Developmental Patterning

Bipolar Order

Science Signaling  06 May 2008:
Vol. 1, Issue 18, pp. ec165
DOI: 10.1126/stke.118ec165

The Drosophila wing has proven valuable in understanding planar cell polarity (PCP), the phenomenon that dictates the packing geometry and polarity of cells in a polarized epithelium. Each cell of the dorsal wing epithelium produces a single hair, and the Frizzled (Fz) PCP pathway aligns all the hairs along the proximodistal (PD) wing axis. Doyle et al. report that mutations that disrupt Fz PCP signaling also caused defects in the alignment of wing ridges. In the posterior wing compartment, ridges are oriented along the PD axis, but in the anterior compartment they are oriented along the anteroposterior (AP) axis, thus making hairs and ridges aligned in the posterior compartment but orthogonal in the anterior compartment. To address the question of how a single PCP pathway could generate two different patterns in the same polarized epithelium, the group focused on Spiny legs (Sple) and Prickle (Pk), two different protein isoforms encoded by the pk gene. Through loss- and gain-of-function genetic experiments, the authors found that disrupting PCP signaling early in wing development [up to 18 hours after pupal formation (APF)] did not affect hair polarity but did affect posterior ridge orientation and that disrupting late PCP signaling (more than 18 hours APF) affected hair polarity all over the wing but only altered ridge orientation in the anterior compartment. The authors propose a model in which the early Sple-dependent phase of PCP patterning establishes a cell-packing pattern that orients all ridges along the PD axis; during the late Pk-dependent phase of PCP, hair polarity is established and the anterior compartment ridges are reoriented. The differential use of two closely related isoforms of a PCP pathway component enables the system to function biphasically.

K. Doyle, J. Hogan, M. Lester, S. Collier, The Frizzled Planar Cell Polarity signaling pathway controls Drosophila wing topography. Dev. Biol. 317, 354-367 (2008). [PubMed]