Functional Importance of Lipin Phosphorylation

Highly conserved throughout evolution, lipins are dual functioning proteins found from yeast to humans. Functioning in the cytoplasm as phosphatidate phosphatase enzymes (PAP), lipins produce diacylglycerol that serves as a precursor for neutral fats and membrane phospholipids. Alternatively, nuclear lipins are responsible for the regulation of metabolic genes. Interestingly, both the mammalian lipin 1 paralog and the single Drosophila Lipin ortholog are highly phosphorylated proteins. Target of rapamycin (TOR) has previously been identified as one of the kinases that controls the subcellular localization of both lipin 1 and Drosophila Lipin. However, other serine and threonine kinases are predicted to be important for the phosphorylation of Lipin. Here, I implement both the GAL4/UAS system as well as CRISPR/Cas9 mutagenesis to systematically mutate individual amino acid residues or clusters of phosphorylation sites of Drosophila Lipin to identify their functional importance. Phenotypic characterization of the phosphosite mutants included fat body histology and fat droplet staining, triglyceride and protein content, starvation resistance, and potential developmental delays. Lipin antibody staining was employed to reveal intracellular distribution of the mutant protein. Results support the prediction that these phosphorylation sites are important for both nuclear function and the role of the protein in fat storage. Data reported here will support the understanding of how the activities of these proteins could be specifically targeted.