Chapter 10 Developmental Bio: Neural and Epidermal Ectoderm
Ectodermal cells express
Sox 6
cells of the inner layer proliferate and generate a variety of glial cells, interneurons, and photoreceptor neurons that collectively make
the neural retina
After the node reaches the posterior of the epiblast, certain cells contribute to what?
the paraxial mesoderm and neural tube
SHH is secreted from the notochord to induce what?
to induce the MHP cells to become the floor plate of the tube, which also secretes SHH (piece of notochord is removed: neural tube adjacent to this region will have no floor plate cells)
remain integral component of the neural tube lining and secrete CSF
ventricular cells
where does asymmetrical division take place?
ventricular zone
where are radial glial cells found?
ventricular zone cells receiving old centriole stay here cells receiving young centriole leave to differrentiate
Image 10.4 Primary Neurulation
a) Folding begins as the MHP cells anchor to the notochord and change their shape while epidermal cells move toward the dorsal midline. b) The neural folds are elevated as the epidermis cells move toward the midline d) convergence of neural folds occurs when DLHP cells become wedge-shaped and the epidermal cells push toward the center e) neural folds contact one another, neural crest cells link the neural tube with the epidermis. Neural crest cells disperse and leave the tube separate from the epidermis.
Where is the neural tube polarized?
along the dorsal-ventral axis
what develops earlier, anterior or posterior?
anterior
what develops first, anterior or posterior
anterior
what are the 3 regions the eye contains?
anterior zone of dividing epithelial cells equatorial zone of cellular elongation posterior and central zone of fiber cells
gray matter
cortical zone
receive signals from other neurons
dendrites
How does the neural plate form?
derived from the prechordal plate and notochord from gastrulation
Give some examples of abnormalities
failure to close site 5-spina bifida failure to close side 2 and 3-anencephaly- forebrain stays in contact with amniotic fluid for too long failure to close at site 1-craniorachischisis
a motor neuron image 10.16
motor end plate = growth cone of axon area right before axon extends = axon hillock receptor is entire chunk to the left need to know: dendrites, receptor, soma, axon hillock, axon, growth cone of axon
ventral portion is involved in:
motor functions
ventral region is where:
motor neurons reside
specialized cell membrane
myelin sheath
N-cadherin is present in the what cells?
neural plate cells
critical molecules that generate many action potentials
neurotransmitters
an embryo undergoing the processes
neurula
refers to the processes that differentiate the three ectodermal regions
neurulation
MHP cells induced by
notochord
axons are insulated at intervals by processes that originate from a glial cells
oligodendocyte
initial differentiation requires contact between:
optic vesicle and lens ectoderm
In the developing brain this protein recruits a complex in the apical portion of the cell that contains receptor for cell division molecules that are present in the cerebrospinal fluid.
par-3
neural crest migrate away from surface ectoderm to become what?
peripheral neural cells glial cells pigment cells
Neural tube matures and this longitudinal groove divides into dorsal and ventral halves
sulcus limitans
the lens and cornea form from what?
surface ectoderm
gap between cells where signals are transferred from one neuron to another
synapse
What do gradient of SHH trigger?
synthesis of TSC factors to specify the neruoepithelium
Mesodermal cells express
tbx6
differentiation is positively regulated by
the Notch pathway
What else do intrinsic and extrinsic forces regulate? Why is this important?
the closing of the neural tube if it doesn't close, there will be abnormalities
The dorsal-vebtral patterning of the tube is done by what?
-proteins of the TGF-B superfamily secreted from the surface of the ectoderm and the roof plate of the tube -and by SHH protein secreted form the notochord and floor plates
How does the human brain differ from primates (5 ways)
-retention of the fetal neuronal growth rate after birth -activity of human-specific RNA genes -high levels of tsc -human specific alleles of developmental regulatory genes -continuation of brain maturation into adulthood
neural tube cells give rise to what 3 main cell types?
-ventricular cells -precursors of neurons that conduct electric potentials, coordinate bodily functions and sensation -precursors of glial cells that in nervous system, neuron insulation, memory
What are the 4 steps in primary neurulation
1. Extension and folding- neural plate cells proliferate and thicken and move anteriorly to posteriorly 2. Bending of neural plate- MHP (medial hinge points) cells become wedge shaped and form furrows at midline 3. Convergence- DLHP (dorsolateral hinge points) secretes Noggin to block BMP and plate bends at hinge regions 4. Closure-close at dorsal midline, folds adhere to each other
How many closer points are there along the ant/post axis?
5
the neocortex has ______ layers
6
early development of the hair follicle and hair shaft
A) signals initiate local proliferation of the basal keratinocytes in the epidermis B) Proliferation of epidermal cells results in formation of the hair follicle placode, which signals the dermal mesenchymal cells to aggregate beneath it into dermal papilla. C) The papilla signals the proliferation of the hair germ, making it into primitive hair shaft. D) Hair shaft engulfs the dermal papilla ad from the inner hair root directly above the papilla. Sebaceous cells and the bulge appear as melanin enters into the cortex. E) sebaceous glands form and the hair canal is made. Hair shaft differentiates into root sheath nd epidermal cells. F) the sebaceous gland is localized on the lateral wall of the follicle while hair shaft extends into hair canal and out past the skin.
See figure 10.21 development of the human spinal cord
A-D: the tube is divided into dorsal and ventral regions, separated by the sulcus lmitans. As the cells form adjacent somites form the spinal vertebrae, the neural tube differentiates into the ventricular, mantle and marginal zones as well as the roof and floor plates. The sulcus limitans separates the dorsal part of the spinal cord that receives info from the ventral part of the spinal cord, which projects motor neurons. E) a segment of the spinal cord with its sensory (dorsal) and motor (ventral) roots
name the 3 responsibilities of the vertebrate ectoderm
Formation of the neural plate and neural tube Formation of the epidermis (outer layer, barrier to world) Formation of the neural crest- (reb/w epidermis and CNS, generates PNS and melanocytes)
in primary neurulation.....
IN ANTERIOR PORTION the surface ectoderm folds into a tube that separates from the surface. similar process in all vertebrates
in secondary neurulation.....
IN POSTERIOR PORTION production of mesenchymal cells via prospective endoderm and ectoderm the ectoderm forms and chord, then forms a cavity within the cord
What plays a major role in retina formation?
Pax6
regulation of the crystallin genes is under control of
Pax6, Sox2 and L-Maf
Neural plate becomes neural tube in what 2 steps?
Primary Neurulation Secondary Neurulation
What are the family of tsp factors that activate the genes to form the neural plate?
SOX FAMILY BY BLOCKING TSC OF BMP TO PREVENT FORMAITON OF EPIDERMIS
What down regulates Pax6 to allow for the formation of two separate eyes instead of one medial eye?
Shh (sonic hedgehog)
major derivatives of the ectoderm germ layer IMAGE TO KNOW (10.1)
The ectoderm is divided into three major domains: the surface ectoderm, the neural crest and the neural tube.
See image 10.2
The head region has undergone neurulation, while the tail region is still undergoing gastrulation
trasnmit signals to other neurons grown from nerve cell body (soma), led by growth cone
axons
what forms the optic nerve?
axons of the retinal ganglion cells
what happens to the forebrain and hindbrain?
become subdivided
What do the intrinsic forces regulate?
bending of the neural plate intrinsic wedging occurs within cells of the hinge regions
type of glial cell that extends a thin process throughout the germinative neuroepithelium
bergmann glia
Building the brain: the division of the prospective brain from the spinal cord is done by what?
blocking the lumen of the neural tube at the boundary between these regions
the specification of one type of cell is often done by what?
blocking the specification of an alternative cell type ex) a cell will become epidermis and prevented from becoming a neural cell
the separation of the newly formed neural tube from epidermis is mediated by what?
cadherins
lens 1 activation is essential for
closing the lens vesicle
Building the brain: neural folds close between brain and spinal cord, dorsal tissues push in to do what
construct the neural tube at the base of the brain
In the cerebellum, migrating neurons form a second germinal zone, called the:
external granular layer
epidermal stem cells divide to produce
differentiated keratinocytes and stem cells
when does neurulation occur?
directly upon gastrulation
how are new neurons formed?
divison of the neural stem cells in the wall of the neural tube, resulting neuroblasts migrate away and form a new layer call the mantle on (gray matter)
DHLP cells are induced by
epidermis
E-cadherin is present in the what cells?
epidermis cells
Building the brain: brain cells secrete CSF into lumen to causing what to happen?
expanding embryonic brain volume
Why does the brain expand?
fluid secretion puts positive pressure on the vesicles
What is important in the mediation of the neural tube closing?
folate
The anterior/posterior axis generates what three primary vesicles?
forebrain (prosencephalon) midbrain (mesenchephalon) hindbrain (rhombocephelon)
Medullary cord
formed in secondary neurulation from the condensation of new mesenchymal cells resides beneath surface ectoderm
what do the photoreceptor cells do?
gather light and transmit electrical impulses through interneurons to retinal ganglion cells
basal layer (inner layer) of the surface ectoderm becomes what?
germinal layer of the skin
no notch can cause what?
hyperproliferation of the dividing cells
where do hair follicular stem cells reside?
in the bulge of the hair follicle
when granule ells migrate back toward the ventricular zone they produce this region:
internal granular layer
What is primary neurulation regulated by?
intrinsic and extrinsic forces
how are the neurons of the brain organized?
laminae (layers) and nuclei (clusters)
white matter
marginal zone
growth cone moves by elongation and contraction of these pointed filopodia
microspikes
What do the extrinsic forces regulate?
migration of the surface ectoderm toward the center of the embryo
what are the major cell type of the cerebellum: -electrical pathway of cerebellum -secrete Shh to systain divisions of granule cell -has *dendritic arbor* that spreads like a tree above cell body
purkinjie neurons
as the neural tube matures, the progeny of the nuroepithilial stem cells become
radial glial cells (RGCs)
what are the two major progenitor cells in the germinal strata?
radial glial cells and intermediate progenitor cells
what type of indication is critical in the specification and differentiation of the retina and lens
reciprocal
the dorsal portion receives input from:
sensory neurons
How does the neural tube form?
shaping and folding of the neural plate from *low levels of BMP*
dorsal region is the place where:
spinal neurons receive input from sensory neurons