Chromosome Research最新文献

Interspecific hybridization is widespread in nature and can result in the formation of new hybrid species as well as the transfer of traits between species. However, the fate of newly formed hybrid lineages is relatively understudied. We undertook pairwise crossing between multiple genotypes of three Brassica allotetraploid species Brassica juncea (2n = AABB), Brassica carinata (2n = BBCC), and Brassica napus (2n = AACC) to generate AABC, BBAC, and CCAB interspecific hybrids and investigated chromosome inheritance and fertility in these hybrids and their self-pollinated progeny. Surprisingly, despite the presence of a complete diploid genome in all hybrids, hybrid fertility was very low. AABC and BBAC first generation (F₁) hybrids both averaged ~16% pollen viability compared to 3.5% in CCAB hybrids: most CCAB hybrid flowers were male-sterile. AABC and CCAB F₁ hybrid plants averaged 5.5 and 0.5 seeds per plant, respectively, and BBAC F₁ hybrids ~56 seeds/plant. In the second generation (S₁), all confirmed self-pollinated progeny resulting from CCAB hybrids were sterile, producing no self-pollinated seeds. Three AABC S₁ hybrids putatively resulting from unreduced gametes produced 3, 14, and 182 seeds each, while other AABC S₁ hybrids averaged 1.5 seeds/plant (0-8). BBAC S₁ hybrids averaged 44 seeds/plant (range 0-403). We also observed strong bias towards retention rather than loss of the haploid genomes, suggesting that the subgenomes in the Brassica allotetraploids are already highly interdependent, such that loss of one subgenome is detrimental to fertility and viability. Our results suggest that relationships between subgenomes determine hybridization outcomes in these species.

Chromosome instability (CIN) is a cancer hallmark that drives tumour heterogeneity, phenotypic adaptation, drug resistance and poor prognosis. High-grade serous ovarian cancer (HGSOC), one of the most chromosomally unstable tumour types, has a 5-year survival rate of only ~30% - largely due to late diagnosis and rapid development of drug resistance, e.g., via CIN-driven ABCB1 translocations. However, CIN is also a cell cycle vulnerability that can be exploited to specifically target tumour cells, illustrated by the success of PARP inhibitors to target homologous recombination deficiency (HRD). However, a lack of appropriate models with ongoing CIN has been a barrier to fully exploiting disease-specific CIN mechanisms. This barrier is now being overcome with the development of patient-derived cell cultures and organoids. In this review, we describe our progress building a Living Biobank of over 120 patient-derived ovarian cancer models (OCMs), predominantly from HGSOC. OCMs are highly purified tumour fractions with extensive proliferative potential that can be analysed at early passage. OCMs have diverse karyotypes, display intra- and inter-patient heterogeneity and mitotic abnormality rates far higher than established cell lines. OCMs encompass a broad-spectrum of HGSOC hallmarks, including a range of p53 alterations and BRCA1/2 mutations, and display drug resistance mechanisms seen in the clinic, e.g., ABCB1 translocations and BRCA2 reversion. OCMs are amenable to functional analysis, drug-sensitivity profiling, and multi-omics, including single-cell next-generation sequencing, and thus represent a platform for delineating HGSOC-specific CIN mechanisms. In turn, our vision is that this understanding will inform the design of new therapeutic strategies.

Chromosomal instability (CIN), an increased rate of chromosomal segregation abnormalities, drives intratumor heterogeneity and affects most human cancers. In addition to chromosome copy number alterations, CIN results in chromosome(s) (fragments) being mislocalized into the cytoplasm in the form of micronuclei. Micronuclei can be detected by cGAS, a double-strand nucleic acid sensor, which will lead to the production of the second messenger 2'3'-cGAMP, activation of an inflammatory response, and downstream immune cell activation. However, the molecular network underlying the CIN-induced inflammatory response is still poorly understood. Furthermore, there is emerging evidence that cancers that display CIN circumvent this CIN-induced inflammatory response, and thus immune surveillance. The STAT1, STAT3, and NF-κB signaling cascades appear to play an important role in the CIN-induced inflammatory response. In this review, we discuss how these pathways are involved in signaling CIN in cells and how they are intertwined. A better understanding of how CIN is being signaled in cells and how cancer cells circumvent this is of the utmost importance for better and more selective cancer treatment.

Micronuclei, small DNA-containing structures separate from the main nucleus, were used for decades as an indicator of genotoxic damage. Micronuclei containing whole chromosomes were considered a biomarker of aneuploidy and were believed to form, upon mitotic exit, from chromosomes that lagged behind in anaphase as all other chromosomes segregated to the poles of the mitotic spindle. However, the mechanism responsible for inducing anaphase lagging chromosomes remained unknown until just over twenty years ago. Here, I summarize what preceded and what followed this discovery, highlighting some of the open questions and opportunities for future investigation.

Telomerase is a ribonucleoprotein ribonucleic enzyme that elongates telomere repeat sequences at the ends of chromosomes and contributes to cellular immortalization. The catalytic component of telomerase, human telomerase reverse transcriptase (hTERT), has been observed to be reactivated in immortalized cells. Notably, most cancer cells have been found to have active hTERT mRNA transcription, resulting in continuous cell division, which is crucial for malignant transformation. Therefore, discovering mechanisms underlying the regulation of hTERT transcription is an attractive target for cancer-specific treatments.Loss of heterozygosity (LOH) of chromosome 3p21.3 has been frequently observed in human oral squamous cell carcinoma (OSCC). Moreover, we previously reported that HSC3 OSCC microcell hybrid clones with an introduced human chromosome 3 (HSC3#3) showed inhibition of hTERT transcription compared with the parental HSC3 cells. This study examined whether hTERT transcription regulators are present in the 3p21.3 region. We constructed a human artificial chromosome (HAC) vector (3p21.3-HAC) with only the 3p21.3-p22.2 region and performed functional analysis using the 3p21.3-HAC. HSC3 microcell hybrid clones with an introduced 3p21.3-HAC exhibited significant suppression of hTERT transcription, similar to the microcell hybrid clones with an intact chromosome 3. In contrast, HSC3 clones with truncated chromosome 3 with deletion of the 3p21.3 region (3delp21.3) showed no effect on hTERT expression levels. These results provide direct evidence that hTERT suppressor gene(s) were retained in the 3p21.3 region, suggesting that the presence of regulatory factors that control telomerase enzyme activity may be involved in the development of OSCC.

In the evolution of many organisms, periods of slow genome reorganization (= chromosomal conservatism) are interrupted by bursts of numerous chromosomal changes (= chromosomal megaevolution). Using comparative analysis of chromosome-level genome assemblies, we investigated these processes in blue butterflies (Lycaenidae). We demonstrate that the phase of chromosome number conservatism is characterized by the stability of most autosomes and dynamic evolution of the sex chromosome Z, resulting in multiple variants of NeoZ chromosomes due to autosome-sex chromosome fusions. In contrast during the phase of rapid chromosomal evolution, the explosive increase in chromosome number occurs mainly through simple chromosomal fissions. We show that chromosomal megaevolution is a highly non-random canalized process, and in two phylogenetically independent Lysandra lineages, the drastic parallel increase in number of fragmented chromosomes was achieved, at least partially, through reuse of the same ancestral chromosomal breakpoints. In species showing chromosome number doubling, we found no blocks of duplicated sequences or duplicated chromosomes, thus refuting the hypothesis of polyploidy. In the studied taxa, long blocks of interstitial telomere sequences (ITSs) consist of (TTAGG)_n arrays interspersed with telomere-specific retrotransposons. ITSs are sporadically present in rapidly evolving Lysandra karyotypes, but not in the species with ancestral chromosome number. Therefore, we hypothesize that the transposition of telomeric sequences may be triggers of the rapid chromosome number increase. Finally, we discuss the hypothetical genomic and population mechanisms of chromosomal megaevolution and argue that the disproportionally high evolutionary role of the Z sex chromosome can be additionally reinforced by sex chromosome-autosome fusions and Z-chromosome inversions.

Chromosomal instability (CIN) is a pervasive feature of human cancers involved in tumor initiation and progression and which is found elevated in metastatic stages. CIN can provide survival and adaptation advantages to human cancers. However, too much of a good thing may come at a high cost for tumor cells as excessive degree of CIN-induced chromosomal aberrations can be detrimental for cancer cell survival and proliferation. Thus, aggressive tumors adapt to cope with ongoing CIN and most likely develop unique susceptibilities that can be their Achilles' heel. Determining the differences between the tumor-promoting and tumor-suppressing effects of CIN at the molecular level has become one of the most exciting and challenging aspects in cancer biology. In this review, we summarized the state of knowledge regarding the mechanisms reported to contribute to the adaptation and perpetuation of aggressive tumor cells carrying CIN. The use of genomics, molecular biology, and imaging techniques is significantly enhancing the understanding of the intricate mechanisms involved in the generation of and adaptation to CIN in experimental models and patients, which were not possible to observe decades ago. The current and future research opportunities provided by these advanced techniques will facilitate the repositioning of CIN exploitation as a feasible therapeutic opportunity and valuable biomarker for several types of human cancers.

We report the first chromosome-length genome assemblies for three species in the mammalian order Pholidota: the white-bellied, Chinese, and Sunda pangolins. Surprisingly, we observe extraordinary karyotypic plasticity within this order and, in female white-bellied pangolins, the largest number of chromosomes reported in a Laurasiatherian mammal: 2n = 114. We perform the first karyotype analysis of an African pangolin and report a Y-autosome fusion in white-bellied pangolins, resulting in 2n = 113 for males. We employ a novel strategy to confirm the fusion and identify the autosome involved by finding the pseudoautosomal region (PAR) in the female genome assembly and analyzing the 3D contact frequency between PAR sequences and the rest of the genome in male and female white-bellied pangolins. Analyses of genetic variability show that white-bellied pangolins have intermediate levels of genome-wide heterozygosity relative to Chinese and Sunda pangolins, consistent with two moderate declines of historical effective population size. Our results reveal a remarkable feature of pangolin genome biology and highlight the need for further studies of these unique and endangered mammals.

Cellular quiescence is an important physiological state both in unicellular and multicellular eukaryotes. Quiescent cells are halted for proliferation and stop the cell cycle at the G₀ stage. Using fission yeast as a model organism, we have previously found that several subunits of a conserved chromatin remodeling complex, Ino80C (INOsitol requiring nucleosome remodeling factor), are required for survival in quiescence. Here, we demonstrate that Ino80C has a key function in the regulation of gene expression in G₀ cells. We show that null mutants for two Ino80C subunits, Iec1 and Ies2, a putative subunit Arp42, a null mutant for the histone variant H2A.Z, and a null mutant for the Inositol kinase Asp1 have very similar phenotypes in quiescence. These mutants show reduced transcription genome-wide and specifically fail to activate 149 quiescence genes, of which many are localized to the subtelomeric regions. Using spike in normalized ChIP-seq experiments, we show that there is a global reduction of H2A.Z levels in quiescent wild-type cells but not in iec1∆ cells and that a subtelomeric chromosome boundary element is strongly affected by Ino80C. Based on these observations, we propose a model in which Ino80C is evicting H2A.Z from chromatin in quiescent cells, thereby inactivating the subtelomeric boundary element, leading to a reorganization of the chromosome structure and activation of genes required to survive in quiescence.