Ectopic expression of bnlScer\UAS.cSa in somatic clones of tracheal cells redirects tracheal progenitor migration. Dual clones induce bifurcation with groups of progenitors mowing toward each ectopic bnlScer\UAS.cSa source. Clones in Tr3 and posterior metameres cause progenitors in these regions to leave the niche, even though they do not normally do so. When bnlScer\UAS.cSa-expressing clones fail to induce migration, the clones appear to be too far from the progenitors or there is competition from another clone close by.
In the CNS, bnlScer\UAS.cSa expression in the midline using Scer\GAL4sim.PS results in the abrogation of ganglionic branching. Higher levels of expression, under the control of Scer\GAL41407 cause a more extreme phenotype, with many cells adopting terminal fate.
Expression of bnlScer\UAS.cSa under the control of Scer\GAL469B has little or no effect on mesoderm monolayer formation in the embryo following gastrulation.
When bnlScer\UAS.cSa is driven by Scer\GAL4bap.3 about a 1/4 of visceral mesoderm parasegments, visceral branches bifurcate, in about 2.4% they show simple misrouting. These defects persist until at least stage 15.
Ectopic expression of bnlScer\UAS.cSa under the control of Scer\GAL4Act5C.PP in clones in the male genital disc results in the migration of btl-expressing cells into a nearby ectopic domain where they are not observed in wild-type discs.
In late third instar bnlScer\UAS.cSa; Scer\GAL4dpp.blk1 larvae ectopic tracheoblasts can be seen adhering to the disc in the vicinity of the dpp expression domain. When somatic clones of bnlScer\UAS.cSa; Scer\GAL4Act5C.PI cells are randomly induced in wing discs, ectopic tracheoblasts migrate along the surface of disc towards these clones.
Branching of the dorsal branch and lateral trunk of the tracheal system is suppressed in embryos expressing bnlScer\UAS.cSa under the control of Scer\GAL4btl.PS and the dorsal trunk appears thickened.
Ubiquitous expression of bnlScer\UAS.cSa driven by Scer\GAL4hs.PB and heatshocked for 1 hour during the first larval instar, causes a dramatic proliferation of terminal branches. However, unlike normal terminal branches, which are distributed evenly over their targets, these remain clumped together in a large tangled mass near the point of origin. Over expression of bnlScer\UAS.cSa when driven by Scer\GAL4A9 in the CNS, transforms the normal ladder-like pattern of GB tracheal branches into a massive tangle of branches that completely cover the CNS. When driven by Scer\GAL4hs.PB, a similar effect is seen in the LG trachea. A similar effect is seen when expressed in most tissues, but the heart and imaginal discs, which normally express bnl but lack tracheal branches, fail to attract branches even when the gene is overexpressed there. When bnlScer\UAS.cSa is driven in the salivary glands (which do not normally express bnl or receive trachea) by Scer\GAL471B during larval development, terminal tracheal branches are attracted to the salivary glands from nearby tissues. When bnlScer\UAS.cSa is driven in muscle fibre 12 by Scer\GAL45053A the LG terminal branches are directed towards this muscle, away from their normal targets at the ventral midline, doubling the number seen terminating on this muscle (as compared to wild-type) when raised at 25oC and quadrupling the number when raised at 29oC. Expression of bnlScer\UAS.cSa in random single cells (Driven by Scer\GAL4Act5C.PP in a Scer\FLP1hs.PS induced clones.), causes a local proliferation of terminal branches that grow out to the expressing cells arborizing on the cells and almost completely engulfing them. Attraction occurs over distances of up to about 10 cell diameters. Cases can be found where a terminal branch bifurcates to target two bnlScer\UAS.cSa expressing cells separated by several cell diameters.
Expression of bnlScer\UAS.cSa under the control of Scer\GAL469B results in marked defects in tracheal branching; primary branching is suppressed and an overabundance of secondary and terminal branches is induced.
When expression is driven at stage 11 by heat induced Scer\GAL4hs.PB the number of cells expression pantip and terminal markers is increased in all tracheal branches. Extra terminal branching occurs.
Expression of bnlScer\UAS.cSa under the control of Scer\GAL469B results in a reduction of primary branching and an increase in the formation of fine secondary and terminal branches in the embryonic tracheal system.
Scer\GAL4C49, Scer\GAL469B or Scer\GAL4hs.PB mediated expression in wild type branches causes a disruption in the normal pattern of branching; a mass of fine branches growing out in random directions from stunted branches.