Lesson 6: Sea Urchin Gastrulation

What type of symmetry do sea urchins have

5 fold symmetry

When does the sea urchin get to its 5 fold symmetry

After metamorphosis

Does the sea urchins embryonic history indicate that it’s going to be 5 fold

No, it just indicates radial cleavage

Pluteus

embryonic stage of the sea urchin, are plagues

Plagues

lives in the ocean

Blastocele

fluid filled cavity

What two subcategories are eukaryotes slit into

Duerostomes and Protostomes

Cillia

swimming hairs, eventually degenerates and dies

Maternal determinant absent in a cell

dauer blastula forms by experimental isolation of animal pole cells of the sea urchin embryo, animalizes it and moves around in water with help of cilia.

Maternal determinant present in a cell

when in vegetal pole of of embryo, ensures development of all three germ layers

What do micromeres exclusively inherit

disheveled

Pathway related dishelved

wnt → frizzled → dishelved –I distruction complex → B catenin → wnt dependent gene expression

What is the function of disheveled

to prevent degradation of B canteinin

Where is b-canetin localized

the nucleus of the micromeres

B-canetin

in all cells, associates with cadherins and a structural protein that can also function as a nuclear protein

Hypothesis 1

stabilizing b-canetin everywhere should alter the fates of an1 and an2 cells

Hypothesis 2

preventing b-catenin from entering the nucleus should alter the fates of veg 1 and veg 2 cells.

Why are the micromeres (site of b-canetin) special

because it has the activation of unit signaling in them

What are the large micromeres fated to become

skeleton

What is driving the fate of the large micromeres becoming something

b-catenin, so it is autonomously “specified”

HesC

transcription factor that represses skeleton formation

What happens if HesC is activated in the micromeres

no skeleton

Pmar1

transcription factor that inhibits HesC

Double negative

an inhibitor of an inhibitor

Delta

interacts with the veg2 cells and notch

Induction

one cell stimulating another cell to do something

Genes in micromeres

Alx, Ets, Tbr

Why are genes necessary in micromeres

to induce and regulate differentiation or primary mesenchymal cells into skeletal cells

Alx

transcription factor necessary for biomineralization and extracellular matrix production

Ets

drives the differentiation of skeletogenic mesenchymal cells needed for the formation of the larval skeleton

Tbr

regulates the formation of the skeletal structures in larva

Feed-forward circuit

activation mechanism

Ectodomain

outside the cell

Endodomain

inside the cell

Notch signaling pathway

delta → notch → notch cleaved → notch diffuses out → notch enters nucleus → functions a transcription cofactor → associated w/ specific transcription factors + driving gene expression

The large macromeres have inductive potential

animal cell fate is conditionally specified and micromere cell fate is autonomously specified

How do small/large macromeres redirect developmental pathway of animal hemisphere

induction taking advantage of the delta notch pathway

Gastrua

latin for stomach

Ingression

migration of individual cells into the embryo

Hyalin layer

a clear substrate, composed of the protein hyaline

Glycoprotein

a little bit of sugar on top of a lot of protein

Protioglycen

highly viscous, lots of sugar wrapped around one protein strand

What does secretion of CSPG cause

water absorption in the inner lamina, causing it to expand and push cells towards the blastocele

What does ingression of micromeres lead to

the loss of b-catenein expression

Upon ingression, micromeres become

primary mesenchymal cells (PMC)

Convergent Extension

move inwards, resulting into elongation

Holoblastic cleavage

Complete division of the egg during early embryonic development. Meridional cleavage

Mesosomes

Small cells formed during cleavage in some embryos.

Micromere

Small cell produced during embryonic cleavage. Macromere

Deuterostome

An animal in which the blastopore develops into the anus, and the mouth forms secondarily.

Protostome

an animal in which the mouth develops from or near the blastopore.

Juxtracrine signaling

Cell signaling requiring direct contact between neighboring cells.

Lamin

Intermediate filament protein forming the nuclear lamina beneath the inner nuclear membrane. Blastopore

Archenteron

Primitive gut cavity formed during gastrulation.

Blastocele

Fluid-filled cavity inside the blastula.

Filopodial

Relating to filopodia, thin cell extensions used for sensing and movement.