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30 Cards in this Set

  • Front
  • Back
Why do we study frogs/amphibians?
- big eggs (easy to see/manipulate)
- they are easy to get/grow
Where does sperm bind on the frog egg? What does this cause to happen? What is now established?
Sperm bind about 30o N of equator

This causes the cortex to rotate towards where the sperm bound, exposing gray crescent

The axis of symmetry is now set up - the sperm bound on the ventral side
How does frog cleavage start & what is unique about it? What happens to the top vs bottom cells?
Meridinal
Meridinal
Equitorial (only in animal)

Division slows down at yolk so 2nd division starts b4 1st is finished

Top cells divide much more quickly so become smaller & more numberous
Where does the blastocoel form? (frog)
Forms in the animal hemisphere by the expansion of the space made by the 1st cleavage
What molecules hold the cells together? (frog)
E-cadherins
Where does amphibian gastrulation occur?
At site of gray crescent
What dictates what will become vegetal cells? (frog)
Transcription factors VegT & Vg1 (without these, will be epidermis instead of endoderm)
What are the three movements of cells (steps) in frog-gastrulation?
1. invagination (bottle cells)
2. involution (prechordal plate)
3. epiboly (chordamesoderm)
What is bottle cell invagination? (frog)
- migrates inward
- specialized group in this region
What is involution (prechordal plate)? (frog)
- creates dorsal blastopore lip
- cells 'turn around and head in'
- moves from a straight line to a curve, then to a circle (yolk plug)
What dives initial gastrulation in frogs?
IMZ cells (involuting marginal zone)
What is epiboly (chordamesoderm)?
(frog)
- outer ectoderm
- extending outward to cover endoderm
- embryo surrounded by ectoderm
What experiment was done to find out 'the organizer'?
(frog)
Spemann forced a zygote to divide where the gray crescent was only on one side. The side without did not develop, so this showed that the gray crescent contained 'the organizer'.
What happens when a dorsal blastoporal lip is transplanted elsewhere on the blastula?
(frog)
TWO gastrulations occur!
What happens if the animal region is put directly on top of the vegetal region?
(frog)
The animal region will become the mesoderm!
What tells the organizer to become the organizer?
What is this composed of?
(frog)
The Nieuwkoop center

This is where the mesoderm signal (from underlying endoderm) and the dorsal signal (B catenin from gray region) overlap
What are the details of the 'dorsal signal'?
(frog)
B-catenin is expressed everywhere
But Disheveled only expressed in area that moves to side when cortex rotates....

Wnk activates
Frizzled activates
Dishevled INHIBITS
GSK-3 from breaking down B-catenin

So B-catenin is high conc in this region - this is the DORSAL SIGNAL
What are the functions of the organizer?
(frog)
1. Self-differentiate dorsal mesoderm (prechordal plate, chordamesoderm)
2. Dorsalize surrounding mesoderm
3. Dorsalize ectoderm (neural tube)
4. Initiate gastrulation movements
What type of cleavage is frog cleavage?
displaced radial mesolecithal holoblastic
What type of cleavage is bird cleavage?
discoidal telolecithal meroblastic
What is the name of the layer on the yolk that becomes the embryo? (bird)
Blastodisk/blastoderm
How does the blastoderm form? (bird)
A layer of cells on top of yolk divide & become 5-6 layers thick
Then all but the top layers & some on the edges die off, leaving 1 cell layer thick

1 cell layer thick - area pellucida
More cells on edges - area opaca
What is the precise layer of cells in the blastoderm that will become the embryo? (bird)
Epiblast
What are the 2 migrations that form the hypoblast? (bird)
1. Delamination
2. Epithelial sheet from posterior margin
What happens in delamination? (bird)
Epiblast cells delaminate & move to form a 2nd layer between epiblast & yolk as hypoblast islands

Cells from the posterior margin migrate forward and link the islands

Forms the hypoblast
What is the area between hypoblast and epiblast? (bird)
Blastocoel
What happens during secondary hypoblast formation? (bird)
Cells originating from Koller's sickle in the posterior margin move forward & push the primary hypoblast cells forward

As the 2nd cells move forward, signal the epiderm above them to thicken & differentiate (& narrow - convergent extention)
& form PRIMATIVE STREAK
Where does the primitive groove form & what else forms there, and what does the essentially act like? (bird)
Primitive groove forms at anterior end with primitive pit

Primitive groove acts like blastopore
What is the order of ingression through Henson's node? (bird)
1st - head in, pharyngeal endoderm
2nd - head in & up, head mesenchyme & prechordal plate
3rd - head in, chordamesoderm
What happens as the cells move inwards? (bird)
pushes out hypoblast