Frogs Flashcards
Which side of the embryo does the organizer form?
The dorsal side of the embryo.
What can the organizer induce cells into?
Neural ectoderm
What are three spots on the early frog blastula that can be distinguished by their color?
The Pigmented animal region, gray crescent, and vegetal region.
Why is the gray crescent visible?
The subcortical crescent is visible after the outer surface of the zygote rotates.
What happens without inclusion of the gray crescent?
You do not have formation of axial structures, and you get a “belly-piece”: Bauschstuck, or Chicken McNugget
What is the orientation of the cortical rotation, and crescent with respect to the sperm entry point?
The sperm entry point is defined as the ventral side. The cortex rotates 30 degrees, the gray crescent is on the dorsal side.
What evidence is there that cortical rotation is a required movement?
A UV irradiated zygote cannot undergo rotation, and ends up as a chicken mcnugget. If tipped in wax, the embryo is rescued.
What cellular component is necessary for cortical rotation?
Microtubules
What happens with an excess of microtubules?
excess of anterior structures.
Are frog eggs in zero gravity normal, or abnormal?
Normal. Microtubules and motors are sufficient for rotation.
What induces functional organizer?
Dorsal vegetal cells from the Nieuwkoop Center.
Dorsal endoderm induces dorsal endoderm. What evidence is there for this?
If you remove the Mesoderm from a blastula, the ectoderm that is now touching the endoderm turns to mesoderm.
What are some molecular accumulations in the dorsal endoderm?
Release of Disheveled, GSK-3 (inhibits GSK-3B which would normally break down B catenin), and Wnt 11
What can cause a Nieuwkoop Center to form?
B catenin
What happens when you deplete B catenin?
YOU have centralized embryos.
What does B-catenin cause expression of by the Nieuwkoop Center?
Siamois, and twin genes.
What does siamos over expression lead to ?
A second axis.
Mesoderm Induction : Step 1
Beta catenin leads to expression of nodal related proteins like VegT and Vg1
Mesoderm Induction: Step 2
Vegetal cells create a spectrum of D-V differences
Mesoderm Induction: Step 3
Mesoderm is induced by vegetal cells that contain those nodal proteins in a spectrum.
How does the Organizer work? Broad
The Organizer inhibits centralizing growth factors
What are some ventral growth factors?
BMPs and Wnt 8
What are some Organizer factors?
Chordin, Noggin, FrzB,Dikkopf, and Cerberus
What Organizer factors inhibit BMPs?
Noggin and Chordin
What Organizer factors inhibit Wnt 8?
FrzB, Dickkopf, and Cerberus.
What type of tissue does BMP usually lead to?
epidermis
Without ventral signals, ectoderm influenced by the Organizer becomes
neural ectoderm
After gastrulation in the frog, Organizer mesoderm lies where in relation to ectoderm?
In a layer beneath the ectoderm.
Difference between superficial and deep cells
Superficial cells are on the surface as epithelial cells, and are joined by junctions. Deep cells are more loosely organized, and can move around more independently.
Dorsal blastopore lip formation
Induced by invagination from bottle cells
What do the deep cells, superficial cells, and dorsal mesoderm of the marginal zone form respectively?
Deep cells form mesoderm, superficial cells form endoderm, and the dorsal marginal zone mesoderm form the Organizer.
NIMZ
Non-involuting marginal zone
What do the dorsal and ventral NIMZ form?
Dorsal non involuting marginal zone become neural ectoderm, and the ventral non-involuting marginal zone become epidermis.
IMZ
Involuting marginal zone
What do the deep cells and superficial cells of the IMZ become?
Deep cells of IMZ become organizer mesoderm, and superficial dorsal IMZ becomes roof of the archenteron
What happens to bottle cells during gastrulation?
They constrict to start the dorsal blastopore lip, and spread to the roof of the archenteron.
LEM
leading edge mesoderm, involutes first, becomes head, heart, and liver
What morphogenic movement do the animal cap cells perform?
Epiboly via radial intercalation
What morphogenic movement do the bottle cells perform?
Invagination by apical constriction, then respreading
What morphogenic movement does the non-involuting marginal zone perform (NIMZ)?
Radial intercalation, followed by convergent extension
What morphogenic movement does the involuting marginal zone perform (IMZ)?
Convergent extension
What experiment shows convergent extension of the IMZ and NIMZ?
Keller’s excising of NIMZ and IMZ produces extension into neural ectoderm and mesoderm.
What mechanics underly convergent extension?
Cell become polarized extending protrusions along the axis of extension via myosin II and the planar cell polarity pathway.
What kind of signaling is necessary for convergent extension?
Planar Cell Polarity Pathway
What kind of motor protein is required for convergent extension?
Myosin II
How does leading edge mesoderm move, and what orients the process?
The leading edge mesoderm extends lamelopodia that crawl along oriented fibronectin fibrils that are attached to the inner face of the blastocoel
What is special about the axolotl ambystoma mexicanum?
Useful for studying leading edge mesoderm, and it exhibits neoteny, (becomes reproductively mature while maintaining juvenile (larval) characteristics.
What are fibronectin fibrils usually oriented as?
From anterior to posterior
How do you distrupt fibronectin fibrils, and what happens?
You add antibodies that are not polarized, and mesoderm can no longer migrate or involute. You get a brain looking animal pole.
