuroepithelium migrate to ECM -- > mesenchymal cells Prolific migration throughout embryo |
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Promoters of cell migration
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Fibronectin
Laminin Type IV collagen |
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Proteins that restrict cell migration
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Chondroitin sulfate rich proteoglycans
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Cells derived from Neural Crest
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1) Ganglia
2) Schwann Cells 3) Odontoblasts (dentin of teeth) 4) Pia & Arachnoid Mater 5) Chromaffin cells of adrenal medulla 6) parafollicular (C ) cells of thyroid 7) melanocytes 8) aorticopulmonary septum 9) pharyngeal arch skeletal components 10) bones of neurocranium |
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Cells derived from Neuroectoderm
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1) neurons of CNS
2) Eye cells (retina, iris epithelium, cilliary body epithelium, optic nerve, optic chiasm, optic tract, dilator and sphincter pupillae muscles 3) astrocytes, oligodendrocytes, ependymocytes, tancytes, choroid plexus cells 4) neurohypophysis 5) pineal gland |
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Neural Tube Lumen
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Ventricular system of brain
Central Canal of spinal cord |
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BMP-4
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Bone morphogenic Protein-4
Inhibited by noggin, chordin, follistatin --> induction of neural plate, formation of notochord, and paraxial mesoderm In mesoderm and ectoderm of gastrula Ectoderm --> epidermis Mesoderm intermediate and lateral plate mesoderm Present in: organizer (primitive node) notochord, prechordal mesoderm |
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Placodes
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- Localized thickenings of surface ectoderm
- Give rise to cells that migrate into mesoderm -- > sensory receptive organs of CN1 and CN 8 and lens of eye - lens placode from optic vesicles - olfactory placode -- > neurosensory cells -- > Olfactory nerve (CN1) -- > olfactory bulbs - otic placodes -- > otic vesicle 1) utricle, semicircular ducts and vestibular ganglion of CN 8 2) Saccule, cochlear duct (organ of Corti), spiral ganglion of CN8 3) vestibulocochlear nerve (abducens) |
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Brain vesicles
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primary vesicles
1) proencephelon (forebrain) Telencephelon -- > cerebral hemispheres, caudate, putamen, amygdalaoid claustrum, lamina terminalis, olfactory bulbs, hippocampus Diencephalon -- > epithalamus, subthalamus, thalamus, hypothalamus, mamillary bodies, neurohypophysis, pineal gland, globus pallidus, retina, iris, cilliary body, optic nerve, optic chiasm, optic tract 2) mesencephelon midbrain 3) rhombencephelon (hindbrain) Metencephalon -- > pons, cerebellum Mylencephalon -- > medulla Flexures 1) cephalic Flexure between proencephelon and rhombencephelon 2) cervical Flexure between rhomencephelon and future spinal cord Primary at 4 weeks, secondary at 6 weeks |
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Glioblasts
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formed afer neuroblasts
exception: radial glial cells form: astroglia, radial glial cells, oligodendroctyes, ependymocytes, tancytes, choroid plexus cells, microglia (hortega cells) |
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astrocytes
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project foot processes to capillaries contribute to BBB
metabolism of NT buffer teh K+ of CNS form glial scars in damaged areas glial fibrillary acidic protein (GFGAP) glutamine synthease |
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Pluripotent
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Cells not have a fixed development, can develop into any type, but not sufficient to generate a whole organism on their own
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Totipotent
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Cell capable of generating a whole organism
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Problems with Cloning from stem cells
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Genome wide demethylation doesn’t occur as efficiently in somatic cell nucleus as it does in germ cells
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Cord Blood stem cells
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Advantages
-their harvesting is not ethically controversial -cord blood stem cells trigger little immune response in the recipient -they have much less of a tendency to form tumors when injected into animals compared to embryonic stem cell Disadvantages -they cannot become every cell type (however they are particularly good at forming blood cells; a very good alternative to bone marrow transplants) -small number in cord blood |
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Cell differentiation
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Once committed, stays that way (arm doesn’t turn into a leg later)
Cells retain “memory” of ancestral signals Once gene is turned on or off, it says on or off |
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How is a gene turned on?
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Activate the transcription factor of desired gene, and it will actively transcribe for life of cell, also keeps everything else the transcription factor affects downstream turned “on”
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How is a gene turned off?
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Methylation of DNA
At fertilization, genome-wide wave of demethylation which allows transcription of every gene Why embryos from artificially induced from somatic cells have severe developmental defects (Dolly the sheep) |
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Signals and Receptors “off “ and “on” signals
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1) transmembrane molecules used for cell adhesion and cell signaling
2) gene regulatory proteins |
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Point of sperm entry
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May determine which cells form embryoblast vs trophoblast in later cell divisions
The (x) cell divides slightly ahead of the other cell, (fact) most often, descendents of the (x) cell form the embryoblast, descendents of the other cell form the trophoblast |
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Response of cell to particular signaling molecule
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Dependent of combination of signals cell receiving at the time
Previous history of cell, what’s already turned on or off (time) Amount of signal the cell is receiving (distance from origin of signal) |
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Sonic Hedgehog (SHH)
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Dependent of combination of signals cell receiving at the time
Previous history of cell, what’s already turned on or off (time) Amount of signal the cell is receiving (distance from origin of signal) Sonic Hedgehog (SHH) Secreted protein, modified by cholesterol moiety (trafficking and signalling) Defects in cholesterol metabolism -- > Autosomal recessive Smith-Lemli-Opitz syndrome Receptor Patched, multipass transmembrane protein Intracell: SHH/Patched/ 3 Gli family of TF |
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SHH patterning found
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-somite development
-formation of anterior-posterior body axis - developing limb bud - developing brain -hair follicle development -tooth development |
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TGF-β
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BMP, nodal and TFG-β in same family
Chordin (Sog) and Noggin inhibit.modulate extracellularly Receptors: single pass R with Serine/Threonine kinase domain 2nd messenger: SMAD associate with other gene regulatory proteins and bind to DNA Activities: L- R symmetry BMP-4 ventralization of mesoderm Nodal- establishment of primitive streak |
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Factors controlling Axis formation
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FGF proximal - distal
Wnt7a dorsal – ventral SHH anterior – posterior |
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Homeobox Gene
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Code for transcription factors involved in embryo development
Homeodomain binds sequence specific DNA motifs Can activate or repress down stream effectors |
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Hox Genes
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Helix turn helix TF
Clustered on chromosomes Anterior – posterior patterning Turn on in sequence Highly conserved Control segment identity Retinoic acid -- > expression -- > defects |
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How do hox genes work?
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Each one switched on in particular place along body
Get different combination of signals Within segment get integrated at enhancer of target genes -- > localized activation Regulate morphogenesis of specifc organs by activating networks of TF and s signalling molecules once developmental pathway is turned on by hox, never turned off polycomb and Trithorax -- > DNA binding proteins stamp the chromatin of Hox complex with the record of embryonic signals continuously synthesized and continuously bound to off or on position |
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Cadherins
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Single-pass transmembrane glycoprotein
Need Ca++ to bind to another cadherins Link by homophillic binding (desmosomes) Keep like cells stuck together, compaction of 8 cell embryo (e-cadherin) condensation of mesoderm formation of neural tube Metastasis in tumor cells occurs with loss of cadherin |
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Integrins
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Transmembrane R for ECM molecules
Can recognize many different ECM Cell migration and sending signals |
