Biology subjects

Reza, M. H.

Publications and source records attributed to Reza, M. H..

6 recordsLinked to original sources

bioRxiv2024

Expansion microscopy reveals unique ultrastructural features of pathogenic budding yeast species

Candida albicans is the most prevalent fungal pathogen isolated from patients with candidemia. As is the case for many other fungi, the complex life cycle of C. albicans has been challenging to study with high-resolution microscopy techniques due to its small size. We employed ultrastructure expansion microscopy (U-ExM) to directly visualise sub-cellular structures at high resolution in the C. albicans yeast and during its transition to hyphal growth. NHS-ester pan-labelling in combination with immunofluorescence (IF) provided the first comprehensive map of nucleolar and mitochondrial dynamics through the C. albicans cell cycle. Analysis of microtubules (MTs) and spindle pole bodies (SPBs) stained with marker proteins suggests that contrary to the pole-to-pole arrangement observed in Saccharomyces cerevisiae, C. albicans yeast cells display a unique side-by-side arrangement of SPBs with a short mitotic spindle and longer astral MTs (aMTs) at the pre-anaphase stage. Modifications to the established U-ExM protocol enabled the expansion of several medically relevant human fungal pathogens, revealing that the side-by-side SPB configuration is a plausible conserved feature shared by many fungal species. We highlight the power of U-ExM to investigate sub-cellular organisation and organellar dynamics at high resolution and low cost in poorly studied, medically relevant microbial pathogens.

cell biology↗

bioRxiv2023

Spindle architecture constrains karyotype in budding yeast

The eukaryotic cell division machinery must rapidly and reproducibly duplicate and partition the cells chromosomes in a carefully coordinated process. However, chromosome number varies dramatically between genomes, even on short evolutionary timescales. We sought to understand how the mitotic machinery senses and responds to karyotypic changes by using a series of budding yeast strains in which the native chromosomes have been successively fused. Using a combination of cell biological profiling, genetic engineering, and experimental evolution, we show that chromosome fusions are well tolerated up until a critical point. Cells with fewer than five centromeres lack the necessary number of kinetochore-microtubule attachments needed to counter outward forces in the metaphase spindle, triggering the spindle assembly checkpoint and prolonging metaphase. Our findings demonstrate that spindle architecture is a constraining factor for karyotype evolution.

cell biology↗

bioRxiv2021

Autophagy-related protein Atg11 preserves asymmetric inheritance of spindle microtubule-organizing centers

Emerging studies hint at the roles of autophagy-related proteins in various cellular processes in a eukaryotic cell. To understand if autophagy-related proteins influence genome stability, we examined a cohort of 35 autophagy mutants in Saccharomyces cerevisiae. We observed cells lacking Atg11 show poor mitotic stability of minichromosomes. Atg11 molecules dynamically localize to the spindle pole bodies (SPBs). Loss of Atg11 leads to a delayed cell cycle progression. Such cells accumulate at metaphase at an elevated temperature that is relieved when the spindle assembly checkpoint is inactivated. Indeed, atg11{Delta} cells have stabilized securin levels, that prevent anaphase onset, confirming chromosome biorientation defects associated with the mutant. Atg11 functions in the Kar9-dependent spindle positioning pathway and maintains Kar9 asymmetry by facilitating proper dynamic instability of astral microtubules (aMTs). Taken together, this study uncovers a non-canonical role of Atg11 in facilitating MT dynamics crucial for chromosome segregation.

genetics↗

bioRxiv2020

Vacuolar transporter Mnr2 safeguards mitochondrial integrity in aged cells

Aging is associated with altered mitochondrial function. Mitochondrial function is dependent on the magnesium (Mg+2) ion flux. The molecular mechanism underlying Mg+2 homeostasis, especially during aging has not been well understood. We previously demonstrated that the absence of a vacuolar ion transporter Mnr2 accelerates cell death in the older part of the colony in Magnaporthe oryzae presumably due to an altered Mg+2 homeostasis. Localization of Mnr2 as dynamic puncta at the vacuolar membrane especially in the older Magnaporthe cells further suggests its association with aged cells. Interestingly, such vacuolar Mnr2 puncta colocalized with the filamentous mitochondria in the aged cells. Further, we show that aged mnr2{Delta} null cells displayed loss of integrity of mitochondria and vacuoles. Remarkably, exogenously added Mg+2 restored the mitochondrial structure as well as improved the lifespan of mnr2{Delta} null cells. Thus, we uncover a mechanism of maintenance of mitochondrial integrity and function by the ion transporter Mnr2-based Mg+2 homeostasis during aging.

cell biology↗

bioRxiv2019

Centromere-mediated chromosome break drives karyotype evolution in closely related Malassezia species

Intra-chromosomal or inter-chromosomal genomic rearrangements often lead to speciation (1). Loss or gain of a centromere leads to alterations in chromosome number in closely related species. Thus, centromeres can enable tracing the path of evolution from the ancestral to a derived state (2). The Malassezia species complex of the phylum Basiodiomycota shows remarkable diversity in chromosome number ranging between six and nine chromosomes (3-5). To understand these transitions, we experimentally identified all eight centromeres as binding sites of an evolutionarily conserved outer kinetochore protein Mis12/Mtw1 in M. sympodialis. The 3 to 5 kb centromere regions share an AT-rich, poorly transcribed core region enriched with a 12 bp consensus motif. We also mapped nine such AT-rich centromeres in M. globosa and the related species Malassezia restricta and Malassezia slooffiae. While eight predicted centromeres were found within conserved synteny blocks between these species and M. sympodialis, the remaining centromere in M. globosa (MgCEN2) or its orthologous centromere in M. slooffiae (MslCEN4) and M. restricta (MreCEN8) mapped to a synteny breakpoint compared with M. sympodialis. Taken together, we provide evidence that breakage and loss of a centromere (CEN2) in an ancestral Malassezia species possessing nine chromosomes resulted in fewer chromosomes in M. sympodialis. Strikingly, the predicted centromeres of all closely related Malassezia species map to an AT-rich core on each chromosome that also shows enrichment of the 12 bp sequence motif. We propose that centromeres are fragile AT-rich sites driving karyotype diversity through breakage and inactivation in these and other species. Significance statementThe number of chromosomes can vary between closely related species. Centromere loss destabilizes chromosomes and results in reduced number of chromosomes to drive speciation. A series of evidence from studies on various cancers suggest that an imbalance in kinetochore-microtubule attachments results in breaks at the centromeres. To understand if such events can cause chromosome number changes in nature, we studied six species of Malassezia, of which three possess eight chromosomes and others have nine chromosomes each. We find signatures of chromosome breakage at the centromeres in organisms having nine chromosomes. We propose that the break at the centromere followed by fusions of acentric chromosomes to other chromosomes could be a plausible mechanism shaping the karyotype of Malassezia and related organisms. ClassificationBiological sciences, Genetics

genomics↗

bioRxiv2018

Cellular dynamics and genomic identity of centromeres in Rice Blast

A series of well-synchronized events mediated by kinetochore-microtubule interactions ensure faithful chromosome segregation in eukaryotes. Centromeres scaffold kinetochore assembly and are among the fastest evolving chromosomal loci in terms of the DNA sequence, length, and organization of intrinsic elements. Neither the centromere structure nor the kinetochore dynamics is well studied in plant pathogenic fungi. Here, we sought to understand the process of chromosome segregation in the rice blast fungus, Magnaporthe oryzae. High-resolution confocal imaging of GFP-tagged inner kinetochore proteins, CenpA and CenpC, revealed an unusual albeit transient declustering of centromeres just before anaphase separation in M. oryzae. Strikingly, the declustered centromeres positioned randomly at the spindle midzone without an apparent metaphase plate per se. Using chromatin immunoprecipitation followed by deep sequencing, all seven centromeres were identified as CenpA-rich regions in the wild-type Guy11 strain of M. oryzae. The centromeres in M. oryzae are regional and span 57 to 109 kb transcriptionally poor regions. No centromere-specific DNA sequence motif or repetitive elements could be identified in these regions suggesting an epigenetic specification of centromere function in M. oryzae. Highly AT-rich and heavily methylated DNA sequences were the only common defining features of all the centromeres in the Rice Blast. Detailed gene synteny analyses helped identify and compare the centromere regions in distinct isolates of M. oryzae and its related species Magnaporthe poae. Overall, this study identifies unusual centromere dynamics and maps the centromere DNA sequences in the top model fungal pathogen M. oryzae, which causes severe losses in global rice production.\n\nSignificanceMagnaporthe oryzae is an important fungal pathogen that causes an annual loss of 10-30% rice crop due to the devastating blast disease. In most organisms, kinetochores are arranged either in the metaphase plate or are clustered together to facilitate synchronized anaphase separation of chromosomes. In this study, we show that the initially clustered kinetochores separate and position randomly prior to anaphase in M. oryzae. Centromeres, identified as the site of kinetochore assembly, are regional type without any shared sequence motifs in M. oryzae. Together, this study reveals atypical kinetochore dynamics and identifies functional centromeres in M. oryzae, thus paving the way to define heterochromatin boundaries and understand the process of kinetochore assembly on epigenetically specified centromere loci.

genetics↗