Meiotic Cytokinesis in Saccharomyces cerevisiae: Spores That Just Need Closure.

In the budding yeast Saccharomyces cerevisiae, sporulation occurs during starvation of a diploid cell and results in the formation of four haploid spores forming within the mother cell ascus. Meiosis divides the genetic material that is encapsulated by the prospore membrane that grows to surround the haploid nuclei; this membrane will eventually become the plasma membrane of the haploid spore. Cellularization of the spores occurs when the prospore membrane closes to capture the haploid nucleus along with some cytoplasmic material from the mother cell, and thus, closure of the prospore membrane is the meiotic cytokinetic event. This cytokinetic event involves the removal of the leading-edge protein complex, a complex of proteins that localizes to the leading edge of the growing prospore membrane. The development and closure of the prospore membrane must be coordinated with other meiotic exit events such as spindle disassembly. Timing of the closure of the prospore membrane depends on the meiotic exit pathway, which utilizes Cdc15, a Hippo-like kinase, and Sps1, an STE20 family GCKIII kinase, acting in parallel to the E3 ligase Ama1-APC/C. This review describes the sporulation process and focuses on the development of the prospore membrane and the regulation of prospore membrane closure.

Meiosis II spindle disassembly requires two distinct pathways.

During exit from meiosis II, cells undergo several structural rearrangements, including disassembly of the meiosis II spindles and cytokinesis. Each of these changes is regulated to ensure that they occur at the proper time. Previous studies have demonstrated that both SPS1, which encodes a STE20-family GCKIII kinase, and AMA1, which encodes a meiosis-specific activator of the Anaphase Promoting Complex, are required for both meiosis II spindle disassembly and cytokinesis in the budding yeast Saccharomyces cerevisiae. We examine the relationship between meiosis II spindle disassembly and cytokinesis and find that the meiosis II spindle disassembly failure in sps1Δ and ama1∆ cells is not the cause of the cytokinesis defect. We also see that the spindle disassembly defects in sps1Δ and ama1∆ cells are phenotypically distinct. We examined known microtubule-associated proteins Ase1, Cin8, and Bim1, and found that AMA1 is required for the proper loss of Ase1 and Cin8 on meiosis II spindles while SPS1 is required for Bim1 loss in meiosis II. Taken together, these data indicate that SPS1 and AMA1 promote distinct aspects of meiosis II spindle disassembly, and that both pathways are required for the successful completion of meiosis.

Development of a coronavirus disease 2019 nonhuman primate model using airborne exposure.

Airborne transmission is predicted to be a prevalent route of human exposure with SARS-CoV-2. Aside from African green monkeys, nonhuman primate models that replicate airborne transmission of SARS-CoV-2 have not been investigated. A comparative evaluation of COVID-19 in African green monkeys, rhesus macaques, and cynomolgus macaques following airborne exposure to SARS-CoV-2 was performed to determine critical disease parameters associated with disease progression, and establish correlations between primate and human COVID-19. Respiratory abnormalities and viral shedding were noted for all animals, indicating successful infection. Cynomolgus macaques developed fever, and thrombocytopenia was measured for African green monkeys and rhesus macaques. Type II pneumocyte hyperplasia and alveolar fibrosis were more frequently observed in lung tissue from cynomolgus macaques and African green monkeys. The data indicate that, in addition to African green monkeys, macaques can be successfully infected by airborne SARS-CoV-2, providing viable macaque natural transmission models for medical countermeasure evaluation.

The Smk1 MAPK and Its Activator, Ssp2, Are Required for Late Prospore Membrane Development in Sporulating Saccharomyces cerevisiae.

During sporulation in the budding yeast Saccharomyces cerevisiae, proper development of the prospore membrane is necessary for the formation of viable spores. The prospore membrane will eventually become the plasma membrane of the newly formed haploid spore and also serves as the template for the deposition of the spore wall. The prospore membrane is generated de novo during meiosis II and the growing edge of the prospore membrane is associated with the Leading Edge Protein (LEP) complex. We find that the Smk1 MAP kinase, along with its activator Ssp2, transiently localizes with the LEP during late meiosis II. SSP2 is required for the leading edge localization of Smk1; this localization is independent of the activation state of Smk1. Like other LEP components, the localization of Smk1 at the leading edge also depends on Ady3. Although prospore membrane development begins normally in smk1 and ssp2 mutants, late prospore membrane formation is disrupted, with the formation of ectopic membrane compartments. Thus, MAP kinase signaling plays an important role in the formation of the prospore membrane.

Identification of MALT1 feedback mechanisms enables rational design of potent antilymphoma regimens for ABC-DLBCL.

MALT1 inhibitors are promising therapeutic agents for B-cell lymphomas that are dependent on constitutive or aberrant signaling pathways. However, a potential limitation for signal transduction-targeted therapies is the occurrence of feedback mechanisms that enable escape from the full impact of such drugs. Here, we used a functional genomics screen in activated B-cell-like (ABC) diffuse large B-cell lymphoma (DLBCL) cells treated with a small molecule irreversible inhibitor of MALT1 to identify genes that might confer resistance or enhance the activity of MALT1 inhibition (MALT1i). We find that loss of B-cell receptor (BCR)- and phosphatidylinositol 3-kinase (PI3K)-activating proteins enhanced sensitivity, whereas loss of negative regulators of these pathways (eg, TRAF2, TNFAIP3) promoted resistance. These findings were validated by knockdown of individual genes and a combinatorial drug screen focused on BCR and PI3K pathway-targeting drugs. Among these, the most potent combinatorial effect was observed with PI3Kδ inhibitors against ABC-DLBCLs in vitro and in vivo, but that led to an adaptive increase in phosphorylated S6 and eventual disease progression. Along these lines, MALT1i promoted increased MTORC1 activity and phosphorylation of S6K1-T389 and S6-S235/6, an effect that was only partially blocked by PI3Kδ inhibition in vitro and in vivo. In contrast, simultaneous inhibition of MALT1 and MTORC1 prevented S6 phosphorylation, yielded potent activity against DLBCL cell lines and primary patient specimens, and resulted in more profound tumor regression and significantly improved survival of ABC-DLBCLs in vivo compared with PI3K inhibitors. These findings provide a basis for maximal therapeutic impact of MALT1 inhibitors in the clinic, by disrupting feedback mechanisms that might otherwise limit their efficacy.

Selective Inhibition of HDAC3 Targets Synthetic Vulnerabilities and Activates Immune Surveillance in Lymphoma.

CREBBP mutations are highly recurrent in B-cell lymphomas and either inactivate its histone acetyltransferase (HAT) domain or truncate the protein. Herein, we show that these two classes of mutations yield different degrees of disruption of the epigenome, with HAT mutations being more severe and associated with inferior clinical outcome. Genes perturbed by CREBBP mutation are direct targets of the BCL6-HDAC3 onco-repressor complex. Accordingly, we show that HDAC3-selective inhibitors reverse CREBBP-mutant aberrant epigenetic programming, resulting in: (i) growth inhibition of lymphoma cells through induction of BCL6 target genes such as CDKN1A and (ii) restoration of immune surveillance due to induction of BCL6-repressed IFN pathway and antigen-presenting genes. By reactivating these genes, exposure to HDAC3 inhibitors restored the ability of tumor-infiltrating lymphocytes to kill DLBCL cells in an MHC class I and II-dependent manner, and synergized with PD-L1 blockade in a syngeneic model in vivo. Hence, HDAC3 inhibition represents a novel mechanism-based immune epigenetic therapy for CREBBP-mutant lymphomas. SIGNIFICANCE: We have leveraged the molecular characterization of different types of CREBBP mutations to define a rational approach for targeting these mutations through selective inhibition of HDAC3. This represents an attractive therapeutic avenue for targeting synthetic vulnerabilities in CREBBP-mutant cells in tandem with promoting antitumor immunity.This article is highlighted in the In This Issue feature, p. 327.

PRMT5 interacts with the BCL6 oncoprotein and is required for germinal center formation and lymphoma cell survival.

The germinal center (GC) reaction plays an important role in generating humoral immunity and is believed to give rise to most B-cell lymphomas. GC entry and exit are tightly regulated processes, controlled by the actions of transcription factors such as BCL6. Herein, we demonstrate that protein arginine methyltransferase 5 (PRMT5), a symmetric dimethyl arginine methyltransferase, is also necessary for GC formation and affinity maturation. PRMT5 contributes to GC formation and affinity maturation at least in part through its direct interaction with and methylation of BCL6 at arginine 305 (R305), a modification necessary for the full transcriptional repressive effects of BCL6. Inhibition of PRMT5 in B-cell lymphoma lines led to significant upregulation of BCL6 target genes, and the concomitant inhibition of both BCL6 and PRMT5 exhibited synergistic killing of BCL6-expressing lymphoma cells. Our studies identify PRMT5 as a novel regulator of the GC reaction and highlight the mechanistic rationale of cotargeting PRMT5 and BCL6 in lymphoma.

Dietary intake of Nova Scotia youth in grades 7 and 11.

PURPOSE: We examined dietary intakes among Nova Scotia youth, and analyzed whether these intakes met existing dietary guidelines. METHODS: Data from 1469 students in grades 7 and 11 from randomly selected schools were collected via a web-based dietary assessment tool, including a 24-hour recall. Nutrient analysis products were subjected to descriptive and inferential statistical analyses. RESULTS: Reported dietary intakes across sexes and grades showed the vast majority of youth did not meet minimum recommendations for fibre (96% to 98%) or vegetable and fruit servings (83.3% to 90.7%). Girls in grade 11 reported greater intakes of folate and lower intakes of saturated fat, and were less likely to report iron intakes at or above the Estimated Average Requirement than were grade 7 girls. Across ages, more than 75% of girls reported low calcium and folate intakes. Boys in both grades reported consuming more energy than did girls, and older boys reported consuming more than did younger boys. Foods outside the four main food groups contributed about 25% of total reported energy intake. Students in grade 7 consumed pop, salty snacks, and french fries more frequently than did students in grade 11. CONCLUSIONS: Adolescents' self-reported dietary intakes may not meet current dietary recommendations. Continued efforts are needed to develop innovative strategies to ensure healthy eating patterns.

Physical activity of children and youth in Nova Scotia from 2001/02 and 2005/06.

OBJECTIVES: This paper reports on physical activity of students in grades 3, 7, and 11 from two surveillance studies (from 2001 and 2005). METHODS: Randomly selected students (Study1 n=1730; Study2 n=2341) from randomly selected schools in Nova Scotia participated. Physical activity was measured for seven consecutive days using Actigraph accelerometers. Descriptive statistics were calculated for moderate, hard, and very hard intensity, and total minutes of physical activity. Between study, grade, and sex differences were determined using univariate Analyses of Variance. RESULTS: Students in Study2 were significantly less active (mean [SD]=531.0 [392.3] min/week) than Study1 (662.2 [495.1] min/week). Girls were significantly less active (525.4 [419.1] min/week) than boys (657.1 [460.3] min/week). Students in grade 11 were significantly less active (225.2 [171.1] min/week) than students in grade 7 (457.5 [227.2] min/week) who were significantly less active than students in grade 3 (1038.4 [387.6] min/week). A significant study-grade interaction indicated that compared to students in grades 7 and 11, the level of physical activity in students in grade 3 was considerably lower in Study2 compared to Study1. CONCLUSIONS: Given the lower level of physical activity found in Study2, efforts at informing public policy and strategies that promote physical activity in children and youth should be made.

Are overweight students in Grades 3, 7, and 11 less physically active than their healthy weight counterparts?

OBJECTIVE: This study compared the accumulated minutes of objectively measured physical activity in 1,790 boys and girls in Grades 3, 7, and 11 classified as healthy weight, at risk of overweight, and overweight. METHODS: Height and weight were measured and body mass index calculated. Minutes of sedentary, light, moderate, hard, and very hard physical activity were obtained from a seven-day measurement of physical activity using an accelerometer (Actigraph, mode 7164; MTI). RESULTS: In Grade 3, boys (p=0.000) and girls (p=0.012) classified as overweight obtained significantly fewer minutes of very hard physical activity compared with their healthy weight counterparts. Boys in Grade 7 considered overweight obtained significantly fewer minutes of hard (p=0.002) and very hard physical activity (p=0.006) compared with boys who were a healthy weight. There were no significant differences in minutes of sedentary, light, moderate, hard, or very hard intensity physical activity in the boys and girls in Grade 11, who were considered a healthy weight, at risk of overweight, or overweight. CONCLUSIONS: Weak and inconsistent support was provided for the notion that boys and girls classified overweight are less physically active than their healthy weight counterparts.

A comparison of energy provision by diet order in a long-term care facility.

Involuntary weight loss (IWL) is common in the North American elderly population and affects as many as 60 per cent of nursing home residents, representing a threat to health and function. Investigation into nutrient provision in a long-term care (LTC) centre showed that mean total energy exposure over the 5-week menu cycle differed significantly between regular and puréed diet orders, with lower mean levels of exposure to all three macronutrients on a puréed diet order. There is sufficient evidence that current LTC menus may provide fewer nutrients in those receiving puréed diets that further investigation in this area is warranted.

Overweight Nova Scotia children and youth: the roles of household income and adherence to Canada's Food Guide to Healthy Eating.

OBJECTIVE: Poor diet quality has been observed in Nova Scotia children and youth, characterized by low intake from the traditional four food groups and a high intake from the Other Foods category. In this study, we addressed how household income and adherence to Canada's Food Guide to Healthy Eating influenced weight status category in Nova Scotia children and youth. METHODS: During the 2005-06 school year, data were collected from 2,296 students and their parents, across Nova Scotia. Questionnaires and anthropometric measurements were obtained from grades 3, 7 and 11 students. The grade 3 students were excluded from the dietary intake assessment. The information collected from the online 24-hour food recalls and food frequency questionnaires were analyzed for adherence to Canada's Food Guide to Healthy Eating recommendations. A general linear model was employed to examine the relationships between household income, food group and weight status category. RESULTS: Overall adherence to Canada's Food Guide to Healthy Eating was low among grades 7 and 11 students. Fewer servings from Grain Products, Milk Products and Vegetables and Fruit were observed in at risk of overweight and overweight students. At risk of overweight and overweight were significantly related to lower household income in grades 3 and 11. Our results show that the rates of overweight in Nova Scotia students are double those reported by the 2004 Canadian Community Health Survey. CONCLUSION: Household income and dietary intake play significant roles in weight status among Nova Scotia children and youth.