Cytogenetic and Genome Research最新文献

Introduction: DNA helicases are vital for preserving genome integrity and ensuring the correct process of meiosis. Despite their recognized significance, the precise roles and spatial dynamics of these enzymes during meiotic prophase I remain largely unexplored.

Methods: The key methodology of this study consisted of immunocytochemical staining and statistical evaluation.

Results: Our results demonstrate that RTEL1 (Regulator of Telomere Elongation 1) helicase is present in regions that have just initiated synapsis, emphasizing that chromosome synapsis is essential for this helicase. Since RTEL1 and replication protein A (RPA) were previously shown to colocalize in somatic cells, we sought to assess this relationship in meiosis. During early pachytene, when RTEL1 and RPA levels are at their peak, several immuno-foci of these proteins exhibited complete or partial overlap, suggesting colocalization in some chromosomal regions, though some remained distinct. The earlier appearance of RPA in meiotic nuclei supports the notion that it may facilitate RTEL1 recruitment for DNA repair. As meiosis progresses from early pachytene to diplotene, the significant decrease in RTEL1 and RPA signals underscores their predominant involvement in early prophase I.

Conclusion: This study identifies RTEL1 as the third helicase, following BLM and FANCJ, to be detected in prophase I, suggesting that additional helicases may be added to this list in the future. Its unique synapsis-dependent behavior distinguishes it from the other two helicases, which do not exhibit such a pattern. Furthermore, our findings suggest that RTEL1 can demonstrate antirecombinase activity within synaptonemal complexes and functions as part of the meiotic helicase complex, which regulates critical aspects of meiotic processes.

Introduction: R1 and R2 retrotransposons specifically integrate into 28S rRNA genes, thereby disrupting many rDNA units within the nucleolar organizer region (NOR) of Drosophila. However, they also appear to play mutualistic roles, contributing to the maintenance of rDNA copy number and the regulation of nucleolar dominance. In addition to their presence in nucleolar rDNA, R1 elements are strongly enriched in the pericentromeric heterochromatin of the X chromosome, located distal to the NOR. This enrichment coincides with several enigmatic genetic phenomena - such as the ABO and cr phenotypes - whose molecular basis remains poorly understood. Notably, this region is one of the least characterized domains of the Drosophila melanogaster genome, lying outside the reference assembly and unresolved in metaphase chromosome preparations.

Methods: We performed cytological mapping of R1 and R2 retrotransposons in D. melanogaster heterochromatin using polytene chromosomes from Rif11 mutant, which suppresses under-replication of all types of heterochromatic sequences. These were combined with classical eu-heterochromatic inversions of the X chromosome.

Results and conclusion: We identified distinct clusters of both R1 and R2 elements within the X chromosome heterochromatin outside the NOR. R1 elements are highly enriched in the region between the heterochromatic Stellate (hSte) gene cluster and the NOR. This zone exhibits a unique response to Su(var)3-9 mutations, characterized by pronounced decondensation and the formation of a pseudo-puff. Proximal to the R1-enriched domain and adjacent to hSte cluster, we observed a region enriched in R2 elements. The edges of the NOR also show R2 enrichment, likely corresponding to intra-nucleolar domains that accumulate transcriptionally inactive rDNA units. In contrast, nucleolar R1 elements - which also mark inactive rDNA units - are more evenly distributed across the entire NOR. Based on these findings, we propose a refined cytological map of X chromosome heterochromatin in D. melanogaster.

Introduction: Supernumerary B chromosomes have been extensively investigated using diverse in vivo approaches, revealing insights into their origin, nature, evolutionary dynamics, maintenance mechanisms, and effects on their carriers. Despite its broad applicability across various biological research fields, in vitro cell culture remains underexplored as a tool for studying B chromosome biology, with studies limited to using cell cultures only as a source of chromosome preparations.

Methods: In the present study, cell cultures of the fish Astyanax mexicanus were established, with (AMEcfB) and without (AMEcf) the B chromosome, using caudal fin tissue collected through nonlethal procedures. These cultures were compared in terms of cell proliferation and in response to environmental stress (pH and temperature) using the MTT and RT-qPCR assay.

Results: The AMEcf and AMEcfB cell lines exhibited karyotypic stability and high proliferative potential, demonstrating their suitability for diverse scientific applications. The B chromosome, found exclusively in a subpopulation of AMEcfB cells, influenced cell physiology by affecting cell division dynamics. Experiments under extreme pH and temperature conditions revealed differences in cell viability and gene expression between the two lines, highlighting the role of the B chromosome in modulating environmental responses.

Conclusion: These findings align with previous reports on the effects of B chromosomes in living organisms. Thus, the A. mexicanus cell cultures established here represent a promising resource for investigations into B chromosome biology, offering significant ethical, economic, and methodological advantages.

Introduction: Partial trisomy of the 6q24qter region is a rare chromosomal disorder characterized by variable clinical features and poorly understood mechanistic origins.

Case presentation: We describe a de novo complex der(6) chromosome in a patient with features consistent with partial 6q trisomy syndrome, including congenital heart disease, growth restriction, developmental delay, and dysmorphic traits. Molecular Findings: Whole-genome sequencing (WGS) identified duplications of 1.5 Mb on 6p25.3 and 23.3 Mb on 6q24.3-qter. While the 6p duplication appears benign, the phenotype is likely driven by dosage-sensitive 6q genes (ARID1B, TAB2, QKI) and possible additive effects from other duplicated genes. No parental pericentric inversion was detected by classical or molecular cytogenetics, and WGS revealed no inversion-associated breakpoints. Instead, chimeric (q-/q+) and truncated reads at the 6q junction support a replication-based origin, such as reversed template switching. FISH confirmed direct insertion of the 6q segment into 6p25.3, without a del/dup pattern typical of inversion-derived recombinants. Notably, WGS detected no direct 6p-6q junction reads but identified chimeric 6p-15q-6q reads with 2-bp microhomologies, suggesting that chromosome 15 transiently mediated the rearrangement. Interspersed telomeric sequences and flanking Alu elements were also found at both breakpoints.

Conclusion: Altogether, these findings support a model in which replication fork stalling and template switching - potentially facilitated by telomere dynamics and repetitive elements - led to the formation of a recombinant-like der(6) chromosome. This case highlights the mechanistic complexity of structural rearrangements and the role of replication-based errors in shaping human genomic variation.

Introduction: Jumping translocations are rare cytogenetic events in hematologic malignancies, involving nonreciprocal translocation of a donor chromosome onto two or more recipient chromosomes.

Case presentation: In this paper, we report the first-ever case of a jumping translocation involving the long arm of chromosome 3 in a patient with mantle cell lymphoma. The basic clone had the translocation t(11;14)(q13;q32) and a der(13)t(3;13)(q12;p11), and the three subclones had an additional jumping translocation, involving the translocation of 3q12 onto recipient chromosomes 14p, 15p, and der(14)t(11;14), thus resulting in partial trisomy and tetrasomy 3q.

Conclusion: Although the underlying mechanism for the formation of jumping translocations is not well understood, their presence is usually associated with poor prognosis and clonal evolution and additional data are needed for their better clinical management.

Introduction: Idiopathic short stature (ISS) refers to non-syndromic growth failure without chronic disorders. The molecular basis of ISS remains largely unknown. Although a variable number of tandem repeats (VNTR) of 57 nucleotides in ACAN is known to correlate with the height of people in the general population, the role of this genetic variant in the etiology of ISS has not been studied.

Methods: We studied 128 Japanese patients with ISS, including 63 patients with prenatal and postnatal growth failure (small-for-gestational age-SS [SGA-SS]), and 100 control individuals. To examine the repeat numbers of ACAN VNTR, we amplified the VNTR-containing genomic region and analyzed the PCR products by gel electrophoresis. The accuracy of the results was confirmed by long-read next-generation sequencing.

Results: The repeat numbers of the patient group were similarly distributed to those of the control group, and no patient had a very small number. Moreover, the repeat numbers of the shorter and longer alleles in each individual, as well as the average number of the two alleles, were comparable between the two groups. The height standard deviation scores obtained from 106 patients did not correlate with the repeat numbers. There was no difference in the repeat numbers between the SGA-SS or non-SGA ISS groups, and the control group.

Conclusion: The results of this study indicate that reduced repeat numbers of ACAN VNTR do not represent a monogenic cause or a major contributing factor for ISS. Our findings await further validation.

Introduction: Germline restricted chromosomes are considered a rather ancient element in the genomes of passerine birds. Obviously, detailed comparative studies on model groups including closely related species are required for a better understanding of GRC evolution. It is especially interesting if GRCs in such closely related species have acquired significant differences.

Methods: In this work we compared three taxonomically close species of the genus Phylloscopus: Ph. sindianus lorenzii, Ph. collybita menzbieri, and Ph. nitidus, which have differences in morphological manifestation of GRCs: macro- and micro-GRCs. We studied synaptonemal complexes using immunocytochemistry methods.

Results: We were able to trace the morphological transformations of macro-GRC at stages from leptotene to diplotene, and describe the complex structure of this chromosome in Ph. nitidus.

Conclusion: We hope that the taxonomic group under study can become a convenient model for comparative studies of GRCs in closely related species in order to understand the evolution of these unusual chromosomes.