Neurulation & Neural Tube

during gastrulation the epiblast cells that do not migrate through the primitive streak become

ectoderm

the ectoderm differentiates into

surface ectoderm, nueral plate, and neural crest cells

the surface ectoderm becomes

epidermis or skin

surface ectoderm generates

placodes

placodes

localized thickenings in the ectodermal epithelium

cranial placodes are important for

eye, ear, nose, pituitary and cranial nerve development

epidermal placodes (body) are important for

hair formation

neural plate will form the

neural tube

the neural tube will form the

central nervous system

regionalization of the neural tube will generate different parts of the

brain and spinal cord

neural crest cells

migratory population of cells that form at the border of the surface ectoderm and neural tube

neural crest cells will form the

peripheral nervous system, adrenal medulla, melanocytes, and many structures in the head including bones and muscles

neurulation

the process by which 3 ectodermal derivates are made physically and functionally distinct from one another

the neural plate forms on the … side of the embryo above the …

dorsal; axial mesoderm (notochord)

epidermis forms at

more lateral and ventral locations

default model of neural induction

idea that ectodermal cells will become neural in the absence of BMP signal

AVE Signaling: BMP4 is expressed

WNT3a and Nodal are induced in the epiblast and the WNT and Nodal antagonists from the AVE prevent WNT3a and Nodal from signaling on the anterior side, WNT3a and Nodal signaling on the posterior side leads to formation of the primitive streak and the posterior end of the embryo

mammalian organizer

the Node

cells passing through the node express … and will form…

chordin and noggin; prechordal plate and notochord

noggin and chordin inhibit BMP signaling which allows

the neural plate to form

BMP antagonists will induce

neural plate formation in the midline ectoderm

the degree of BMP signal will determine

ectodermal fate

high BMP =

epidermis

moderate BMP =

neural crest

no BMP =

neural

neural plate

thickening in the ectodermal epithelium

neural plate cells in the midline, just above the notochord will apically constrict and form

a medial hinge point

medial hinge point

allows the neural plate to fold and form a neural groove at the midline

the lateral edges of the neural plate rise to generate

neural folds

dorsal lateral hinge points apically constrict allowing neural folds to

connect and the midline

the neural folds fuse to generate

the closed neural tube, with a fluid filled lumen in the center

once neural tube is formed, the neural crest cells, located at the dorsal side of the neural tube

delaminate from the neural epithelium and begin migrating away

the anterior of the embryo is developmentally

older than posterior

the neural tube first closes in the _ region and zips up in both directions

hindbrain

the open ends of the neural tube are called the

anterior and posterior neuropores

in mammals, the neural tube closure occurs

separately in multiple regions (especially in the head)

defects in neural tube closure result in

neural tube defects

craniorachischisis

when the entire length of the neural tube remains open

anencephaly

closed spinal cord but open brain

myeloschisis

an open spinal cord, typically in lumbosacral levels (type of spina bifida)

spina bifida aperta

bifid (split in two) vertebral spines, aperta = open so it is not covered by skin

meningocele

type of spina bifida where neural tube is closed but membranes that surround the neural tube will protrude

myelomeingocele

when there is both an open neural tube and protruding membranes

spina bifida occulta

“closed” neural tube (covered by skin), vertebral defects but closed nt and no protruding membranes, skin is usually marked by a tuft fo hair, mole birthmark, lipoma or dimple

women with folate deficiencies have a

higher incidence of children with neural tube defects

folate (vitamin B9) is used

to make nucelotides and SAM, which is used for methylation

not certain about how folate deficiency causes neural tube defects but it is thought that it has to do with

epigenetic regulation of neural progenitors during development

since the US began enriching bread with folic acid, neural tube defects have

decreased by 35%

tail bud formation: tissues in the most caudal portion of the embryo (sacral & coccygeal regions) are formed during

secondary body development

tail bud formation: as gastrulation ends, a population of cells is formed known as

the tail bud

the tail bud consists of

neruomesodermal stem cells

neruomesodermal stem cells can form

either mesoderm or neural cells

primary neurulation

formation of the neural plate, which forms to form the neural tube

secondary neurulation

occurs when mesenchymal cells of the tail bud aggregate into a solid cord, which will form cavities that coalesce into a lumen

where does secondary neurulation occur in mammals

the level of the sacral vertebrae

the neuromesodermal progenitors come together into

the medullary cord

the medullary cord cavitates to form spaces that

come together into a lumen

the lumen fuse with

the neural canal of the more cranial neural tube

primary neurulation is

the rolling up of the neural plate to form the neural tube

secondary neurulation uses

cavitaion of the solid medullary cord to form the neural tube

regions of the neural tube

prosencephalon, mesencephalon, rhombecephalon, spinal cord

prosencephalon

forebrain

mesencephalon

midbrain

rhombencephalon

hindbrain

prosencephalon subdivided into the

telencephalon and diencephalon

the rhombencephalon is divided into

the metencephalon and myelencephalon

telencephalon will generate the

cerebrum

the diencephalon generates the

hypothalamus

mesencephalon generates

midbrain

metencephalon generates

the cerebellum

the myelencephalon generates

the medulla

the caudal end of the embryo expresses

WNT3a

WNT3a induces the expression of

Gbx2 and provides posterior identity to the early neural tube

the AVE secretes

WNT inhibitors

WNT inhibitors

Cerberus and DKK-1

Cerberus and Dkk-1 antagonize the WNT signal and

promote Otx2 expression, providing anterior identity

the boundary between Otx2 and Gbx2 is where the

midbrain-hindbrain boundary will form

each signaling center secretes _ signals that initiate what

paracrine; transcriptional responses in neighboring tissues

isthmic organizer

• at MHB

• secretes FGF and WNT

  • pattern the mesencephalon and rhombencephalon

anterior neural ridge secretes

FGF and SHH to pattern the telencephalon

the zona limitans intrathalamica (ZLI) secretes

SHH and patterns the diencephalon

the rhombencephalon has a _ morphology

segmented

rhombomere

segments of the rhombencephalon (r1-r7)

r2 nerve

trigeminal nerve

r4 nerve

facial nerves

hox genes are _ factors

transcription factors

humans have four copies of the hox genes on four different chromosomes:

HOXA, HOXB, HOXC, HOXD

each mammalian Hox cluster can have up to _ genes

13 (but some genes are missing in some clusters)

the order of the paralogous genes on the chromosome is conserved between

flies and humans

Hoxa6 is most similar to

Antp

labial and Hoxa1 are paralogues and expressed

cranially

AbdB and Hoxa13 are paralogues and are expressed

caudally

most Hox paralogues have _ genes

3

hommeotic mutants

mutations in drosophila hox genes

mutation in ultrabithorax will produce a fly with 4 wings by

changing T3 into T2

mice missing Hox10 genes transform

lumbar vertebrae into thoracic vertebrae

mice missing Hox11 genes transform

sacral vertebrae into lumbar vertebrae

motor neurons have cell bodies in the

ventral spinal cord

motor neurons have axons that

leave the spinal cord to innervate muscles and organs

interneurons are

neurons that make connections between other neurons in the CNS