The partitioning of fatty acids between membrane and storage lipids controls ER membrane expansion.

The biogenesis of membrane-bound organelles involves the synthesis, remodelling and degradation of their constituent phospholipids. How these pathways regulate organelle size, remains still poorly understood. Here we demonstrate that a lipid degradation pathway inhibits the expansion of the endoplasmic reticulum (ER) membrane. Phospholipid diacylglycerol acyltransferases (PDATs) use endogenous phospholipids as fatty acyl donors to generate triglyceride stored in lipid droplets. The significance of this non-canonical triglyceride biosynthetic pathway has remained elusive. We find that the activity of the yeast PDAT Lro1 is regulated by a membrane-proximal domain facing the luminal side of the ER bilayer. To reveal the biological roles of PDATs, we engineered an Lro1 variant with derepressed activity. We show that active Lro1 mediates the retraction of ER membrane expansion driven by phospholipid synthesis. Furthermore, the subcellular distribution and membrane turnover activity of Lro1 are controlled by diacylglycerol, produced by the activity of Pah1, a conserved member of the lipin family. Collectively, our findings reveal a lipid metabolic network that regulates endoplasmic reticulum biogenesis by converting phospholipids into storage lipids.

Magnetosomes and Magnetosome Mimics: Preparation, Cancer Cell Uptake and Functionalization for Future Cancer Therapies.

Magnetic magnetite nanoparticles (MNP) are heralded as model vehicles for nanomedicine, particularly cancer therapeutics. However, there are many methods of synthesizing different sized and coated MNP, which may affect their performance as nanomedicines. Magnetosomes are naturally occurring, lipid-coated MNP that exhibit exceptional hyperthermic heating, but their properties, cancer cell uptake and toxicity have yet to be compared to other MNP. Magnetosomes can be mimicked by coating MNP in either amphiphilic oleic acid or silica. In this study, magnetosomes are directly compared to control MNP, biomimetic oleic acid and silica coated MNP of varying sizes. MNP are characterized and compared with respect to size, magnetism, and surface properties. Small (8 ± 1.6 nm) and larger (32 ± 9.9 nm) MNP are produced by two different methods and coated with either silica or oleic acid, increasing the size and the size dispersity of the MNP. The coated larger MNP are comparable in size (49 ± 12.5 nm and 61 ± 18.2 nm) to magnetosomes (46 ± 11.8 nm) making good magnetosome mimics. All MNP are assessed and compared for cancer cell uptake in MDA-MB-231 cells and importantly, all are readily taken up with minimal toxic effect. Silica coated MNP show the most uptake with greater than 60% cell uptake at the highest concentration, and magnetosomes showing the least with less than 40% at the highest concentration, while size does not have a significant effect on uptake. Finally, surface functionalization is demonstrated for magnetosomes and silica coated MNP using biotinylation and EDC-NHS, respectively, to conjugate fluorescent probes. The modified particles are visualized in MDA-MB-231 cells and demonstrate how both naturally biosynthesized magnetosomes and biomimetic silica coated MNP can be functionalized and readily up taken by cancer cells for realization as nanomedical vehicles.

Loss of Deacetylation Enzymes Hdac6 and Sirt2 Promotes Acetylation of Cytoplasmic Tubulin, but Suppresses Axonemal Acetylation in Zebrafish Cilia.

Cilia are evolutionarily highly conserved organelles with important functions in many organs. The extracellular component of the cilium protruding from the plasma membrane comprises an axoneme composed of microtubule doublets, arranged in a 9 + 0 conformation in primary cilia or 9 + 2 in motile cilia. These microtubules facilitate transport of intraflagellar cargoes along the axoneme. They also provide structural stability to the cilium, which may play an important role in sensory cilia, where signals are received from the movement of extracellular fluid. Post-translational modification of microtubules in cilia is a well-studied phenomenon, and acetylation on lysine 40 (K40) of alpha tubulin is prominent in cilia. It is believed that this modification contributes to the stabilization of cilia. Two classes of enzymes, histone acetyltransferases and histone deacetylases, mediate regulation of tubulin acetylation. Here we use a genetic approach, immunocytochemistry and behavioral tests to investigate the function of tubulin deacetylases in cilia in a zebrafish model. By mutating three histone deacetylase genes (Sirt2, Hdac6, and Hdac10), we identify an unforeseen role for Hdac6 and Sirt2 in cilia. As expected, mutation of these genes leads to increased acetylation of cytoplasmic tubulin, however, surprisingly it caused decreased tubulin acetylation in cilia in the developing eye, ear, brain and kidney. Cilia in the ear and eye showed elevated levels of mono-glycylated tubulin suggesting a compensatory mechanism. These changes did not affect the length or morphology of cilia, however, functional defects in balance was observed, suggesting that the level of tubulin acetylation may affect function of the cilium.