Pitchfork Regulates Primary Cilia Disassembly and Left-Right Asymmetry

Abstract

SUMMARY A variety of developmental disorders have been associated with ciliary defects, yet the controls that govern cilia disassembly are largely unknown. Here we report a mouse embryonic node gene, which we named Pitchfork (Pifo). Pifo associates with ciliary targeting complexes and accumulates at the basal body during cilia disassembly. Haploinsufficiency causes a unique node cilia duplication phenotype, left-right asymmetry defects, and heart failure. This phenotype is likely relevant in humans, because we identified a heterozygous R80K PIFO mutation in a fetus with situs inversus and cystic liver and kidneys, and in patient with double-outflow right ventricle. We show that PIFO, but not R80K PIFO, is sufficient to activate Aurora A, a protooncogenic kinase that induces cilia retraction, and that Pifo/PIFO mutation causes cilia retraction, basal body liberation, and overreplication defects. Thus, the observation of a disassembly phenotype in vivo provides an entry point to understand and categorize ciliary disease.

Cilia and cell cycle re-entry

“…23,24 Remarkably, these cells retained cilia during mitosis. 24 Similar cellular phenotypes were seen when Aurora A kinase activity was inhibited by overexpression of a pathogenic mutant of Pifo, R80K. 24 Mice or humans heterozygous for mutations in Pifo were shown to have laterality defects, possibly due to structural defects of the cilia in the embryonic node, 24 suggesting that the pool of Pifo at the basal body during the initial course of cilia resorption may account for proper left-right patterning.…”

“…Kinzel and colleagues showed that Pifo accumulates at the basal body during the early stages of cilia disassembly and participates in the ciliary resorption process working along with Aurora A. 24 The authors reported defects in ciliary disassembly, centriole overduplication and multipolar spindle formation in cells lacking one allele of Pifo. 23,24 Remarkably, these cells retained cilia during mitosis.…”

“…24 The authors reported defects in ciliary disassembly, centriole overduplication and multipolar spindle formation in cells lacking one allele of Pifo. 23,24 Remarkably, these cells retained cilia during mitosis. 24 Similar cellular phenotypes were seen when Aurora A kinase activity was inhibited by overexpression of a pathogenic mutant of Pifo, R80K.…”

“…24 All of these structures are extremely sensitive to cilia-based signaling during embryonic development. Kinzel and colleagues showed that Pifo accumulates at the basal body during the early stages of cilia disassembly and participates in the ciliary resorption process working along with Aurora A.…”

“…21 Recent work indicates that the retraction process of the cilia upon growth factor stimulation involves several proteins, such as human enhancer of filamentation 1 (HEF1), Aurora A kinase, Pitchfork (Pifo) and Tctex-1. [23][24][25] Pugacheva and colleagues first showed that growth factor stimulation of serumdeprived cells induces ciliary disassembly through the sequential activation of HEF1 and Aurora A, which, in turn, activates histone deacetylase 6 (HDAC6) at the axoneme.…”