Gopalan, A. B. | bioRxiv Science

bioRxiv2024

Caging of membrane-to-cortex attachment proteins can trigger cellular symmetry breaking

To migrate, divide, and change shape, cells must regulate the mechanics of their periphery. The cell surface is a complex structure that consists of a thin, contractile cortical actin network tethered to the plasma membrane by specialized membrane-to-cortex attachment (MCA) proteins. This active and constantly fluctuating system maintains a delicate mechanochemical state which permits spontaneous polarization and shape change when needed. Combining in silico, in vitro, and in vivo experiments we show how membrane viscosity and MCA protein length regulate cortical dynamics. We reveal a novel mechanism whereby caging of linker proteins in the actin cortex allows for the amplification of small changes in these key parameters, leading to major alterations of cortical contractility. In cells, this mechanism alone gives rise to symmetry breaking phenomena, suggesting that local changes in lipid composition, in combination with the choice of MCA proteins, contribute to the regulation of cellular morphogenesis and function.

biophysics↗

bioRxiv2022

Lipotype acquisition during neural development in vivo is not recapitulated in stem cell-derived neurons

During development, different tissues acquire distinct lipotypes that are coupled to tissue function and homeostasis. In the brain, where complex membrane trafficking systems are required for neural function, specific glycerophospholipids, sphingolipids, and cholesterol are highly abundant, and defective lipid metabolism is associated with abnormal neural development and neurodegenerative disease. Notably, the production of tissue-specific lipotypes requires appropriate programming of the underlying lipid metabolic machinery, but when and how this occurs is unclear. To address this, we used high-resolution mass spectrometry-based (MSALL) lipidomics to perform a quantitative and comprehensive analysis of mouse brain development covering early embryonic and postnatal stages. We discovered a distinct bifurcation in the establishment of the neural lipotype, whereby the canonical brain lipid biomarkers 22:6-glycerophospholipids and 18:0-sphingolipids begin to be produced in utero, whereas cholesterol attains its characteristic high levels after birth. In contrast, when profiling rodent and human stem cell-derived neurons, we observed that these do not acquire a brain lipotype per se. However, upon probing the lipid metabolic wiring by supplementing brain lipid precursors, we found that the stem cell-derived neurons were partially able to establish a brain-like lipotype, demonstrating that the cells are partially metabolically committed. Altogether, our report provides an extensive lipidomic resource for brain development and highlights a potential challenge in using stem cell-derived neurons for mechanistic studies of lipid biochemistry, membrane biology and biophysics that can be mitigated by further optimizing in vitro differentiation protocols. Significance StatementWe report an extensive time-resolved resource of lipid molecule abundances across mouse brain development, starting as early as 10 days post-fertilization. The resource reveals a bifurcation in the establishment of the neural lipotype where the canonical 22:6-glycerophospholipid and 18:0-sphingolipid biomarkers are attained in utero, whereas cholesterol is attained after birth. Furthermore, we uncover that the neural lipotype is not established in rodent and human stem cell-derived neurons in vitro.

developmental biology↗