The tracheal system of arthropods is a complex tubular network which
is necessary for the gas exchange. It’s systematically spread through the
organism to enable the required oxygen supply. In Drosophila larvae a
central tracheal tube, coated with an apical membrane, ranges the
body.
The detailed mechanism of its formation is still unknown, whereas Dong
et al. searched for Drosophila mutants whose dorsal trunk (DT) is
altered. They observed an elongated and wavy tracheal tube in
shrub mutants. The shrub gene encodes a subunit of the endosomal
sorting complex required for transport III (ESCRT III), which is
necessary for membrane deformation, internalization and scission. To
study the cause of the abnormal elongation they performed different
reporter gen assays and immunohistochemical stainings and
investigated that the apical surface amount was increased in
shrub mutants. Their results illustrate that the shrub mutation promotes
the overgrowth of the DT apical membrane.
To identify possible downstream processes controlled by shrub Dong et
al. focused on the known membrane determinant Crumbs (Crb). In the
shrub mutant, Crb was delocalized and formed cytoplasmic aggregates
at the endosomal membrane and also the Crb level was increased in
comparison to the wildtyp. They speculated whether the delocalized
and upregulated Crb activity stimulates apical membrane overgrowth
and thereby the elongated DT. To examine this hypothesis, they
reduced the Crb level in a shrub mutant by knocking out one allele of
crumbs. Indeed, the DT phenotype was less elongated and less wavy.
Recent studies had shown, that the tyrosine protein kinase Src42A
promotes the apical membrane growth in DT cells and the anteriorposterior axis orientation. In this work Dong et al. newly investigated
that Shrub is also part of the apical membrane formation by regulating
Crp. These results allow a more detailed knowledge about the tracheal
formation but further research is still needed.
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