Tolerance to fluconazole in Candida albicans is regulated by temperature and aneuploidy

Candida albicans is a prevalent human fungal pathogen. Azoles are the most widely used antifungal drugs. Drug tolerance in bacteria is well defined and thoroughly studied, but in fungi, the definition of drug tolerance and the mechanism that drive it are not well understood. Here, we found that a large proportion of clinical isolates were intrinsically tolerant to fluconazole, and/or could be induced by high temperature (37°C) to become tolerant (conditionally tolerant). When treated with inhibitory doses of fluconazole, non-tolerant strains became tolerant by forming aneuploids involving different chromosomes, with chromosome R duplication as the most recurrent mechanism. Tolerance determines the ability to grow in the presence of fluconazole and other azoles, in a manner independent of the MIC. Both temperature conditional tolerance and the associated aneuploidy were sensitive to FK506, an inhibitor of calcineurin. Intrinsic and conditional tolerance were also abolished by deletions of genes encoding the calcineurin (CMP1 and CNB1). However, the dependence of tolerance on calcineurin could be bypassed by a different aneuploid chromosome. Thus, fluconazole tolerance in C. albicans is regulated by temperature and by aneuploidy and is dependent upon aneuploidy, but this dependence can be bypassed by an additional aneuploidy.

Mouse models of aneuploidy to understand chromosome disorders

An organism or cell carrying a number of chromosomes that is not a multiple of the haploid count is in a state of aneuploidy. This condition results in significant changes in the level of expression of genes that are gained or lost from the aneuploid chromosome(s) and most cases in humans are not compatible with life. However, a few aneuploidies can lead to live births, typically associated with deleterious phenotypes. We do not understand why phenotypes arise from aneuploid syndromes in humans. Animal models have the potential to provide great insight, but less than a handful of mouse models of aneuploidy have been made, and no ideal system exists in which to study the effects of aneuploidy per se versus those of raised gene dosage. Here, we give an overview of human aneuploid syndromes, the effects on physiology of having an altered number of chromosomes and we present the currently available mouse models of aneuploidy, focusing on models of trisomy 21 (which causes Down syndrome) because this is the most common, and therefore, the most studied autosomal aneuploidy. Finally, we discuss the potential role of carrying an extra chromosome on aneuploid phenotypes, independent of changes in gene dosage, and methods by which this could be investigated further.

Application of mosaicism ratio to multifetal gestations

Mosaicism ratio, or MR, is a laboratory metric that can be calculated using massively parallel sequencing data from cell-free DNA (cfDNA) screening. MR compares the amount of cfDNA present from a particular chromosome or chromosomal region to the overall fetal fraction of the specimen. In singleton gestations, MR may be used to refine the positive predictive value of an abnormal cfDNA screening result by identifying cases that could be impacted by various biological factors, such as placental mosaicism or prior co-twin demise. The current study was designed to examine the behavior of mosaicism ratio (MR) in multifetal gestations. Multifetal cfDNA specimens with positive results for trisomies 21, 18, or 13 and confirmed diagnostic outcomes were compiled to examine MR of the aneuploid chromosome based on the number of affected fetuses/placentas. A second multifetal cohort was assembled to analyze the MR of the Y chromosome in cases with at least one male fetus. For aneuploid cases, the average MR of affected singletons (used as a biological proxy for two affected twins) was significantly higher than the average MR for twins in which one fetus was affected. The average MR of the aneuploid chromosome for one affected twin was 52%, 42%, and 48% of that of singleton gestations for trisomy 21, 18, and 13 cases, respectively. MR cutoffs of 0.7 for trisomy 21, and 0.5 for trisomies 18 and 13 may help predict whether one versus both twins are affected with aneuploidy when clinical concern arises. For male cases, the Y MR of XX/XY gestations was 48% of the Y MR for XY/XY gestations. Using a Y MR cutoff of 0.8 allowed determination of XX/XY versus XY/XY gestations with 92.3–94.9% accuracy. Based on the data presented, MR may have utility in the analysis and interpretation of cfDNA data from multifetal gestations.

The total mRNA concentration buffering system in yeast is global rather than gene-specific

Gene expression in eukaryotes does not follow a linear process from transcription to translation and mRNA degradation. Instead it follows a circular process in which cytoplasmic mRNA decay crosstalks with nuclear transcription. In many instances this crosstalk contributes to buffer mRNA at a roughly constant concentration. Whether the mRNA buffering concept operates on the total mRNA concentration or at the gene-specific level, and if the mechanism to do so is a global or a specific one, remain unknown. Here we assessed changes in mRNA concentrations and their synthesis rates (SRs) along the transcriptome of aneuploid strains of the yeast Saccharomyces cerevisiae. We also assessed mRNA concentrations and their SRs in non sense-mediated decay (NMD) targets in euploid strains. We found that the altered SRs in the genes from the aneuploid chromosome and the changes in their mRNA stabilities were not balanced. In addition, the stability of NMD targets was not specifically counterbalanced by the changes in SR. We conclude that there is no genetic compensation of NMD mRNA targets, and total mRNA buffering uses mostly a global system rather than a gene-specific one in yeast.

The ploidy level of triticale plant regenerants, obtained by in vitro selection for resistance to abiotic stresses

Aim. To analyze the ploidy level of plant regenerants of winter triticale, obtained by in vitro selection for resistance to osmotic and salt stresses. Methods. By cytological analysis and flow cytometry methods there was determined the ploidy level in the plant regenerants of winter triticale obtained by in vitro selection for resistance to abiotic stresses. Results. The somaclonal variability of plant regenerants of winter triticale resistant to osmotic and salt stresses by ploidy level was observed. The cytological instability of resistant’s regenerants was revealed that was due in appearance of aneuploidy plants. Plants with aneuploid chromosome set (38–41) were characterized by reduced viability and abnormal generative organs resulting they are not formed normal ears and not received seeds. Conclusions. Among the obtained regenerants euploids were in most cases indicating a selective advantage of hexaploid cells in ability to morphogenesis. Keywords: Triticale, plant regenerants, cytological analysis, aneuploids, abiotic stresses.

Chromosome mis-segregation and cytokinesis failure in trisomic human cells

Cancer cells display aneuploid karyotypes and typically mis-segregate chromosomes at high rates, a phenotype referred to as chromosomal instability (CIN). To test the effects of aneuploidy on chromosome segregation and other mitotic phenotypes we used the colorectal cancer cell line DLD1 (2n = 46) and two variants with trisomy 7 or 13 (DLD1+7 and DLD1+13), as well as euploid and trisomy 13 amniocytes (AF and AF+13). We found that trisomic cells displayed higher rates of chromosome mis-segregation compared to their euploid counterparts. Furthermore, cells with trisomy 13 displayed a distinctive cytokinesis failure phenotype. We showed that up-regulation of SPG20 expression, brought about by trisomy 13 in DLD1+13 and AF+13 cells, is sufficient for the cytokinesis failure phenotype. Overall, our study shows that aneuploidy can induce chromosome mis-segregation. Moreover, we identified a trisomy 13-specific mitotic phenotype that is driven by up-regulation of a gene encoded on the aneuploid chromosome.

Aneuploidy Alnus formosana Selection and ISSR Analysis

the chromosomal counting was carried out with 51 of annual Taiwan alder (Alnus formosana) by the wall degradation and hypotonic flame-drying method, and 6 aneuploid plants has been selected from these seedings. The viable aneuploid chromosome numbers included 2n=52 (No.4),2n=42 (No.19),2n=54(No.21),2n=50(No.24),2n=56,112 (No.25),2n=52(No.33). Subsequently, the ISSR was taken to analyze the genome of these aneuploid plants,and 5 primers were obtained from 57 which could separate 6 aneuploid plants. And the ratio of polymorphism was more than 78.2%.

Ploidy dimorphism and reproductive biology in Stenodrepanum bergii (Leguminosae), a rare South American endemism

This is the first report on chromosome numbers and the reproductive behaviour in Stenodrepanum Harms, a rare endemic and monotypic legume genus from the arid and salty areas of central–western Argentina. Sixty individuals belonging to two populations from two salty areas (“salinas”) were surveyed and included mostly triploid (2n = 3x = 36) and only two diploid (2n = 2x = 24) plants. Meiosis in diploids is regular, with bivalent pairing and uniform and viable pollen. In contrast, meiosis in triploids is characterized by high trivalent pairing, with irregularly shaped pollen and variation in cytoplasm content and stainability, which is in agreement with an unbalanced segregation occurring in anaphases I and II. However, different triploid plants/individuals showed various degrees of pollen fertility, which may be attributed to particular genotypes. Research on reproductive biology events indicates sexual cross-pollinated reproduction enhanced by protogyny in both cytotypes. All plants produced seeds, but seedlings were only recovered from diploid plants pollinated with triploids, and even those eventually perished. Chromosome counts in these seedlings revealed aneuploid chromosome numbers owing to the combination of unbalanced gametes.