Phosphoinositide acyl chain diversity: comparative analysis across species and mouse tissues

Cells create acyl chain compositions for their phosphoinositide (PIPn) pools that are distinct from other phospholipid classes. While some lower eukaryotes present highly heterogeneous PIPn (e.g., yeast, fly), more complex organisms typically display PIPn enriched in fewer molecular species (e.g., the C38:4 species in fish, frog and mice). A comprehensive analysis of murine tissues (using both LC-MS/MS and MSI) confirms a general enrichment for C38:4-PIPn but also highlights the existence of several cell populations with strikingly divergent acyl chain compositions, characterised by the prevalence of shorter-chain, more saturated species (e.g., C32:0 in the testes and C34:1 in the prostate). The evolutionary pressures driving the creation of these specific acyl chain compositions are still unclear; current evidence suggests there is probably a balance to be achieved in different cell types between the biophysical constraints imposed by PIPn as membrane-captive ‘messengers’ (e.g., flexibility in head group presentation in different membrane environments), the demand for substantial de novo lipid synthesis (e.g., in rapid membrane expansion), the need for acyl chain remodelling (e.g., in molecular segregation of functional pools) and fatty acid availability. Moreover, it would appear inevitable that this balance will be distorted under most cell culture conditions in vitro.