Biology Reference
In-Depth Information
an early indication that cell polarity must already have begun to change, or at least relax its
constraints, before contact takes place. DE-cadherin-mediated adhesion between fusing
tracheal tips is important to the process, which fails in shotgun (
DE-cadherin) mutants.
6
It
also fails in fear of intimacy mutants, which lack a zinc-importing protein
7
that is necessary
(presumably indirectly, via cytoplasmic zinc concentration) for post-transcriptional stability
of the DE-cadherin transcript.
8
Fusion also fails in mutants lacking
ΒΌ
-catenin (encoded by
the armadillo gene), which is an essential internal component on DE-cadherin-containing
adherens junctions.
9
In cultured mammalian cells, the direction of cell polarity is determined,
at least in part, by the location of E-cadherin-mediated adhesion.
10
If this is also true of D. mel-
anogaster, DE-cadherin-mediated adhesion may be responsible for the full repolarization of
touching cells so that the contacting surfaces, previously basal, are now regarded as lateral.
They will, after all, have to be lateral from the perspective of the fused tube system.
The protein Kakapo provides an important link between integrins and the actin and micro-
tubule cytoskeletons in D. melanogaster.
11
During normal tracheal fusion, Kakapo protein
b
FIGURE 19.5
The fusion of dorsal branches in D. melanogaster. (a) In this case, the fusion cell is not the tip cell.
(b) Sketch of the meanings of 'seamless' and 'seamed' as used in the text. (c) sequence of events in creation of
a continuous lumen.
