Segmentation Flashcards
(20 cards)
What is segmentation?
Division of the body into repeating units (somites)
What tissue gives rise to somites?
Paraxial mesoderm
What is somitogenesis?
The sequential formation of somites from presomitic mesoderm
What model explains somitogenesis?
Clock and wavefront model
What is the segmentation clock?
Oscillating gene expression (e.g. Notch, Her/Hes genes)
What is the wavefront?
A moving boundary of FGF/Wnt (posterior) and RA (anterior)
Where is Mesp2 expressed?
At the future somite boundary; initiates segmentation
What do Eph/ephrins do in segmentation?
Establish boundaries between somites via repulsive interactions
What does the sclerotome become?
Vertebrae and ribs
What does the myotome become?
Skeletal muscles
What does the dermatome become?
Dermis of the back
How often to human somites form?
About every 90 minutes
What regulates anterior-posterior identity in somites?
Hox genes
What happens if Hox genes are misexpressed?
Homeotic transformations of vertebrae
Which signalling molecule is highest posteriorly?
FGF8
Which molecule promotes anterior maturation of somites?
Retinoic acid (RA)
What happens in congenital scoliosis?
Disruption of somite boundary formation
Is the clock and wavefront model conserved?
Yes, across vertebrates
What triggers clock oscillations?
Notch signalling
Where do somites first form?
Just behind the Hensen’s node
