Question

The Wnt planar polarity signaling pathway normally ensures that each wing cell in Drosophila has a single hair. Overexpression of the Frizzled gene from a heat-shock promoter (hs-Fz) causes multiple hairs to grow from many cells (Figure 1A). This phenotype is suppressed if hs- Fz is combined with a heterozygous deletion (Dsh) of the Dishevelled gene (Figure 1B). Do these results allow you to order the action of Frizzled and Dishevelled in the signaling path- way? If so, what is the order? Explain your reasoning. (B) hs-Fz/+ Dsh4/+ Figure 1. Pattern of hair growth on wing cells in genetically different Drosophila. hs-Fz/+ +/+

Answer 1

If the over-expression phenotype of a gene X is suppressed by a recessive mutation at another locus Y, it shows that Y is required for the function of X.
i.e. Y acts downstream to X.

In the given case,
Over-expression of Frizzled in the presence of WT Dishevelled ----> Multiple hairs
Over-expression of Frizzled in the presence of Dishevelled deletion ----> Suppression of multiple hairs

It shows that Frizzled acts through Dishevelled to produce multiple hairs.
i.e. Dishevelled acts downstream to Frizzled

Pathway:
Frizzled ----> Dishevelled ----> Hair formation