Coding 12 Flashcards
Which pole contains more yolk?
The vegetal pole
What does the vegetal pole do?
It determines the lower part of the egg however the higher yolk content slows cell division
What happens when the sperm central enters the egg?
It organizes the egg’s microtubules so they are parallel to the vegetal cytoplasm
What does cortical rotation expose?
The inner cytoplasm opposite to sperm entry
What is the gray crescent?
Where gastrulation bgins and makes the dorsal portion
What type of cleavage occurs in frogs and salamanders?
Radial holoblastic
What is unequal radial holoblastic cleavage?
Whent the second division is taking place in the animal pole but the first division is still being completed in the first vegetal pole
What layer does the animal pole make?
Ectoderm
What layer does the vegetal pole make
Endoderm
What layer do the cells below the cavity form?
Mesoderm
What are the 3 main steps in gastrulation?
- Bring the embryo in through invagination most likely to make the endoderm
- Surround the embryo to make the ectoderm
- Place the mesoderm between the endoderm and ectoderm
What forms when the cells invaginate the egg?
Blastopore
Following the blastopore what forms?
The blastopore lip
What do the cells on the outside form?
Ectoderm
What happens through involution?
The cells are brought in to form the endoderm and the yolk plug is the final bit to be enveloped
What does beta catenin produce?
The anterior-posterior axis
Which proteins are secreted that form the dorsal-ventral specification?
BMP
What did the calcium waves control?
Mitosis and integrated spindles and cytoskeleton movement
What is the left-right axis?
This axis forms when there are certain genes that are active in one half and not the other
What makes the dorsal lip blastopore?
The organizers
What happens to the cells that gastrulate through the organizer?
They become the mesoderm
What is the grey crescent?
The region 180 degrees from the sperm entry
What happens at the sperm entry?
The centrioles are brought in and there is a microtubule formation
What is the corticol rotation?
There is a 30 degree rotation using the microtubules
What are the key movements in Xenopus gastrulation?
- Epiboly
- Vegetal rotation
- Invagination
- Involution and migration
- Convergent extension
What is the vegetal rotation?
When the vegetal cells push to the blastocoel
What is the blastocoel?
The cavity that forms
What are bottle cells?
They are cells that intiate gastrulation and form the blastopore
What do the first cells to involute form?
- Pharyngeal endoderm
- Prechordal plate - head mesoderm
- Chordal mesoderm - notochord
- Somitic mesoderm
What was the main finding of the Spemann experiment?
Exploring how the gray crescent forms the dorsal and the dorsal lip leads to organizers generating the axes
What are the signals that induce the organizer formation?
- Nuclear beta catenin
- Nieuwkoop centre
Where is chordin made?
The organizers at the dorsal lip blastopore
What do the vegetal cells induce?
The formation of the mesoderm above the endoderm it forms
When is Vg1 translated?
The late blastula stage
What does Vg1 induce?
The Wnt inhibitor dickkopf
What type of genes are Vg1 and VegT?
MEG in the ventral region
What does VegT activate?
Nodal genes
What do nodal proteins activate?
Eomesodermin in the presumptive mesoderm
What does SMAD2 and eomesodermin activate?
VegT in the nuclear expression of the mesoderm
What does VegT do?
Controls the mesoderm and endoderm formation
What happens without VegT?
No blastopore, gastrulation, DV axis, AP axis
Where do the nodal gene products diffuse to?
Animal pole
What makes beta catenin?
MEG
Where is beta catenin found?
Dorsal
What is synergy?
The transcription factors working together to activate organizers
What is the process with activating organizers using beta catenin?
- Wnt 11
- Disheveled
- Beta at the dorsal during cleavage binds to Tcf3
- Activates siamosis and twin
- Interacts with SMAD2 (from VegT)
- Activates organizer genes
What happens if there is too much noggin?
Dorsal and anterior form at the expense of the ventral and posterior regions
Which inhibitors are made at the pharyngeal endoderm?
Wnt
Which inhibitors are made at the prechordal plate?
Wnt and BMP
Which inhibitors are made at the notochord?
BMP
For brain formation which proteins do you need?
No Wnt or BMP
For spinal chord formation which proteins do you need?
Wnt only
For epidermis formation which proteins do you need?
Wnt and BMP
