The Puzzling Conservation and Diversification of Lipid Droplets from Bacteria to Eukaryotes

Abstract

Membrane compartments are amongst the most fascinating markers of cell evolution from prokaryotes to eukaryotes, some being conserved and the others having emerged via a series of primary and secondary endosymbiosis events.Membrane compartments comprise the system limiting cells (one or two membranes in bacteria, a unique plasma membrane in eukaryotes) and a variety of internal vesicular, subspherical, tubular, or reticulated organelles. In eukaryotes, the internal membranes comprise on the one hand the general endomembrane system, a dynamic network including organelles like the endoplasmic reticulum, the Golgi apparatus, the nuclear envelope, etc. and also the plasma membrane, which are linked via direct lateral connectivity (e.g. between the endoplasmic reticulum and the nuclear outer envelope membrane) or indirectly via vesicular trafficking. On the other hand, semiautonomous organelles, i.e. mitochondria and chloroplasts, are disconnected from the endomembrane system and request vertical transmission following cell division.Membranes are organized as lipid bilayers in which proteins are embedded. The budding of some of these membranes, leading to the formation of the so-called lipid droplets (LDs) loaded with hydrophobic molecules, most notably triacylglycerol, is conserved in all clades. The evolution of eukaryotes is marked by the acquisition of mitochondria and simple plastids from Gram-positive bacteria by primary endosymbiosis events and the emergence of extremely complex plastids, collectively called secondary plastids, bounded by three to four membranes, following multiple and independent secondary endosymbiosis events. There is currently no consensus view of the evolution of LDs in the Tree of Life. Some features are conserved; others show Josselin Lupette and Eric Maréchal contributed equally with all other contributors.

Biogenesis and Breakdown of Lipid Droplets in Pathological Conditions

“…As mentioned, the biology of LD has recently received the attention of multiple research fields, opening a wide window of knowledge in science. Given that LD are conserved structures in prokaryotic and eukaryotic cells (Walther et al, 2017;Zhang and Liu, 2017;Lupette and Maréchal, 2020), a role in every studied biological process should not be surprising. Pathogen invasion, as well as the unlimited proliferation of cancer cells, are processes that impose a huge cellular remodeling, with a consequent energy demand satisfied by LD metabolism.…”

Phylogeny and lipid profiles of snow-algae isolated from Norwegian red-snow microbiomes

“…In nature, they are often exposed to very high (inhibitory) levels of photosynthetically active radiation (PAR) coupled with elevated UV light levels, low nutrient concentrations, freeze-thaw cycles, and very low temperatures (Řezanka et al 2008 ). Lipids are key molecules that perform structural, metabolic, and signalling functions in cell environmental adaptation, provide taxonomic markers, and distinguish the physiological status of communities in the field (Goold et al 2015 , Lutz et al 2015 , Davey et al 2019 , Lupette and Marechal 2020 ). The stress conditions prevalent in snow habitats are known to trigger neutral lipid and secondary carotenoid accumulation in cytoplasmic lipid droplets (LDs) in many algal species, including the characteristic red-coloured encysted snow-algae cells observed in nature (Leya et al 2009 , Procházková et al 2019a ).…”