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M. Affolter
organs which are built as a result of local induction events, our studies
might provide insight into the basic mechanisms by which induction
shapes tissues and organs in vertebrates.
A few years ago, we became interested in the development of the
tracheal system, a network of oxygen-transporting tubules, during
Drosophila embryogenesis. Tracheal development relies on cell migration and cell extension (in the absence of concomitant cell division), and
we anticipated that the establishment of this complex tubular system
would require numerous cell-cell and cell-substrate interactions. In the
meantime, tracheal development has emerged as a valuable model system to study the genetics of cell migration in Drosophila. The proposition that complex cellular interactions would help in establishing the
tubular network have been confirmed, and I would like to concentrate in
the second part of this chapter on the results we and other groups have
obtained regarding the genetic control of the establishment of branched
tubular epithelia in Drosophila.
5.2 Cell Migration in Development
During the development of multicellular animals, a large number of
cells originate at a considerable distance from the site within the organism at which they fulfill their essential function. To reach that site, these
cells have to migrate over other tissues or extracellular substrates receiving and interpreting instructions from their environment. Such precise
cell movements are a prerequisite for the concerted development and the
subsequent interconnection of tissues within developing organisms. Although a coherent picture of how cells generate force and motility is
beginning to emerge (Lauffenburger and Horvitz 1996; Mitchison and
Cramer 1996), the understanding of how mobility is regulated during
development is less advanced. Locally distributed signals dictating the
direction of migration are most likely molecules anchored to cell membranes of the migration surface, molecules associated with the extracellular environment of the migration path, or diffusible factors. Receptors
recognizing these guidance molecules as attractive or repulsive must be
expressed on the surface of migrating cells and their activation should
ultimately lead to the intracellular changes that cause directed migration.
M. Affolter
organs which are built as a result of local induction events, our studies
might provide insight into the basic mechanisms by which induction
shapes tissues and organs in vertebrates.
A few years ago, we became interested in the development of the
tracheal system, a network of oxygen-transporting tubules, during
Drosophila embryogenesis. Tracheal development relies on cell migration and cell extension (in the absence of concomitant cell division), and
we anticipated that the establishment of this complex tubular system
would require numerous cell-cell and cell-substrate interactions. In the
meantime, tracheal development has emerged as a valuable model system to study the genetics of cell migration in Drosophila. The proposition that complex cellular interactions would help in establishing the
tubular network have been confirmed, and I would like to concentrate in
the second part of this chapter on the results we and other groups have
obtained regarding the genetic control of the establishment of branched
tubular epithelia in Drosophila.
5.2 Cell Migration in Development
During the development of multicellular animals, a large number of
cells originate at a considerable distance from the site within the organism at which they fulfill their essential function. To reach that site, these
cells have to migrate over other tissues or extracellular substrates receiving and interpreting instructions from their environment. Such precise
cell movements are a prerequisite for the concerted development and the
subsequent interconnection of tissues within developing organisms. Although a coherent picture of how cells generate force and motility is
beginning to emerge (Lauffenburger and Horvitz 1996; Mitchison and
Cramer 1996), the understanding of how mobility is regulated during
development is less advanced. Locally distributed signals dictating the
direction of migration are most likely molecules anchored to cell membranes of the migration surface, molecules associated with the extracellular environment of the migration path, or diffusible factors. Receptors
recognizing these guidance molecules as attractive or repulsive must be
expressed on the surface of migrating cells and their activation should
ultimately lead to the intracellular changes that cause directed migration.