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