66
M. Affolter
shape changes, depends on numerous interactions between different
groups of cells and the surrounding extracellular substrates. In both
systems, a member of the TGF~ superfamily of secreted signaling
molecules plays an important role which will be highlighted and will
serve as a guide through this chapter.
5.1.1 Induction in Development:
A Genetic Approach in Drosophila melanogaster
One of the major challenges of embryological studies over the last
decades has been the determination of the molecular mechanisms by
which the spatial organization of an animal emerges as it develops from
a fertilized egg. A leading role in this process has been attributed to
mechanisms by which a signal generated by a group of cells controls the
fate of a neighboring cell(s), a phenomenon generally referred to as
induction. In vertebrates, where induction was first described, most
organs are formed through interactions between cells of different germ
layers. In invertebrates, genetic studies have demonstrated that induction is also one of the prevailing mechanisms that steers developmental
decisions.
Using the powerful genetic model of Drosophila melanogaster, we
have been studying embryonic induction processes occurring between
cells of two different cell layers (Bienz 1994, 1996). As a result of these
inductions, positional information laid down in the visceral mesoderm
(VM) is transmitted via cell--cell communication to the underlying
endoderm, leading to its patterning along the anterior-posterior axis. A
particular induction cascade culminating in the development of copper
cells in the responding endoderm is mediated in part by DECAPENTAPLEGIC (DPP), a member of the TGF~ superfamily of secreted signaling molecules. Based on studies in vertebrates by the group of Joan
Massague, we have isolated, in collaboration with Konrad Basler's
group in ZUrich, the two essential cell surface receptors which bind the
DPP ligand and transmit the signal across the membrane (Nellen et al.
1994; Ruberte et al. 1995). These receptors were encoded by the genes
PUNT (PUT, a type II receptor) and THICK VEINS (TKV, a type I
receptor). Mutations in these genes were previously identified by
NUsslein-Volhard and colleagues in their screens for zygotic effect em-
M. Affolter
shape changes, depends on numerous interactions between different
groups of cells and the surrounding extracellular substrates. In both
systems, a member of the TGF~ superfamily of secreted signaling
molecules plays an important role which will be highlighted and will
serve as a guide through this chapter.
5.1.1 Induction in Development:
A Genetic Approach in Drosophila melanogaster
One of the major challenges of embryological studies over the last
decades has been the determination of the molecular mechanisms by
which the spatial organization of an animal emerges as it develops from
a fertilized egg. A leading role in this process has been attributed to
mechanisms by which a signal generated by a group of cells controls the
fate of a neighboring cell(s), a phenomenon generally referred to as
induction. In vertebrates, where induction was first described, most
organs are formed through interactions between cells of different germ
layers. In invertebrates, genetic studies have demonstrated that induction is also one of the prevailing mechanisms that steers developmental
decisions.
Using the powerful genetic model of Drosophila melanogaster, we
have been studying embryonic induction processes occurring between
cells of two different cell layers (Bienz 1994, 1996). As a result of these
inductions, positional information laid down in the visceral mesoderm
(VM) is transmitted via cell--cell communication to the underlying
endoderm, leading to its patterning along the anterior-posterior axis. A
particular induction cascade culminating in the development of copper
cells in the responding endoderm is mediated in part by DECAPENTAPLEGIC (DPP), a member of the TGF~ superfamily of secreted signaling molecules. Based on studies in vertebrates by the group of Joan
Massague, we have isolated, in collaboration with Konrad Basler's
group in ZUrich, the two essential cell surface receptors which bind the
DPP ligand and transmit the signal across the membrane (Nellen et al.
1994; Ruberte et al. 1995). These receptors were encoded by the genes
PUNT (PUT, a type II receptor) and THICK VEINS (TKV, a type I
receptor). Mutations in these genes were previously identified by
NUsslein-Volhard and colleagues in their screens for zygotic effect em-