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We are using Drosophila follicle cells to study the mechanisms that promote cell motility.  Using genetics we identified a gene regulatory network that controls the dynamic pattern of activation of JAK/STAT in anterior follicle cells. Under the influence of a graded signal, Unpaired (UPD), JAK/STAT becomes activated first in a graded fashion.  STAT, in turn, locally activates its own repressor, Apontic (APT), a new feedback regulator of JAK/STAT signaling.  High levels of JAK/STAT also activate Slow Border Cells (SLBO), which undermines APT-mediated repression.  In this way, cells that achieve a high JAK/STAT level maintain SLBO expression and form border cells, which then migrate out of the cell layer.  Cells with lower JAK/STAT activity express more APT than SLBO, ultimately lose STAT activity, and remain in the follicular epithelium.  To better understand how the graded signal is converted to an all-or-none decision to move or stay, we developed a mathematical model.  Simulations using the model reproduce the observed dynamics of JAK/STAT expression in the wild type and in several mutant situations.  By combining biological experiments and mathematical modeling, we can achieve a more sophisticated understanding of how cells interpret molecular gradients.

This protocol describes a method for the dissection of egg chambers from intact Drosophila females and culture conditions that permit live imaging of them, with a particular emphasis on stage 9. This stage of development is characterized by oocyte growth and patterning, outer follicle cell rearrangement and migration of border cells. Although in vitro culture of egg chambers of later developmental stages has long been possible, until recently stage 9 egg chambers could only be kept alive for short periods, did not develop normally, and border cell migration failed entirely. We have established culture conditions that support overall egg chamber development including border cell migration in vitro. This protocol makes possible direct observation of molecular and cellular dynamics in both wild-type and mutant egg chambers, and opens the door to testing of pharmacological inhibitors and the use of biosensors. The entire protocol takes ∼24 h while the preparation of egg chambers for live imaging requires only 15–20 min.

Temporal and spatial controls of cell migration are crucial during normal development and in disease. Our understanding, though, of the mechanisms that guide cells along a specific migratory path remains largely unclear. We have identified wunen 2 as a repellant for migrating primordial germ cells. We show that wunen 2 maps next to and acts redundantly with the previously characterized gene wunen, and that known wunen mutants affect both transcripts. Both genes encode Drosophila homologs of mammalian phosphatidic acid phosphatase. Our work demonstrates that the catalytic residues of Wunen 2 are necessary for its repellant effect and that it can affect germ cell survival. We propose that spatially restricted phospholipid hydrolysis creates a gradient of signal necessary and specific for the migration and survival of germ cells.