Global and Gene-Specific Regulation in Freeze-Tolerant Anuran Dryophytes chrysoscelis

Cope’s Gray Treefrog, Dryophytes chysoscelis, seasonally tolerates freezing. During this process, it is subject to cellular stress from factors such as metabolic starvation, DNA damage, toxin accumulation (from cellular metabolism), and the risk of protein misfolding. Preliminary transcriptome data indicates that many mRNA transcripts vary in relative abundance within hepatocytes of D. chrysoscelis during discrete periods of warm acclimation, cold acclimation, freezing, and thawing. Physiological changes that occur in this frog are likely the result of epigenetic regulation—an alteration in gene expression that does not influence DNA sequence. This modification in gene expression can be observed by the subsequent change in relative abundance of mRNA transcripts. This thesis investigates the relative abundance of the hepatic mRNA transcripts for (1) NDUF7, a methyltransferase gene that mediates some epigenetic regulation by transferring methyl groups (global regulation) and (2) ACADV and BFAR–genes that mediate stress responses contributing to freeze tolerance (local regulation). All of the genes selected are orthologous counterparts to those found in humans. Based on preliminary transcriptome data, we hypothesized that methyltransferases important to the freezing process will be differentially regulated (either up-regulated or down-regulated) as compared to the warm condition, whereas stress genes that enhance the survivability of the frogs during freezing will be up-regulated and those that are metabolically costly will be downregulated. These results demonstrate trends in mRNA expression within four biological groups (warmacclimated, cold-acclimated, frozen, and freshly thawed) that may be relevant to the freezing process. mRNA was isolated from livers from frogs of the four biological group. cDNA was synthesized and the relative abundance of each transcript was identified using RTqPCR techniques and compared to the abundance of a housekeeper gene Dc LS-14, which served as a control. The results from the experimental groups were analyzed using ΔΔCt logarithm to calculate the fold change. The results showed that all in genes were down-regulated in expression relative to the warm-acclimated control. NDUF7 showed respective fold changes of -5.82 (cold), -4.40 (frozen), and -6.54(thawed). ACADV demonstrated negative fold changes of -3.74, -3.06, and -3.68, while BFAR had fold changes of -1.14, -1.13, and -1.78 respectively. These data indicate that global down-regulation of gene expression at the transcript level may be an important energy conservation mechanism necessary for surviving freezing and thawing in Cope’s gray treefrog

Hospital admission and emergency care attendance risk for SARS-CoV-2 delta (B.1.617.2) compared with alpha (B.1.1.7) variants of concern: a cohort study

Background: The SARS-CoV-2 delta (B.1.617.2) variant was first detected in England in March, 2021. It has since rapidly become the predominant lineage, owing to high transmissibility. It is suspected that the delta variant is associated with more severe disease than the previously dominant alpha (B.1.1.7) variant. We aimed to characterise the severity of the delta variant compared with the alpha variant by determining the relative risk of hospital attendance outcomes. Methods: This cohort study was done among all patients with COVID-19 in England between March 29 and May 23, 2021, who were identified as being infected with either the alpha or delta SARS-CoV-2 variant through whole-genome sequencing. Individual-level data on these patients were linked to routine health-care datasets on vaccination, emergency care attendance, hospital admission, and mortality (data from Public Health England's Second Generation Surveillance System and COVID-19-associated deaths dataset; the National Immunisation Management System; and NHS Digital Secondary Uses Services and Emergency Care Data Set). The risk for hospital admission and emergency care attendance were compared between patients with sequencing-confirmed delta and alpha variants for the whole cohort and by vaccination status subgroups. Stratified Cox regression was used to adjust for age, sex, ethnicity, deprivation, recent international travel, area of residence, calendar week, and vaccination status. Findings: Individual-level data on 43 338 COVID-19-positive patients (8682 with the delta variant, 34 656 with the alpha variant; median age 31 years [IQR 17–43]) were included in our analysis. 196 (2·3%) patients with the delta variant versus 764 (2·2%) patients with the alpha variant were admitted to hospital within 14 days after the specimen was taken (adjusted hazard ratio [HR] 2·26 [95% CI 1·32–3·89]). 498 (5·7%) patients with the delta variant versus 1448 (4·2%) patients with the alpha variant were admitted to hospital or attended emergency care within 14 days (adjusted HR 1·45 [1·08–1·95]). Most patients were unvaccinated (32 078 [74·0%] across both groups). The HRs for vaccinated patients with the delta variant versus the alpha variant (adjusted HR for hospital admission 1·94 [95% CI 0·47–8·05] and for hospital admission or emergency care attendance 1·58 [0·69–3·61]) were similar to the HRs for unvaccinated patients (2·32 [1·29–4·16] and 1·43 [1·04–1·97]; p=0·82 for both) but the precision for the vaccinated subgroup was low. Interpretation: This large national study found a higher hospital admission or emergency care attendance risk for patients with COVID-19 infected with the delta variant compared with the alpha variant. Results suggest that outbreaks of the delta variant in unvaccinated populations might lead to a greater burden on health-care services than the alpha variant. Funding: Medical Research Council; UK Research and Innovation; Department of Health and Social Care; and National Institute for Health Research