No abstract

No abstract

Chromatin-associated phospholipids are well recognized. A report that catalytically active endonuclear CTP:choline-phosphate cytidylyltransferase ␣ is necessary for cell survival questions whether endonuclear, CDP-choline pathway phosphatidylcholine synthesis may occur in situ. We report that chromatin from human IMR-32 neuroblastoma cells possesses such a biosynthetic pathway. First, membrane-free nuclei retain all three CDP-choline pathway enzymes in proportions comparable with the content of chromatin-associated phosphatidylcholine. Second, following supplementation of cells with deuterated choline and using electrospray ionization mass spectrometry, both the time course and molecular species labeling pattern of newly synthesized endonuclear and whole cell phosphatidylcholine revealed the operation of spatially separate, compositionally distinct biosynthetic routes. Specifically, endogenous and newly synthesized endonuclear phosphatidylcholine species are both characterized by a high degree of diacyl/alkylacyl chain saturation. This unusual species content and synthetic pattern (evident within 10 min of supplementation) are maintained through cell growth arrest by serum depletion and when proliferation is restored, suggesting that endonuclear disaturated phosphatidylcholine enrichment is essential and closely regulated. We propose that endonuclear phosphatidylcholine synthesis may regulate periodic nuclear accumulations of phosphatidylcholine-derived lipid second messengers. Furthermore, our estimates of saturated phosphatidylcholine nuclear volume occupancy of around 10% may imply a significant additional role in regulating chromatin structure.Considerable evidence supports the existence of an endonuclear pool of phospholipid, in association with the nuclear matrix and distinct from the nuclear envelope (1-4). This endonuclear phospholipid is remarkable for several reasons. Although all the major membrane phospholipids, predominantly phosphatidylcholine (PtdCho), 1 phosphatidylethanolamine (PtdEtn), phosphatidylserine, and phosphatidylinositol (PtdIns), may be present typically at 4 -10% of total cell content (2), transmission electron microscopy has failed to reveal endonuclear membranous systems (5). Hence the molecular organization of endonuclear phospholipids in eukaryotic cells is still unclear. Extensive histochemical and cytochemical studies suggest that their spatial distributions overlap that of decondensed chromatin domains (3, 4). A number of in vitro studies suggest a functional relationship between various endonuclear phospholipids and gene expression/transcription (6 -10). Moreover, cell studies have shown that the amounts of endonuclear phospholipids change during progression through the cell cycle (4). The potential physiological importance of intranuclear phospholipid has recently been highlighted by the recognition that the ␣ isoform (CCT␣) of CTP:choline-phosphate cytidylyltransferase, the principal regulatory enzyme of PtdCho biosynthesis (11), is confined to the nucleus throughout the ce...

Background: Phosphatidylinositol transfer protein, cytoplasmic 1 (PITPNC1) (alternative name, RdgB␤) promotes metastatic colonization and angiogenesis in humans. Results: We demonstrate that RdgB␤ is a phosphatidic acid (PA)-and phosphatidylinositol-binding protein and binds PA derived from the phospholipase D pathway. Conclusion: RdgB␤ is the first lipid-binding protein identified that can bind and transfer PA. Significance: PA bound to RdgB␤ is a likely effector downstream of phospholipase D.

No abstract

Climate change-induced global warming threatens the survival of key ecosystems including shallow water coral reefs. Elevated temperatures can disrupt the normal physiological functioning of photosynthetic organisms by altering the fluidity and permeability of chloroplast membranes that is defined and regulated by their lipid composition. Since the habitat-forming reef corals rely on the obligatory symbiosis with dinoflagellates of the family Symbiodiniaceae, their heat stress response can be expected to be strongly influenced by the symbiont's lipid metabolism. However, in contrast to the steady increase in the knowledge of the functioning of coral symbionts at the genomic and transcriptomic level, the understanding of their membrane lipid composition and regulation in response to temperature stress is lagging behind. We have utilised mass spectrometry-based lipidomic analyses to identify the key polar lipids that form the biological membranes of reef coral symbionts, comparing the thermotolerant species Durusdinium trenchii with the thermosensitive taxon Cladocopium C3, both hosted by Acropora valida. Our results indicate that the superior thermotolerance D. trenchii inside the host corals could be achieved through (1) the amount and saturation of sulfoquinovosyldiacylglycerols, in particular through putative photosystem II interactions, (2) the increased digalactosyldiacylglycerol to monogalactosyldiacylglycerol ratio with the potential to stabilise thylakoid membranes and integrated proteins, and (3) the chaperone-like function of lyso-lipids. Thereby, our study provides novel insights into the heat tolerance of coral symbionts, contributing to the understanding of the potential of coral reef ecosystems to respond and adjust to heat stress events that are becoming more frequent due to climate change. Finally, our identification of multiple mechanisms of heat tolerance in Symbiodiniaceae furthers the knowledge of the general stress physiology of photosynthetic organisms.

No abstract

Late pregnancy in the rat (gestational ages 16-21 days) was accompanied by a specific increase in hepatic phosphatidylcholine (PC) and phosphatidylethanolamine (PE) molecular species containing C16:0 at the sn-1 position and polyunsaturated essential fatty acids (PUFA), in particular C22:6(n-3), at the sn-2 position. Incorporation of either CDP:[Me-14C]choline or CDP:[1,2-14C]-ethanolamine into hepatic microsomal sn-1 C16:0 PC or PE molecular species in vitro was greater at term than in non-pregnant animals, suggesting modifications to the composition of specific diacylglycerol (DAG) pools destined for synthesis of either PC or PE. Also, incorporation of [Me-14C]choline or [Me-14C]methionine into hepatic PC in vivo over 6 h in term pregnant rats was consistent with decreased phospholipase A1-dependent acyl remodelling of sn-1 C16:0 to sn-1 C18:0 molecular species. There was, however, no evidence to support any change to the specificity of acyl remodelling. The rate of PC synthesis by the de novo pathway in vivo was increased in term liver compared with non-pregnant animals, accompanied by increased choline-phosphotransferase activity in vitro in d21 liver microsomes. The rate of PC synthesis by PE N-methylation did not appear to change during pregnancy. Changes in composition of plasma PC species at term reflected those of newly synthesized hepatic PC. Our data suggest supply of PUFA to the developing fetal rat is the result of specific adaptations to maternal hepatic phospholipid biosynthesis rather than passive transfer from the maternal diet.