Mechanisms and models of segmentation Flashcards
what is a segment
repetition along the AP axis of a structural unit
groups where most segmentation is seen
annelids, arthropods, chordates
fundamentals of clock and wavefront
‘molecular oscillator’ underpinning somite formation
cells oscillating on their own, when on a larger scale creates a pattern of travelling waves of gene expression
parasegment
segment during development of arthropods which is slightly offset from morphological segments in the adult
what might be the point of parasegments
morphological segments protect the stuff in the middle of parasegments (e.g. important boundaries between bits of nervous system)
which of short vs long band is ancestral
short (sequential) is ancestral
where do segments come from in sequential patterning
segment addition zone- SAZ
some features of the SAZ (not that deep if i dont know all of this)
wnt in the posterior
notch/eve and cad in the anterior
clock and wavefront evolution
seems like arthropods and vertebrates both converged towards a similar mechanism
differences between arthropod and vertebrate CW
periodicity is much more fixed in vertebratea- can form multiple segments per cycle in arthropods
some principles of drosophila development
longe range gradients, and the genes regulate each other to make overlapping domains
7 bands, then get doubling as genes regulate each other in the 7 band stage
‘early’ and ‘late’ network which trigger each other
just gets more and more complicated
what kind of interactions seem to be most important in the vertebrate segmentation clock
autorepressive
three gene ring oscillating in Tribolium SAZ
Eve Runt Odd
what we don’t know about the regulatory genes in the SAZ?
which genes are linked, if the circuit is enough to generate oscillations on its own
notch and somatogenesis
seems to be involved (oscillates and stuff), but it’s hard to tell because it has loads of other roles
‘remnants’ of ancestral segmentation system in simeltaneous systems
changes through time still occur, and there are a lot of similarities in spatio-temporal gene expression
segmentation tissue in vertebrates
presomitic mesoderm (PSM)
drivers of PSM elongation
cell division and rearrangements
standard PSM development pattern
rises and falls in size- more extreme in some species (chicken) vs others (zebrafish)
‘halves’ of a somite
rostral/caudal
re-segmentation
vertebra forming from two consecutive ‘halves’ of somites, something to do with aligning muscles and vertebra
what determines the length of a somite
velocity of wavefront and time period of the clock- slower clocks make bigger somites
‘kinematic wave’
wave where there is no/negligible transport- changing state of individual parts is what creates the pattern
