For example, in the wing disc, ectopic expression of Cut, a Notch-responsive target, takes place only in Smr1 clones that are in juxtaposition to the dorsal-ventral boundary where Notch is activated, whereas Br, a target of ecdysone, is elevated in Smr1 cells throughout the wing disc (Fig. 6).
Copper bicrystals with isoaxial [1̄49] twist boundaries and a (1̄49)/(001) "random" boundary were notched at the interface, left or right regarding the slip geometry, and intergranular cracks were propagated under strain control, to study how dislocation structure, crystallography and strain localization affect crack growth.
Furthermore, the DT/DB and DT/TC boundaries delimit Notch expression and of its ligands Delta and Serrate, suggesting that Notch signaling is involved in the formation and maintenance of those borders, just like in the D/V border in the wing disc.
Boundary cells lacking Notch activity express Senseless (Figures 3E' and 3F').
Whether specified by the apposition of distinct segments or another mechanism, boundary formation involves Notch and Wnt signaling [27], [28], [29], [30], [31].
When boundary cells lack Notch activity, either by mutation or by expression of a dominant negative form of Delta known to titrate out the Notch receptor, these cells start to express target genes of Wg (Figures 3E and 3F, and also Figure S1).
It will be interesting to see if other Notch-dependent boundary formation processes involve similar Notch signaling states and dynamics (Irvine, 1999).
Notch and Wnt1 are expressed in boundary cells whereas the Notch ligand Delta is expressed in adjacent stripes also named paraboundary domains, and Notch activity in the boundaries is enhanced by the modifier Radical Fringe, a glycosyltransferase [27], [29], [30], [31].
Although wingless appears to be the main growth-promoting signal emanating from the D/V boundary, a second Notch-induced signal at the D/V boundary also non-autonomously induces wing growth [ 5].
Open image in new window Fig. 5 FE model of dog-bone specimens: a full model, b close look of notch, c boundary conditions.
