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. 2013 May 1;377(1):1–8. doi: 10.1016/j.ydbio.2013.01.030

Fig. 2.

Fig. 2

The polarity effects of ptc—en— clones. This model is puzzling, but it illustrates some important facts and principles about the two PCP systems operating in the Drosophila abdomen. Anterior is at the top. In the wildtype, we envisage two gradient systems, one (Ds activity) from the Ds/Ft system shown in grey and one (Fz activity) from the Fz/Stan system shown in red. The Ds/Ft gradient peaks at the A/P compartment border (dashed line) and runs downwards from there in both anterior and posterior directions. The Fz gradient may have a more complex topography than shown but most likely peaks at the front of the A compartment, declining posteriorwards from there to the back or middle of the P compartment. In both the A and P compartments the hairs point down the Fz activity gradient but the two compartments read the Ds gradient with opposite sign, pointing up the Ds slope in the A compartment, and down the Ds slope in the P (Casal et al., 2002). In the A compartment the slopes of both the Fz and Ds activity gradients act together to point the hairs backwards while in the P compartment the two gradients act with opposite sign. In both the A and the P compartments, clones that lack the ptc and en genes make cuticle that shows the identity of cells that are located in the wildtype just anterior to the A/P compartment boundary; within these clones the levels of the gradients are indicated by the colour intensities. These cell identities correspond to high levels of Ds activity (dark grey) and medium levels of Fz activity (pale pink). The arrows indicate the directions of the local slopes of Ds activity (white) and Fz activity (blue) near the clones; in the A compartment these local slopes orient hairs near the clones down the Fz activity gradient and up the Ds activity gradient. However in the P compartment the P cells orient their hairs down the Ds slope (Casal et al., 2002). Thus in the P compartment of the wildtype, hairs near ptc—en— clones are subject to two opposing influences; explaining perhaps why these clones have no consistent effect on the cells around them.