First published online February 9, 2006
Development 133, 501e (2006)
© The Company of Biologists Limited
A leg up for tracheal evolution and development
Very small organisms get the oxygen they need for life by diffusion across
their body surface, but larger organisms need specialized respiratory organs
to do the same job. In insects, the main respiratory organs are the tracheae,
an internal tubular network that develops from clusters of ectodermal cells on
either side of the thoracic and abdominal embryonic segments. Two papers in
this issue of Development provide new information about the evolution
and development of tracheae. On
p. 785, Franch-Marro
and colleagues raise the possibility that an evolutionary relationship exists
between insect tracheae and the external respiratory gills of crustaceans.
These gills are associated with appendages, and Franch-Marro et al. show that
Drosophila tracheal placodes arise next to leg primordia in the
thoracic segments and next to cryptic leg primordia in the abdominal segments;
the different fates of the tracheal placode and leg primordia are controlled
by Wingless signalling. The researchers also report that homologues of
tracheal-inducing genes are expressed in the developing gills of crustaceans.
Based on these results, they propose that the ancestors to arthropods had
areas on the surface of their body that were specialized for gas exchange,
which evolved into crustacean gills and insect tracheae. On
p. 957, Matusek and
co-workers reveal new details about the development of the Drosophila
tracheal system by reporting that the formin DAAM (Dishevelled-associated
activator of morphogenesis) regulates the tracheal cuticle pattern. The
tracheal cuticle resembles a corrugated vacuum-cleaner hose. This structure
gives the tracheae rigidity but allows them to bend as the insect moves. The
researchers report that in the absence of DAAM, an array of actin
cables beneath the apical surface of the tracheal cells fails to form properly
- formins are key regulators of the cytoskeleton - and consequently the
pattern of ridges (taenidial folds) in the tracheal cuticle is disrupted and
the tracheal tubes collapse. Other results indicate that DAAM
activity is regulated by RhoA and that DAAM works with the
non-receptor tyrosine kinases Src42A and Tec29 to organise
the actin cytoskeleton and thus determine the cuticle pattern of
Drosophila tracheae.
Related articles in Development:
- Association of tracheal placodes with leg primordia in Drosophila and implications for the origin of insect tracheal systems
- Xavier Franch-Marro, Nicolás Martín, Michalis Averof, and Jordi Casanova
Development 2006 133: 785-790.
[Abstract]
[Full Text]
- The Drosophila formin DAAM regulates the tracheal cuticle pattern through organizing the actin cytoskeleton
- Tamás Matusek, Alexandre Djiane, Ferenc Jankovics, Damian Brunner, Marek Mlodzik, and József Mihály
Development 2006 133: 957-966.
[Abstract]
[Full Text]
