Inborn errors of purine metabolism manifest as complex syndromes with developmental and neurological phenotypes. Given the importance of purines as critical building blocks and key molecules for energy storage and signaling, it isn't surprising that disruption of purine biosynthesis causes pleiotropic effects. However, the molecular links between altered purine biosynthesis and phenotypic outcome are mysterious. We use C. elegans to probe the mechanisms causing phenotypic outcomes upon dysregulation of purine biosynthesis. Purines are synthesized de novo from PRPP and by salvage synthesis from scavenged purine bases. Adenylosuccinate lyase (ADSL) is a de novo enzyme. Loss of ADSL is likely embryonic lethal in humans. Most patients have reduced activity and present with seizures, ataxia and autistic-like behaviors. Similar to the human disorder,
adsl-1(RNAi) induces multiple phenotypes, including slow body bending in a liquid thrashing assay, larger intestinal fat droplets and an altered phenotype in a gustatory plasticity assay. Progeny of L4 animals treated with RNAi are 20% embryonic lethal and sterile. Defects in oogenesis can also be induced in fertile animals by
adsl-1(RNAi). In general, reduced enzyme activity will increase levels of substrates and decrease levels of products, and both effects have potential phenotypic consequences. We have assessed the relative importance of lack of purine production versus substrate accumulation upon
adsl-1(RNAi). The neuromuscular phenotypes of
adsl-1(RNAi) animals are rescued by treatment with aminopterin, which blocks purine biosynthesis at an early step, as well as by RNAi of the enzyme that precedes ADSL. We conclude that defects in muscle function are a result of toxic buildup of ADSL substrate. Consistent with this result, the neuromuscular phenotypes are not rescued by supplementation with hypoxanthine to allow for more purine biosynthesis via salvage biosynthesis. In contrast, hypoxanthine supplementation rescues
adsl-1 sterility, suggesting that the oogenesis phenotype is a result of lack of purine biosynthesis. We also examined functions of other purine biosynthetic enzymes. RNAi of the adenylosuccinate synthetase gene
adss-1 causes phenotypes like that of
adsl-1. And RNAi of the gene encoding HPRT, which is associated with Lesch-Nyhan disease in humans, results in fat storage defects.