ANS Quiz 2

Layer formation

• Irreversible ________ of cell lineages

  1. Segregating cell lineages adds _______,

  2. Adding complexity diminishes cell _______,

  3. Diminishing cell potency reduces # _________ (irreversible, usually)

• Physical separation of cell lineages (once differentiated)

  • Forms:

    • _______ (birds, reptiles, many mammals)

    • _______ (rodents)

• Begins prior to: ________ (avian) / _________ (mammal)

• segregation

  • complexity

  • potency

  • # genes being expressed

• Hypoblast, Visceral endoderm

• oviposition, implantation 

Layer formation

• Begins prior to oviposition / implantation 

  • Beginning – Avian 

    • Blasto_____ (64 cell stage)

      • Most central cells = ______

      • Regions of ______ cells pushed out to periphery

  • Beginning – Mammalian

    • Blasto_____ w cavitation in progress

    • 2 cell lineages

      • 1. ICM

      • 2. Trophectoderm

• Blastoderm

  • central = closed

  • periphery = open

• Blastocyst w cavitation

Avian - setting up for layer separation

• Area pellucida

  • 1. Blasto____ undergoes ______ via _______

    • → _______ of central daughter cells (ones closest to ______ / most ventral)

    • → Delaminated cells undergo _______

  • 2. Fluid-filled _______________ forms

    • Blasto______ cells absorb ______ from albumen then pump into space btwn _______ surface & yolk, forming _______

      • Similar to mammalian _______ during cleavage (tight ______ forming, ______ pumps activated, water pumped in)

      • ______ (egg white) surrounds blasto_____+yolk

• Blastoderm, reduction, cell shedding

  • Delamination, yolk

  • apoptosis

• subgerminal cavity

  • Blastoderm, H2O, ventral, cavity

    • cavitation (tight junctions, sodium pumps)

    • Albumen, blastoderm+yolk

Avian - setting up for layer separation

• Area pellucida (AP)

  • “Clear” ______ area of ______ cells

    • we have reduced blastoderm to 1 layer of cells, making it _______

  • ______ portion of blastoderm (bull’s eye); undergoing rapid _______

• Marginal zone (MZ) 

  • Mixture of ____&____ cells

  • Area of ______ cells between AP & AO 

• Area opaca (AO) 

  • Area of ______ cells, in contact w _____

  • (outer ring)

• (P = pinpoint center)

  • central, closed

    • translucent

  • Central, division

• (M = middle)

  • closed & open

  • dividing

• (O = outer)

  • open, yolk

Avian - setting up for layer separation

• Area pellucida (AP)

  • Becomes _________

  • (less _______ than AO/MZ bc cant become ________ tissue)

• MZ & AO become

  • ________ tissues

  • TEMPORARY ________ structures 

    • ie temporary contribution to ________

• embryo proper

• (potent, extraembryonic)

—

• Extraembryonic

• embryonic 

  • embryo proper

Avian - setting up for layer separation

• Bullseye effect = ____ center circle, ____ middle ring, ____ outer ring

• Epiblast = Continuous ______-cell layer of ____+_____+____

  • Only _____-most layer of cells of _____/_____ contribute to epiblast & developing embryo

  • The more _______ cells of the MZ & AO will either be very _______ structures or will contribute to _________ membranes

• All of these new cell lineages must emerge to set up for layer formation; ie must emerge before physical separation of the layers

• AP center, MZ middle, AO outer

• single-cell, AP + MZ + AO

  • dorsal, MZ / AO

  • ventral, temporary, extraembryonic

Avian - Separation of layers

1. __________

   • physical separation occurs around this time

2. ________ formation

3. _________

   • Explosion of cell activity

1. Oviposition

2. Hypoblast formation

3. Incubation

Avian - Separation of layers

1. Oviposition

   • _________ occurs around time of oviposition

2. Hypoblast formation

   • Hypoblast = 1st layer that is ________ from another layer

     • ________ structure

     • Prepares _______ for explosion of cellular ________

     • Well-studied in _______; not so much for mammals

     • Mammalian pattern = analogous structures to avian, but different processes & terminology (_______ (PE) differentiates into Hypoblast/_______ (VE))

3. Incubation

   • Explosion of cell _______

• physical separation

—

• different

• Transitory

• embryo, complexity

• birds

• Primitive endoderm, Visceral endoderm

—

• activity

Avian Layer formation

• Hypoblast = 1st layer formed; ________ must occur

• 1st cell movements that change shape of blasto____:

  • Some cells of ___ epiblast ______ & migrate toward yolk (______ cells)

  • These delaminated cells are what become the _______

  • This activity is not visible from _______ view, but is from ventral

• delamination must occur

• blastoderm

  • AP, delaminate, Hypoblast

  • hypoblast

  • dorsal

Avian Layer formation

• ________ = 1st layer of cells

  • Delaminated from ________

  • Forms in __________, below ______ epiblast

  • Transitory / ________

    • maybe gives rise to Primordial germ cells (PGCs)? (hypothesis)

  • Transient layer/sheet of cells

    • Does not contribute to ________ or ________

    • Maybe moves ________ from epiblast → germinal crescent??

• hypoblast

• AP

• subgerminal cavity, AP epiblast

• temporary

• embryo, extra-embryonic membraned

• PGCs

Avian Layer formation

• Epiblast = Creates _______

  • ____ + outermost _____ cells + outermost _____ cells 

• Blastocoel = Cavity btwn _______ & _______

• Subgerminal cavity = fluid filled layer between _______ & _______

• Blastula = ______+______

  • _______ structure (2 true layers)

  • Topmost / dorsal most layer = _______; _______ below it

• embryo

  • AP + MZ + AO  

• epiblast & hypoblast

• hypoblast & yolk

• Epiblast + Hypoblast

  • Bilaminar structure (2 true layers)

  • Top = epiblast; hypoblast below

Mammal - setting up for layer separation

• Remember the compacted morula after cavitation?

  • ICM changes (2nd cell fate)

    • Some cells undergo apoptosis

    • Remaining cells bunch up along one side

  • Blastocoel = Resulting fluid-filled cavity

• _____potent ICM cells undergo _______

  • 1. _______ progenitor cells

    • (→ epiblast → embryo proper)

  • 2. _______ progenitor cells

    • (→ PE)

• _____potent trophectoderm cells ________

• Now we are ready for physical layer separation

• Pluripotent ICM, determination

  • Epiblast

  • Primitive endoderm (PE)

• Multipotent trophectoderm, proliferate

Mammal - Layer separation

• ________ation & Blasto_____ elongation

  • Oval blasto_____ = rodent; undergoes dramatic elongation

• _______ / _______ formation

  • _______ = most mammal

  • _______ = rodent

• Hypoblast

  • ________ structure

  • Prepares _______ for explosion of cellular complexity

  • Well-studied in birds; not so much for mammals

  • Mammalian pattern = analogous structures to avian, but different processes & terminology (________ differentiates into Hypoblast/VE)

• Implantation & Blastocyst elongation

  • blastocyst

• Hypoblast / Visceral endoderm (VE)

  • Hypoblast = mammal

  • VE = rodent

• Hypoblast

  • Transitory

  • embryo

  • primitive endoderm (PE)

Mammal - Layer separation conclusion

• Hypoblast/VE = _______ layer/ sheet of cells

  • Forms from ______

  • Does not contribute to _______ or _______

• Epiblast = formerly _______

  • (→ embryo _______)

• ________ = Cavity btwn epiblast & hypoblast/VE

• _______ (bilaminar) = Epiblast + Hypoblast/VE

• _______-_______ axis

• Transient

  • PE

  • embryo / extraembryonic membranes

• ICM

  • Embryo proper

• Blastocoel

• Blastula

• Anterior-posterior axis

Mammal - Layer formation

• ______&______ progenitors undergo differentiation

  • Express diff ______

  • Separate into _____

• Multipotent ________(________) cells continue to proliferate

• Epiblast & PE

  • proteins, layers

• trophectoderm/trophoblast

Mammal - Layer formation

• Elongation

  • During elongation, cells w/in ________ proliferate

  • ______/_____ begins to line the inner side of blast______

    • Formation of _____ sac & yolk sac _______ (multipotent endoderm cells)

    • _______ splits ⇉ ______/Hypoblast + ______

• hypoblast

• hypoblast/PE, blastocoel

  • yolk sac & yolk sac endoderm

  • PE splits ⇉ VE/Hypoblast + YSE

Mammal - Layer formation

• Elongation

  • Epiblast forms _______ cavity

    • Proximal cell lineage (closest to maternal body) = _______

      • Epiblast undergoes _______ to form ________ below amnion

    • Distal cell lineage (farthest from maternal body) = _______ 

      • Cells on underside of amnion are still _______ cells

• amniotic cavity

• Proximal = Amnion

  • cavitation, amniotic cavity

  Distal = Epiblast 

  • epiblast

Mammalian blasto______ diversity among species

blastocyst

Mammal - Layer formation

• 1 more function:

  • Establishing anterior-posterior axis

    • based on rodents

    • 1. Continued cell ________

    • 2. Determination & differentiation among _______ cells

      • ________ splits ⇉ ________/Hypoblast + ________

    • 3. Distal ________ becomes activated

      • (most distal point of _____)

    • 4. DVE migrates “up” one side of blasto______

      • => _______ visceral endoderm

      • as cells expand/proliferate, they move up one side; this is now called ________

        • proliferation/movement of ________

      • ______’s location signals anterior of embryo

• proliferation

• PE

  • PE ⇉ VE/Hypoblast + YSE

• DVE

  • VE

• blastocyst

  • => Anterior VE

  • AVE, AVE, AVE’s

Gastrulation

• Gastrulation from “gastric”, meaning stomach

  • 1st population of cells will differentiate & become _______ of gut

• Highly integrated tissue ________ & loss of ________

  • Places cells in appropriate ________ to trigger differentiation

  • Only process that begins @ _______ end of embryo & proceeds _______

  • Results in ___laminar embryo of multipotent 1^o germ layers:

    • ______derm

    • ______derm

    • ____ ______derm

• Well‐documented in birds; not so much for mammals

• lining of gut

• migrations, pluripotency

  • position

  • posterior → anteriorly

  • trilaminar

    • Ectoderm

    • Mesoderm

    • Definitive Endoderm

Gastrulation

• Results in tri‐laminar embryo of multipotent 1^o germ layers:

  • 1. Ectoderm of ____blast

  • 2. Mesoderm indirectly from ____blast

  • 3. Definitive endoderm replaces ____blast/____blast

• (all 3 germ layers initially come from ____blast)

• epiblast

• epiblast

• hypoblast/ endoblast

(epiblast)

Gastrulation

• Occurs in 2 phases

  • 1. ________

    • Primitive streak formation

  • 2. ________

    • Primitive streak degeneration

• 1. Ingression (formation)

• 2. Regression (degeneration)

Gastrulation

• Primitive streak

  • Site of _______ in epiblast

    • So many cells that they overflow & “fall down” into ______ of embryo 

  • Serves as passageway for ________ cells to enter deeper layers of embryo

    • Massive cell _______

• ingression

  • blastocele

• epiblast

  • proliferation

Gastrulation

1. Ingression

   • Epiblast cells collectively descend into _________

     • Undergo determination into _____derm & _____derm*

       • * These cells straddle between true _____potency & ______potency (e.g., all 3 stem cell lines vs 1 stem cell line)

       • Lose ability to express ____derm genes

   • Begins _______/caudally & elongates _______/rostrally

• primitive streak

  • mesoderm & endoderm

    • pluripotency & multipotency

    • ectoderm

• posteriorly → anteriorly

Gastrulation

1. Ingression

• Koller’s sickle (KS)

  • Clustering of cells beginning to form from _____&_____

  • Group of ________ forming the vanguard of posterior __________

    • Appears ________‐shaped from dorsal view

    • Crucial to avian _________ formation

    • Enables _____blast to replace _____blast (ie enables _____blast formation)

• AO & MZ

• Blastomeres, posterior marginal zone

  • crescent

  • primitive streak

  • endoblast, hypoblast, endoblast

Gastrulation

1. Ingression

• Hypoblast = _________ cannot form (induction)

  • (induction = interaction btwn 2 cells / tissues in which 1 affects the _________ of the other)

• Hypoblast replaced by sheet of ______blast cells (_____blast)

  • Absence of hypoblast => epiblast cells overlying __________ condense

    •  Marks beginning of gastrulation

• Endoblast formation:

  • ________ cells migrate from _______ & form a layer

  • Push hypoblast cells _______ly as they migrate forward

  • ________ structure

• Primitive streak

  • differentiation

• endoblast , Endoblast

  • Koller’s sickle

• Endoblast, Koller’s Sickle

  • anteriorly

  • Temporary

Gastrulation

1. Ingression

• Primitive streak 

  • Hypoblast replaced by ________

  • Epiblast cells above ______ ⇉ groove (primitive streak)

    • Triggers _______ across epiblast

      • → migrated ______ cells get replaced by sheet of future _____derm cells

  • Cells tumble over edge of primitive streak & fall into ________

• Endoblast

• KS

  • epiboly

    • epiblast, ectoderm

• blastocele

1) Ingression: Primitive streak 

• As cells tumble over edge of primitive streak & fall into blastocele…

  • some undergo _______ & lose more potency & only able to express _____derm cells (migrating cells = _____derm)

  • Others fall all the way down the blastocele & hit the endoblast; start displacing _______ cells & undergo determination to become _______ cells

  • So in the course of primitive streak formation:

    • gradual loss of potency of a particular population of _______ cells

    • as they first fall in, they lose ______dermability,

    • ones that hang out in the middle of the blastocele are going to become ______derm

    • ones that fall to bottom undergo determination & can no longer make _____derm / _____derm, (can only express _____derm); these displace _____blast

• determination, mesoderm

• endoblast, endoderm

—

• epiblast

  • ectodermability

  • mesoderm

  • ectoderm / mesoderm, endoderm; endoblast

1) Ingression: Primitive streak 

• Migrated epiblast cells form 2 new layers in blastocoel:

  • 1. ________ (replaces endoblast)

  • 2. ________

  • (lose potency, cant become ________ cells anymore)

• Migrated cells will become:

  • 1. ________

  • 2. ______ process & _______

    • (cells of _______ lying directly below primitive streak differentiate into _______)

  • 3. ________

• Endoderm

• Mesoderm

• (ectoderm)

• Migrated cells will become:

  • 1. Mesoderm

  • 2. Head process & notochord

    • (mesoderm, notochord)

  • 3. Endoderm

1) Ingression:

• Primitive streak Completion

  • Forms ________ at _______ end

    • ________ = Specialized, thickened region in primitive streak

    • _____&_____ sides of embryo become fully determined

• Hensen’s node @ anterior end

  • Hensen’s node

  • Left & right

Gastrulation

• Summary: Primitive streak ingression

  • Cell migration results in:

    • ______derm

    • ______derm

      • (displaces endoblast (hypoblast/all VE))

    • Epiboly gives rise to _______ in epiblast

  • Epiblast loses ______ outward → inward

• Mesoderm

• Endoderm

• Ectoderm

—

• potency

Mammal Gastrulation

• Not entirely sure what happens w mammals

• Possible that posterior ________ play analogous role as ________

• Posterior Visceral Endoderm (PVE), endoblast

Gastrulation = bilaminar ________ becomes trilaminar _______ (loss of potency)

• Blastula (bilaminar; 2 layers)

  • ________

  • ______/______

• Gastrula (trilaminar; 3 Germ layers)

  • _______ (epiblast)

  • _______

  • _______ (replaces endoblast/ hypoblast/ all VE)

bilaminar blastula → trilaminar gastrula

—

• Epiblast

• Hypoblast/ VE

—

• Ectoderm

• Mesoderm

• Endoderm

Gastrulation 

2. Regression

• Primitive streak starts to ________

  • Moves ________ (or just _____) from center of epiblast to more _______ position

• As primitive streak regresses, ________ moves from _______→______

  • From this point on, development begins @ _______ and moves _______

  • Leaves behind “______” of notochord (at ______)

• As primitive streak regresses, completes _______

• degenerate

  • Hensen’s node (node), center → posterior

• Hensen’s node, anterior → posterior

  • anterior, posteriorly

  • head process, anterior

• notochord

Gastrulation 

2. Regression

• Regression initiates ________ by creating head process & notochord 

  • (________ begins before _______ concludes)

• Regression concludes w formation of ______ region of embryo (where ________ stops)

• neurulation

  • (neurulation, gastrulation)

• anal, hensens node

Gastrulation Summary

• Gastrulation occurs in 2 phases:

  • 1. Primitive streak formation

    • 1st wave: Formation of 3 _______ lineages (_____, _____, & _____)

      • Displacement of _____blast/______/_____

    • 2nd wave: Further migration of _______

  • 2. Primitive streak regression

    • Creates ________

• Embryo exhibits distinct gradient (_____to_____)

  • ______ more mature than ______

• Result = _______ (trilaminar)

• germ cell, (ectoderm, mesoderm, endoderm)

  • hypoblast/endoblast/VE

• mesoderm

—

• notochord

—

• anterior‐to‐posterior

  • Anterior, posterior

• Gastrula

Neurulation

• Formation of spinal cord ________ from epiblast _______ 

• Next major event “following” _______

  • Begins during latter portion of _______, as primitive streak ______

• precursors, ectoderm 

• gastrulation

  • gastrulation, regresses

Neurulation

• Morphological boundaries:

  • Begins w 1st traces of _______ formation

  • Ends with closure of _______

• neural plate

• neural tube

Neurulation

• Morphological boundaries:

  • Begins w 1st traces of neural plate formation

    • _______ sends signals to epiblast cells above it to become _______ cells

    • _______ invaginates to become _______

  • Ends with closure of neural tube

    • Followed by _______ development

• notochord, neural plate

• neural plate, neural tube

• brain

Neurulation

• ______ events + formation of _______

  • Neural tube = rudiment of ________

    • (becomes brain & spinal)

  • ________ process = specific to chordates

• Induction, neural tube

  • CNS

    • Becomes brain & spinal

  • Developmental

Neurulation

• Notochord

  • notochord = Mesoderm cells activated by _________ form a rod of _______ under midline of _______

  • Once formed, notochord induces/sends messages to epiblast _______, which initiates _______ formation

  • Notochord = _______ structure

    • Becomes encased in ______

• Hensen’s node, mesoderm, epiblast

• ectoderm, CNS

• Temporary, vertebrae

Neurulation

• Primordial CNS = from ______

• Neural tube formation = via ________

• ectoderm

• invagination

Neurulation

• Neural tube formation via invagination

  • ______ induces epiblast ______ ↠ neural _____ cells

  • Bending of neural _____ into neural _____

  • Closure/pinching off of neural _____ into neural _____

• Notochord, epiblast ectoderm, neural plate

• plate, groove

• groove, tube

Neurulation - Sequence of events

(anterior → posterior)

1. During Ingression, epiblast cells differentiate into ________ w/in blastocoel

2. _________ activates mesoderm to form ________ as primitive streak _________

3. Notochord induces overlying ________ to form neural ______

4. Neural ______ invaginates into a ______, then pinches off as a closed neural _______

5. Within neural ______, cells proliferate & differentiate in _______

   • _____teriorly – Series of thickenings & constrictions => Presumptive ______

   • _____teriorly – Remains tube‐like => ________

1. mesoderm

2. Hensen’s node, notochord, degenerates

3. ectoderm, neural plate

4. plate, groove, tube

5. tube, CNS

   • Anteriorly; presumptive brain

   • Posteriorly; spinal cord

Neurulation - Brain Development

• Neural _______ constricts & thickens via cell ______

  • Regional differentiation & proliferation

  • Progresses from ____ part brain to ____ part brain

• Walls = Neural tube _______

• tube, cell division

  • 3 → 5

• ectoderm

3 part brain:

• Prosencephalon = ________

• Mesencephalon = ________

• Rhombencephalon= ________

• forebrain

• midbrain

• hindbrain

3 part brain → 5 part brain:

• _______ (________)

  • → Tele ncephalon

  • → Dien cephalon

• _______ (________)

  • does not divide

• _______ (________)

  • → Meten cephalon

  • → Myen cephalon

• Forebrain (prosencephalon)

• Midbrain (mesencephalon)

• Hindbrain (rhombencephalon)

Distal visceral endoderm (DVE)

• Region of rodent VE at most distal end of _______ that undergoes activation to initiate ____________ formation

Anterior visceral endoderm (AVE)

• DVE after it has migrated up one side of the rodent _______ to signal the anterior of the developing _______

• blastocyst

• anterior‐posterior axis

—

• blastocyst, embryo

Blastocyst

• Mass of cells in the ________ egg that undergoes rapid cell division during ________

Blastoderm

• Mass of cells in the ________ egg that undergoes rapid cell division during ________

Blastomere

• Cell produced by cleavage that has a completely ________ cell membrane

• mammalian, cleavage

• avian, cleavage

• enclosed

________

• Bilaminar mass of rapidly dividing cells

• consists of epiblast + hypoblast/VE

Blastula

Endoblast

• Transient sheet of endoblast cells from ____________ that displaces the hypoblast and initiates primitive streak formation

• contributes to ______ stalk

• [NOTE: Some sources will refer to this as the “hypoblast” or “definitive hypoblast”]

Epiblast = cells that create _______

Epiboly = increase in # of cells on _____ surface

• posterior marginal zone

• yolk sac

—

• embryo

• outer

Gastrulation

• Process involving massive cell _______ with highly integrated cell migration that results in differentiation of primary _________

• accompanied by loss of _________

Gastrula

• _____laminar embryo that consists of primary germ layers

  • + Ectoderm (of _______)

  • + Mesoderm

  • + Endoderm

• proliferation, germ layers

• pluripotency

—

• Trilaminar

• epiblast

Hypoblast = transient sheet of cells; forms below ______

• Avian hypoblast:

  • Sheet of delaminated _______ cells

  • replaced by _______ cells from posterior ________

  • may participate in ______ formation

• Mammalian hypoblast (most):

  • Differentiates from & forms when ________ splits

• epiblast

—

• Area Pellucida (AP)

• endoblast, posterior Marginal Zone (MZ)

• PGC

—

• primitive endoderm (PE)

________ = temporary rod of mesoderm that triggers neural tube formation

Neural plate

• ectodermal cells of epiblast that undergo induction by _______ & undergo determination to begin __________ formation

Neural groove

• ________ cells that are undergoing ingression & invagination into _______

• (ingression = division/migration of cells into internal area to form separate layer)

Neural tube

• outcome once ________ completely separates from epiblast; concludes _________

• Notochord

• plate = notochord, neural tube

• groove = neural plate cells, blastocoel

• tube = neural groove, neurulation

Primitive endoderm

• Cells from the _______ that will eventually differentiate & split into the ______/______ & _________

Primitive streak

• Condensation of _______ cells that become a groove due to ingression of cells into _______

• ICM, hypoblast/VE, yolk sac endoderm

• epiblast, blastocoel

Regression

• Primitive streak _______

• Begins _______ and moves _______

• Initiates _______

degeneration

anterior, posteriorly

neurulation

Subgerminal space

Fluid‐filled cavity below ________

area pellucida (AP)

Visceral endoderm (VE)

Rodent _______ that differentiates from / is formed when primitive _______ splits in 2

hypoblast

endoderm

What needs to occur immediately before neural tube formed?

Notochord-induced epiblast ectoderm must differentiate into neural plate cells