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