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54 Cards in this Set
- Front
- Back
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In what order are the axes of the nervous system set up?
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First: Anterior/posterior
Then: |
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When can you first see regionalization in an embryo?
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Even before it is an embryo - regionalization can be set up by maternal transcripts in the egg during meiosis.
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What is the very initial thing that induces neurulation?
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Cellular movements that occur during gastrulation - creating TISSUE PROXIMITIES.
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So when is polarity set up in an embryo?
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Prior to fertilization.
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What event follows fertilization to prepattern the blastula?
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Calcium release activated by the union of sperm and egg.
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Poles of the developing embryo:
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Animal (dorsal)
Vegetal (ventral) |
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What 3 layers does the mesoderm underlying ectoderm differentiate into?
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-Ventral mesoderm (left)
-Intermediate mesoderm (middle) -Dorsal mesoderm (right) |
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Where is the Organizing center for neurulation induction?
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In dorsal mesoderm
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What does a Comparitive species diagram of gastrulation show?
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That although morphologically different, the cell-cell interactions and molecular signals are conserved for gastrulation and NS induction.
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How does the dorsal organizer induce neurulation?
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It secretes molecules that REPRESS ectoderm formation and as a result NEURAL TISSUE results as a default.
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What is the molecule that must be repressed in order for ectoderm to not become ectoderm?
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BMP4
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BMP is what
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Bone morphogenetic protein - if it is not repressed, neural ectoderm will not become that.
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What inhibitor molecules are secreted from the Dorsal organizing center?
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-Chordin
-Noggin -Follistatin -Xnr3 |
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What do the factors secreted by the dorsal organizing center do?
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Inhibit BMP4 from allowing ectodermal conversion into epidermis, so that it will by default become neuroectoderm.
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What other type of factors are produced by the mesoderm underlying the developing NS?
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Regionalization factors
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What factor induces Anteriorization?
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Antivin - it inhibits Activin
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What factor induces Posteriorization?
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Retinoic Acid
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What happens if Antivin is overexpressed?
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No trunk region will develop, only anterior.
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What is an important factor in determining regionalization and neuroectodermal conversion?
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CONCENTRATION GRADIENTS of the secreted factors.
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How do the eyes develop?
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From one single field of cells - part of the diencephalon, but able to be distinguished as one field via the use of markers.
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What allows for 2 eyes to develop from one region?
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Morphogenic movements of Diencephalic precursors that migrate into the retinal field under the influence of Sonic Hedgehog factors.
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What would happen to the eyes if there were no Sonic Hedgehog factors?
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Cyclopia
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WHEN DOES ANTERIOR TO POSTERIOR PATTERNING OCCUR IN THE NEURAL TUBE?
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PRIOR TO REGIONALIZATION IN THE DORSAL-VENTRAL DIRECTIONS.
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What genes are primarily responsible for A-P patterning?
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Hox genes
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What are Hox genes?
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Highly conserved DNA-binding factors that pattern the hindbrain - they work by regulating whole NETWORKS of differentiation.
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What do mutations in the Hox genes result in?
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Conversion of whole tissues and organs into mutant types.
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What is it called when a Hox gene undergoes mutation?
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Homeotic Transformation
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How do Hox genes compare between Humans and Drosophilae?
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There is synteny - homology not only at the Amino Acid level, but also in how they are arranged on chromosomes.
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What is different about how Hox genes function in humans/mammals compared to Drosophilae?
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Drosophilae: patterns the entire body plan
Humans: provides molecular addressing to the nervous system |
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What part of the nervous system development is directed by Hox genes in humans?
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From the hindbrain to the spinal cord.
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What are the actual structures that are affected by Hox genes to cause AP axis development in the hindbrain and spinal cord?
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Rhombomeres
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What are Rhombomeres?
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Little bumps in the hindbrain; microflexures that develop and will produce the cranial nerves.
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How many rhombomeres are there?
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7
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What makes the rhombomeres different from one another?
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The combination of factors that their genes encode; includes Hox genes, Ephrins, Eph-kinases, and other trscrp factors
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What is the actual function of Hox genes themselves in rhombomeres?
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Gives individual identification to the neurons that will develop in those rhombomeres - e.g. which cranial nerve will develop.
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What causes a homeotic mutation?
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A mutation in one of the genes for the rhombomeres, making its molecular address look similar to that of another rhombomere.
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what TYPE of regulation is illustrated by the COMBINATORIAL CODING of Hox genes?
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Autonomous self-regulation
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What is a type of Inductive signalling that is important for morphogenesis in the Cerebellum and Midbrain?
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The midbrain-hindbrain organizing center - THE ISTHMUS.
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What does the Isthmus do?
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Secretes FGF8, which induces the expression of Engrailed 2 in a concentration dependent manner.
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How does Engrailed2 act?
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It induces different morphogenesis cascades based on whether it is in Anterior or Posterior regions of the mid/hindbrain.
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What happens to the nervous system after the Anterior/posterior axis is set up?
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Dorsal-ventral regionalization
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What allows for D/V regionalization in the spinal cord?
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Prepatterning by the Alar roof plate and basal floorplate.
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What induces ventralization of the spinal cord?
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Sonic hedgehog from the NOTOCHORD.
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What happens if you don't have sonic hedgehog?
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-No ventral nerves (MOTOR)
-Cyclopia -Prosencephaly |
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What induces dorsalization of the spinal cord?
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Signals from the overlying ectoderm - BMP7
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What determines the neurons that will develop in the dorsal to ventral axis in the spinal cord?
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The concentration gradients of the factors (BMP7 and Sonic Hedgehog) at each level.
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What is the mechanism by which very subtle differences in cells can cause morphological differentiation?
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Feedback mechanisms - like lateral inhibition.
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What is the mechanism that specifies neuronal subtype differentiation?
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Combinatorial Coding - expression of different factors and receptors determines the differentiation that will occur.
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3 Types of Neural Tube Disorders:
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1. Anencephaly
2. Encephalocele 3. Spina bifida |
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What is anencephaly?
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incomplete devo and subsequent degeneration of forebrain.
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What is Encephalocele?
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Herniation of neural tissue usually due to incomplete closure of the neural tube.
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What are 2 types of Spina bifida?
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Meningocele - protrusion of neural tissue thru vertebral column
SB Occulta - incomplete fusion of spine thats asymptomatic. |
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What prevents NTDs?
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Folic acid
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Why does folic acid help prevent neural tube defects?
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Because it allows metabolism of Homocysteine which is a teratogen.
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