Biology subjects

Boutry, M.

Publications and source records attributed to Boutry, M..

5 recordsLinked to original sources

bioRxiv2025

STARD3 coordinates Endoplasmic Reticulum-late endosome/lysosome contacts and organelle positioning through a GSK3-regulated phosphorylation switch

Membrane contact sites (MCS) are dynamic regions where the membranes of two organelles come into close apposition. MCSs play many roles in cellular homeostasis by facilitating inter-organelle lipid and ion exchange as well as organelle positioning. The late endosome/lysosome (LE/Lys) cholesterol transfer protein STARD3 (StAR-related lipid transfer (START) domain containing protein 3) forms reversible contacts between the LE/Lys and the endoplasmic reticulum (ER). This tether protein contains a Phospho-FFAT motif (two phenylalanines (FF) in an acidic tract (AT)) whose interaction with ER-resident VAP proteins is phosphorylation-dependent. In this study, we identify Glycogen Synthase Kinase 3 (GSK3 and GSK3{beta}) as the kinases responsible for phosphorylating serine 209 within the Phospho-FFAT motif of STARD3. This phosphorylation event is both necessary and sufficient to activate STARD3s tethering activity, thereby promoting ER-LE/Lys contacts. Furthermore, we show that the ER-LE/Lys tethering activity made by STARD3 regulates endosome positioning, revealing an additional function for STARD3 on endosome biology. Our findings establish a direct and critical role for GSK3 in regulating MCS dynamics via STARD3 phosphorylation. This novel insight into GSK3-mediated phosphorylation expands our understanding of the molecular mechanisms governing inter-organelle communication.

cell biology↗

bioRxiv2023

Arf1-PI4KIIIβ positive vesicles regulate phosphatidylinositol-3-phosphate signalling to facilitate the fission of lysosomal tubules.

Formation and fission of tubules from lysosomal organelles, such as autolysosomes, endolysosomes or phagolysosomes, are required for lysosome reformation. However, the mechanisms governing these processes in the different forms of lysosomal organelles are poorly understood. For instance, the role of phosphatidylinositol-4-phosphate (PI(4)P) is unclear as it was shown to promote the formation of tubules from phagolysosomes but was proposed to inhibit tubule formation on autolysosomes because the loss of PI4KIII{beta} causes extensive lysosomal tubulations. Using super-resolution live-cell imaging, we show that Arf1-PI4KIII{beta} positive vesicles are recruited to tubule fission sites from autolysosomes, endolysosomes and phagolysosomes. Moreover, we show that PI(4)P is required to form autolysosomal tubules and that increased lysosomal tubulation caused by loss of PI4KIII{beta} represents impaired tubule fission. At the site of fission, we propose that Arf1-PI4KIII{beta} positive vesicles mediate a PI(3)P signal on lysosomes in a process requiring the lipid transfer protein SEC14L2. Our findings indicate that Arf1-PI4KIII{beta} positive vesicles and their regulation of PI(3)P are critical components of the lysosomal tubule fission machinery.

cell biology↗

bioRxiv2022

Spatacsin regulates directionality of lysosome trafficking

The endoplasmic reticulum (ER) forms contacts with the lysosomal compartment, regulating lysosome positioning and motility. The movement of lysosomes are controlled by the attachment of molecular motors to their surface. However, the molecular mechanisms by which ER controls lysosome dynamics are still elusive. Here, we demonstrate that spatacsin is an ER-resident protein that regulates ER-lysosomes contacts to promote lysosome motility, shown by the presence of tubular lysosomes. Tubular lysosomes, which are highly dynamic, are entangled in a network of tubular ER. Screening for spatacsin partners required for tubular lysosome formation showed spatacsin to act by regulating protein degradation. We demonstrate that spatacsin promotes the degradation of its partner AP5Z1, which regulates the relative amount of spastizin and AP5Z1 at lysosomes. Spastizin and AP5Z1 contribute to lysosome trafficking by interacting with anterograde and retrograde motor proteins, kinesin KIF13A and dynein/dynactin subunit p150Glued, respectively. Ultimately, investigations in polarized neurons demonstrated that spatacsin-regulated degradation of AP5Z1 controls the directionality of lysosomes trafficking. Collectively, our results identify spatacsin as a protein regulating the directionality of lysosome trafficking.

cell biology↗

bioRxiv2019

Unveiling two new trichome-specific promoters of interest for metabolic engineering in Nicotiana tabacum

Main conclusion pRbcS-T1 and pMALD1, two new trichome-specific promoters of Nicotiana tabacum, were identified and their strength and specificity were compared to those of previously described promoters in this species. Nicotiana tabacum has emerged as a suitable host for metabolic engineering of terpenoids and derivatives in tall glandular trichomes, which actively synthesize and secrete specialized metabolites. However, implementation of an entire biosynthetic pathway in glandular trichomes requires the identification of trichome-specific promoters to appropriately drive the expression of the transgenes needed to set up the desired pathway. In this context, RT-qPCR analysis was carried out on wild-type N. tabacum plants to compare the expression pattern and gene expression level of NtRbcS-T1 and NtMALD1, two newly identified genes expressed in glandular trichomes, with those of NtCYP71D16, NtCBTS2, NtCPS2, and NtLTP1, which were reported in the literature to be specifically expressed in glandular trichomes. We show that NtRbcS-T1 and NtMALD1 are specifically expressed in glandular trichomes like NtCYP71D16, NtCBTS2, and NtCPS2, while NtLTP1 is also expressed in other leaf tissues as well as in the stem. Transcriptional fusions of each of the six promoters to the GUS-VENUS reporter gene were introduced in N. tabacum by Agrobacterium-mediated transformation. Almost all transgenic lines displayed GUS activity in tall glandular trichomes, indicating that the appropriate cis regulatory elements were included in the selected promoter regions. However, unlike for the other promoters, no trichome-specific line was obtained for pNtLTP1:GUS-VENUS, thus in agreement with the RT-qPCR data. These data thus provide two new transcription promoters that could be used in metabolic engineering of glandular trichomes.

plant biology↗

bioRxiv2019

Loss of spatacsin impairs cholesterol trafficking and calcium homeostasis

Mutations in SPG11, leading to loss of spatacsin function, impair the formation of membrane tubules in lysosomes and cause the accumulation of lipids in lysosome compartment. However, the full nature of lipids accumulating in lysosomes and the physiological consequences of such accumulation are not known. Here we show that loss of spatacsin, but also downregulation of clathrin, inhibited the formation of tubules on late endosomes/lysosomes and prevented the clearance of cholesterol from this subcellular compartment. Using spatacsin-deficient cells, we evaluated the consequences of impaired cholesterol clearance from late endosomes/lysosomes. The accumulation of cholesterol in late endosomes/lysosomes led to lower cholesterol levels in the plasma membrane, enhancing the entry of extracellular calcium by store-operated calcium entry and increasing resting cytosolic calcium levels. Higher cytosolic calcium levels promoted the nuclear translocation of the master regulator of lysosomes TFEB. Downregulation of TFEB or decrease in resting calcium levels in absence of spatacsin partially corrected the formation of tubules and the accumulation of cholesterol in lysosomes, suggesting that spatacsin could be indirectly implicated in the formation of tubules. Our work reveals a homeostatic balance between cholesterol trafficking and cytosolic calcium levels and shows that loss of spatacsin impairs this homeostatic equilibrium.

cell biology↗