unit 3 Flashcards
What is a neural crest?
- transient, multipotent, migratory cells that differentiate into many tissues and organs
- start as 1 thing (neural crest) and go to many types
- epithelial to mesenchymal transition
What surrounds the neural crest?
somites
How does migration occur in the neural crest?
- neural crest to neural plate
- neural plate closes and promigratory cells close in
- delamination of neural crest cells
- then migratory cells
What are the regions of the neural crest?
- cranial
- cardiac
- vagal
- trunk
What is the cranial region of the neural crest?
- forms face, neck, cranial nerves, cartilage, bone, neurons
What is the cardiac region of the neural crest?
- division between aorta and pulmonary artery, cartilage and connective tissue and melanocytes
What is the vagal region of the neural crest?
- parasympathetic ganglia
What is the trunk region of neural crest?
- medulla portion of adrenal gland, sympathetic ganglia, melanocytes, and neurons
How do you study the neural crest?
- use multicolored organisms with CRE
- use mice
How is fate determined in the neural crest?
- start as progenitors and use paracrine signals to determine fate
How is the epidermis formed?
WNT + BMP
How is the placodal cells formed?
Wnt to BMP
How is the neural crest formed?
- Wnt to WNT and BMP
How are neural cells formed?
straight from wnt
What do ecadherins do?
- cell adhesion in stationary cells
What do n cadherins do?
- cell adhesion in migratory cells
What does C6B do?
- stabilizes neural crest
What does SOX2 do?
- keeps neural crest in progenitor stage as delamination progresses allowing for specification
What does snail 2 do?
- TF promoting epithelial to mesenchymal transition
What do lamelpodia and fillipodia do?
- directs growth with RAC1
What do actin and myosin do?
- retract with RHO1
What is contact inhibition?
- if they touch each other they repress and run the other way
What is the contact inhibition pathway?
- touching to cells rearranging to cells looking for vacant openings to populate to proper distribution
What is the premigratory domain?
- high BMP WNT SNAIL2
- repression of E+N cadherin
- SNAIL 1 and C6B upregulated
What do chase and run placodes do?
- form streams and keep cells from mixing
How is collective migration regulated?
- cell to cell adhesion is mediated by low N cadherin
- migratory crest cells secrete attractive signals delineated by chemical cues on the way to target
How does the chase and run placodes work?
- placodes release SEF1 (Chemoattractor) to receptors CXCR4
- placodes attract than the chase begins
- repellants (semaphorins and ephrins keep the cells in line
- contact forms co-inhibition there is a stop of signals so they repel, then they chase again
Where is beta galactosidase expressed?
expressed with WNT and mesoderm derived cells
What do birds and placental organisms have in common?
- amniotic cavity
- embryo
- ammion
- allanlois
- chorion
- yolk sac
- mammary glands
What does an egg have that a placenta doesn’t?
- shell
What does a placenta have that an egg doesn’t
- placenta itself
- umbilical cord
What happens before a chick lays an egg?
- fertilization
- division and growth of living cells
- segregation of cells into layers and tissues
What happens during egg incubation?
- rapid growth
- by day 3 all chicken anatomy is in place
What is the chicken reproductive tract?
- ovary surrounded by infundibulum to capture egg
- to mangum in chicken but fallopian tube in mammals
- narrows to isthmus
- enters into uterus or shell gland where egg undergoes rotation
- layed through cloaca
What is discoidal meroblastic cleavage?
- yolk doesn’t cleave
- all development on top of yolk
What is the zona pellucida?
- zone on top of egg yolk that appears clear
What is the suddermanal cavity?
- between cells and yolk
- like a blastocoel
- allows gastrulation
When does hypoblast formation happen?
- as soon as reductive division and cleavage hypoblasts form and migrate underneath epiblast
- hypoblast cells don’t contribute to embryo, but help gastrulation to take cells from epiblast in
Where does the cell undergo cleavage?
blastodisk
What is the chilazza?
- suspends yolk in shell gland and helps rotate
What is the difference between a blastodisk and blastoderm?
- disk = 1 cell
- derm = many cells
What happens to the maternal determinants in the blsatoderm?
- swept to one side similar to cortical rotation
- cillia goes to molecular sweep leading to biochemical assymetry
- left = cerebrus, nodal BMP
- right = FGF8
What is kohlers sickle?
- helps organizer, gradient of gene products and stabilizes beta catenin
- directs hypoblasts into sudural cells
- form hensons nodes where cells will gastrulate
How does the primitive streak form?
- primary hypoblast to secondary hypoblasts to ingression of epiblasts to subdural mesoderm and endoderm to primitive streak
How does opeca cell formation happen?
epiblast ingression to hypoblast to endoderm to embryonic endoderm
What does the endoderm form?
- respiratory and digestive system
What does the primitive streak do?
- forms anterior posterior axis and undergoes anterior migration
How can you track how cells move?
- use gfps and voltage to force DNA in
- graft cells and implant into recipeint and watch where it goes and how it migrates
Where do cells move if they are anterior to the node?
- move anteriorly
Where do cells move if they are posterior to the node?
- lateral and slightly foward
Where do cells move if they are far posterior?
- only lateral
What is the primative streak equivilant to?
- DBL
What is the convergence of the primative streak?
- ripcurrent causing convergent extension
- uses WNT non-canonical pathway leading to RHO and RAT
What does planar cell polarity cause?
- changes in cytoskeletal dynamics
What happens when henson’s node gets to the posterior?
- it regresses and leaves nodal chord
- moves anteriorly
- noggin is expressed leaving BMP free node
What does FGF to RA to WNT lead to?
FGF blocks RA which blocks wnt
What are the steps to mammalian fertilization?
- capacitation in female reproductive tract uses serum albuteral and calcium, so bicarb goes to camp to PKA to phosphorylation to capacitation
- sense and follow progesterone gradient and thermal gradient
- undergo acrosome reaction qith zona pellucida - proteolytic enzymes breakdwon egg barrier
- fusion of sperm and egg with izumo and juno
- zinc spark activates egg to block acrosomal reaction
Where does early cleavage occur?
- oviduct/ fallopian tube
When does implantation occur?
- when embryo is a blastocyte
What type of cleavage do mammals undero?
- holoblastic isolecithal rotational cleavage
What does cleavage lead to?
- blastocyst
- 8 cells and compaction to morula to blastocyte
What is compaction?
- cell to cell adhesion and loss of individuality using e-cadherins
What does the morula form?
- trophoblast precursors (extra embryonic and lead to placental formation)
- intercell mass ( embryonic cells, extra embryonic cells and membranes
When does the blastocoel form?
16-32 days
How does the blastocoel form?
- highly equal and synchronized division
- embryo cavitates to form blastocoel
- trophoblast cells go inside
- allows Na in and pushes H+ out
- Na+ increases osmatic pressure and blastocoel expansion
Where is OCT4 found?
- in intermast cells
- trophoblast cells don’t have it
- extraembryonic cells don’t have this
What do extraembryonic cells form?
- hypoblast cells that form more extraembryonic structures
What is a pluripotent cell?
- can form many different cells but not all
- requires Oct 4
What type of cell is an epiblast?
- pluripotent
- can self renew
Is a fertilized egg pluripotent?
- no its totipotent
What are the levels of Oct4 expression?
- high = extraembryonic endoderm and mesoderm
- middle = embryonic stem cell
- low = trophectoderm
What do yamenaka cells do?
- can undifferentiate buccal cells into embryonic stem cells
- induce pluripotency
What is the difference between trophoblast and ICM cells?
- trophoblast cells have CDX2
- ICM have oct4
- CDX2 knockouts express Oct 4
- CDX2 cells is trophoblasts requires Tread4
What is Tread4?
- part of hippo pathway
- transcription factor
- binds to Yap leading to CDX2 in outer cells and trophoblast
- hippo in inner cells and destruction of YAP means no CDX2
What does Nanog form?
- future epiblast
What does GATA6 form?
- future primitive endoderm
- 2 types of primitive endoderm
- visceral = below epiblast
- parietal = along inner side of trophectoderm cells
How does hatching occur?
- through degradation of zona pellucida
What occurs 7 days post fertilization?
- trophoblast cells in ICM invade uterine lining
What occurs 8 days post fertilization?
- ammonium forms
- fluid accumulates between ammonium and epiblast
- syncytial trophoblasts invade uterine lining which then forms nuclear division without cells or fusion of cells
What happens 9 days post fertilization?
- ammonium forms covering over epiblast
- synctiotrophoblast develops over lacunae cavities
What happens 10 or 11 days post fertilization?
- gastrulation
- primitive streak formation and ingression
- the yolk sac becomes extraembryonic separating from the blast cells
- definitive endoderm and mesoderm then form epiblast
What is the organizer in mammals?
- hensons node and anterior visceral endoderm form the organizer
What does the mammal organizer secrete?
- lefty 1
- cerberus
- dickopf
What does lefty 1 do?
- binds nodal and antagonizes it
What does cerberus do?
- inhibits nodal, wnt, or bmp
What does dickopf do?
- inhibits WNT
What does the mammal organizer do?
- supresses nodal, bmp, and wnt so anterior structures can be formed
- induces nervous system formation and AP axis
What drives left right patterning in mammals?
- dyenin cilia
- motile cilia
How are anterior visceral endoderm and node connected to form the organizer?
- connected by ntochord
- notochord emerges beneath node
- gives us chordin and noggin
How do chordin and noggin move in mammals?
- chordin starts in node and moves towards anterior visceral endoderm inhibiting BMP
- cerberus goes from node and anterior visceral endoderm inhibiting nodal, WNT, BMP
How does the formation of anterior visceral endoderm occur?
- through mecahnical stress
- forces come from maternal tissues and breach basememnt membrane
- forces growht down and forms visceral endoderm
What transcription factors does the AP axis use?
- BMP
- WNT
- FGF
- RA needs to be kept away from brain or genital regions
What is the key part of neuralation?
- different transcription factors work in different areas
- gradients will work against each other
- BMP is morphogen that activates Pax7
- sonic hedgehog activates gli and represses pax 7 at high concentrations
- no distinct boundaries
What is neuralation?
- folding in vertebrates which transforms neural plate and neural tube, embryo is called neurula
- uses lamelpodia and fillipodia to bring cells together to form junctions
How does neuralation happen?
through hollow dorsal nere chord
What are the major features of chordates?
- notochord
- pharyngeal stilts (pouches and arches)
- endostyle (thryroid)
How does the rostral nervous system form?
- thickening of neural plate
- hollows while sides come together
- nodal chord causes bending and hinge point
- elevation of neural chord then forms DL hinge
- forms 3 total hinge points
- medial ONC uses nodal chord, side ones dont
- after hinges form cells come in contact and form hollow tube
How does secondary neurulation happen?
- forms caudal nervous system
- rosettes form to close sides
How to hinge points form?
- notochord signaling inhibits noggin by limiting BMP repression
- notochord and noggin work together to contract where noggin is but there is no repression where noggin is repressed
- sonic hedgehog goes to gli which goes to the transcription factor
- during closure the cells express lamellipodia and filipodia together
- as they connect they form adherins junctions through e cadherin
How is sonic hedgehog expressed?
- ventral to dorsal
How do roe and rac move?
- rho moves anterior
- rac is posterior
What do rho and rac do?
- both help with actin cytoskeleton rearangement
What happens after a node is formed?
- after the ectoderm seals the neural tube is enclose and high BMP is expressed
What happens if BMPS are hyperactive?
- failure of neural tube to close and spina bifida
- create hingepoint failure because sonic hedge hog can’t overcome BMP
What happens if there are too little BMPs?
- cant activate SMAD so there is an overexagerated hinge point
What are the parts of the WNT pathway and what does it (planar pathway) do?
- helps with neural tube closure
- pdz domain
- dep domain
What is the pdz domain?
- dissheveled to xdd1 to cononical wnt and planar cell polarity
What is the DEP domain?
- dissheveled goe to xdshdz to plannar cell polarity only
Is the DEP or PDZ domain more important?
- DEP is more detremental
- plannar cell polairy pathway is more important and helps with actin cortical cytoskeleton formation
-vangal is important to help activate Actin cytoskeleton reorganization
What does pep inhibition lead to?
- spina bifida
What does the midbrain lead to?
- the mesencephalon
What does the forebrain lead to?
- telencephala
- diencephala
What does the telencephala lead to?
- cerebral hemisphere
What does the diancephala lead to?
- future retina and hypothalamus
what does the hind brain lead to?
- rhombomeres
-rhombencephalon
What does the rhombencephalon form?
- metencephalon
- myelincephalon
What does teh metencephalon form?
- cerebellum
What does the myelincephalon form?
- medulla
What do alternating domains of ephrin and ephrin receptor expression do?
- allows rhombomere formation in hind brain
- functions as chemorepulsive pair
- juxtacrine signaling
What is the ephrin receptor?
- erythropoetin producing human hepatocellular receptors
- uses tyrosine kinase
What does constriction of the posterior neural tube do?
- allows brain ventricles to form
What does activation of Ephrine receptor do?
by binding to ephrin ligand leading to an increase in tyrosine kinase medaited phosphorylation in receptor containing its movement away from the ligand
- Ephrine 4a is needed for rhombimere boundary formation
What does teh dorsal side of the nervous system have?
- sensory nuerons arrive
What happens on the ventral side of the nervous system?
- motor nuerons leave
How id the DV axis of the nervous system formed?
- BMP and Sonic Hedge Hog pattern Dorsal ventral axis
- TGFBeta family
- BMP is higher in dorsal sie, Sonic hedgehod is higher in ventral
- these gradiets regualte all other transcription factor gradients
What are the notochord inductive properties?
- early source of sonic hedge hog
- if you transplant an extra notochord you get a second set of motor neurons
- ## neural tube formation depends on concentration and duration of sonic hedgehog
Which side of the embryo develops faster?
- posterior
- has neural tube closure sooner
- has somites
- higher cell density sooner
- has more advancements and differentiation
Why does the posterior side of the embryo have mroe growth?
- because it has less differentiation
What are neural mesodermal progenitors?
- source of neural cells and meodermal cells
What does retinoic acid do?
- pushes for differentiation but not expressed in brain
- activates Hox gene expression and bone and muscle patterning
What does the hox gene do?
- vertebrae disks tendons ligaments associated musle
What do placodal cells develop into?
- retina
What does the dorsal edge of the rhombomere form?
neural crest, will go into eye field
What must happen for the eye field to develop properly?
- the neural crest must separate
- chase and run causes eye fields to separate, move apart, and allows for the passage of neural crest cells.
- if this doesn’t happen there will be a cyclops.
How does anterior brain growth happen?
- cranial neural crest that forms facial skeleton is needed
- FgF8 is needed
- forms telencephalon
- in forebrain neural crest helps activate FgF8
What happens if you add FgF8 to the anterior of the brain?
you can replicate it
How do cells travel between the epiderms and dermis?
- dorsal lateral path
- goes over lateral plate
How do cells travel to the anterior sclerotome?
ventrally
under the lateral plate
Do neural crest progenitors cross paths?
- no
How do neural progenitors not cross paths?
- ephrin protein sof the sclerotome help
- anterior has extensive migration and posterior has no migration
- cells bind more effectively to regions with no ephrin
Does ephrin help cellls bind?
- no they bind more effectively to regions of no ephrin
Do posterior neural cells move?
no, only anterior
Are vertebrae placodes neural crest placodes?
no but it interacts with them
What are the types of vertebral placodes?
- ectodermal and neurogenic placodes
What are neurogenic ganglia?
- placodes that give rise to neurons
Do you want HOX in the brain regions?
no, because of Cyp26b1 and otx
What is pax 6 importnat for?
lens formation
What is pax 6 activated by?
- ET and RTI which are typically repressed by OTX2 and noggin before we are ready for the eye
What happens if there is no optic vesicle?
no eye
What does the optic vesicle do?
- can induce ectoderm in competent tissues
What is Pax6?
- primary inducer of lens formation
What is required for Hox formation?
- homeobox
What is homeosis?
- replaceemtn of 1 body structure with another
- typically in a segmented organism
What is spatial colinearity?
- gene in space is the same area its supposed to be developed in
What do hox genes encode for?
members of the homeodomain
- helix loop helix
What determines if hox genes are expressed?
- transition to active chromatin states
What determines what develops where?
- RA and FGF
What does high FGF and low RA form?
nueral progenitor cells and NMPs going into neural tube
What are the migration pathways?
- paraxial mesoderm and spine (anterior to posterior)
Where are FGF and WNT repressed?
- repressed by HOX genes in the organizer
What forms vertebraes?
- somites
How is the shape of the vertebrae determined?
- what hox genes are expressed
Where are more hox genes expressed?
-posterior
- had a higher number hox genes too
- distinct domains of hox expression
Do all animals have the same comp of of hox genes in each vertebrae?
- no
What is it called if you switch the amount of hox genes in each vertebrae?
- homeotic transformation
How is presomatic vertebrae formed?
- from the region of embryo that will form thoracic vertebrae is specified before emergence of ribbed vertebrae
- because of early hox gene expression
What is the target of HOX Genes?
- somites
What type of transition is somite formation?
- mesenchymal to epithelal
What does paraxis signify?
- paraxial mesoderm
What does PAX2 signify?
- intermediate mesoderm
What does chordin signify?
- notochord
How are somites patterned?
- noggin and chordin expressing cells transplanted into lateral plate mesoderm
- lateral plate mesoderm is respecified into paraxial/ intermediate mesoderm
- paraxial mesoderm patterns into somites
What are neural mesodermal progenitors?
- contribute to neural tube formation and paraxial mesoderm
- regulated by RA, Cyp26B1, FgF8 gradients help this
What do eph and ephrin do?
regulates epithelialization during somite boundary formation
Where do somites form junction?
- at anterior RA and posterior FGF domains
If FgF8 is only in cells with transcribed FgF8 gene what type of cell is it?
cell non-autonomous
If RAIDH2 is located in cells that transcribed RAIDH gene?
- cell autonomous
MESP is located in cells that transcribed MESP gene, what type of gene is it?
- cell autonomous
How is hairy expressed?
- posterior to anterior
Why does somite formation happen in waves?
- due to oscillations in delta notch pathway
What does the dermatome form?
skin
What does the mytotome form?
- muscle
What does cleratome form?
cartilage
What does the syndetome form?
- ligaments and tendons
- forms later in development after reorganization
