Lecture #2 Flashcards
what will the cells of the ectoderm form?
skin and the CNS
what is the specific subpopulation of cells arising from the anterior region of the developing notochord?
Hensen’s node
how could you form an ectopic CNS?
transplant the notochord → extremely potent signaling region able to induce the formation of a new and complete CSN
At what time does neurogenesis stop, and the complex process of neuroinduction begin?
17 days
what is the most famous signal released by the notochord?
Sonic hedgehog (Shh)
what does the neural crest become?
central nervous system tube and the epidermis → soon after the closure of the neural tube they start to detach from the nt and ectoderm and start to migrate and spread inside of the developing embryo
what do detached neural crest cells form?
contribute to the generation of many tissues and organs
what does it mean if cells are pseudo-stratified?
they re attached to the apical and basal membranes, and their nuclei are organized in different levels
their nuclei have particular molarity and they can move up and downside the cytoplasm doing the cell-cycle progression
how does the bending of the tube occur to form the notochord?
a certain type of nuclei start to accumulate in a specific position close to the basal membrane and at the same time there is also a force coming from the ectoderm the is pushing the two crests leading to their fusion to create a v-shaped structure and finally a tube
once the tube has formed, what still needs to happen?
the anterior neuropore and the posterity neuropore are still open meaning they still have contact with the fluid in the amniotic cavity
what type of mechanism occurs to close the neural tube?
the “zip” mechanism
give two reasons why the formation of the notochord is so important:
- it is positioned centrally in the embryo with respect to both the dorsal ventral (DV) and left-right (LR) axis → produces secreted factors signaling to the surrounding tissues providing position and fate information
- becomes the ossified region forming the vertebrae and contributes to the center of the intervertebral disks
what are neuroectodermal cells?
elongated cells that derive from the ectoderm but are converted towards a neural fate by the notochord
differentiate into neurons and microglia (astrocytes and oligodendrocyte progenitors)
what are neuroectodermal cells?
elongated cells that derive from the ectoderm but are converted towards a neural fate by the notochord
differentiate into neurons and microglia (astrocytes and oligodendrocyte progenitors)
what are neuroectodermal cells?
elongated cells that derive from the ectoderm but are converted towards a neural fate by the notochord
differentiate into neurons and microglia (astrocytes and oligodendrocyte progenitors)
what are the cells called that are located in between the neuroepithelial cells and the ectoderm cells, that detach and start to infiltrate the embryo?
neural crest cells (NC)
describe neural crest cells:
star-shaped cells that migrate inside of the embryo; some of them undergo the ectoderm to mesoderm conversion
what types of cells can neural crest cells generate?
- melanocytes
- dorsal root ganglia neurons
- autonomic ganglia neurons
- adrenal medulla
- submucosal nerve plexus of the gut
all bones composing the chest, vertebrae, etc have a mesodermal origin - what is the exception?
the skull → derive from neural crest cells and therefore from the ectoderm
what cells do the meninges derive from?
neural crest cells and some cells belonging to to the mesenchymal subpopulation
what cells do the meninges derive from?
neural crest cells and some cells belonging to to the mesenchymal subpopulation
what are the three layers of the meninges?
dura mater, arachnoid, and pia mater
why is the arachnoid complex?
there is a trabecula between the arachnoid and the Pia mater the is filled with cerebrospinal fluid
what is the combination of the pia mater and the arachnoid?
leptomeninges
what is the function of the meninges?
they have a huge number of immune cells that are patrolling the CNS to interact with viruses, bacteria, etc
what is the most famous neural tube defect?
spina bifida
what is spina bifida occulta?
when there is something wrong with the two neural arches of the vertebrae to where they can’t close, leading to the presence of an empty space between the skin and the two arches
what physical feature is present in some spina bifida babies that allows for diagnosis?
the presence of a tuft of hair on the skin in the lumbar-sacral position right above the region of the spina bifida occulta
what is meningocele?
a condition where the spinal cord is in the correct position but there is a cyst filled with spinal fluid
what is myelomeningocele?
a more severe condition in which the spinal cord is not localized in the right position and therefore the system doesn’t work
what other condition can coincide with myelomeningocele?
Arnold-Chiari malformation: anterior hydrocephalus → the tube circulating cerebralspinal fluid (constantly produced) must be drained, and if not it leads to an accumulation causing the babies not to survive
What supplement is able to reduce the incidence of defects by up to 75%?
folic acid (400 mg)
why is folic acid important?
it is a progenitor of DNA protein synthesis and DNA methylation - something can go wrong with cell proliferation
what occurs after the closer of the neural tube?
the first subdivision → a few hours after the closure we can see the formation of these subdivision: forebrain, midbrain, hindbrain, and long spinal cord
what is the term for the forebrain?
prosencephalon
what is the tern for the midbrain?
mesencephalon
what is the term for the hindbrain?
rhombencephalon
what forms from the forebrain?
two balloons the are growing anterior laterally in the CNS which are the two telencephalic vesicles: the biggest structures we have in the CNS
Then the formation of the diencephalon
what is the diencephalon?
a piece of the tube connecting the telencephalon with the posterior regions
what two things are generated from the hindbrain?
metencephalon and the myelencephalon
what is the mesencephalon?
a piece of tissue of the CNS connecting the anterior brain to the spinal cord
what is formed from the metencephalon?
cerebellum: part of the CNS driving movement and coordination
how many points of bending are there in the neural tube?
three
why is the binding of the neural tube important?
it allows the embryo to begin to acquire the so called fetal position → midbrain flexure plus the cervical flexure
what is the most important part of our CNS?
telencephalon vesicle
where does the formation of the optical vesicles occur?
in the region between the diencephalon and the telencephalon
what will the optical vesicles produce?
optic stalk, retina, and sensory part of the eye
what is the function of the choroid plexa in the telencephalon?
they are able to release the cerebrospinal fluids inside the cavity
describe the connection of the telencephalon with the two balloons formed:
the two telencephalon vesicles are emerging laterally from the tube and they are connected with the diencephalon, and two foramen allow the connection of the cerebrospinal fluid in the tube, but with the cerebrospinal fluid contained in the two tele cephalic vesicles
what does the extreme growth of the CNS cause?
the invagination of the cerebral cortex forming succi and gyri called gyrihecephalia
what does the extreme growth of the CNS cause?
the invagination of the cerebral cortex forming succi and gyri called gyrihecephalia
why are the folds in the cortex important?
initially the surface of the cerebral hemisphere is smooth, but grooves (sulci) and and tortuous convolutions (gyri) allow for a significant increase in surface area
describe myeloencephaly and meningoencelphalocele:
formation of cysts due to alterations in the closure of the skull causing mental deficiency and retardation
what are the two branches of the autonomic nervous system and what are their functions?
sympathetic and parasympathetic divisions - not voluntary bur fundamental for the innervation of blood vessels, capillaries, organs, the gut, and the fight or flight response
what happens to the nucleus in neuroepithelial cells?
it is moving up and down in the cytoplasm
where does mitosis always occur?
at the boundary between the ventricular cavity and the apical membrane
what occurs after the division?
the two daughter cells cam inherit filaments connecting the apical and the basal membrane, or sometimes only one of the two cells is connected with he apical and basal membrane while the other enters a new cell fate (differentiation) and this descendant stars to become a young neuroblast and then a neuron
describe the tight association with the nuclear position in the cells and cell cycle:
the nucleus moves from the CNS wall to the basal membrane and when the nucleus was in the basal membrane, it starts the S phase division, while in G2 division occurred when the nucleus had returned to the apical membrane
then mitosis occurred in a position not far from the apical membrane
what is the significance o the inter kinetic nuclear movement?
we don’t know - but we know that altering the interkinetic nuclear movement genetically for example can completely destroy the development of the CNS in rodents
what occurs during an asymmetrical division?
when the spindle is perpendicular to the ventricular cavity → one of the two cells will still be a neuroepithelial cell and able to continue its round of proliferation, but the other will differentiate into neurons
what occurs during a symmetrical division?
the spindle is parallel to the membrane and the two daughter cells are identical, so they are both neuroepithelial cells that are able to proliferate
during development, which type of division is more common?
the vast majority of mitosis were parallel oriented suggesting that from this division we had two epithelial cells being able to proliferate again and again so this is why we have a huge tangential expansion
what is the hypothesis for the difference in division outcomes?
in the apical part of the epithelial cells there is a short piece of submemnrane that contains specific factors and if they two cells are dividing along this plane (perpendicular) then the two daughter cells can inherit the same part of the apical membrane and this means they obtain the same proliferative phenotype
on the other hand, the mitotic spindle which is perpendicular, generates two daughter cells and only one of them can inherit the vertical part of the membrane
what are some determinants for the difference in division?
notch receptos and many other transmembrane proteins that are often associated with stemness not only in the brain but also in other tissues seem to cluster here in the apical part of the cell and therefore the two cells can inherit the determinants and stay in the epithelial or embryonic cell fate
what happens to cells that are dividing with a mitotic plane that is not perpendicular?
the other starts to acquire the phenotype of a young neuroblast and soon after the division it enters into contact with the neuroepithelial cell and starts to climb using this connection between the neuroepithelial cells like a rope to move from the germinal region to the post-mitotic region
they are proliferating progenitors but at the same time they are also scaffolds because they allow the descendants that re not stem to use part of their cytoplasm to climb
what is the inside out rule?
the first neurons generated by asymmetric cell division can cluster just a move the geminal region to form the so called layer 6 of the future cerebral cortex
neurons generated later on can overcome this later and form layer five, and then overcome these two to form layer 4, etc
what are these cells called in rodents starting from E10?
radial glial cells: radial becyae they re connected to the basal and apical membrane with thin cytoplasmic bundles, and glia because they start to express some markers that are similar to markers expressed by astrocytes
what happens when the cells are in position at the cortical plate?
they can detach from the rope and differentiate into an adult post-mitotic and functionally active neuron
what is this migration mechanism called?
early mechanism is called soma translocation
locomotion because the cells are climbing
what happens to neuroepithelial cells at the end of neurogenesis?
it seems that after the last asymmetric division, the remaining neuroepithelial cells start to detach from the apical membrane, and the retraction of this cytoplasmic bundle allows for the migration of the bodies of these cells from the germinal niche to the cortical plate, and in the cortical plate these cells start to proliferate again, but only for the generation of astrocytes
