View Program - 63rd Annual Drosophila Research Conference

Lipins constitute a conserved family of eukaryotic metabolic regulators. They are dual-functions proteins, acting as phosphatidate phosphatases in lipid synthesis in the cytoplasm and as transcriptional regulators of metabolism in the nucleus. The single Drosophila Lipin ortholog contains 26 serine and threonine phosphorylation sites that were identified by mass spectrometry, suggesting complex posttranslational control of Lipin functions. Indeed, in both flies and mammals, nuclear translocation of Lipin has been shown to be controlled by TORC1-dependent phosphorylation. To identify additional functions of phosphorylation, we have carried out a systematic mutational analysis of single phosphorylation sites and groups of sites, replacing serine and threonine residues with alanine residues or the phosphomimetic glutamic acid. CRISPR/Cas9-generated mutants were then characterized for Lipin expression, metabolic defects, and starvation resistance. Notably, we found that one of these mutants, carrying an amino acid substitution at serine residue 820 (S820), exhibited a significant difference in starvation resistance in the male and female sex. Interestingly, S820 is strategically located between the catalytic and transcriptional co-regulator motifs of the protein. Both males and females expressing Lipin S820E, in which the serine residue is replaced by phosphomimetic glutamate, showed reduced starvation resistance. In contrast, female flies expressing non-phosphorylatable Lipin S820A displayed significantly increased starvation resistance, whereas males showed reduced starvation resistance. These data suggest that the phosphorylation status at specific sites of the Lipin protein differentially affects functions of the protein in males and females. Thus, it may contribute to sex-specific differences in metabolism. The metabolic consequences of S820 phosphorylation in males and females are currently under investigation.

Mutational characterization of phosphorylation sites suggests sex-specific regulation of the metabolic regulator Lipin