Bio 127 - Section III Organogenesis The Neural Crest and Axonal Specification Gilbert 9e Chapter 10 Student Learning Objectives 1. You should understand that the neural crest is an evolutionary advancement unique to vertebrates. a. Led to jaws, face, skull, sensory neural ganglia b. Transient structure: exists briefly at neural tube closure 2. You should understand that the neural crest is specified into four overlapping regions along the anterior-posterior axis: a. Cranial neural crest b. Cardiac neural crest c. Trunk neural crest d. Vagosacral neural crest Student Learning Objectives 3. You should understand that most cells of the neural crest are either multipotent progenitor cells or are already determined to a fate. a. Large majority of early chick cranial NC can form all cranial fates but only ~10 of the total population that migrates out. b. Nearly half of chick trunk NC are restricted to one fate c. Other cells from chick trunk NC can produce: 1. sensory neurons 2. melanocytes 3. adrenomedullary cells 4. glia 4. You should understand that it is unknown if any NC population is a true stem cell, capable of generating stem cells or multiple progenitors
Around the time of neural tube closure... Neural crest cells migrate laterally and ventrally from the dorsal side of the tube. Usually the migration is a fire drill and all cells leave the a tube... Distances can vary from short to very long migrations. Anterior-Posterior patterning of tube extends to the crest Cranial NC Vagosacral NC Vagal NC Cardiac NC Trunk NC Sacral NC
Cranial Neural Crest Craniofacial Mesenchyme chondrocytes Neural Crest Cell Fates osteoblasts of head and face cranial neurons glia fibroblasts, face connective tissue Pharyngeal Mesenchyme thymic cells odontoblasts of tooth primordia bone of inner ear and jaw Cardiac Neural Crest Otic Placode to Third Somite melanocytes neurons cartilage connective tissue smooth muscle of outflow connective tissue of outflow cardiac septal mesenchyme Trunk Neural Crest Ventrolateral Anterior Sclerotome dorsal root sensory ganglia sympathetic ganglia adrenomedullary cells aortic nerve clusters Dorsolateral melanocytes Vagosacral Neural Crest Somites 1 7, Posterior to Somite 28 parasympathetic neurons of gut Anterior-Posterior patterning of tube extends to the crest Your starting position limits (specifies) your fate choices and your experiences on the road choose (determine) the one. Figure 10.17 The influence of mesoderm and ectoderm on the axial identity of cranial neural crest cells and the role of Hoxa2 in regulating second-arch morphogenesis
Figure 10.10 Cranial neural crest cell migration in the mammalian head Cranial Neural Crest Midbrain osteoblasts of f frontonasal process FGF, BMP, Edn 1, Nppc, Ihh Twist, Snail, Runx2 Head and 1 st Arch myoblasts of facial muscles FGF Twist, Snail, Rhomb 1,2, 3 osteoblasts, incus & malleus FGF, BMP, Edn 1, Nppc, Ihh Twist, Snail,Runx2 1 st Pharyngeal Arch osteoblasts of jaw FGF, BMP, Edn 1, Nppc, Ihh Twist, Snail,Runx2 neurons of trigeminal ganglion FGF, neurotrophin, GDNF Twist, Snail neurons of ciliary ganglion FGF, neurotrophin, GDNF Twist, Snail glial cells FGF, neuregulin, Edn 3 Twist, Snail fibroblasts, face connective tissue FGF Twist, Snail odontoblasts of tooth primordia FGF, BMP Twist, Snail, Barx1, Msx1,2 Rhombomere 3, 4, 5 chondrocytesof hyoid FGF, BMP Twist, Snail, Osteopontin 2 nd Pharyngeal Arch osteoblasts, stapes of inner ear FGF, BMP, Edn 1, Nppc, Ihh Twist, Snail, Runx2 neurons of facial ganglion FGF, neurotrophin, GDNF Twist, Snail glial cells FGF, neuregulin, Edn 3 Twist, Snail Rhombomere 6 8 chondrocytesof hyoid BMP Twist, Snail, Osteopontin 3 rd and 4th Arches thymic cells FGF Twist, Snail thyroid cells FGF Twist, Snail parathyroid cells FGF Twist, Snail clavicular tendon FGF Twist, Snail thymic cells FGF Twist, Snail Cardiac neural crest Pax3 in outflow tract arteries Contribution to cardiac septum
Cardiac Neural Crest melanocytes FGF, Steel, Edn 3, a MSH Twist, Snail, Pax3 Cardiac Neural Crest Otic Placode to neurons FGF, neurotrophin, GDNF Twist, Snail, Pax3 Third Somite chondrocytes BMP Twist, Snail, Pax3 fibroblasts, heart connective tissue FGF Twist, Snail, Pax3 3 rd, 4 th, 6th Arches smooth muscle of outflow FGF Twist, Snail, Pax3 fibroblasts, outflow connect. tissue FGF Twist, Snail, Pax3 cardiac septal mesenchyme FGF Twist, Snail, Pax3 The Trunk Neural Crest The cells of the Trunk NC can head off one of two directions (the other is the ventral pathway) Trunk neural crest cell migration Some individual cells can contribute to multiple fates
Ventrolateral dorsal root sensory ganglia FGF, neurotrophin, GDNF Twist, Snail Trunk Neural Crest Anterior Sclerotome sympathetic ganglia FGF, neurotrophin, GDNF Twist, Snail adrenomedullary cells FGF Twist, Snail aortic nerve clusters FGF, neurotrophin, GDNF Twist, Snail glia, Scwann cell FGF, neuregulin, Edn 3 Twist, Snail Dorsolateral melanocytes FGF, Steel, Edn 3, a MSH Twist, Snail Ventrolateral cell migration through anterior sclerotome only Restriction due to the ephrin proteins of the sclerotome
Anterior-Posterior patterning of tube extends to the crest Cranial NC Vagosacral NC Vagal NC Cardiac NC Trunk NC Sacral NC Vagosacral Neural Crest Somites1 7 parasympathetic neurons of gut FGF, neurotrophin, GDNF Twist, Snail, Phox2b Posterior to Somite 28 Figure 10.8 Entry of neural crest cells into the gut and adrenal gland
Figure 10.18 Plasticity and pre-patterning of the neural crest both play roles in beak morphology Neuronal Specification and Axonal Specificity 100 billion neurons in the adult 300 billion born! All with a single axon, one or a few synapses All with a single phenotype, neurotransmitter Making the right synapse is critical Motor neurons better find a skeletal muscle Retinal neurons better find the optic tectum Neuronal Specification and Axonal Specificity 1. Induction and patterning of brain region 2. Birth and migration of neurons and glia 3. Specification of cell fates 4. Guidance of axons to specific targets 5. Formation of synaptic connections 6. Competitive rearrangement of synapses 7. Survival and final differentiation by signal 8. Continued plasticity throughout life
Heirarchical Specification ectoderm blocking BMP epidermis neural crest neuroepithelium Delta-Notch Shh/TGF-B neuron glia ependyma motor sensory interneuron Hox genes jaw forelimb hindlimb tail Heirarchical Specification hindlimb birthday retinoic acid columns of terni (CT) medial motor columns (MMC) lateral motor columns (LMC) Lhx-3 TF lateral subdivision Isl-2, Lim-1 express Eph-A4 repelled by ephrin-a5 forces them into hamstring cadherins Lim family TF medial subdivision Isl-1, Isl-2 express neuropilin-2 repelled by semaphorin-3f forces them quadriceps axial muscles express FGF-R positive chemotaxis Guidance of Axons to Specific Targets signals in the membranes of cells along the migratory path
Guidance of Axons to Specific Targets Ephrins and semaphorins can cause the growth cone to collapse semaphorin 3 expressing cells semaphorin 3 expressing cells Guidance of Axons to Specific Targets guidance of the growth cone Guidance of Axons to Specific Targets Netrin is a secreted chemotactic signal for axons Remember DSCAM? 38,016 splice variants in Drosophila
Guidance of Axons to Specific Targets Few neuronal axons cross the midline of the CNS creating the hemispheres Slit is secreted Robo-1 is repelled Robo-3 overcomes Robo-1 Guidance of Axons to Specific Targets BMPs are secreted from targets, different BMP receptors guide branches to different targets Formation of Synaptic Connections Reciprocal induction Requires synaptic transmission
Formation of Synaptic Connections Multiple axons compete for final innervation Survival and final differentiation by signal Apoptosis is often a dominant influence More than half of the neurons may die regionally, two-thirds of the total born! This is less consistent across species than most neural development events 80% of cat retinal ganglion cells die 40% in chick 0% in fish, amphibians Survival and final differentiation by signal Neurotrophic factors block default apoptosis Huntington s corea is a loss of Huntingtin protein which upregulates BDNF and the survival of striatum neurons coordinate movement, balance, walking Parkinson s disease is death of dopaminergic neurons which respond to GDNF and CDNF therapy?
Continued plasticity throughout life Many organisms have behaviors before birth We can alter synaptic connections thru life Less so when we get older