* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chapter 13- The neural crest
Neuroethology wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Neural coding wikipedia , lookup
Biological neuron model wikipedia , lookup
Neural oscillation wikipedia , lookup
Multielectrode array wikipedia , lookup
Axon guidance wikipedia , lookup
Stimulus (physiology) wikipedia , lookup
Convolutional neural network wikipedia , lookup
Synaptogenesis wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Neuroanatomy wikipedia , lookup
Neural correlates of consciousness wikipedia , lookup
Subventricular zone wikipedia , lookup
Artificial neural network wikipedia , lookup
Optogenetics wikipedia , lookup
Metastability in the brain wikipedia , lookup
Nervous system network models wikipedia , lookup
Types of artificial neural networks wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Recurrent neural network wikipedia , lookup
Neural binding wikipedia , lookup
Channelrhodopsin wikipedia , lookup
The neural crest Chapter 13- The neural crest Recall lineages Ectoderm-skin/nerves Mesoderm-Blood, heart, kidney, bones Endoderm- Gut and associated organs Recall- Ectoderm has three fates 1.Epidermis 2.Neural crest cells 3.Neural tube Fig. 12.3 Epidermis (skin) Peripheral neurons, facial cartilage Brain and spinal chord This process is called neurulation The neural crest Neural crest cell fate depends largely on where they migrate The neural crest is a transient structure Potential cell fates include1. neurons and glia 2. medulla of adrenal gland (produces epinephrine) 3. Pigment cells of epidermis 4. Skeletal/connective tissue of head Neural crest- four functional domains 1. Cranial- cartiledge, bone, neurons, glia of face 2. Cardiac 3. Vagal- parasympathetic ganglia 4. Trunk- melanocytes (produce pigment); sensory and sympathetic neurons, medulla Fig. 13.1 Sensory pathways- conduct info to brain-, spinal cord A quick review of nerve nomenclature 1. Autonomic nervous system -“involuntary controlled muscles”- CNS sends signals to smooth muscles of heart, blood vessels, iris, pancreas liver, digestive tract, kidney 1.Parasympathetic- -homeostasis of body systems, originate from hindbrain 2. Sympathetic-fright and flight reactionsoriginate form spinal chord 2. Somatic nervous system-“voluntary controlled organs”- CNS sends signals to striated muscles communication between various parts of the body (e.g. thallumus, cerebellum) with muscles Figure not in text The neural crest A. Start with the Trunk Neural crest Two major paths taken Path 1-cells travel under epidermis, become melanocytes, colonize hair and skin follicles Epidermis Neural tube Sclerotome Notochord Path 2-cells to side of neural tube and through anterior sclerotome to become sympathetic and sensory neurons Fig. 13.2 This is a somite Note – Sclerotome will become vertebral cartilage The neural crest How do these neural crest cells know where to migrate? 1. Epidermis secrete BMP-4 and BMP-7 - BMP-4 and –7 induce neural crest cells to produce slug and RhoB - Slug dissociates cell-cell tight junctions 2. N- cadherin expression is also lost then regained once reaching final destination 3. Ephrin proteins in extracellular matrix guide cells • Neural crest cells have Eph receptors • Trunk sclerotome express Eph ligand • Binding of Eph receptor to Eph ligand interferes with migration • Thus, Eph proteins tell neural crest cells where not to go Neural Crest cells Fig. 13.4 Ephrinin sclerotome 4. Stem cell factor allows continued proliferation 5. Other chemotactic and maintenance factors The neural crest •Trunk neural crest cells are pluipotent (can become many cell types) However, it may be that only certain populations of cells are pluripotent • Some transcription factors have been identified that dictate cell fate Mash-1 Sympathetic and parasympathetic neurons Trunk neural crest cell Neurogenin Sensory neuron Final cell fate is determined by final environment Fig. 13.6- Fate of a trunk neural crest cell is influenced by FGF2 and glucocorticoids The neural crest B. The Cranial neural crest Like the trunk neural crest cells, these can produce glia, neurons and melanocytes But, only cranial neural crest cells can produce cartilage and bone Rhombomeres Recall – the neural tube subdives into forebrain, midbrain and hindbrain • The hind brain then further subdivides into rhombomeres • Each rhombomere is a territory, each produces ganglia, but each has a distinct fate •Rhombomeres sit behind the pharyngeal arches Pharyngeal arches Fig. 13.1 Three paths for cranial neural crest cells Pharyngeal arches 1 2 The neural crest Rhombomeres in hind brain of neural tube 1. Rhombomere 1+2- to 1st Ph. Arch 2. Rhombo. 4- to 2nd Ph. Arch 3 4 3. Rhombo. 6 to 3rd and 4th Ph. Arch Fig. 13.7 Rhombomeres 3 and 5 do not migrate through arches Fate map of pharyngial arches contributions to face formation The neural crest What determines distinct fates of cranial neural crest cells? Answer- The combination of hox genes Evidence 1. Hoxa-2 KO- neural crest cells of 2nd Ph. Arch transformed into 1st Ph. Arch structures 2. Hoxa-1 and Hoxb-1 double KO- no rhombomere 4 migration + retinoic WT acid 3. Retinoic acid induces more anterior expression of certain Hox genes- - rhombomeres 2 and 3 assume role of rhombomeres 4 and 5 No ear Fig. 13.8 How is neuronal diversity achieved?? 5 ways1. Blocking BMP signal allows formation of dorsal neural tube (recall chapter 12) 2. Notch-delta specifies neural fate (not epidermal or glial) 3. Initial location determines neuronal type 4. Migration route further dictates specificity 5. Specific connection made with target organs or other neurons 3 parts described 1. Pathway selection- axons travel along a given route 2. Target selection- axons reach a target, then bind to specific cells 3. Address selection- axons now refine interactions- bind to only a subset of possible targets A. Hypotheses for pathway selection1. Cell adhesions- Growth cone can adhere to certain cells, but not others • Laminin – a glycoprotein which appears to pave the road for several axonal migrations • N-CAM 2. Physical barriers- Growth cone can adhere to certain cells, but not others 3. Labeled pathway hypothesis- in insects, a neuron can precisely follow the path of a prior neuron Kallmann syndrome- an infertile man with lack of smell Reason- a single protien directs migration of both olfactory axons and hormone-secreting nerve cells 4. Repulsiona. Ephrin (recall Fig 13.4) – Growth cones contain Eph receptors- binding prevents migration into undesirable areas b. Semaphorin proteins- important in directing axon turns Hypotheses for pathway selection- (Cont.) 5. Diffusible moleculesa. Netrin-1 and –2 are chemotactic Rat dorsal spine explant Fig. 13.20 Neuron Outgrowth Neutrin producing cell •Netrins are homologues of the UNC-6 protein in C. Elegans Loss of Unc-6 prevents migration of both sensory (to ventral) and motor (to dorsal) neurons Fig. 13.21 Sensory Neuron b. Slit proteins are repulsive Motor WT Neuron Unc-6 -/- B. Hypotheses for target selection- 0 min 2 min Target cells secrete short-range chemotactic or chemorepulsive factors Example- NT-3 attracts axons C. Hypotheses for address selection- Fig. 13.25 Growth cone makes contact with a cell, acetylcholine receptors cluster on target cell surface, and a synapse is formed 6 min 10 min Fig. 13.24 Additional axons synapse target cell, but eventually only one/cell remains