Hedgehog and Drosophila germ cell migration.

The functional gonads, essential for the continuity of a species, have both somatic and germline components. Newly formed germ cells are quiescent and are often physically isolated from the rest of the soma, protecting them from the signals that control somatic specification and differentiation. Nonetheless, the sequestered germ cells must ultimately navigate through the embryo to meet up with the somatic gonadal components. Forward genetic screens conducted in Drosophila have uncovered several crucial factors that generate both attractive and repulsive signals controlling germ cell movement. Efforts to reveal how the range of molecular players coordinate their activities to ensure that navigation is a robust and reproducible process have led to exciting, albeit sometimes contentious, discoveries. Herein, we summarize evidence for Hedgehog functioning in a single pathway from the signal source to signal reception to the downstream cytoskeletal events controlling the directed movement of germ cells to the site of gonad formation.