Developmental patterns in sea urchins Flashcards
Are sea urchins protostomes or deuterostomes?
Deuterostomes
What is karyokinesis?
Separation of genetic material
What are the 4 types of yolk distribution?
Isolecithal, mesolecithal, telolecithal, and centrolecithal
What is an isolecithal yolk distribution? What animals have it?
Evenly distributed yolk that is quite sparse. Found in echinoderms and mammals
What is an mesolecithal yolk distribution? What animals have it?
Moderate yolk distribution. Found in amphibians
What is an telolecithal yolk distribution? What animals have it?
Dense yolk throughout the cell. Found in fish and birds
What is an centrolecithal yolk distribution? What animals have it?
Yolk is clustered in the middle of the egg. Found in insects
What are the 2 cleavage types?
Holoblastic and meroblastic
What is holoblastic cleavage?
Complete cleavage, mitosis happens throughout cytoplasm, cytokinesis with each division. Found in echinoderms, mammals, and amphibians
What is meroblastic cleavage?
Incomplete cleavage, cytoplasm is split unevenly and cytokinesis doesn’t always occur. Found in fish, birds, and insects
Is the first mitotic division of a sea urchin egg meridional or equatorial? Which axis does the cell divide along? How many cells does the embryo end up with?
Meridional along animal-vegetal axis. 2 cells
Is the second mitotic division of a sea urchin egg meridional or equatorial? Which axis does the cell divide along? How many cells does the embryo end up with?
Meridional along animal-vegetal axis, perpendicular to division 1. 4 cells
Is the third mitotic division of a sea urchin egg meridional or equatorial? Which axis does the cell divide along? How many cells does the embryo end up with?
Equatorial, perpendicular to divisions 1 and 2. 8 cells
Is the fourth mitotic division of a sea urchin egg meridional or equatorial? Which axis does the cell divide along? How many cells does the embryo end up with?
The animal pole divides meridional and evenly into 8 mesomeres. The vegetal pole divides equatorial and unevenly into 4 macromeres and 4 micromeres. 16 cells total
What happens in the sixth mitotic division? How many cells does the embryo end up with?
Animal 1, animal 2, vegetal 1, and vegetal 2 layers form. End up with 60 cells because the small micromeres have stopped dividing
What happens to an embryo after the vegetal hemisphere, large micromeres, and small micromeres are removed?
It forms a Dauerblastula, an animal blastula, but won’t develop further because it is just ectoderm
What happens to an embryo after the vegetal hemisphere, large micromeres, and small micromeres are removed. Then the large micromeres are reintroduced?
The animal cells organized themselves into a recognizable pluteus larva, and formed endoderm layers
What is a logic circuit/gene regulatory network?
Gene product cascade that leads to induction, specification, and morphogenesis
What is a feed forward circuit?
A gene product of an upstream gene enhances transcription/function of a gene product downstream
What is a double negative circuit?
The gene product represses the function of a downstream product, which leads to an even more downstream product being activated because the gene product that was repressing it is no repressing it
How are the large micromeres autonomously specified to become the organizers?
Dishevelled is localized at the vegetal pole, and it deactivates GSK3 so beta-catenin can enter the nucleus and act as a transcription factor. Other cells don’t have the localized Dishevelled, so the genes that get activated by beta catenin stay off in those cells
What happens when embryos are treated with drugs to increase beta catenin activity?
It gets expressed in the vegetal 2 cells and not just the micromeres, which causes the digestive tract to develop outside the body
What happens when embryos are treated with drugs to stop beta catenin activity?
Completely animalized blastula, same as the micromeres being removed
What gene does beta catenin activate in the large micromeres?
Pmar1
What does Pmar1 do?
Deactivates HesC
What happens when HesC is deactivated?
Alx1 and Delta get expressed in the large micromeres
How do Alx1 and Delta stay deactivated in any other cells that aren’t the large micromeres?
No beta catenin to turn on Pmar1, so HesC stays active and it represses Alx1 and Delta
What does Delta do in the large micromeres?
It gets expressed on the surface of the micromeres, and interacts with Notch receptors on the Veg2 cells
What does the Delta-Notch interaction cause the Veg2 cells to do?
Become non-skeletogenic mesenchyme cells that will direct gastrulation
What do the large micromeres become for gastrulation?
Skeletogenic mesenchyme
What happens to the skeletogenic mesenchyme cells right before gastrulation?
They undergo an EMT and ingress into the blastocoel
What signals trigger the ingression of the skeletogenic mesenchyme into the blastocoel?
VEGF, FGF, beta catenin
What do Snail and Alx1 do?
Promote endocytosis of the cell membrane with the adhesion molecules
What cells deposit the spicules in the gastrula?
Skeletogenic mesenchyme
Which cells trigger gastrulation?
The Veg2 cells: non-skeletogenic mesenchyme
How does the blastopore form?
Invagination of the non skeletogenic mesenchyme
What creates the force needed for the invagination that creates the blastopore?
Contraction of the actin filaments on the apical membrane of some non-skeletogenic mesenchyme epithelial cells
What are the cells with the actin filaments on the apical membrane called?
Bottle cells
What happens once the blastopore is formed?
The archenteron elongates inside, driven by non-skeletogenic mesenchyme cells grabbing on to the epithelial cells on the opposite side
