Chromosome Research最新文献

Over the past decades, transposable elements (TEs) have been shown to play important roles shaping genome architecture and as major promoters of genetic diversification and evolution of species. Likewise, TE accumulation is tightly linked to heterochromatinization and centromeric dynamics, which can ultimately contribute to speciation. Despite growing efforts to characterize the repeat landscape of species, few studies have focused on mapping the accumulation profiles of TEs on chromosomes. The few studies on repeat accumulation profiles in populations are biased towards model organisms and inbred lineages. Here, we present a cytomolecular analysis of six mobilome-extracted elements on multiple individuals from a population of a species of wild-captured beetle, Dichotomius schiffleri, aiming to investigate patterns of TE accumulation and uncover possible trends of their chromosomal distribution. Compiling TE distribution data from several individuals allowed us to make generalizations regarding variation of TEs at the gross chromosome level unlikely to have been achieved using a single individual, or even from a whole-genome assembly. We found that (1) transposable elements have differential accumulation profiles on D. schiffleri chromosomes and (2) specific chromosomes have their own TE accumulation landscape. The remarkable variability of their genomic distribution suggests that TEs are likely candidates to contribute to the evolution of heterochromatin architecture and promote high genetic variability in species that otherwise display conserved karyotypes. Therefore, this variation likely contributed to genome evolution and species diversification in Dichotomius.

CLASPs are key modulators of microtubule dynamics throughout the cell cycle. During mitosis, CLASPs independently associate with growing microtubule plus-ends and kinetochores and play essential roles in chromosome segregation. In a proteomic survey for human CLASP1-interacting proteins during mitosis, we have previously identified SOGA1 and SOGA2/MTCL1, whose mitotic roles remained uncharacterized. Here we performed an initial functional characterization of human SOGA1 and SOGA2/MTCL1 during mitosis. Using specific polyclonal antibodies raised against SOGA proteins, we confirmed their expression and reciprocal interaction with CLASP1 and CLASP2 during mitosis. In addition, we found that both SOGA1 and SOGA2/MTCL1 are phospho-regulated during mitosis by CDK1. Immunofluorescence analysis revealed that SOGA2/MTCL1 co-localizes with mitotic spindle microtubules and spindle poles throughout mitosis and both SOGA proteins are enriched at the midbody during mitotic exit/cytokinesis. GFP-tagging of SOGA2/MTCL1 further revealed a microtubule-independent localization at kinetochores. Live-cell imaging after siRNA-mediated knockdown of SOGA1 and SOGA2/MTCL1 showed that they are independently required for distinct aspects of chromosome segregation. Thus, SOGA1 and SOGA2/MTCL1 are bona fide CLASP-interacting proteins during mitosis required for faithful chromosome segregation in human cells.

DNA methylation is an essential epigenetic mark that regulates normal mammalian embryonic development. DNA methylation profiles are not always static, especially during germline development. In zygotes, DNA is typically highly methylated but, during preimplantation, DNA methylation is erased globally. Then, at the start of post-implantation development in mouse embryos, DNA again becomes dramatically hypermethylated. Chromatin structure regulates the accessibility of DNA-modifying enzymes to target DNA. Beyond that, however, our understanding of the pathway by which chromatin regulation initiates changes in global DNA methylation during mouse embryonic development remains incomplete. To analyse the relationship between global regulation of DNA methylation and chromatin status, we examined 5-methylcytosine (5mC), modified by the DNA methyltransferase DNMT, and the oxidative derivative 5-hydroxymethylation (5hmC), converted from 5mC by TET-family enzymes, by means of immunofluorescence staining of mitotic chromosomes in mouse embryonic stem cells (ESCs). Our comparison of immunostaining patterns for those epigenetic modifications in wild-type, DNMT-deficient, and TET-deficient ESCs allowed us to visualise cell cycle-mediated DNA methylation changes, especially in euchromatic regions. Our findings suggest that DNA methylation patterns in undifferentiated mouse ESCs are stochastically balanced by the opposing effects of two activities: demethylation by TET and subsequent remethylation by DNMT.

Loss of mitosis regulation is a common feature of malignant cells that leads to aberrant cell division with inaccurate chromosome segregation. The mitotic checkpoint is responsible for faithful transmission of genetic material to the progeny. Defects in this checkpoint, such as mutations and changes in gene expression, lead to abnormal chromosome content or aneuploidy that may facilitate cancer development. Furthermore, a defective checkpoint response is indicated in the development of drug resistance to microtubule poisons that are used in treatment of various blood and solid cancers for several decades. Mitotic slippage and senescence are important cell fates that occur even with an active mitotic checkpoint and are held responsible for the resistance. However, contradictory findings in both the scenarios of carcinogenesis and drug resistance have aroused questions on whether mitotic checkpoint defects are truly responsible for these dismal outcomes. Here, we discuss the possible contribution of the faulty checkpoint signaling in cancer development and drug resistance, followed by the latest research on this pathway for better outcomes in cancer treatment.

The most often detected tumor in intact bitches is mammary tumors and represents a significant clinical problem throughout the world. Mammary neoplasms in canine have heterogeneous morphology, so the choice of the most appropriate biomarker is the biggest challenge in CMT detection. We performed a retrospective analysis and evaluated the canine cancer antigens and miRNA expression profiles as potential biomarkers. Sixty dogs based on histological examination divided into three groups, viz., dogs with a benign mammary tumor, malignant mammary tumor, and control/healthy. The CA 15-3 was found more sensitive than CEA but detection of both will increase sensitivity. miR-21 expression differed significantly in all three groups. miR-29b expression differed significantly between the control and benign group and control and malignant group. The miR-21 overexpression and miR-29b downregulation with CMT are associated with clinical stage and can be used as non-invasive diagnostic and prognostic biomarkers. Hence, evaluation of CA 15-3 along with CEA would be a non-invasive technique for detecting canine mammary tumors. Evaluation of deregulated circulating miR-21 could be a valuable prognostic marker for early detection of mammary tumors in canines while miR-29b can add sensitivity in the detection of the canine mammary tumors if evaluated with miR-21.

The organization of chromatin into higher-order structures and its condensation process represent one of the key challenges in structural biology. This is important for elucidating several disease states. To address this long-standing problem, development of advanced imaging methods has played an essential role in providing understanding into mitotic chromosome structure and compaction. Amongst these are two fast evolving fluorescence imaging technologies, specifically fluorescence lifetime imaging (FLIM) and super-resolution microscopy (SRM). FLIM in particular has been lacking in the application of chromosome research while SRM has been successfully applied although not widely. Both these techniques are capable of providing fluorescence imaging with nanometer information. SRM or "nanoscopy" is capable of generating images of DNA with less than 50 nm resolution while FLIM when coupled with energy transfer may provide less than 20 nm information. Here, we discuss the advantages and limitations of both methods followed by their contribution to mitotic chromosome studies. Furthermore, we highlight the future prospects of how advancements in new technologies can contribute in the field of chromosome science.

Visualization of the chromosome ultrastructure has revealed new insights into its structural and functional properties. The use of new methods for revealing not only the surface but also the inner structure of the chromosome has been emerged. Some methods have long been used, such as conventional transmission electron microscopy (TEM). Although it has indispensably contributed to the revelation of the ultrastructure of the various biological samples, including chromosomes, some challenges have also been encountered, such as laborious sample preparation, limited view areas, and loss of information on some parts due to ultramicrotome sectioning. Therefore, a more advanced method is needed. Scanning electron microscopy (SEM) is also advantageous in the surface visualization of chromosome samples. However, it is limited by accessibility to gain the inner structure information. Focused ion beam/scanning electron microscopy (FIB/SEM) provides a way to investigate the inner structure of the samples in a direct slice-and-view manner to observe the ultrastructure of the inner part of the sample continuously and further construct a three-dimensional image. This method has long been used in the material science field, and recently, it has also been applied to biological research, such as in showing the inner structure of chromosomes. This review article presents the contributions of this new method to chromosome research and its recent developments in the inner structure of chromosome and discusses its current and potential applications to the high-resolution imaging of chromosomes.

This review describes image analyses for chromosome visible structures, focusing on the chromosome imaging system CHIAS (Chromosome Image Analyzing System). CHIAS is the first comprehensive imaging system for the analysis and characterization of plant chromosomes. A simulation method for human vision for capturing band positive regions was developed and used for the image analysis of large plant chromosomes with bands. Applying this method to C-banded Crepis chromosomes enabled recognition of band positive regions as seen by human vision. Furthermore, a new image parameter, condensation pattern was developed and successfully applied to identify small plant chromosomes such as rice and brassicas. Condensation profile (CP) derived from condensation pattern was also effective in developing quantitative chromosome maps. The result was quantitative chromosomal maps of several plants with small chromosomes, including Arabidopsis, diploid brassicas, rapeseed, rice, spinach, and sugarcane. In the final chapter, various applications of imaging techniques to the analysis of pachytene chromosomes, improved visibility of multicolor FISH images, 3D reconstruction of a human chromosome based on cross-section images obtained by a FIB/SEM, automatic extraction of chromosomal regions by machine learning, etc. are described.