Verification of a Cryptic T(Y;15) Translocation in a Male With an Apparent 45,X Karyotype

BackgroundA rare disease is that an individual with a non-chimeric karyotype of 45, X develops into a male. We explored the genetic aetiology of an infertility male with an apparent 45, X karyotype, which was subsequently verified as cryptic translocation between chromosomes Y and 15. MethodsPeripheral blood sample was collected from the patient and subjected to a range of genetic testing, including conventional chromosomal karyotyping, short tandem repeat (STR) analysis for azoospermia factor (AZF) region, fluorescence in situ hybridization (FISH) with specific probes for CSP X/CSP Y, CSP Y/D15Z1/PML and SRY/D15Z1/PML, and chromosomal microarray analysis (CMA) for genomic copy number variations (CNVs). ResultsThe patient was found to have an apparent 45,X karyotype. STR analysis showed that he possessed a short arm of the Y chromosome, including the SRY gene but the absence of a long arm of the Y chromosome, including AZFa+b+c and Yqter. A FISH assay using CSP X and CSP Y probes showed a green signal at the centromere of the X chromosome and a red signal for the Y centromeric sequence on a D-group-sized chromosome. By FISH assaying with D15Z1 and CSP Y probes, chromosomes 15 and Y centromeric signals appeared closely on a single chromosome, as ascertained by the PML control probe. A further FISH assay with D15Z1 and SRY probes revealed a signal of the SRY gene at the end of one arm of chromosome 15. The result of the CMA indicated a deletion with an approximate size of 45.31 Mb spanning from Yq11 to Yter. ConclusionAlthough the 45,X male patient did not harbour an intact Y chromosome, his genome contained the SRY gene derived from the translocation of the Yp, which probably triggered the male differentiation and development. Imbalanced translocations of Yp to other chromosomes can result in short stature and infertility among patients. Delineation of the genetic aetiology can guide early intervention and assisted reproduction in adulthood.

Klinefelter Syndrome with Azoospermia：Identification of a Neocentromic Y Chromosome with No Detectable DYZ3 Centromeric Sequence

Background Individuals with rare cytogenetic variants have contributed to our understanding of the genetics of sex chromosome and its disorders. Here, we report on a 23 years old man with a de novo 47,XX,+mar.ish der(Y)neo(Y)(pter-->p11.2::q11.23-->neo-->q11.23-->qter)(DYZ3-,SRY+,WCPY+) chromosome complement, accompanying with azoospermia and some of other clinical features suggestive of Klinefelter's Syndrome. The constitution of the patient was verified by GTG-banding, QFQ-banding, Fluorescence in Situ Hybridization and Polymerase Chain Reaction. Accordingly, we report the finding of a structurally abnormal chromosome Y with no detectable DYZ3 centromeric sequence and with no detection of AZF a, AZF b and AZF c, with clinical features suggestive of Klinefelter's Syndrome. This is the first reported case of Klinefelter's Syndrome involving a neocentromic Y among previously described cases with a neocentromere. Case presentation we report on a 23 years old man with a de novo 47,XX,+mar.ish der(Y)neo(Y)(pter-->p11.2::q11.23-->neo-->q11.23-->qter)(DYZ3-,SRY+,WCPY+) chromosome complement, accompanying with azoospermia and some of other clinical features suggestive of Klinefelter's Syndrome. The constitution of the patient was verified by GTG-banding, QFQ-banding, Fluorescence in Situ Hybridization FISH and Polymerase Chain Reaction PCR. Conclusions It can be inferred that a neocentromic Y is formed by identification of FISH, PCR and the fact that this markerof Y chromosome is present in 100% of peripheral blood cells and has been efficiently retained through cell divisions despite the absence of the endogenous cen­tromere region. To our knowledge, this is the first reported case of Klinefelter's Syndrome involving a neocentromic Y among previously described cases with a neocentromere, which adds to the catalog of chromosomal aberrations. The present study not only improves the understanding of karyotype/phenotype relationships between neocentric marker Y chromosomes and KFS male infertility, but also supports the hypothesis that the combined application of molecular cytogenetic analysis might help to identify breakpoints, origins, and the constitution of the marker chromosomes.

GRIDSS2: harnessing the power of phasing and single breakends in somatic structural variant detection

Here we present GRIDSS2, a general purpose structural variant caller optimised for tumour/normal somatic calling. Using cell line, patient sample validation and cohort-level comparisons, we show GRIDSS2 outperforms recent state-of-the-art tools. We demonstrate GRIDSS2 retains high sensitivity and precision even for small events by identifying a small (32-100bp) duplication signature strongly associated with colorectal cancer using 3,782 metastatic cancers that have been deeply sequenced by the Hartwig Medical Foundation. Essential to the high precision achieved by GRIDSS2 is the novel reporting of single breakend variants: structural variants in which only one side can be unambiguously determined. We show that the inclusion of single breakends reduces the false negative rate from 10.4% to 3.4%. Demonstrating the power single breakend calling has in genomic regions traditionally considered inaccessible to short read callers, we find that 47% of somatic centromeric breaks are repaired to non-centromeric sequence, with chromosome 1 exhibiting a unique centromeric rearrangement signature. Finally, we show that somatic structural variants are highly clustered with GRIDSS2 able to phase 16% of somatic structural variants in the Hartwig cohort from short read sequencing alone.

Repetitive DNA sequences accelerate molecular cytogenetic research in plants with small chromosomes

Repetitive DNA sequences are highly abundant in plant genomes and are favorable probes for chromosome identification in plants. However, it is difficult to conduct studies on the details of metaphase chromosome structures in plants with small chromosomes due to their highly condensed status. Therefore, identification of homologous chromosomes for karyotyping and analyzing chromosome structures is a challenging issue for cytogeneticists without specific probes and precise chromosome stages. In this study, five repetitive DNA probes, i.e., 5S and 45S ribosomal DNAs (rDNAs), melon centromeric sequence (Cmcent), cucumber subtelomeric sequence (Type I), and microsatellite (CT)10 repeats, were used to identify primary constrictions and homologous chromosomes for karyotyping. Four and two loci of 45S rDNA were respectively observed on metaphase and pachytene chromosomes of Abelia × grandiflora. Cmcent was detected on both primary constrictions of melon pachytene and metaphase chromosomes. Furthermore, one pair of 5S rDNA signals were hybridized on melon metaphase chromosomes. Eight and two loci of 45S and 5S rDNA were respectively detected on cucumber chromosomes. Type I and (CT)10 probes were specifically hybridized on subtelomeric and interstitial regions on the chromosomes, respectively. These results suggest that repetitive DNA sequences are versatile probes for chromosome identification in plants with small chromosomes, particularly for karyotyping analyses.

Cryo-EM reconstruction of AlfA fromBacillus subtilisreveals the structure of a simplified actin-like filament at 3.4-Å resolution

Low copy-number plasmid pLS32 ofBacillus subtilissubsp.nattocontains a partitioning system that ensures segregation of plasmid copies during cell division. The partitioning locus comprises actin-like protein AlfA, adaptor protein AlfB, and the centromeric sequenceparN. Similar to the ParMRC partitioning system fromEscherichia coliplasmid R1, AlfA filaments form actin-like double helical filaments that arrange into an antiparallel bipolar spindle, which attaches its growing ends to sister plasmids through interactions with AlfB andparN. Because, compared with ParM and other actin-like proteins, AlfA is highly diverged in sequence, we determined the atomic structure of nonbundling AlfA filaments to 3.4-Å resolution by cryo-EM. The structure reveals how the deletion of subdomain IIB of the canonical actin fold has been accommodated by unique longitudinal and lateral contacts, while still enabling formation of left-handed, double helical, polar and staggered filaments that are architecturally similar to ParM. Through cryo-EM reconstruction of bundling AlfA filaments, we obtained a pseudoatomic model of AlfA doublets: the assembly of two filaments. The filaments are antiparallel, as required by the segregation mechanism, and exactly antiphasic with near eightfold helical symmetry, to enable efficient doublet formation. The structure of AlfA filaments and doublets shows, in atomic detail, how deletion of an entire domain of the actin fold is compensated by changes to all interfaces so that the required properties of polymerization, nucleotide hydrolysis, and antiparallel doublet formation are retained to fulfill the system’s biological raison d’être.

Cryo-EM reconstruction of AlfA fromBacillus subtilisreveals the structure of a simplified actin-like filament at 3.4 Å resolution

Low copy-number plasmid pLS32 ofBacillus subtilissubsp.nattocontains a partitioning system that ensures segregation of plasmid copies during cell division. The partitioning locus comprises actin-like protein AlfA, adaptor protein AlfB and the centromeric sequenceparN. Similar to the ParMRC partitioning system fromE. coliplasmid R1, AlfA filaments form actin-like double helical filaments that arrange into an antiparallel bipolar spindle, which attaches its growing ends to sister plasmids, through interactions with AlfB andparN. Since, compared with ParM and other actin-like proteins, AlfA is highly diverged in sequence, we determined the atomic structure of non-bundling AlfA filaments to 3.4 Å resolution by cryo-EM. The structure reveals how the deletion of subdomain IIB of the canonical actin-fold has been accommodated by unique longitudinal and lateral contacts, whilst still enabling formation of left-handed, double helical, polar and staggered filaments that are architecturally similar to ParM. Through cryo-EM reconstruction of bundling AlfA filaments we obtained a pseudo-atomic model of AlfA doublets: the assembly of two filaments. The filaments are antiparallel, as required by the segregation mechanism, and exactly anti-phasic with 8-fold integer helical symmetry, to enable efficient doublet formation. The structure of AlfA filaments and doublets shows, in atomic detail, signs of the strong evolutionary pressure for simplicity, placed on plasmids: deletion of an entire domain of the actin fold is compensated by changes to all interfaces so that the required properties of polymerisation, nucleotide hydrolysis and antiparallel doublet formation are retained to fulfil the system's biological raison d'être.Significance StatementProtein filaments perform a vast array of functions inside almost all living cells. Actin-like proteins in archaea and bacteria have previously been found to form a surprising diversity of filament architectures, reflecting their divergent cellular roles. Actin-like AlfA is unique in that it is much smaller than all other filament forming actin-like proteins. With an atomic structure of the AlfA filament, obtained by high-resolution electron cryo-microscopy, we have revealed—at atomic level of detail—how AlfA filaments form dynamic filaments capable of transporting plasmid DNA in cells and how these filaments arrange into antiparallel bundles required for the segregation mechanism.

Characterization of a Maize Chromosome 4 Centromeric Sequence: Evidence for an Evolutionary Relationship With the B Chromosome Centromere

Previous work has identified sequences specific to the B chromosome that are a major component of the B centromere. To address the issue of the origin of the B and the evolution of centromere-localized sequences, DNA prepared from plants without B chromosomes was probed to seek evidence for related sequences. Clones were isolated from maize line B73 without B chromosomes by screening DNA at reduced stringency with a B centromeric probe. These clones were localized to maize centromere 4 using fluorescence in situ hybridization. They showed homology to a maize centromere-mapped sequence, to maize B chromosome centromere sequences, and to a portion of the unit repeat of knobs, which act as neocentromeres in maize. A representative copy was used to screen a BAC library to obtain these sequences in a larger context. Each of the six positive BACs obtained was analyzed to determine the nature of centromere 4-specific sequences present. Fifteen subclones of one BAC were sequenced and the organization of this chromosome 4-specific repeat was examined.