Biology subjects

Ramalho, J.

Publications and source records attributed to Ramalho, J..

3 recordsLinked to original sources

bioRxiv2026

The cell polarity landscape in Arabidopsis male and female gametophytes

Plant cell polarity underlies the capacity to directionally transport auxin and other small molecules, but also precedes asymmetric cell division in the stomatal lineage. Except for specific contexts, mechanisms underlying cell polarization are poorly understood. Most insights on plant cell polarity have come from studies on flowering plant sporophytes, while no polar protein localization has yet been reported in flowering plant gametophytes, despite clear anisotropic growth and asymmetric cell divisions in this generation. Inspired by the identification of deeply conserved SOSEKI proteins and their associated partners that mark polar domains in bryophyte gametophytes and Arabidopsis sporophytes, we here investigate cell polarity in Arabidopsis gametophytes. We discover a rich landscape of polar domains throughout male and female gametophyte development, marked by one or more polar proteins. We find that successive steps in male gametophyte polarization can be mechanistically uncoupled, and the first polarization step precedes asymmetric cell division. Using ectopic expression, we find that there is a near-universal capacity for polar protein localization in gametophytes through a single polarity system. Our work offers the first insight into gametophyte cell polarity in Arabidopsis, identifies novel polar domains, and presents a starting point for future dissection of mechanisms underlying plant cell polarity.

plant biology↗

bioRxiv2021

A novel Rab11-Rab3a cascade required for lysosome exocytosis

Lysosomes are dynamic organelles, capable of undergoing exocytosis. This process is crucial for several cellular functions, namely plasma membrane repair. Nevertheless, the molecular machinery involved in this process is poorly understood. Here, we identify Rab11a and Rab11b as regulators of calcium-induced lysosome exocytosis. Interestingly, Rab11-positive vesicles transiently interact with lysosomes at the cell periphery, indicating that this interaction is required for the last steps of lysosome exocytosis. Additionally, we found that the silencing of the exocyst subunit Sec15, a Rab11 effector, impairs lysosome exocytosis independently of the exocyst complex, suggesting that Sec15 acts together with Rab11 in the regulation of lysosome exocytosis. Furthermore, we show that Rab11 binds the guanine nucleotide exchange factor for Rab3a (GRAB) and also Rab3a, which we described previously as a regulator of the positioning and exocytosis of lysosomes. Thus, our studies suggest that Rab11-positive vesicles transport GRAB to activate Rab3a on lysosomes, establishing a Rab11-Rab3 cascade that is essential for lysosome exocytosis.

cell biology↗

bioRxiv2021

Cholesteryl Hemiazelate Induces Lysosome Dysfunction and Exocytosis in Macrophages

OBJECTIVEA key event in atherogenesis is the formation of lipid-loaded macrophages, lipidotic cells, which exhibit irreversible accumulation of undigested modified low-density lipoproteins in lysosomes. This event culminates with the loss of cell homeostasis, inflammation and cell death. In this study we propose to identify the chemical etiological factors and understanding the molecular and cellular mechanisms responsible for the impairment of lysosome function in macrophages. APPROACH AND RESULTSUsing shotgun lipidomics we have discovered that a family of oxidized lipids (cholesteryl hemiesters, ChE), end products of oxidation of polyunsaturated cholesteryl esters, occurs at higher concentrations in the plasma of two cohorts of cardiovascular disease patients than in the plasma of a control cohort. Macrophages exposed to the most prevalent ChE, cholesteryl hemiazelate (ChA) exhibit lysosome enlargement, peripheral lysosomal positioning, lysosome dysfunction and lipidosis which are irreversible. The transcriptomic profile of macrophages exposed to ChA indicates that the lysosome pathway is deeply affected and is well correlated with lysosome phenotypic and functional changes. Interestingly, the dysfunctional peripheral lysosomes are more prone to fuse with the plasma membrane, secreting their undigested luminal content into the extracellular milieu with potential consequences to the pathology. CONCLUSIONWe identify ChA not only as one of the molecules involved in the etiology of irreversible lysosome dysfunction culminating with lipidosis but also as a promoter of exocytosis of the dysfunctional lysosomes. The latter event is a new mechanism that may be important in the pathogenesis of atherosclerosis.

cell biology↗