lectures - gastrulation

what are the 2 phases of gastrulation

ingression

regression

ingression is generally

primitive streak formation

regression is generally

primitive streak degeneration

what is the primitive streak generally

site of ingression in epiblast

transitory structure

how does the primitive streak function

acts like a passageway for massive epiblast cell proliferation allowing them to shove down into the blastocoel

describe the epiblast cells that will fall into the primitive streak

massive proliferation followed by det into mesoderm and endoderm within blastocoel

lose ability to express ectoderm expressing genes

why do cells that fall into the blastocoel undergo determination

because they are neighbor dependent and their neighborhood changes as it falls

how does primitive streak formation occur directionally

only process that moves posterior to anterior

what is Koller's sickle

thick area between the AP and post MZ where hypoblast blastomeres form + cluster to block endoblast cells so they can build up

kollers sickle is crucial for which mammalian or avian primitive stream formation

avian

what does kollers sickle allow for

enables endoblast to replace hypoblast

with the creation of Koller's sickle what happens to cells in the posterior region

post MZ and AO cells undergo diff and det to form endoblast cells

what do Koller's Sickle cells looks like

have milky cytoplasm making them look darker

how does the hypoblast inhibit primitive streak formation

it produces signals that block its formation

when a signal is sent, what happens to the hypoblast and endoblast cells

moving post→ant, endoblast cells rush in and replace hypoblast cells

what happens to the epiblast cells overlaying the Koller sickle

they unstick to each other and condense and diff + det into cells forming primitive streak down midline and are freely able to prolif

the endoblast is a...

temporary structure

what becomes the primitive streak

epiblast cells directly above the koller sickle

what does primitive streak formation do to epiblast

trigger epiboly across epiblast

what are the consequences of the migrating epiblast cells

form 2 new layers within the blastocoel

under go diff + det and lose potency to form ectoderm

what are the 2 layers formed by migrating epiblast cells as they move into the blastocoel

endoderm replacing the endoblast

mesoderm

what replaces the epiblast cells that fall into the primitive streak

replaced by sheets of future ectoderm cells

what do mesoderm cells right below the primitive streak get signals to do

get signals to det and diff to express genes to form notochord only

what establishes the left and right axis of the embryo

full formation of the primitive streak

what forms at the end of primitive streak completion

Henson's node

describe hensons node

specialized thickened region within primitive streak

allows for establishment of L/R axis

cell migration through the primitive streak results in

mesoderm

endoderm - replacing endoblast

ectoderm - epiboly gives rise to this in epiblast

in mammalian gastrulation, what is hypothesized

that Posterior VE is analogous to endoblast

through the process of gastrulation, bilaminar blastula becomes...

trilaminar gastrula

what does trilaminar mean

3 germ layers

gastrulation is loss of potency to

to multipotency

what happens during regression

moves ant → post

hensens node moves ant→ post

leaves behind head process of notochord

describe the notochord during regression

formation completes during primitive streak regression

what is the notochord important for

neurulation

very generally describe the meaning behind gastrulation

gastric - stomach

1st pops of cells will diff and become gut lining

at the end of gastrulation, what describe the embryo gradient of maturity

anterior end is more mature than posterior regions

where Hensen's node stops posteriorly what is formed

forms anal region of embryo