Neurogenesis and Migration III Flashcards
beginning migration
neural crest cells downregulate the expression of a CAM (neural cadherin) and genes for proteins forming tight junctions
to commence migration…
neural crest cells must dissolve the basal lamina with metalloproteases
ECM examples
collagen, laminin, fibronectin
CAMs help….
form the basal lamina which anchors and attaches cells together
how neural crest breaks free from basal membrane and neural tube
secretes a class of proteases called metalloproteases
metalloproteases
enzymes that break down proteins and require a metal such as zinc to help break down the protein
MMPs
matrix metalloproteases
orientation of cells after breaking free from neural tube
form discrete streams, each from a different spinal segment; they avoid passing through the caudal/posterior half of each of the somites, which are laying alongside the neural tube
ephrin
family of membrane-bound signaling molecules that bind to ephrin receptors, which are part of the receptor tyrosine kinase
purkinje cells
class of GABAergic cells located in the cerebellum; one of the largest neurons in the human brain
migration of purkinje cells
dorsally from 4th ventricle along radial glia, settle in a single layer and begin growing massive dendrites toward cerebellar pial surface
population of small cells migrate…
leave edge of pons, rhombic lip, and move along the outer surface of the cerebellar cortex until they aggregate on dorsal side
purkinje cells secrete…
Shh which promotes mitosis in granule cells
bergmann glia
long, slender glial cells in cerebellar cortex that guide neurons migrating from external granule cell layer to the internal granule layer
post mitotic granule cells begin migrating…
ventrally into the cortex, climbing down bergmann glia
granule cell grow process
differentiate into axons, extending into a straight line perpendicular to purkinje cell dendrites
parallel fibers
axonal processes of granule cells grow parallel to one another (of cerebellum, innervate purkinje neuron dendrites)
mossy fibers
give excitatory input to granule cells from pontine neurons and make excitatory synapses with purkinje cell dendrites via parallel fiber they send out behind them during migration
riding glial monorail
glia formed long processes and granule cells and granule cells would clasp on and migrate along them; once they end they reverse and migrate back in the other direction
isolating only glia…
will not form long processes unless cocultures with neurons
weaver mice experiment test
place granule cells and glia together in vitro to observe migration; wildtype granule cells with glia from weaver mice in some ad weaver granule cells with wildtype glia in other culture
weaver mice result
granule cells from wildtype mice migrated equally well along either wildtype or weaver; granule cells from weaver mutant never attached to glia
weaver mice conclusion
defect cause by gene mutation does not affect glia to support migrating neurons, failure of cerebellar migration due to inability of granule cells to grip glial fibers in order to climb along them (deficient n ability to direct glial partner)
astrotactin
encodes a protein expressed in granule cells to help them grip glial fibers for migration
reelin
gene that encodes the protein that is secreted into ECM
secretion of reelin
secreted by granule cells in developing cerebellum when present at external granule cell layer on the plial surface of cerebellum
reelin gradient
uniform along outer surface
purkinje cell migration and reelin
purkinje cells stop migrating once they reach a particular concentration of reelin; migrate much more when reelin not present; lack of orderly purkinje cell layer seems affect granule cell migration down from external to internal granule layer
olfactory placode
plate-shaped collection of ectodermal cells that migrate through the olfactory bulb and to the rest of the brain
incoming cells from olfactory placode
migrate toward young olfactory bulb and take on several different fates
GnRH expressing cells
settle into hypothalamus, where they differentiate into neurons that send axons to the hypothalamic-pituitary blood portal system
release of GnRH
into portal system, reach pituitary gland and stimulate cells there to release FSH and LH
FSH and LH
gonadotropins > stimulate development of gonads
kallmann syndrome
the failure of the pituitary gland to release gonadotropins to stimulate the gonads at puberty, plus the lack of a sense of smell (hypogonadotropic hypogonadism); may be deaf
cause of kallmann syndrome
mutations in several genes
commonality in kallmann syndrome
failure to produce the olfactory ensheathing glia and primary olfactory sensory neurons with axons leading from olfactory epithelium into olfactory bulb
