Chapter 10 - Test 3 - Ectoderm

neural plate cells are specified by the ____ family of transcription factors

Sox (Sox1, Sox2, Sox3)

What is germinal neuroepithelium

The original neural tube that is composed of a single layer of rapidly dividing neural stem cells, one cell layer thick

In primary neurulaton, the neural plate invaginates and pinches off to form a hollow tube.

This divides the ectoderm into neural tube cells and epidermal cells, as well as neural crest cells that form from the former neural fold cells in the neural tube in the region that connects the rest of the neural tube to the epidermis (on the dorsal side).

Shh and the TGF-B morphogens activate different combinations of transcription factors along the dorsal-ventral axis. What does this lead to?

Unique combinations that specify particular neurons forming

In the anterior region, the neural tube balloons into 3 primary vesicles:

the forebrain (prosencephalon) midbrain (mesencephalon) hindbrain (rhombencephalon)

The optic vesicle evaginates from the diencephalon of the brain to induce what?

the formation of the lens placode in the epidermis

The prosencephalon becomes subdivided into

the more anterior telencephalon and the more posterior diencephalon

In secondary neurulation

the neural tube forms from mesenchyme cells that coalesce into a solid cord that then forms cavities that merge to create a hollow tube.

BMPs promote epidermal specification and block neuronal differentiation. Mammalian epidermis starts as one layer but soon becomes a ___ layered structure

two

Interneurons relay information from sensory and motor neurons. Signals from the notochord specify _____ pattern, while signals from the epidermis specify ______ pattern

ventral; dorsal

In the spinal cord, as germinal epithelium gives rise to more migrating cells, the migrating cells form a second layer around the original neural tube. The new layer is the cortical mantle (or intermediate zone) and the germinal epithelium becomes the ____ ____

ventricular zone

The lens placode is Cranial ectodermal placode on the epidermis What is a placode?

a placode is a thickened portion of germ layer tissue from which an organ develops

A series of reciprocal inductions between the epidermis and the mesoderm-derived mesenchymal dermis creates the sweat glands and _______ ______ (Hairs, scales, or feathers)

cutaneous appendages

The skin is the largest organ in out body and protects against

dehydration, injury, and infection, and is constantly renewed

The placode induces the formation of _____ _____ beneath the hair germ (reciprocal induction)

dermal papilla

Transplantation of Shh secreting cells to a dorsal region induces new floor plate and the production of ___ neurons in dorsal regions

motor

Intermediate levels of BMP specify ____________

neural crest

The dorsalmost cells of the neural tube become ______ _______ cells (migrating cells)

neural crest

During primary neurulation, shorly after the neural plate forms, its edges thicken and move upward to form the

neural folds

In between the neural folds is the the __-- ___ which forms along with the anterior posterior midline

neural groove

Surface ectoderm pushes toward the midline of the embryo, forming the neural folds that surrounds the ____ ____

neural groove

Low levels of BMP specify ________

neural plate

vertebrates use both primary and secondary neurulation pathways to form the neural tube from the ______ _______

neural plate

The inner layer cells proliferate rapidly to form glia, ganglion cells, interneurons, and photoreceptor neurons, making up the _____ ____

neural retina

ectoderm forms the epidermis and ______ tissues

neural tissues

Neural folds eventually fuse to create the

neural tube

Openings where the neural folds have not fused are called _____. So chicks have one anterior and one posterior neuropore; humans have more

neuropores

The process of forming an interior neural tube from the neural plate is called ______________, and an embryo undergoing such changes is called a _______

neurulation; neurula

The lens reciprocally induces the optic vesicle to become the ____ ____

optic cup

The diencephalon will form the ____ ____ and other structures

optic vesicles (future retina)

The outer layer gives rise to the ______, a temporary covering that is shed once the inner layer differentiates to form the true epidermis

periderm

In vertebrates in general, only the ____ s formed by secondary neurulation

tail

In chicks, closure is initiated at the future midbrain and zips up in both directions. Humans have ___ sites where neural tube closure is initiated

5

Differentiation of the neural tube involves

Bulging and constricting to form the chambers of the brain and spinal cord. Arrangement of the cells to form functional regions of the brain and spinal cord. Differentiation of neuroepithelia cells into different types of neurons and glia cells.

The folds adhere to each other and merge. Cells at this junction form the neural crest tissue

Closure of the neural tube does not happen simultaneously along the anterior-posterior axis. In general, cephalic (head) region is well advanced of caudal (tail) region.

Dramatic sequence changes in gene regulatory systems, not in the proteins themselves (i.e. not dramatic changes in amino acid sequences). HAR1 (human accelerated region-1) is a miRNA gene that contains many sequence changes and is expressed in developing brains of humans and apes, and may be involved in neuronal migration. GADD45G gene (a growth suppressor) has its forebrain enhancer deleted in humans.

Dramatic changes in gene expression levels: overall mRNA is more than five times higher in human brains. Human specific alleles of developmental regulatory genes. Two amino acid changes in the brain FOXP2 gene, which is responsible for the regulation of more than 100 genes. Involved in fine motor control of the larynx and mouth. Continued rapid development of the brain until puberty.

Failure to close the neural rube causes serious birth defects:

Failure to close closure site 5 results in spina bifida (exposed spine). Failure of closure site 2 or 3 keeps the anterior neuropore open and causes anencephaly (forebrain degeneration). Neural tube defects are common (1 in 1000 live births), and is much more prevalent where folate (vitamin B9) is limiting.

Human Brain

High human brain/body ratio (encephalization index), 3.5 times that of apes. Asymmetric, highly plastic development. Retention of fetal neuronal growth rate after birth. The "extrauterine fetuses" and compromise between brain size and pelvic width.

Each Ehombomere has a different fate, specified by ___ gene components

Hox

The anterior portion of the neural tube is specified by Noggin, which promotes the expression of ___, leading to the sequential activation of ET, Rx, and Pax6, which specified the retina and produces the factors necessary for inducing the lens

Otx2

Melanocytes are neural crest derived cells that reside in the ______ epidermis and provide the skin's pigmentation

basal

The inner layer (called the basal layer) contains epidermal stem cells attached to a basement membrane also called the ____ ____ that the stem cells help to make

basal lamina

During vertebrate embryo development how is the neural plate specified?

by mesoderm to become neural tissue, and is distinguished by the columnar appearance of its cells

Cell nuclei move according to the ___ ___

cell cycle

In primary neurulation

cells surrounding the neural plate direct the neural plate cells to proliferate, invaginate, and pinch off from the surface to form a hollow tube.

the metencephelon gives rise to the _____

cerebellum (muscle control and coordination)

This pattern becomes more complex in cerebellum and ___- _____

cerebral cortex

The telencephalon will form the ______ and other structures

cerebrum (cerebral hemispheres)

The other hinge points (along with the MHP) are the _____ ____ ___ ____ (DLHP) in each neural fold.

dorsal lateral hinge points; These help promote convergence of the two neural folds together

High levels of BMP specify _________

epidermis

Sonic Hedgehog (Shh) from the notochord signals the medial hinge point cells to become the ____ ____ of the neural tube

floor plate

Lumens do what to make a tube

form and fuse

Neural crest cells above each rhombomere will form _____ clusters of neuronal cell bodies whose axons form a nerve, each termed a ______ ______

ganglia; cranial nerve

What connects the neural retina to the brain?

ganglion cell axons

Int he cortical mantle, cells differentiate into either neurons or ___

glia

The intermediate zone with cell bodies is also referred to as ___ ____, while the axons in the marginal zone end up wrapped in myelin sheaths, and forms ____ _____

gray matter; white matter

The neural plate consists of elongated cells (vs. flatter epidermal cells) Up to __ of the ectoderm is included in the neural plate

half

During gastrulation, first the foregut endoderm and then the heart forming mesoderm interact with the ____ ____ to give it a lens-forming bias

head ectoderm

The lens placode then invaginates to form the __

lens

When the stem cells start producing neurons (instead of more neuronal stem cells) one daughter (stem) cell remains attached to the _____ while the differntiating daughter cell migrates out. This is called the neuron's birthday

lumen

Neurons send connections away from the lumen, forming a third layer with few cell bodies called the _____ _____

marginal zone

The ectoderm becomes anchored to the mesoderm (notochord) at the _____ ____ ____ (MHP) in birds and mammals

medial hinge point

the myelencephalon becomes the _____ _____

medulla oblongata for involuntary functions

Secondary neurulation (in the posterior region) involves the production of mesenchyme cells from the ectoderm and endoderm, followed by condensation of these cells into a ____ _____ beneath the surface ectoderm. This is a mesenchyme-to-epithelial transition.

medullary cord

The hindbrain separates into the

metencephalon and mylencephalon

The outer layer of the optic cup produces melanin and ultimately becomes the _____ _______

pigmented retina

These interactions first form a ______ in the epidermis that in mammals is the base precursor for hair follicles

placode

the rhombenecephalon develops segments called ______ that specify where certain nerves originate

rhombomeres; Cells from different rhombomeres do not mix

TGF-B superfamily members (including BMP4) are secreted from the epidermis and specify __ ___ cells

roof plate

The dorsal-ventral axis of the neural tube is polarized:

sensory neurons connect on the dorsal side motor neurons connect on the ventral side