Altered phenotypes due to genetic interaction between the mouse phosphoinositide biosynthesis genes Fig4 and Pip4k2c

Loss-of-function mutations of FIG4 are responsible for neurological disorders in human and mouse that result from reduced abundance of the signaling lipid PI(3,5)P(2). In contrast, loss-of-function mutations of the phosphoinositide kinase PIP4K2C result in elevated abundance of PI(3,5)P(2.) These opposing effects on PI(3,5)P(2) suggested that we might be able to compensate for deficiency of FIG4 by reducing expression of PIP4K2C. To test this hypothesis in a whole animal model, we generated triallelic mice with genotype Fig 4(−/−), Pip4k2c(+/−); these mice are null for Fig 4 and haploinsufficient for Pip4k2c. The neonatal lethality of Fig 4 null mice in the C57BL/6J strain background was rescued by reduced expression of Pip4k2c. The lysosome enlargement characteristic of Fig 4 null cells was also reduced by heterozygous loss of Pip4k2c. The data demonstrate interaction between these two genes, and suggest that inhibition of the kinase PIPK4C2 could be a target for treatment of FIG4 deficiency disorders such as Charcot-Marie-Tooth Type 4J and Yunis-Varón Syndrome.