The function of Prickle in planar polarity and the generation of specificity between wingless and planar cell polarity signaling. D.R. Tree 1 2, J. Axelrod 2, D. Gubb 1. 1) Dept Genetics, Univ Cambridge, Cambridge, England; 2) Stanford University School of Medicine, 300 Pasteur Drive, Stanford.
prickle (pk) is a member of the core group of planar cell polarity (PCP) genes with a critical role in PCP specification. It encodes three alternatively spliced transcripts which encode LIM domain proteins. Three classes of mutant alleles exist that result from the loss of either of two of the transcripts or the loss of all of the transcripts. The former class of allele leads to phenotypes in reciprocal body areas whereas the latter class of allele leads to phenotypes in all body areas. PK is the first of the PCP genes to have an asymmetric protein distribution in third instar imaginal discs. The distribution of PK in the different classes of pk mutant alleles suggests that the different isoforms of PK are required for the each others post-translational stability. However, the wild-type distribution of PK in all the other PCP genes studied suggests that they are not required for the transcription or post-translational stability of PK. Previously, the epistatic relationship of PK with regards to FZ and DSH was unknown. Using overexpression phenotypes of PK we show that PK is upstream of DSH but not FZ in a novel bifurcation of the PCP signaling pathway. Overexpression phenotypes in the wing suggest that the PK mediated branch of the PCP pathway is antagonistic to the FZ mediated branch. We present data that suggests that the function of this antagonism is to modulate the signal perceived by FZ and thus prevents the activation of the PCP pathway by wingless signaling. When the PCP pathway is over-activated in a null pk background the wingless pathway is ectopically activated. This suggests that one element of the function of PK is to provide functional specificity between these two important developmental pathways that share at least two components.