Mesoderm Development Flashcards
(86 cards)
How does the Primitive groove from
posterior to anterior, starting at the node (organiser)
How does Mesoderm move / form in gastrulation
Epiboly of Epiblast into primitive groove pushes Mesoderm into the centre of the embryo
what are the 4 types of mesoderm and what do they give rise to
Axial - Notochord
Paraxial - Somites
Intermediate - Kidneys
Lateral - Limbs
How were cell fate maps created for mesoderm tissues
Dye injections for lineage tracing
Structure of Somites
Highly organised
Separated structures
Repeated
What does the No. of Somites dictate
The no. of vertebrae, which is fixed for each species
Do somites start appearing anteriorly of posteriorly
Anteriorly
When does somitogenesis occur
At the same time paraxial mesoderm is forming
How is the timing of Somite formation conserved between species
Each species have a fixed time for somite formation
How long does somite formation take in Mice, Chicks and zebrafish
MIce- 120min
Chick- 90min
Zebrafish- 45min
Generally how do somites form
By budding off of pre-somatic mesoderm
What must cells in the pre-somatic mesoderm respond to, to create somites
Positional info
Mechanism that coordinates paired formation
Mechanism that generates anterior boundary
Mechanism that generates posterior boundary
Formation of cleft
What model explains somite formation
Clock wavefront model - A clock ticks in posterior pre-somatic mesoderm that drives a molecular occilator that dictates periodicity of somites.
Where cells hit the travelling wavefront, an abrupt change occurs.
What is the molecular occilator described in pre-somatic mesoderm
C-Hairy1 - chicks
(Hes - mice)
(Her - Zebrafish)
How are C-Hairy1 (and homologs) controlled and what do they in turn control
They are targets of Notch signalling
They are broken down by proteosomes
Dimerization of C-Hairy1 self represses its expression
They are bHLH protein transcriptional repressors
How many cycles of C-Hariy1 expression to cells undergo before forming somites
12
What major genes are involved in the clock mechanism
Notch-Delta
Wnts
FGFs
What is the determination front and how is it specified
It is the ‘line’ where cells stop occilating. This causes somite formation.
FGF8 from the node is present in posterior regions.
Retinoic Acid is present Anteriorly.
They are antagonistic to each other and create a hard boundary
What is the fgf8 - RA interaction
RA –|FGF8
FGF8–> Cyp28 –|RA
What causes the determination front to move
Convergent extension of the posterior region pushes the node further posteriorly, moving the determination form posteriorly at a regular rate.
How is the anterior of the forming somite patterned
Mesp2 is maintained in the anterior half of the somite due to tbx6 and notch
How is the posterior of the somite patterned
Cycle is stopped a bit later causing Notch signalling to be active.
How does the determination front stop the occilating cycle
FGF8 only present posteriorly before the DF is the driver of the occilation cycle. So once cells stop seeing fgf8 the cycle stops
How are boundaries between Somites formed and result in Budding off
Posterior region of somite experiences Notch signalling. After enough time, Ephrin builds up on posterior. Anterior region past the DF express Ephs as a result of Mesp2. Ephs and Ephrins are extremely antagonistic and cause tissue separation.
