Chapter 10 sea urchins Flashcards
Sea urchins undergo _______ cleavage
radial holoblastic cleavage
in sea urchins, cell division is _______ and perpendicular to one another in the 1st and 2nd division, and _______ in the 3rd division
meridional
equatorial
in sea urchins animal pole cells: _______ division yielding 8 equally sized _______
meridional
mesomeres
in sea urchins vegetal pole cells:
unequal _______ division yielding _______ and _______
equitorial
micromeres
macromeres
sea urchins:
By the _______ division, the cells become specified and develop cilia on the region outer face of the membrane
10th division
Sea urchins:
the ciliated blastula begins to _______ within the fertilization envelop and vegetal pole cells thicken and form the _______
rotate
vegetal plate
Sea urchins:
The animal pole cells secrete _______ that dissolves the fertilization envelop
hatching enzyme
- once this occurs it becomes a free-swimming hatched blastula
Sea urchin fate maps:
animal half consistently forms _______
ectoderm
- skin and neurons
Sea urchin fate maps:
Veg1 cells form _______ and _______
ectoderm and endodermal organs
Sea urchin fate maps:
Veg2 cells form several fates (3), what are they?
1) endoderm
2) coelom
3) non-skeletogenic mesenchyme
What are 3 examples of what non-skeletogenic mesenchyme turn into?
1) pigment cells
2) immunocytes
3) muscle cells
Large micromeres will end up forming _______
skeletogenic mesenchyme
Small micromeres have _____ role in development, they end up becoming a part of the _______
no
coelom
The large micromeres are _______ specified
autonomously
Large micromeres inherit ________ determinants deposited in the vegetal pole of the egg
maternal
- segregated into micromeres in the 4th division
- determines skeletogenic mesenchyme
Large micromeres will separate from the _______ and enter the blastocoel, attach to various points on the inside of the wall and differentiate into the larval skeleton
epithelium
The large micromeres _______ specify their neighbors
conditionally
- via paracrine and juxtacrine factors
Cells above the Large micromeres are conditionally specified to become _______, and will _______ during gastrulation
endoderm
invaginate
Skeletogenic mesenchyme cells from the large micromeres are specified by a _______ ciruit
double negative circuit
_______, _______, and _______ are inherited maternal cytoplasmic factors (TFs)
disheveled
Otx
β-catenin
β-catenin and Otx activate _______, which is a repressor of _______
Pmar1
HesC
Repression of _______ allows the transcription of the genes involved in micromere specification
ex) Alx1, Ets1, Tbr, Tel, SoxC
HesC
_______ regulation: a single gene activates the transcription of many others
feed-forward
Once specified, sea urchin _______ genes are activated by a feed-foward system
skeletal differentiation
β-catenin and Otx in micromeres also activate _______ transcription
Blimp1
- they also activate Pmar1 (see above)
Blimp1 and β-catenin together activated the _______ gene
Wnt8
Wnt8 is a paracrine/autocrine signal that does what 2 things?
1) stimulates producing cells to produce more β-catenin
2) sets up a positive feedback loop ensuring β-catenin production
_______, a juxtacrine protein controlled by the double-negative gate, activates the production of _______ protein in adjacent vegetal cells
delta
- produced by large micromere
notch
- in Veg2
Notch activation specifies these adjacent vegetal cells to become _______
Non-skeletogenic mesenchyme
Sea urchin gastrulation begins with a _______ blastula of about 1000 cells flattened at one end
single-layered
The first step to sea urchin gastrulation is _______ of skeletogenic mesenchyme
ingression
ingression:
Large micromeres lose their affinity for their _______ and the _______ membrane and ingress into the blastocoel
neighbors
hyalin
- in turn gain affinity for basal lamina
Micromeres _______ their membrane cadherins and other receptors and replace them
endocytose
The process of endocytosing cadherins and receptors is controlled by _______
Snail
Snail is a protein activated by the _____ transcription factor of the double-negative gate
Alx1
Ingressing micromeres acquire a strong affinity for several proteins lining the blastocoel (paracrine factors) such as: (2)
1) VEGF
2) Fibroblast Growth Factor (FGF)
Skeletogenic mesenchyme cells accumulate near the sites of VEGF/FGF productinon and fuse into _______ which will form the axis of Calcium Carbonate Spicules that form the larval skeleton
syncytial cables
cells remaining at the vegetal plate after the departure of the skeletogenic mesenchyme flatten and begin to invaginate about 1/4 to 1/2 of the way into the blastocoel. The invaginated region is called the _______
archenteron
The opening formed at the vegetal pore as a result of invagination is called the _______
blastopore
Cells become specified as they are ingressing into the archenteron:
1) First: non-skeletogenic mesenchyme will become the _______ cell, _______ around the gut
2) deepest archenteron cells become _______
3) medium depth cells become the _______
4) last cells to enter become the _______ and _______
1) pigment; musculature
2) foregut
3) midgut
4) hindgut and anus
The archenteron then extends dramatically via a process of _______
convergent extension
- cells move over one another and flatten archenteron
During the 2nd-3rd stages of archenteron invagination, continued cell division at the top of the archenteron form _______ and _______ cells
endodermal
secondary mesenchymal
Secondary mesenchyme cells at the top send out small projections called _______
filipodia
Once filipodia find the correct cells, they are _______ so that the archenteron comes into contact with the inside of the animal pole cells
PULLED
As contact is made between filipodia and animal pole cells, 2nd mesenchyme cells disperse to form _______
internal organs
A _______ forms at the point of contact and fuses with the archenteron completing the digestive tube
mouth
