Fray, a Drosophila serine/threonine kinase homologous to mammalian PASK, is required for axonal ensheathment

Fray is a serine/threonine kinase expressed by the peripheral glia of Droso phila, whose function is required for normal axonal ensheathment. Null fray mutants die early in larval development and have nerves with severe swelli ng and axonal defasciculation. The phenotype is associated with a failure o f the ensheathing glia to correctly wrap peripheral axons. When the fray cD NA is expressed in the ensheathing glia of fray mutants, normal nerve morph ology is restored. Fray belongs to a novel family of Ser/Thr kinases, the P F kinases, whose closest relatives are the PAK kinases. Rescue of the Droso phila mutant phenotype with PASK, the rat homolog of Fray, demonstrates a f unctional homology among these proteins and suggests that the Fray signalin g pathway is widely conserved.