Phosphoinositides modulate several cellular behaviours including cell proliferation, cell survival, cytoskeletal changes and vesicular trafficking. Many of these processes are regulated by enzymes that use phosphatidylinositol 4,5 bisphosphate (PI4,5P 2 ) as a substrate or by proteins that bind PI4,5P 2 directly. PI4,5P 2 can be made by 5’ phosphorylation of PI4P by Type I phosphatidylinositol phosphate kinase (Type I PIPK) or by 4’ phosphorylation of PI5P by Type II PIPK. However, while Type I PIPK is required to produce functional PI4,5P 2 in vivo , no one has yet demonstrated a requirement for Type II PIPK, an enzyme found only in metazoans. In mammals, there are at least three isoforms of Type I PIPK and three isoforms of Type II PIPK. C. elegans contains only one of each, named
ppk-1 (F55A12.3) and
ppk-2 (predicted as two genes – Y48G9A.g and Y48G9A.h) respectively.
ppk-1 RNAi applied to L4 larvae results in a sterile phenotype (Fraser et al. 2000, Maeda et al. 2001), consistent with a requirement for PI4,5P 2 in the spermathecae (Clandinin et al. 1998). We have isolated a deletion allele (
pk1343 ) of
ppk-2 , which lacks a large part of the catalytic domain. Unlike worms treated with
ppk-1 RNAi, worms homozygous for
pk1343 are viable, develop and move normally, and respond like wild type to
ppk-1 RNAi. However,
ppk-2 (
pk1343 ) larvae show an increased sensitivity to oxidative stress. Thus, we have confirmed that
ppk-1 and
ppk-2 have separate functions, and, for the first time in any organism, we have evidence for an in vivo function of a Type II PIP kinase. To investigate the effect of Type II PIPK on in vivo lipids, we will analyse in vivo phosphoinositide levels in wild type and mutant worms. References : Fraser et al. 2000 Nature 408,
p325, Maeda et al. 2001 Current Biology 11,
p171, Clandinin et al. 1998 Cell 92,
p523