Metabolic control of cytosolic‐facing pools of diacylglycerol in budding yeast

Abstract

Diacylglycerol (DAG) is a key signaling lipid and intermediate in lipid metabolism. Our knowledge of DAG distribution and dynamics in cell membranes is limited. Using live‐cell fluorescence microscopy we investigated the localization of yeast cytosolic‐facing pools of DAG in response to conditions where lipid homeostasis and DAG levels were known to be altered. Two main pools were monitored over time using DAG sensors. One pool was associated with vacuolar membranes and the other localized to sites of polarized growth. Dynamic changes in DAG distribution were observed during resumption of growth from stationary phase, when DAG is used to support phospholipid synthesis for membrane proliferation. Vacuolar membranes experienced constant morphological changes displaying DAG enriched microdomains coexisting with liquid‐disordered areas demarcated by Vph1. Formation of these domains was dependent on triacylglycerol (TAG) lipolysis. DAG domains and puncta were closely connected to lipid droplets. Lack of conversion of DAG to phosphatidate in growth conditions dependent on TAG mobilization, led to the accumulation of DAG in a vacuolar‐associated compartment, impacting the polarized distribution of DAG at budding sites. DAG polarization was also regulated by phosphatidylserine synthesis/traffic and sphingolipid synthesis in the Golgi.

Quantitative live-cell PALM reveals nanoscopic Faa4 redistributions and dynamics on lipid droplets during metabolic transitions of yeast

“…When cells in the stationary phase are diluted back to fresh medium, LDs are rapidly consumed for membrane expansion during cell proliferation. Previous studies have shown that LD resident lipases (Tgl3) are required for the lipolysis of TAGs to generate DAG and FAs (Ganesan et al, 2019;Kurat et al, 2006;Ouahoud et al, 2018). The resulting FAs in turn need to be activated by fatty acid activating enzymes to serve together with DAG as building blocks for the synthesis of membrane phospholipids.…”

“…At the same time, LDs at Nuclear Vacuolar Junctions (NVJs) increase their TAG content using the activated FAs (Hariri et al, 2018(Hariri et al, , 2019. Upon growth resumption from the stationary phase, TAGs stored in LDs are rapidly broken down by LD resident lipases to release and channel DAGs and FAs towards the ER and the vacuole for membrane proliferation (Ganesan et al, 2019;Kurat et al, 2006;Markgraf et al, 2014;Ouahoud et al, 2018). Again, Faa4 is needed to reactivate the released FAs for membrane synthesis.…”

Molecular-dynamics-simulation-guided membrane engineering of Saccharomyces cerevisiae by overexpression of plant FAE1 and GPAT5 genes increases fatty acid chain length in membrane lipids

“…Previously published results of membrane simulations show that high levels of DAGs are able to break the lamellar structure of the plasma membrane, reducing its integrity (28). Other research has shown that DAGs can be highly localised in specific areas of the membrane during cellular growth (29), potentially increasing the damage to the lamellar structure of the membrane. However, low concentrations of DAGs can replace ERG in membrane microdomains (30), making the membrane more rigid (11).…”

Sticking With It: ER-PM Membrane Contact Sites as a Coordinating Nexus for Regulating Lipids and Proteins at the Cell Cortex

“…Because DAG is readily consumed in the synthesis of phospholipids and TAG, DAG generally represents a minor fraction of total membrane lipids (Ejsing et al, 2019). In growing yeast cells, however, DAG is enriched in the vacuolar membrane and a minor DAG pool resides in the ER membrane (Ganesan et al, 2019). The pool size and trafficking of DAG is also affected by other lipids including PS and also sphingolipid synthesis, which generates DAG (Figure 2A; Ganesan et al, 2019).…”

“…In growing yeast cells, however, DAG is enriched in the vacuolar membrane and a minor DAG pool resides in the ER membrane (Ganesan et al, 2019). The pool size and trafficking of DAG is also affected by other lipids including PS and also sphingolipid synthesis, which generates DAG (Figure 2A; Ganesan et al, 2019). In yeast strains defective in sphingolipid synthesis, DAG is primarily localized to the PM rather than the vacuolar membrane (Ganesan et al, 2019).…”