Early Development and axis formation in Amphibians Flashcards
organisms of choice for experimental biology
amphibian embryos
suited for transplantation experiments due to their large cells and rapid development
salamander and frog embryos
new molecular techniques that allowed researchers to return to studying amphibian embryos and to integrate molecular analyses of development with earlier experimental findings
in situ hybridization
antisense oligonucleotides
dominant negative proteins
it could be induced to mate throughout the year, thus replacing Rana frog
Xenopus laevis
has four copies of each chromosome rather than the more usual two, and takes 1-2 years to reach sexual maturity
Xenopus laevis
It has all the advantages of X. laevis plus it is diploid and reaches sexual maturity in a mere 6 months.
X. tropicalis
Cleavage in most frog and salamander embryos is _ and _ just like echinoderm cleavage
radially symmetrical and holoblastic
The amphibian egg contains much more _,that is concentrated in the vegetal hemisphere, which is an impediment to cleavage.
yolk
The first division of cleavage in amphibians begins at _ and slowly extends to _.
begins at animal pole, extends at vegetal region
bisects the gray crescent and then slows down to a mere 0.02-0.03 mm per minute as it approaches vegetal pole
cleavage furrow
first and second cleavage
meridional
first and second cleavage: meridional; third cleavage: _
equatorial
due to the vegetally placed yolk, the cleavage furrow in amphibian eggs is not actually at the equator but is dispalced toward the animal pole, it divides the frog into
4 small animal blastomeres (micromeres)
4 large blastomeres (macromeres)
in vegetal region.
The unequal holoblastic cleavage establishes two embryonic regions:
rapidly dividing region of micromeres in animal pole
slowly dividing vegetal macromere area/
An amphibian embryo containing 16-64 cells is commonly called
morula
what is the plural of morula
morulae
where did morula came from
Mulberry
At 128-cell stage, the blastocoel becomes apparent, and the embryo is considered a
blastula
The formation of the blastocoel has been traced back to the
first cleavage furrow
He demonstrated that in the frog Xenopus laevis, the first cleavage furrow widens in the animal hemispehere to create a small intercellular cavity that is sealed off from the outside by tight intercellular junctions.
Kalt (1971)
2 major function of blastocoes in frog embryos
permits cell migration during gastrulation
prevent the cells beneath it from interacting prematurely with the cells above it
Who took the embryonic newt cells from the roof of the blastocoel, in the animal hemisphere, and placed them next to the yolky vegetal cells from the base of the blastocoel, these animal cells differentiated into mesodermal tissue instead of ectoderm
Nieuwkoop (1973)
keeps the blastomeres together while the cells are activity dividing
cell adhesion molecules
one of the most important cell adhesion molecules
EP-cadherin
The mRNA for EP-cadherin is supplied in the ______
oocyte cytoplasm
If the message is destroyed (by injecting oligonucleotides complementary to this mRNA in the oocyte), the EP-cadherin is not made and the adhesion between the blastomeres is dramatically reduced resulting in the obliteration of the blastocoel
Heasman et al
oldest and one of the newest areas of experimental embryology
amphibian gastrulation
The study of amphibian has been complicated by the fact that there is no single way amphibians gastrulate. Different species employ different means toward the same goal.
Smith and Malacinski; Minsuk and Keller)
The movement whereby the bringing inside th embryos those areas destined to form ectodermal organs, surround the embryo with cells capable of forming the ectoderm, and place the mesodermal cells in the proper positions are visualized by the technique
visual dye staining
has shown that cells of the Xenopus blastula have different fates depending on whether they are located in the deep or the superficial layers of the embryo
Fate mapping
In xenopus, the mesodermal precursors exist mostly in the _ layers of the cell while the ectoderm and endoderm arise from the _ layer on the surface of the embryo
ectoderm and endoderm - superficial layer
mesoderm - deep
most of the precursors for the notochord and other mesodermal tissues are located beneath the surface in the _ region of the embryo
equatorial
In urodeles, and some frogs other than the Xenopus, many more of the notochord and mesoderm precursors are among the _
surface cells
