HIM-17 regulates the position of recombination events and GSP-1/2 localization to establish short arm identity on bivalents in meiosis

The position of recombination events established along chromosomes in early prophase I and the chromosome remodeling that takes place in late prophase I are intrinsically linked steps of meiosis that need to be tightly regulated to ensure accurate chromosome segregation and haploid gamete formation. Here, we show that RAD-51 foci, which form at the sites of programmed meiotic DNA double-strand breaks (DSBs), exhibit a biased distribution toward off-centered positions along the chromosomes in wild-type Caenorhabditis elegans, and we identify two meiotic roles for chromatin-associated protein HIM-17 that ensure normal chromosome remodeling in late prophase I. During early prophase I, HIM-17 regulates the distribution of DSB-dependent RAD-51 foci and crossovers on chromosomes, which is critical for the formation of distinct chromosome subdomains (short and long arms of the bivalents) later during chromosome remodeling. During late prophase I, HIM-17 promotes the normal expression and localization of protein phosphatases GSP-1/2 to the surface of the bivalent chromosomes and may promote GSP-1 phosphorylation, thereby antagonizing Aurora B kinase AIR-2 loading on the long arms and preventing premature loss of sister chromatid cohesion. We propose that HIM-17 plays distinct roles at different stages during meiotic progression that converge to promote normal chromosome remodeling and accurate chromosome segregation.

25 Effect of taxol and epothilone B on meiotic spindle stabilization in vitrified bovine oocytes

Vitrification has the potential to be a valuable technique for preservation of bovine oocytes; however, this method often results in abnormal microtubule and chromosome arrangement. The aim of this experiment was to evaluate taxol and epothilone B as meiotic spindle stabilising pretreatments in a vitrification protocol. Bovine oocytes were purchased and matured invitro during shipment. At 18h of maturation, oocytes were divided randomly into control, taxol, and epothilone B treatments (Table 1). All treatments were prepared in invitro maturation (IVM) medium (IVF Biosciences). Partially denuded oocytes were incubated in either control or treatment medium for 15min at 38.5°C before vitrification. Oocytes were incubated in an equilibration solution (10% dimethyl sulfoxide, 10% ethylene glycol) for 5min, transferred to a vitrification solution (20% dimethyl sulfoxide, 20% ethylene glycol, 0.5M sucrose), loaded onto a Cryolock, and plunged into liquid nitrogen within 45s. For warming, a Cryolock was placed directly into a 0.5M sucrose solution and incubated for 3min. Oocytes were transferred to a 0.25M solution for 3min and washed in the basal solution used for vitrification and warming media (Dulbecco’s phosphate-buffered saline, 20% fetal bovine serum). Once warmed, oocytes were transferred to IVM medium for a 4-h recovery period and completely denuded before staining. Staining to evaluate spindle morphology was performed with anti α-tubulin primary antibody and secondary antibody Alexa Fluor 488. Oocytes were also stained with Hoechst to evaluate chromosome arrangement. Both spindle morphology and chromosome arrangement data were analysed using a logistic regression with a binomial response variable (normal/abnormal). Both 0.5μM and 1.0μM Taxol treatments had no effect on either meiotic spindle or chromosome arrangement compared with the control group (P>0.05). The 2.0μM taxol treatment improved chromosome configuration (P<0.05) with no effect on microtubule distribution compared with the control group (P>0.05). All epothilone B treatments resulted in disruption of microtubule distribution and chromosome arrangement compared with control (P<0.001) and resulted in a consistent abnormality hypothesised to be tubulin polymerization. These results indicate that taxol is capable of increasing the occurrence of normal chromosome arrangement in vitrified bovine oocytes and that epothilone B may cause additional harm to the oocyte that is not associated with the metaphase plate. Table 1. Effect of stabilisation agents on meiotic spindle of invitro-matured bovine oocytes Treatment n Normal microtubule distribution (%) Normal chromosome arrangement (%) Control 100 44 47 0.5μM Taxol 104 44 37 1.0μM Taxol 98 43 56 2.0μM Taxol 102 49 62a 0.5μM Epothilone B 103 11b 11b 1.0μM Epothilone B 97 6b 8b 2.0μM Epothilone B 100 2b 1b aP<0.05;. bP<0.001: Different superscripts within a column indicate a significant difference.

Molecular Characterization of Mosaicism for a Small Supernumerary Marker Chromosome Derived from Chromosome Y in an Infertile Male with Apparently Normal Phenotype: A Case Report and Literature Review

Small supernumerary marker chromosomes (sSMCs), equal in size or smaller than chromosome 20 of the same metaphase, can hardly be identified through traditional banding technique. They are usually associated with intelligent disability, growth retardation, and infertility, but the genotype-phenotype correlations are still complicated for their complex origins and constitutions. Herein, we identified a 26-year-old Chinese infertile male who carried a mosaic sSMC and was diagnosed as severe oligospermia. The G-banding analysis initially described his karyotype as mos 47, XY, +mar[32]/46, XY[18]. The chromosomal microarray analysis results showed a 25.5 Mb gain in Yp11.31q11.23 and a 0.15 Mb loss in Yq12. Two SRY signals were discovered in the “seemingly” normal chromosome Y in both cell lines using SRY probe: one normal SRY was located on the distal tip of the short arm of chromosome Y while the other SRY was located on the terminal of long arm in the same chromosome Y. The sSMC(Y) was finally identified as der(Y) (pter ⟶ q11.23) (SRY-). To our knowledge, the chromosomal Y anomalies, SRY gene translocated from der(Y) (pter ⟶ q11.23) to qter of normal chromosome Y, were not reported before. Our findings indicated that the mosaic presence of sSMC(Y) may be the main cause of severe oligospermia although no other apparent abnormalities were observed in the proband. Further research on association between sSMC(Y) and spermatogenesis impairment should be investigated. It is recommended measures of traditional and molecular cytogenetic analysis should be taken to determine the origins and constitutions of sSMC so as to offer more appropriate genetic counseling for the infertile sSMC carriers.

Phase separation of Polo-like kinase 4 by autoactivation and clustering drives centriole biogenesis

Tight control of centriole duplication is critical for normal chromosome segregation and the maintenance of genomic stability. Polo-like kinase 4 (Plk4) is a key regulator of centriole biogenesis. How Plk4 dynamically promotes its symmetry-breaking relocalization and achieves its procentriole-assembly state remains unknown. Here we show that Plk4 is a unique kinase that utilizes its autophosphorylated noncatalytic cryptic polo-box (CPB) to phase separate and generate a nanoscale spherical condensate. Analyses of the crystal structure of a phospho-mimicking, condensation-proficient CPB mutant reveal that a disordered loop at the CPB PB2-tip region is critically required for Plk4 to generate condensates and induce procentriole assembly. CPB phosphorylation also promotes Plk4’s dissociation from the Cep152 tether while binding to downstream STIL, thus allowing Plk4 condensate to serve as an assembling body for centriole biogenesis. This study uncovers the mechanism underlying Plk4 activation and may offer strategies for anti-Plk4 intervention against genomic instability and cancer.

Poor Prognosis Associated with Gains of CCND1 in Mantle Cell Lymphoma Treated By First Line Immuno-Chemotherapy — a Study By the Lysa Group

Background Mantle cell lymphoma (MCL) is a lymphoproliferative disorder characterized by the t(11;14) balanced translocation, involving on chromosome 11 the gene encoding cyclin D1, CCND1. The enhancer of IGH, on chromosome 11, induces aberrant Cyclin D1 overexpression. A few reports have shown that the CCND1 oncogene locus is a recurrently amplified region in MCL. However, the prognostic value of this copy number abnormality (CNA) is not known. The incidence and clinical impact of CCND1 CNA were investigated on diagnostic samples from patients enrolled in the first-line randomized controlled trial LyMa (S. Le Gouill et al. NEJM 2017). Patients and methods A series of 100 lymph node biopsies performed at diagnosis for patients enrolled in the LyMa trial (n=299) was selected. After DNA extraction, CNAs were investigated in these samples using the innovative Oncoscan® SNP-array technique adapted to analyze highly degraded DNA extracted from formalin-fixed paraffin-embedded (FFPE) tissues. Ninety-four samples were informative for CNAs. CCND1 gains were controlled by fluorescence in situ hybridization on interphase nuclei, following standard procedures using LSI IGH/CCND1 XT Dual color, dual fusion translocation probes (Abbott Molecular, Des Plaines, IL). Progression-free and overall survivals were calculated from the date of inclusion until relapse/death or last news and death or last news respectively. Cumulative incidence of relapse (CIR) was estimated from the date of inclusion until the date of relapse or last news Results Amplifications of a large portion of 11q, beginning at the t(11;14) breakpoint, were observed with Oncoscan® in 7 patients. All these cases with a gain of 11q13-14 (CCND1) also had a gain of the 14q32 locus (IGH) suggesting amplification of the rearranged IGH-CCND1 region of t(11;14). This was confirmed by FISH analysis which disclosed three different configurations. The first was the classical CCND1-IGH rearrangement (CCND1 on normal chromosome 11, IGH on normal chromosome 14 and two fusion signals from the t(11;14)(CCND1-IGH)). The second configuration associated CCND1-IGH fusion signals and a gain of both CCND1 and IGH signals. The third configuration was a duplication of a CCND1-IGH fusion signals (3 signals). Both in SNP and in FISH, the amplification was always identified as sub-clonal, concerning only part of the cells. In some patients, different configurations coexisted. Compared to other patients of the series, those with amplification of IGH and CCND1 regions had a higher-risk bio-MIPI (11q13-14, p=0.015; 14q32, p=0.004). Patients with large gains at 11q13-14 (CCND1 N=7) had poorer median PFS (18 months vs not reached (NR); p=0.004), OS (35 months vs NR; p=0.01) and CIR (33 months vs not NR; p=0.004). The same was observed for patients with gains at 14q32 (IGH; N=8), with significantly different median PFS (23 months vs NR; p<0.001), OS (38 months vs NR; p=0.001) and CIR (28 months vs NR; p<0.001). Conclusion Gains of the IGH-CCND1 rearrangement or involved genes appear to be a potential new biomarker predictive of poor response to first line immunochemotherapy in young MCL patients. Disclosures Hermine: Novartis: Research Funding; Hybrigenics: Research Funding; AB Science: Consultancy, Equity Ownership, Honoraria, Research Funding; Erythec: Research Funding; Celgene Corporation: Research Funding.