final exam all bio 4400, Cell Fate and Specification, Exam 2: Neurulation, Exam 2: Neurons, Exam 2 - Neural Crest cells, Exam 2: Sensory placodes and organs, Cell-cell interactions and signaling

Lateral inhibition

*"Do as I say, Not(ch) as I do"* - sending cell tells neighboring target cells to adopt a different cell fate than that of the sending cell (especially via the *Notch signaling pathway*) - *Juxtacrine signaling*

lessons from development: "All that you change..."

"All that you change changes you." - Most entities are both passive and active. (in development: "reciprocal induction")

Juxtacrine signaling

"Juxta" = nearby or close ligand and receptor are both *physically attached* to the two communicating cells - usually via membrane bound proteins

Mantle zone = _________ matter

grey matter (cell bodies)

lessons from development: Local changes can...

have a global impact.

Fate mapping: Painting (modern)

**Genetic fate mapping** - Creating transgenic animals that make fluorescent proteins (e.g. GFP) in certain cell types. - Aequorea victoria jellyfish makes it naturally (bioluminescence) - Osamu Shimomura, Roger Y. Tsien, Martin Chalfie won the 2008 nobel prize in chem for this experiment

Cell adhesion complexes - Cadherins

*Calcium dependent adhesion* 1) connect to actin microfilaments 2) bind in a homophilic (tissue specific) manner ex: E-cadherin binds more strongly to another E-cadherin than N-cadherin, and vice versa *cell sorting based on type and # of cadherins present*

Brain development in humans: - when does it start? - when is it (myelination) complete?

1) starts late 4 weeks post fertilization 2) complete at age 20!

Ectoderm derivatives: Epidermis (surface) ectoderm

*HIGH BMP LEVELS* 1) Epidermis 2) Hair 3) Nails 4) Sebaceous glands 5) Olfactory epithelium 6) Lens, cornea 7) Mouth epithelium - Anterior pituitary - Tooth enamel - Cheek epithelium

Neural crest cell derivatives

*INTERMEDIATE BMP LEVELS* 1) Adrenal medulla 2) Craniofacial bones and cartilage 3) Dentine of teeth 4) Melanocytes 5) PNS - Glial cells - Schwann cells - Sympathetic and Parasympathetic nervous systems

Ectoderm derivatives: Neural plate (neural tube)

*LOW BMP LEVELS* 1) CNS (brain and spinal cord) 2) Neural pituitary 3) Motor neurons 4) Retina of eye

Ectoderm derivatives: Neural crest cells

*MODERATE BMP LEVELS* 1) PNS - Schwann cells - Glial cells - Sympathetic & Parasympathetic nervous systems 2) Melanocytes 3) Adrenal medulla 4) Facial cartilage 5) Dentine of teeth

Establishment of the eye field...

- 1 central to 2 bilateral areas of competence before optic vesicles form - Development of bilateral eye fields by Shh

Neuroepithelial cells divide _________ in order to make ________.

1) symmetrically 2) more neural progenitors (radial glial cells)

Sensory placode induction and specification: Secondary signals

- What specify if cells become placodes or neural crest - Wnt signaling and the amount of time its turned on

Neocortex:

- contained within the cortical plate of the cerebral cortex - this is where higher processing occurs - 6 layers within the neocortex, layered by the number, type, and function of the neurons it contains

Neural crest cells as the _________ only in vertebrates! Neural crest cells as the _________ because of their extensive migration

1) "4th germ layer" 2) "the explorers of the embryo"

Human brain contains _________ cells, with __________ numbers of neurons and supporting cells

1) 170 billion cells 2) roughly equal numbers of neurons and supporting cells

Without neural crest, you would...

1) Be very pale - Melanocytes 2) Be slow moving and relatively insensate - Much of PNS 3) Have a face that would make a hagfish look lovely in comparison - Craniofacial bones and cartilage

5 examples of cellular responses during cell signaling

1) Change in gene expression (another way to have amplification) 2) Activating an enzyme to break down a protein 3) Actin assembles into filament and cell changes shape 4) Change in subcellular localization of a protein 5) Instigating cell death

Fate mapping: Painting (original)

1) Developed in 1929, but versions still used today 2) Inject or place inert dye in early embryo, then examine at later time points

Steps of primary neurulation (4 of them):

1) Elongation of neural plate via *convergent extension* (sheet thins out, makes it easier to fold) 2) Folding and elevation of neural folds via BMP signals and Shh signals (from the notochord) - folding occurs first (creates the medial hinge point superior to the Notochord) - Hinge points and elevation of neural folds via *apical constriction* (Development lesson 4: Local changes have a global impact) 3) Convergence of neural folds - dorsolateral hinge points apically constrict, bringing neural folds back to midline (regulative via BMP signaling) 4) Closure of the neural tube

Sperry chemoaffinity hypothesis

1) Eph receptors (retina) and ephrins ligands (brain) are both expressed in posterior (most concentrated) to anterior (least concentrated) gradients 2) Eph/ephrin *juxtacrine signaling* results in changes to the actin cytoskeleton *and are REPULSIVE* *step 3 of neural crest cell development*

Patterning of neural tube (CNS): - anterior to posterior via _________. - dosal to ventral via ________ and ________

1) Hox genes 2) BMP and Shh gradients

Steps of neural crest cell development (4 of them)

1) Induction and determination 2) Concurrent delamination and epithelial-to-mesenchymal transition (EMT) 3) Migration 4) Differentiation

what are 4 types of cell interactions?

1) Internal/mechanical 2) Juxtacrine signaling 3) Paracrine signaling 4) Endocrine signaling Note: these are arranged in order of closest interaction to longest distance interaction

what are the 3 primary ectoderm derivatives?

1) Neural plate (Neural tube) - BMP levels are low - Sox transcription factors expressed 2) Neural crest cells - BMP levels are moderate 3) Epidermis (surface) ectoderm - BMP levels are high

cranial placodes:

1) Olfactory 2) Lens 3) Otic

give 3 examples of signal transduction events

1) Phosphorylation 2) a change in protein conformation 3) protein cleavage

External ear

1) Pinna (Auricle) - catches sound waves and passes them along deeper into the ear 2) External acoustic meatus - auditory canal

What are the 3 general steps of neurulation?

1) Primary neurulation - anterior (rostral) end 2) Junctional neurulation (transition zone) - intermediate between anterior (rostral) and posterior (caudal) ends 3) Secondary neurulation - posterior (caudal) end

3 stages of cell signaling *in target cell*

1) Reception - signaling molecule (ligand) interacts with the receptor 2) Transduction - relay molecules in a signal transduction pathway 3) Response - Activation of cellular response

what are the 3 necessary components of a cell signaling pathway?

1) Sending cell - releases ligands (signals) into environment 2) Signal (ligand) 3) Target cell - has a receptor specific to the ligand, making the cell receptive to receive the signal

neurons of the autonomic nervous system (3 types)

1) Sympathetic 2) Parasympathetic 3) Enteric

Three fundamental rules of development:

1) Timing is everything 2) Location, location, location 3) Both of the above are true

Ectoderm doesn't move through the __________ or __________

1) blastopore (frogs and fishes) or 2) primitive streak (birds and humans)

Chemoattractants and chemorepellants guide ________ and control _________.

1) guide axon extension 2) control neural crest cell migration *step 3 of neural crest cell development*

Sensory placodes induced by...

1) neural plate and mesoderm *directly* 2) endoderm *indirectly* - signals from the endoderm induce gene expression in the mesoderm - mesoderm then either directly induces the placode, or signals the neural plate to release signals (which then induce the placode)

radial glial cells are... (two functions) are neural progenitors

1) neural progenitors - asymmetrically divide to produce a daughter neuron and another radial glial cell 2) a scaffold for neuron migration - new neurons use the cytoplasmic extensions of RGC's as a scaffold to climb up, migrating towards outer layers of the brain

Signal transduction

1) often occurs via a string of *"second messengers" = transduction cascade* 2) can have amplification of the signal - each activated receptor can activate multiple second messengers in parallel

Steps of neural crest cell development: Migration 1) Neural crest cells migrate... 2) Balance of ________ and ________ to get collective migration 3) Collective migration to... 4) ________ and ________ control neural crest cell migration

1) throughout the embryo - *"explorers of the embryo"* 2) attraction and repulsion 3) go in the right direction 4) chemoattractants and chemorepellants

preformation

17th century idea that the sperm or egg contains a pre-formed miniature human ("homunculus") that simply becomes larger during development. - Now we know that development involves *cells acquiring different fates*

Notochord:

A defining feature of chordates: - transient cartilage- like rod of *mesoderm* that induces the nervous system (neurulation) - Forms under the primitive streak in birds and mammals

Diseases of color vision: Red-green color blindness

Affects ~8% males and 0.6% females - Pair of opsin genes on the X chromosome

splitting of common sensory pre-placodal region

Anterior: FGF↑ BMP↑ Wnt↓ Intermediate: FGF↑ Wnt↑ Posterior FGF↑ BMP↓ Wnt↑ RA↑

Steps of neural crest cell development: Differentiation

Based on transcription factors 1) Cartilage derivatives 2) Melanocytes 3) Schwann cells 4) sensory neurons of the PNS *fate mapping*

Ectoderm in birds and humans vs. frogs and fishes

Birds and humans: - Ectoderm = Epiblast that does not ingress Frogs and Fishes: - Ectoderm = epithelia that undergoes epiboly and remains on outside

lessons from development: ____________ matters!

Context! The response to a signal depends on: 1) other signals 2) neighbors, 3) the type of tissue 4) the competence of a cell to receive that signal.

Fate mapping

Creating chimeras with transplants. - Established in 1969, but still used today - Exploits 2 key factors: 1) Chicken and quail embryos develop similarly 2) Quail cells stain, but chicken cells don't, with a specific DNA stain

what are the two major types of cells in the embryo?

Epithelium 1) Highly organized into sheet or tube 2) Tightly linked together - Junctional complexes (*cadherins*) 3) Stationary 4) Polarized (apical side vs. basal side) 5) little ECM Mesenchyme 1) Loosely organized 2) Loss of adhesion 3) Ability to migrate and invade - most cancer cells that are metastasizing are mesenchyme - can operate as an independent unit 4) No polarity 5) Lots of ECM

The 6 word key to development:

Find it - mRNA or protein has to be in the right place (at the right time) in order for a developmental step to take place Move it - moving specific cells to a new location - does this start a new process? if so then, those cells are probably important for the process

Steps of neural crest cell development: Induction and determination

First step: 1) Neural crest cells form at the crest of the neural folds and later neural tube 2) Induced by neural plate, mesoderm, and epidermis 3) Neural crest cell gene regulatory network (GRN) - Hierarchy of regulatory genes - (inhibitory) BMP signaling is at the top - combines with other signals to repress things involved with the neural plate

____________ is necessary for proper hinge formation

Intermediate BMP signaling - too much BMP signaling (SMAD activation) causes hinge point failure - too little BMP signaling (SMAD activation) causes exaggerated hinge points

what is an example of a mechanism that is capable of generating a pattern from a uniform sheet of cells

Lateral inhibition

combinations of signaling pathways ("cross-talk")

Logic A: "and" - second messenger is only active when phosphorylated by BOTH pathways Logic B: "or" - active when phosphorylated by either one pathway or the other, but not both

Neural crest cell EMT and cancer metastasis

Mesenchyme are mobile and can spread out (migration/metastasis) Factors that help them move: 1) Signaling pathways 2) Transcription factors (regulators) 3) Cadherin switch (effector) 4) Cadherin shedding and matrix remodeling (effector) 5) Make use of pre-existing structures to spread *many of the same signaling pathways, transcription factors, and catherine shedding/matrix remodeling is used in both neural crest cells undergoing EMT and metastatic cancer cells*

24 findings or experiments in the past 100 years that most impacted the field of developmental biology, chosen by 35 experts in the field

Milestones of developmental biology from the journal Nature

what is the another name for the cell body of a neuron?

Soma

Myelination of axons in the CNS via...

Oligodendrocytes

Non-neuronal (supporting) cells known as ________ are necessary for proper functioning of neurons

Oligodendrocytes - they myelinate the axons of neurons

Rods and cone photoreceptors in the retina

Rods: light-sensing - Rhodopsin Cones: color-sensing - Opsin

Holoprosencephaly is related to...

SHH levels Holoprosencephaly = brain doesn't split into left and right hemisphere

Contact inhibition of locomotion

Step 2 of neural crest cell development: 1) Migratory neural crest cells (that have undergone delamination) interact with each other - When they interact, they realize its crowded and move the opposite way 2) Moves them away from the neural tube 3) How we get spreading of neural crest cells

Steps of neural crest cell development: Concurrent delamination and epithelial-to-mesenchymal transition (EMT)

Step 2: 1) occurs right at the crest of the neural tube where folds finally meet - where neural crest cells form 2) Intermediate BMP levels 3) Peel away epidermis 4) Hypoblast delaminates from epiblast? - Epiblast split, hypoblast below it? 5) EMT 6) Contact inhibition of locomotion

Neurulation IMMEDIATELY follows...

gastrulation

lessons from development: _________ can change a lot.

Time - Some structures only exist in the embryo to form other structures that make it to the adult

Ectopic expression of Pax6 results in...

additional eyes

Ventricular zone:

adjacent to the inside of the neural tube, secretes CSF into the lumen

just like gastrulation, neurulation proceeds...

anterior to posterior

anterior part of neural tube = _________

brain

__________ = the former inside of neural tube

cerebrospinal fluid

lessons from development: Who you surround yourself with...

changes your path. - Your community and neighbors are important.

lessons from development: No one influence...

controls everything—it's usually a combination of things.

Fate map:

diagram "mapping" larval or adult cell fate on the region of an embryo from which it arose (relative to developmental time) *one of the first major milestones in developmental biology*

Cadherins: pattern formation via...

differential affinity based on intrinsic properties of cell adhesion proteins (cadherins) ex: if you mix two different cell types and then take a cross section of them, *the cell type with more cadherin will be in the center* and the cell type with less on the periphery

the process of specification

differentiation

Neurula:

embryo undergoing neurulation

Cylopia from...

environmental influences - Corn lily has high levels of the chemical cyclopamine

lessons from development: Two negatives...

equals a positive. - The enemy of my enemy is my friend

Reciprocal inductions during...

eye development - between lens ectoderm and neural ectoderm (presumptive retina)?? - whole process in humans takes approximately 4-8 weeks

Timing of neurulation is not synchonous in birds and mammals, but always occurs...

immediately after gastrulation

Eye is formed by

induced expression of eye master regulatory Pax6

Like neural crest cells, sensory placodes form at...

intermediate BMP levels

Notch signaling..........

lateral inhibition

Internal interactions generate ________ and _________. Give examples...

mechanical forces and cell movements 1) Apical constriction 2) Apical/basal cell shortening

lessons from development: There can be multiple

paths to the same end. - Redundancy is often built-in.

Sensory organs all begin in the head as...

placode - thickenings of surface ectoderm

Neural crest cell EMT vs. cancer metastasis: both make use of ____________ to spread

pre-existing structures

Neurulation:

process of folding the neural plate to generate the neural tube (precursor to central nervous system)

lessons from development: There are both ______ and ________.

pushes and pulls. - The signal to become A is often combined with a signal not to become B.

Convergent extension:

several layers of cells intercalate into one (sheet thins out, makes it easier to fold)

Radial glial cell =

single cell thick layer of neural tube

posterior part of neural tube = _________

spinal cord

Delamination

splitting of one cellular sheet into two more or less parallel sheets - While on the cellular basis it resembles ingression, the result is the formation of a new (additional) epithelial sheet of cells - occurs during step 2 of neural crest cell development

neurulation is induced by...

the notochord (mesoderm)

during signal transduction, what serves as the first messenger??

the signal (ligand) from the sending cell

Marginal zone = _________ matter

white matter (myelinated sheaths of axon extensions)

location of the neocortex

within the cortical plate of the cerebral cortex

when does neural crest cell development begin? (weeks post fertilization)

~3-4 weeks post fertilization

when is sensory placode induction and specification initiated in humans?

~3-4 weeks post fertilization (around neurulation)