74
5.2.4 Identification of Genes Required for the Migration
of Specific Tracheal Branches
M. Affolter
As mentioned above, we have also isolated a number of mutants which,
in contrast to bnl, btl, and doJ, lack specific branches only. These
mutations appeared very interesting to us since they disturb migration
along distinct directions, their effects being comparable to those observed in unc-5 and unc-6 mutants in C. elegans, in which migrations
along the dorsal-ventral axis are selectively disturbed (see references in
Wadsworth et al. 1996). It turned out that two of the mutations which
affected the development of branches growing dorsally and ventrally,
exclusively, mapped to the genes encoding the two essential DPP receptors TKV and PUT (Affolter et al. 1994; Ruberte et al. 1995). Our
detailed analysis of tracheal development in these two mutants (using
many tools generated in the course of our studies on midgut development) revealed that DPP plays a dual role during tracheal cell migration
(Vincent et al. 1997; see also Wappner et al. 1997; Llimargas et al.
1997). On the one hand, DPP controls the region-specific activation of
bnl in the dorsal part of the embryo. On the other hand, DPP expression
dorsal and ventral to the tracheal placode at the onset of migration,
instructs small groups of tracheal cells with respect to their migration
behavior. In the absence of DPP signaling, dorsal and ventral tracheal
cells lose their ability to migrate along the dorsal-ventral body axis.
Ectopic DPP signaling in the center of the tracheal placode inhibits
anterior migration, and reprograms cells to adopt a dorsal-ventral migration behavior. Our studies suggest that other factors in addition to BNL
dictate the direction of migration along the dorsal-ventral axis; some of
these factors might be recognized by tracheal cells only upon the reception of the DPP signal, and might be distributed in an axis-specific
fashion during early embryogenesis.
Further studies in collaboration with the laboratory of Reinhard
Schuh in Gottingen demonstrated that two genes encoding the zinc
finger transcription factors KNIRPS and KNIRPS RELATED possess
multiple and redundant functions during tracheal development.
knirpslknirps related expression is induced in dorsal and ventral tracheal
cells as a result of DPP receptor activation. KNIRPS and KNIRPS
RELATED are required for the migration of cells forming the dorsal and
ventral branches. In addition, ectopic knirps or knirps related expression
5.2.4 Identification of Genes Required for the Migration
of Specific Tracheal Branches
M. Affolter
As mentioned above, we have also isolated a number of mutants which,
in contrast to bnl, btl, and doJ, lack specific branches only. These
mutations appeared very interesting to us since they disturb migration
along distinct directions, their effects being comparable to those observed in unc-5 and unc-6 mutants in C. elegans, in which migrations
along the dorsal-ventral axis are selectively disturbed (see references in
Wadsworth et al. 1996). It turned out that two of the mutations which
affected the development of branches growing dorsally and ventrally,
exclusively, mapped to the genes encoding the two essential DPP receptors TKV and PUT (Affolter et al. 1994; Ruberte et al. 1995). Our
detailed analysis of tracheal development in these two mutants (using
many tools generated in the course of our studies on midgut development) revealed that DPP plays a dual role during tracheal cell migration
(Vincent et al. 1997; see also Wappner et al. 1997; Llimargas et al.
1997). On the one hand, DPP controls the region-specific activation of
bnl in the dorsal part of the embryo. On the other hand, DPP expression
dorsal and ventral to the tracheal placode at the onset of migration,
instructs small groups of tracheal cells with respect to their migration
behavior. In the absence of DPP signaling, dorsal and ventral tracheal
cells lose their ability to migrate along the dorsal-ventral body axis.
Ectopic DPP signaling in the center of the tracheal placode inhibits
anterior migration, and reprograms cells to adopt a dorsal-ventral migration behavior. Our studies suggest that other factors in addition to BNL
dictate the direction of migration along the dorsal-ventral axis; some of
these factors might be recognized by tracheal cells only upon the reception of the DPP signal, and might be distributed in an axis-specific
fashion during early embryogenesis.
Further studies in collaboration with the laboratory of Reinhard
Schuh in Gottingen demonstrated that two genes encoding the zinc
finger transcription factors KNIRPS and KNIRPS RELATED possess
multiple and redundant functions during tracheal development.
knirpslknirps related expression is induced in dorsal and ventral tracheal
cells as a result of DPP receptor activation. KNIRPS and KNIRPS
RELATED are required for the migration of cells forming the dorsal and
ventral branches. In addition, ectopic knirps or knirps related expression