Biology subjects

Davis, D. L.

Publications and source records attributed to Davis, D. L..

3 recordsLinked to original sources

bioRxiv2025

The individual isoforms of ORMDL, the regulatory subunit of serine palmitoyltransferase, have distinctive sensitivities to ceramide.

AbstractSphingolipids play crucial roles in cell membrane structure and in multiple signaling pathways. Sphingolipid de novo biosynthesis is mediated by the serine palmitoyltransferase (SPT) enzyme complex. Homeostatic regulation of this complex is dependent on its regulatory subunit, the ORMDLs, of which there are three isoforms. It is well established that the ORMDLs regulate SPT activity, but it is still unclear whether the three ORMDL isoforms have distinct functions and properties. Here, we focus on understanding the physiological importance of ORMDL isoforms (ORMDL1, ORMDL2, and ORMDL3) in regulating SPT activity and sphingolipid levels. This study delves into the differential responses of the SPT complexes containing different ORMDL isoforms to cellular ceramide levels. By using the CRISPR/Cas9 gene editing tool, we have developed Hela cell lines each of which harbor only one of the three ORMDL isoforms as well as a cell line deleted for all three isoforms. Consistent with other studies, we find that deletion of all three ORMDL isoforms desensitizes SPT to ceramide and dramatically increases levels of cellular sphingolipids. In contrast, each ORMDL isoform alone is capable of regulating SPT activity and maintaining normal levels of sphingolipid. Strikingly, however, we find that each ORMDL isoform exhibits isoform-specific sensitivity to ceramide. This suggests that the inclusion of specific ORMDL isoforms into the SPT complex may accomplish a fine-tuning of sphingolipid homeostasis. The study not only emphasizes the need for further investigation into the distinct roles of ORMDL isoforms but also sheds light on their potential as therapeutic targets. HighlightsO_LIRMDL isoforms detect varying ceramide levels to regulate SPT. C_LIO_LIHeLa cells, there is no compensation for the absence of the ORMDL isoform, neither at the total protein level nor at the mRNA level. C_LI

biochemistry↗

bioRxiv2022

SARS-CoV-2 Omicron BA.1 variant infection of human colon epithelial cells

Omicron B.1.1.529 became the predominant SARS-CoV-2 variant in early 2022, causing a new wave of public anxiety. Compared to the ancestral strain, Omicron has 50 mutations, with over 30 mutations in the spike protein. These differences likely underlie the changes in Omicron biology noted in other studies, including an attenuation in the lung parenchyma, compared to the ancestral SARS-CoV-2 strain and other variants, as well as a preference for endosomal entry, in place of the TMPRSS2-mediated membrane fusion pathway. This raises questions on Omicron tropism and infectivity in various target organ systems, including the gastrointestinal (GI) tract. Up to 70% of COVID-19 patients report GI symptoms, including nausea, vomiting, and diarrhea. Here, we show that in the context of donor intrinsic genetic heterogeneity, the SARS-CoV-2 Omicron variant infects human colonoids similarly, if not less effectively, than the ancestral WT (WA1) strain or the Delta variant. Additionally, we note a higher ratio of viral RNA to infectious virus titer, which may suggest that Omicron is potentially less infectious in the intestine. This study lays the foundation for further work defining mechanisms mediating intestinal infection and pathogenesis by Omicron.

microbiology↗

bioRxiv2020

Dynamics of sphingolipids and the serine-palmitoyltransferase complex in oligodendrocytes during myelination.

Myelin is a unique, lipid-rich membrane structure that accelerates neurotransmission and supports neuronal function. Sphingolipids are critical components of myelin. Here we examined sphingolipid synthesis during the peak period of myelination in the postnatal rat brain. Importantly, we made measurements in isolated oligodendrocytes, the myelin-producing cells in the central nervous system. We analyzed sphingolipid distribution and levels of critical enzymes and regulators in the sphingolipid biosynthetic pathway, with a focus on the serine palmitoyltransferase (SPT) complex, the rate-limiting step in this pathway. During myelination levels of the major SPT subunits increased and oligodendrocyte maturation was accompanied by extensive alterations in the composition of the SPT complex. These included changes in the relative levels of alternate catalytic subunits, SPTLC2 and -3, the relative levels of isoforms of the small subunits ssSPTa and -b, and in the isoform distribution of the SPT regulators, the ORMDLs. As myelination progressed there were distinct changes in both the nature of the sphingoid backbone and the N-acyl chains incorporated into sphingolipids. The distribution of these changes among sphingolipid family members indicates that there is selective channeling of the ceramide backbone towards specific downstream metabolic pathways during myelination.

neuroscience↗