Chapter 8 Flashcards
Why amphibians as a model organism?
- large cells
- rapid development
- easy transplantation & observations
why NOT amphibians as model?
terrible genetics
- tetraploidy (alter 4x genes)
- massive genome
- very few mutants
what are frogs called? salamanders?
anurans
urodeles
types of anurans? types of urodeles?
xenopus laevis, x. tropicalis, rana pipens
ambystoma mexicanum, a. maculatum, notophthalmus viridescens
what axis does the spot of sperm entry become?
ventral side (belly)
what happens once the sperm enters an amphibian embryo?
sperm centriole organizes microtubules that push proteins toward dorsal side (becomes darker)
what is the cortical rotation?
outer layer rotates 30 around inner cytoplasm & exposes gray crescent (animal pole, dorsal side)
- where gastrulation will begin
what type of cleavage do amphibians have?
displaced radial
- vegetal divisions are delayed, hard to divide thru yolk
what helps to prevent the blastocoel cells from induction?
tight intercellular junctions (watertight seal)
- the help of EP-cadherins
what is Nieuwkoop (1969) do?
grafting experimenter #1
- cut off top of blacocoel (animal cap) and move it to the vegetal pole
- animal cap normally becomes ectoderm
- when being moved, it became mesoderm instead
describe when the MBT starts in amphibians
at the 12th division
- embryo starts using it’s own genes and activates the genome
- differential gene expression, blastomere motility
describe the experiment that shows when the cell knows to be in the MBT
removed cytoplasm from cells so there were less cytoplasmic proteins
- determined there were demethylated promoters that started MBT
what is VegT?
maternal mRNA part of endoderm in vegetal pole
- binds to demethylated promoters to allow for new genes to be activated
- secrete endoderm-forming genes & mesoderm-inducing factors
- turns on Nodal
what are Nodal and Vg1?
maternal mRNA paracrines
- in the endoderm of vegetal pole
- turns on mesoderm
what are the three goals of amphibian gastrulation?
bring endodermal tissues inside
surround w/ ectoderm
coordinate mesodermal cells in b/w
what are bottle cells?
move inside blastocoel cavity & pull along a line of cells w/ them
- leave an indentation behind that becomes the primitive gut
- forms the dorsal blastopore lip
what is a marginal zone? what are the two types?
area where cells debate if they stay outside or move in
- involuting marginal zone (IMZ)
- non-involuting marginal zone (NIMZ)
what is the IMZ?
cells go inside
- form mesoderm and makes the blastocoel start to disappear by making the archenteron
- induces cells to become nervous tissue
what is the NIMZ?
cells stay put
- epiboly of the cells to push the outer layer together to cover the yolk
- mitosis & migration
describe the steps of amphibian gastrulation
- bottle cells invaginate to form dorsal blastopore lip
- following cells invaginate to form archenteron
- IMZ cells involute to form mesoderm
- archenteron displaces blastocoel
- ventral & lateral bottle cells ingress
- epiboly of NIMZ cells
- yolk plug forms
- blastocoel obliterated
what is fibronectin?
apart of inner side of blastocoel roof
- allows a highway for IMZ cells to follow
what did Hans Spemann do?
grafting experimenter #2
- used his daughters hairs to show blastomere potency & blastomere non-equivalence (1938) during cleavage
- determined when presumptive neural ectoderm is induced
- inspired his undergrad student Hilde Mangold to experiment (won a Nobel Peace Prize)
describe how Hans Spemann showed blastomere potency
used daughter’s thin hair to tie around embryo (8-cell)
- didn’t split completely, only pinched
- caused all nuclear divisions to occur on one side
- waited for cell to divide to 16-cell & pinched off completely
- generated 2 whole animals
- blastomeres are totipotent & can make every part of an embryo
describe how Hans Spemann showed blastomere non-equivalence
used daughter’s hair to tie around embryo before first division
- made the first tie exactly the same way as blastomere potency experiment, but he made a second tie so the gray crescent was only on one half
- developed one normal embryo, and a belly piece (endoderm)
- w/o gray crescent, cells aren’t totipotent (not all cells can develop an embryo on it’s own)
describe the experiment of the color newts and when presumptive neural ectoderm is induced by Hans Spemann
took the cells of the presumptive neural ectoderm from an early gastrula
- moved them to a new spot on the embryo
- cells became epidermis, no longer NS tissue
took the cells of the presumptive neural ectoderm from a late gastrula
- the IMZ cells had already migrated under ectoderm & induced cells above
- developed a NS in a spot it wasn’t suppose to
who is Hilde Mangold?
grafting experimenter #3
- undergrad student of Hans Spemann
- won a Nobel Peace prize but died before it was given to her
- determined the function of IMZ cells and created the Spemann’s Organizer
describe Hilde Mangolds experiment with grafting IMZ cells
took IMZ cells & grafted them into a different spot
- spot where IMZ cells were moved to started to form NS
- due to the cells releasing inducing factors to the cells above
- OG blastopore lip is telling the cells about to be NS too
- grew two embryos conjoined (share a gut, have two NS)
describe the function of the dorsal blastopore lip region that was discovered by Hilde Mangolds
induce dorsal axis & notocord / neural tube formation
- known as Spemann’s Organizer
what is the function of Nieuwkoop Center? describe how it works (step by step)
induces the organizer to be dorsal
- disheveled is produced from maternal mRNA
- during cortical rotation, dsh moves to the dorsal side
- Dsh blocks Gsk-3 & allows b-catenin to accumulate
- b-catenin & VegT creates lots of Nodal
- nodal makes a BMP4 gradient (makes skin)
- organizer blocks BMP by making goosecoid
- BMP is low on the dorsal side
- allows for the NS to form on the dorsal side
