Download MCB141 103/104 Quiz #6!!!! 1. How would the following

MCB141 103/104
Quiz #6!!!!
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1. How would the following manipulations affect somite number in the developing
zebrafish/chick/mouse embryo? (2pts)
Increase the speed of the clock (destabilize
Notch target genes)
Borders established more frequently
Slow the speed of the clock (stabilize Notch
target genes)
Borders established less frequently
Knock out FGF in the mesoderm
Tissue differentiates immediately, in one
wave
Constitutively expresses FGF in the
mesoderm
Tissue doesn’t differentiate easily
Knock out Hox genes
More somites Fewer somites
X
No change
X
X
X
X
2. Fill in the blanks (3 pts):
Shh secreted by the floor plate induces the somitic mesoderm closest to it to form
_____sclerotome_______, which will contribute to _____skeleton________ in the adult mouse.
The dermamytotome will differentiate into dermatome and mytome. The dermatome receives
______BMP + Wnt_______ signals from the overlaying epidermis, and will later contribute to
the _______dermis______ in the adult mouse. Regions of the somite exposed to Wnt + Shh will
form _______epaxial ____, which will later contribute to dorsal musculature in the adult mouse.
Regions of the somite exposed to BMP + Wnt form _______hypaxial_____, which will later
contribute to ventral/lateral body wall muscles in the adult mouse. .
3. Fill in the two blanks and circle one answer in each of the 4 parenthetical choices (2pts):
The transmembrane ligand ______Ephrin_______ is expressed in the ( anterior / posterior )
portion of the somite, and engages in (attractive / repulsive ) interactions with
_______EphR________ expressed by migrating neural crest cells. This (extrinsic / intrinsic)
signaling event causes the neural crest cells to to migrate over only the ( anterior /
posterior ) part of the somite.
4. Quiz #1 throwback question!! Describe the selection procedure employed by Yamanaka to
identify IPS cells. Why was it necessary for Yamanaka to employ a selection procedure? (1pt)
The induction of cells to a pluripotent state was an incredibly rare event, therefore a
selection procedure (i.e. antibiotic selection or lacZ) was used to easily identify cells in
which pluripotency had been induced.
Yamanaka drove the expression of lacZ/neomycin with a ESC specific enhancer. Only
when the cell had been induced to pluripotency, would this enhancer drive the expression
of lacZ/neo.
Without a selection procedure, it would have been impossible to pick out the cells that had
been successfully induced.
5. Describe 2 experiments you could conduct to demonstrate that BMP2 secreted by the aorta
causes neural crest (NC) cells to stop migrating and differentiate into the neurons of the
sympathetic ganglia. (2pts)
- Culture undifferentiated neural tube in media containing BMP protein, and see if cells
adopt dorsal fates
- Culture undifferentiated neural tube with dissected-out roof plate, and see if cells adopt
dorsal fates.
- Do the same as in the second experiment, but with a bmp-/- roof plate – and see that the
cells do not adopt dorsal fates
6. Describe an experiment to show that cycling of the segmentation “clock” that contributes to
somitogenesis operates cell-autonomously. (2pts)
Dissect out cells of PSM, culture, and observe expression of destabilized GFP driven by the
hairy promoter. GFP expression will still cycle in the absence of other cells / the rest of the
presomitic mesoderm.
Or, cut off/out part of the PSM, and observe the remaining cells still cycling (hairy:GFP, or
growing the left and right halves of what’s left at different temperatures / fixing at different
times for insitu hybridization to see that oscillations still occur).