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M. Affolter
spond to the DPP signal in order to be attracted and migrate towards the
dorsal and ventral spots of BNL. Similarly, cells migrating anteriorly to
form the dorsal trunk have to respond to EGF signaling which leads to the
activation/maintenance of expression of the transcription factor SPALT;
SPALT enables dorsal trunk cells to move towards the anteriorly located
BNL spot (Kiihnlein et al. 1996; Wappner et al. 1997; Chen et al. 1998).
The genes regulated by KNIRPS/KNIRPS RELATED and SPALT
remain to be identified. These targets might encode components which
are essential for the proper interpretation of FGFR signaling, components which regulate the affinity of groups of tracheal cells, or components which recognize essential migration cues distinct from BNL. We
have already identified several transcription units that are under the
control of KNIRPS and are in the process of cloning and characterizing
the corresponding genes.
The developing tracheal system represents a unique system to study
cell migration in Drosophila since both a guidance molecule (BNL) and
its receptor (BTL) have been identified. Several other components
(DOF, DPP signaling, EGF signaling, KNIRPS/KNIRPS RELATED,
and SPALT) have been isolated and a future challenge will be to integrate all these components into a comprehensive network of interactions
controlling directed cell migration.
5.3 Prospects
Many similarities between the development of the tracheal system of
Drosophila and the vertebrate vascular system are emerging. Particularly striking is the interaction between TGF~ and FGF in cell migration
during angiogenesis (Gadjusek et al. 1993), which argues for a more
general role of the combined activity of these two signaling pathways in
inducing cell migration. Even more striking is the conservation of aspects of the molecular control of branching in the Drosophila tracheal
system and vertebrate lung development, and the involvement ofFGF in
the initial dispersion of mesodermal cells during early mouse development. It will be interesting to compare the regulatory networks upstream
and downstream of FGFs in the distinct developmental contexts. These
studies might ultimately lead to a better understanding of basic molecular strategies in development and disease.
M. Affolter
spond to the DPP signal in order to be attracted and migrate towards the
dorsal and ventral spots of BNL. Similarly, cells migrating anteriorly to
form the dorsal trunk have to respond to EGF signaling which leads to the
activation/maintenance of expression of the transcription factor SPALT;
SPALT enables dorsal trunk cells to move towards the anteriorly located
BNL spot (Kiihnlein et al. 1996; Wappner et al. 1997; Chen et al. 1998).
The genes regulated by KNIRPS/KNIRPS RELATED and SPALT
remain to be identified. These targets might encode components which
are essential for the proper interpretation of FGFR signaling, components which regulate the affinity of groups of tracheal cells, or components which recognize essential migration cues distinct from BNL. We
have already identified several transcription units that are under the
control of KNIRPS and are in the process of cloning and characterizing
the corresponding genes.
The developing tracheal system represents a unique system to study
cell migration in Drosophila since both a guidance molecule (BNL) and
its receptor (BTL) have been identified. Several other components
(DOF, DPP signaling, EGF signaling, KNIRPS/KNIRPS RELATED,
and SPALT) have been isolated and a future challenge will be to integrate all these components into a comprehensive network of interactions
controlling directed cell migration.
5.3 Prospects
Many similarities between the development of the tracheal system of
Drosophila and the vertebrate vascular system are emerging. Particularly striking is the interaction between TGF~ and FGF in cell migration
during angiogenesis (Gadjusek et al. 1993), which argues for a more
general role of the combined activity of these two signaling pathways in
inducing cell migration. Even more striking is the conservation of aspects of the molecular control of branching in the Drosophila tracheal
system and vertebrate lung development, and the involvement ofFGF in
the initial dispersion of mesodermal cells during early mouse development. It will be interesting to compare the regulatory networks upstream
and downstream of FGFs in the distinct developmental contexts. These
studies might ultimately lead to a better understanding of basic molecular strategies in development and disease.