Chapter 8

Question 1

Why amphibians as a model organism?

Answer 1

• large cells
• rapid development
• easy transplantation & observations

Question 2

why NOT amphibians as model?

Answer 2

terrible genetics
- tetraploidy (alter 4x genes)
- massive genome
- very few mutants

Question 3

what are frogs called? salamanders?

Answer 3

anurans
urodeles

Question 4

types of anurans? types of urodeles?

Answer 4

xenopus laevis, x. tropicalis, rana pipens

ambystoma mexicanum, a. maculatum, notophthalmus viridescens

Question 5

what axis does the spot of sperm entry become?

Answer 5

ventral side (belly)

Question 6

what happens once the sperm enters an amphibian embryo?

Answer 6

sperm centriole organizes microtubules that push proteins toward dorsal side (becomes darker)

Question 7

what is the cortical rotation?

Answer 7

outer layer rotates 30 around inner cytoplasm & exposes gray crescent (animal pole, dorsal side)
- where gastrulation will begin

Question 8

what type of cleavage do amphibians have?

Answer 8

displaced radial
- vegetal divisions are delayed, hard to divide thru yolk

Question 9

what helps to prevent the blastocoel cells from induction?

Answer 9

tight intercellular junctions (watertight seal)
- the help of EP-cadherins

Question 10

what is Nieuwkoop (1969) do?

Answer 10

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

Question 11

describe when the MBT starts in amphibians

Answer 11

at the 12th division
- embryo starts using it’s own genes and activates the genome
- differential gene expression, blastomere motility

Question 12

describe the experiment that shows when the cell knows to be in the MBT

Answer 12

removed cytoplasm from cells so there were less cytoplasmic proteins
- determined there were demethylated promoters that started MBT

Question 13

what is VegT?

Answer 13

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

Question 14

what are Nodal and Vg1?

Answer 14

maternal mRNA paracrines
- in the endoderm of vegetal pole
- turns on mesoderm

Question 15

what are the three goals of amphibian gastrulation?

Answer 15

bring endodermal tissues inside
surround w/ ectoderm
coordinate mesodermal cells in b/w

Question 16

what are bottle cells?

Answer 16

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

Question 17

what is a marginal zone? what are the two types?

Answer 17

area where cells debate if they stay outside or move in
- involuting marginal zone (IMZ)
- non-involuting marginal zone (NIMZ)

Question 18

what is the IMZ?

Answer 18

cells go inside
- form mesoderm and makes the blastocoel start to disappear by making the archenteron
- induces cells to become nervous tissue

Question 19

what is the NIMZ?

Answer 19

cells stay put
- epiboly of the cells to push the outer layer together to cover the yolk
- mitosis & migration

Question 20

describe the steps of amphibian gastrulation

Answer 20

1. bottle cells invaginate to form dorsal blastopore lip
2. following cells invaginate to form archenteron
3. IMZ cells involute to form mesoderm
4. archenteron displaces blastocoel
5. ventral & lateral bottle cells ingress
6. epiboly of NIMZ cells
7. yolk plug forms
8. blastocoel obliterated

Question 21

what is fibronectin?

Answer 21

apart of inner side of blastocoel roof
- allows a highway for IMZ cells to follow

Question 22

what did Hans Spemann do?

Answer 22

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)

Question 23

describe how Hans Spemann showed blastomere potency

Answer 23

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

Question 24

describe how Hans Spemann showed blastomere non-equivalence

Answer 24

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)

Question 25

describe the experiment of the color newts and when presumptive neural ectoderm is induced by Hans Spemann

Answer 25

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

Question 26

who is Hilde Mangold?

Answer 26

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

Question 27

describe Hilde Mangolds experiment with grafting IMZ cells

Answer 27

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)

Question 28

describe the function of the dorsal blastopore lip region that was discovered by Hilde Mangolds

Answer 28

induce dorsal axis & notocord / neural tube formation
- known as Spemann’s Organizer

Question 29

what is the function of Nieuwkoop Center? describe how it works (step by step)

Answer 29

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