Comparative genomics of Cryptococcus and Kwoniella reveals pathogenesis evolution and contrasting karyotype dynamics via intercentromeric recombination or chromosome fusion

A large-scale comparative genomic analysis was conducted for the global human fungal pathogens within the Cryptococcus genus, compared to non-pathogenic Cryptococcus species, and related species from the sister genus Kwoniella. Chromosome-level genome assemblies were generated for multiple species of both genera, resulting in a dataset encompassing virtually all of their known diversity. Although Cryptococcus and Kwoniella have comparable genome sizes (about 19.2 and 22.9 Mb) and similar gene content, hinting at pre-adaptive pathogenic potential, our analysis found evidence in pathogenic Cryptococcus species of specific examples of gene gain (via horizontal gene transfer) and gene loss, which might represent evolutionary signatures of pathogenic development. Genome analysis also revealed a significant variation in chromosome number and structure between the two genera. By combining synteny analysis and experimental centromere validation, we found that most Cryptococcus species have 14 chromosomes, whereas most Kwoniella species have fewer (11, 8, 5 or even as few as 3). Reduced chromosome number in Kwoniella is associated with formation of giant chromosomes (up to 18 Mb) through repeated chromosome fusion events, each marked by a pericentric inversion and centromere loss. While similar chromosome inversion-fusion patterns were observed in all Kwoniella species with fewer than 14 chromosomes, no such pattern was detected in Cryptococcus. Instead, Cryptococcus species with less than 14 chromosomes, underwent chromosome reductions primarily through rearrangements associated with the loss of repeat-rich centromeres. Additionally, Cryptococcus genomes exhibited frequent interchromosomal translocations, including intercentromeric recombination facilitated by transposons shared between centromeres. Taken together, our findings advance our understanding of genomic changes possibly associated with pathogenicity in Cryptococcus and provide a foundation to elucidate mechanisms of centromere loss and chromosome fusion driving distinct karyotypes in closely related fungal species, including prominent global human pathogens.

Macronuclear development in ciliates, with a focus on nuclear architecture

Ciliates are defined by the presence of dimorphic nuclei as they have both a somatic macronucleus and germline micronucleus within each individual cell. The size and structure of both germline micronuclei and somatic macronuclei varies tremendously among ciliates. Except just after conjugation (i.e. the nuclear exchange in sexual cycle), the germline micronucleus is transcriptionally-inactive and contains canonical chromosomes that will be inherited between generations. In contrast, the transcriptionally-active macronucleus contains chromosomes that vary in size in different classes of ciliates, with some lineages having extensively-fragmented gene-sized somatic chromosomes while others contain longer multigene chromosomes. Here, we describe the variation in somatic macronuclear architecture in lineages sampled across the ciliate tree of life, specifically focusing on lineages with extensively fragmented chromosomes (e.g. the classes Phyllopharyngea and Spirotrichea). Further, we synthesize information from the literature on the development of ciliate macronuclei, focusing on changes in nuclear architecture throughout life cycles. These data highlight the tremendous diversity among ciliate nuclear cycles, extend our understanding of patterns of genome evolution, and provide insight into different germline and somatic nuclear features (e.g. nuclear structure and development) among eukaryotes.

Effects of 36.6 GHz and static magnetic field on degree of endoreduplication in Drosophila melanogaster polytene chromosomes

Purpose To study the effect of microwave (MW) irradiation and consistent action of microwaves and static magnetic field (MF) on the giant chromosomes endoreduplication in Drosophila melanogaster Meig. Materials and methods Experiments were carried out on inbred wild type Canton-S strain. Exposure to microwaves (frequency - 36.64 GHz, power density - 1 W/m(2), exposure time - 30 sec) and static magnetic field (intensity - 25 mT, exposure time - 5 min) applied at the egg stage after a 2-h oviposition. Giant chromosomes were investigated in squashed preparations of the salivary glands stained by acetoorcein by the cytomorphometric method. Preparations were obtained from Drosophila larvae at the 0 h prepupae stage. Results Exposure to microwaves increased the degree of polyteny in chromosomes (DPC) by 7.5%, and the statistical power of the impact was: h(2) = 35.3%. A similar effect occurred after the sequential action of microwaves and static magnetic field: The polyteny level of chromosomes increased by 7.4%, statistical power was: h(2) = 30.6%. Conclusions Exposure to microwaves on the stage of embryogenesis has a stimulating effect on endoreduplication in Drosophila development. The effect of microwaves was not modified by the action of the static magnetic field.