SARS-CoV-2 incidence among teaching staff in primary and secondary schools-Wales, 2020-2021.

BACKGROUND: During the COVID-19 pandemic, face-to-face delivery of education in schools across Wales was disrupted with repeated school closures to limit risk of infection. Evidence describing the incidence of infection amongst school staff during times when schools were open is limited. A previous research study found infection rates were higher in English primary school settings when compared with secondary. An Italian study suggested teachers weren't at greater risk of infection in comparison to the general population. The aim of this study was to identify whether educational staff had higher incidence rates than their counterparts in the general population in Wales, and secondly whether incidence rates amongst staff differed between primary and secondary school settings and by teacher age. METHODS: We performed a retrospective observational cohort study using the national case detection and contact tracing system implemented during the COVID pandemic. Age stratified person-day COVID-19 incidence rates amongst teaching staff linked to primary or secondary schools in Wales were calculated for the autumn and summer terms during 2020-2021. RESULTS: The observed pooled COVID-19 incidence rates for staff across both terms was 23.30 per 100,000 person days (95% CI: 22.31-24.33). By comparison, the rate in the general population aged 19-65, was 21.68 per 100,000 person days (95%: CI 21.53-21.84). Incidence among teaching staff was highest in the two youngest age groups (< 25 years and 25-29 years). When compared to the age matched general population, incidence was higher in the autumn term amongst primary school teachers aged ≤ 39 years, and in the summer term higher only in the primary school teachers aged < 25 years. CONCLUSION: The data were consistent with an elevated risk of COVID-19 amongst younger teaching staff in primary schools when compared to the general population, however differences in case ascertainment couldn't be excluded as a possible reason for this. Rate differences by age group in teaching staff mirrored those in the general population. The risk in older teachers (≥ 50 years) in both settings was the same or lower than in the general population. Amongst all age groups of teachers maintaining the key risk mitigations within periods of COVID transmission remain important.

A heat-sensitive Osh protein controls PI4P polarity.

BACKGROUND: Phosphoinositide lipids provide spatial landmarks during polarized cell growth and migration. Yet how phosphoinositide gradients are oriented in response to extracellular cues and environmental conditions is not well understood. Here, we elucidate an unexpected mode of phosphatidylinositol 4-phosphate (PI4P) regulation in the control of polarized secretion. RESULTS: We show that PI4P is highly enriched at the plasma membrane of growing daughter cells in budding yeast where polarized secretion occurs. However, upon heat stress conditions that redirect secretory traffic, PI4P rapidly increases at the plasma membrane in mother cells resulting in a more uniform PI4P distribution. Precise control of PI4P distribution is mediated through the Osh (oxysterol-binding protein homology) proteins that bind and present PI4P to a phosphoinositide phosphatase. Interestingly, Osh3 undergoes a phase transition upon heat stress conditions, resulting in intracellular aggregates and reduced cortical localization. Both the Osh3 GOLD and ORD domains are sufficient to form heat stress-induced aggregates, indicating that Osh3 is highly tuned to heat stress conditions. Upon loss of Osh3 function, the polarized distribution of both PI4P and the exocyst component Exo70 are impaired. Thus, an intrinsically heat stress-sensitive PI4P regulatory protein controls the spatial distribution of phosphoinositide lipid metabolism to direct secretory trafficking as needed. CONCLUSIONS: Our results suggest that control of PI4P metabolism by Osh proteins is a key determinant in the control of polarized growth and secretion.

Tricalbin proteins regulate plasma membrane phospholipid homeostasis.

The evolutionarily conserved extended synaptotagmin (E-Syt) proteins are calcium-activated lipid transfer proteins that function at contacts between the ER and plasma membrane (ER-PM contacts). However, roles of the E-Syt family members in PM lipid organisation remain incomplete. Among the E-Syt family, the yeast tricalbin (Tcb) proteins are essential for PM integrity upon heat stress, but it is not known how they contribute to PM maintenance. Using quantitative lipidomics and microscopy, we find that the Tcb proteins regulate phosphatidylserine homeostasis at the PM. Moreover, upon heat-induced membrane stress, Tcb3 co-localises with the PM protein Sfk1 that is implicated in PM phospholipid asymmetry and integrity. The Tcb proteins also control the PM targeting of the known phosphatidylserine effector Pkc1 upon heat-induced stress. Phosphatidylserine has evolutionarily conserved roles in PM organisation, integrity, and repair. We propose that phospholipid regulation is an ancient essential function of E-Syt family members required for PM integrity.

Systematic analysis of membrane contact sites in Saccharomyces cerevisiae uncovers modulators of cellular lipid distribution.

Actively maintained close appositions between organelle membranes, also known as contact sites, enable the efficient transfer of biomolecules between cellular compartments. Several such sites have been described as well as their tethering machineries. Despite these advances we are still far from a comprehensive understanding of the function and regulation of most contact sites. To systematically characterize contact site proteomes, we established a high-throughput screening approach in Saccharomyces cerevisiae based on co-localization imaging. We imaged split fluorescence reporters for six different contact sites, several of which are poorly characterized, on the background of 1165 strains expressing a mCherry-tagged yeast protein that has a cellular punctate distribution (a hallmark of contact sites), under regulation of the strong TEF2 promoter. By scoring both co-localization events and effects on reporter size and abundance, we discovered over 100 new potential contact site residents and effectors in yeast. Focusing on several of the newly identified residents, we identified three homologs of Vps13 and Atg2 that are residents of multiple contact sites. These proteins share their lipid transport domain, thus expanding this family of lipid transporters. Analysis of another candidate, Ypr097w, which we now call Lec1 (Lipid-droplet Ergosterol Cortex 1), revealed that this previously uncharacterized protein dynamically shifts between lipid droplets and the cell cortex, and plays a role in regulation of ergosterol distribution in the cell. Overall, our analysis expands the universe of contact site residents and effectors and creates a rich database to mine for new functions, tethers, and regulators.

Tricalbin-Mediated Contact Sites Control ER Curvature to Maintain Plasma Membrane Integrity.

Membrane contact sites (MCS) between the endoplasmic reticulum (ER) and the plasma membrane (PM) play fundamental roles in all eukaryotic cells. ER-PM MCS are particularly abundant in Saccharomyces cerevisiae, where approximately half of the PM surface is covered by cortical ER (cER). Several proteins, including Ist2, Scs2/22, and Tcb1/2/3 are implicated in cER formation, but the specific roles of these molecules are poorly understood. Here, we use cryo-electron tomography to show that ER-PM tethers are key determinants of cER morphology. Notably, Tcb proteins (tricalbins) form peaks of extreme curvature on the cER membrane facing the PM. Combined modeling and functional assays suggest that Tcb-mediated cER peaks facilitate the transport of lipids between the cER and the PM, which is necessary to maintain PM integrity under heat stress. ER peaks were also present at other MCS, implying that membrane curvature enforcement may be a widespread mechanism to regulate MCS function.