Wnt polarity relay

Arelay team of embryonic cells passes the baton of polarity, say Marcus Bischoff and Ralf Schnabel (Technische Universität Carolo Wilhelmina, Braunschweig, Germany). At the finish line is an anterior–posterior (a-p) axis resulting from the passing of a Wnt signal from cell to cell.

The a-p axis of the worm embryo is defined at the very first division, which results in an anterior AB cell and a posterior P₁ cell. How this axis is maintained as the embryo rapidly amasses more cells is unclear. Now, descendents of P₁ are shown to provide a continuous posterior-defining signal to the AB-derived cells.

Left alone, AB descendents were polarity blind. They divided with spindles that oriented with an average orientation of ∼60 degrees with respect to the a-p axis. The addition of the P_1...