Biology subjects

Nath, V. R.

Publications and source records attributed to Nath, V. R..

4 recordsLinked to original sources

bioRxiv2025

Ceramide transfer protein regulates G-protein coupled phospholipase signalling in Drosophila photoreceptors.

The non-vesicular transfer of lipids between organelles at membrane contact sites (MCS) has been proposed as a key principle in the regulation of cell physiology. While several proteins with lipid transfer activity have been identified and localized to MCS, their functional significance for supporting physiology is poorly understood. Ceramide transfer protein (CERT) is one such molecule that can transfer ceramide between membranes in vitro. However, evidence for the mechanism and in vivo significance of CERT function is limited. In this study, we have analyzed the function of the only gene (dcert) encoding CERT in Drosophila. We find that loss of function alleles of dcert (dcert1), show elevated levels of short chain ceramide species along with a reduction in the levels of its metabolite phosphatidyl ethanolamine ceramide. Physiological analysis of dcert1 mutant alleles showed reduced electrical responses in the eye to light stimulation although photoreceptors did not undergo retinal degeneration, and this phenotype could be rescued by reconstitution of dcert1 with the wild type gene. The altered light response in dcert1 was associated with a reduction in the rate of phosphatidylinositol 4,5 bisphosphate (PIP2) resynthesis following light induced phospholipase C (PLC) stimulation. The reduced electrical response of dcert1 could be suppressed by reducing ceramide synthesis at the ER. Taken together, our findings suggest that ceramide synthesized at the ER and transferred to the Golgi by CERT regulates G-protein coupled phospholipase C signaling in vivo.

cell biology↗

bioRxiv2024

Ca2+ binding to Esyt is required to modulate membrane contact site density in Drosophila photoreceptors

Membrane Contact Sites (MCS) between the plasma membrane (PM) and endoplasmic reticulum (ER) have been shown to regulate Ca2+ influx into animal cells. However, the mechanisms by which cells modulate ER-PM MCS density is not understood and the role of Ca2+, if any, in regulating this process is not known. We report that in Drosophila photoreceptors, MCS density is dependent on the activity of the Ca2+ permeable channels-TRP and TRPL. This regulation of MCS density by Ca2+ is mediated by extended synaptotagmin (dEsyt), a protein localised to ER-PM MCS in photoreceptors and previously shown to regulate MCS density. We find that the Ca2+ binding activity of dEsyt is required for its functional activity in vivo. dEsytCaBM, a Ca2+ non-binding mutant of dEsyt is unable to modulate MCS structure in a manner equivalent to its wild type counterpart. Further, when reconstituted in dEsyt null photoreceptors, in contrast to wild type dEsyt, dEsytCaBM is unable to rescue ER-PM MCS density and other key phenotypes. Finally, when expressed in wild type photoreceptors, dEsytCaBM phenocopies loss of dEsyt function. Taken together, our data supports a role for the Ca2+ binding activity of dEsyt in regulating the ER-PM MCS density in photoreceptors thus tuning signal transduction in response to Ca2+ influx triggered by ambient illumination. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=196 SRC="FIGDIR/small/588361v1_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@f8faacorg.highwire.dtl.DTLVardef@114009org.highwire.dtl.DTLVardef@8337f0org.highwire.dtl.DTLVardef@cd7c2f_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2023

A genetic screen to uncover molecular mechanisms underlying lipid transfer protein function at membrane contact sites and neurodegeneration.

Lipid transfer proteins mediate the transfer of lipids between organelle membranes in eukaryotes and loss of function in these has been linked to neurodegenerative disorders. However, the mechanism by which loss of lipid transfer protein function leads to neurodegeneration is not understood. In Drosophila photoreceptors, depletion of Retinal Degeneration B (RDGB), a phosphatidylinositol transfer protein localized to endoplasmic reticulum-plasma membrane contact sites leads to defective phototransduction and retinal degeneration but the mechanism by which RDGB function is regulated and the process by which loss of this activity leads to retinal degeneration is not understood. RDGB is localized to membrane contact sites (MCS) and this depends in the interaction of its FFAT motif with the ER integral protein VAP. To identify regulators of RDGB function in vivo, we depleted more than 300 VAP interacting proteins and identified a set of 52 suppressors of rdgB. The molecular identity of these suppressors indicates a role for novel lipids in regulating RDGB function and for transcriptional and ubiquitination processes in mediating retinal degeneration in rdgB. The human homologs of several of these molecules have been implicated in neurodevelopmental diseases underscoring the importance of VAP mediated processes in these disorders.

neuroscience↗

bioRxiv2019

Extended synaptotagmin regulates plasma membrane-endoplasmic reticulum contact site structure and lipid transfer function in vivo

Inter-organelle communication between closely apposed membranes is proposed at Membrane Contact Sites (MCS). However the regulation of MCS structure and their functional relevance in vivo remain debated. The extended synaptotagmins (Esyt) are evolutionarily conserved proteins proposed to function at MCS. However, loss of all three Esyts in yeast or mammals shows minimal phenotypes questioning the functional importance of Esyt. We report that in Drosophila photoreceptors, MCS number is regulated by PLC{beta} activity. Photoreceptors of a null allele of Drosophila extended synaptotagmin (dEsyt) show loss of ER-PM MCS. Loss of dEsyt results in mislocalization of RDGB, an MCS localized lipid transfer protein, required for photoreceptor structure and function, ultimately leading to retinal degeneration. dEsyt depletion enhanced the retinal degeneration, reduced light responses and slower rates of plasma membrane PIP2 resynthesis seen in rdgB mutants. Thus, dEsyt function and PLC{beta} signaling regulate ER-PM MCS structure and lipid transfer in Drosophila photoreceptors.

cell biology↗