Crossing-over ensures accurate chromosome segregation during meiosis, and every pair of chromosomes obtains at least one crossover, even though the majority of recombination sites yield non-crossovers. A putative regulator of crossing-over is RNF212, which is associated with variation in crossover rates in humans. We show that mouse RNF212 is essential for crossing-over, functioning to couple chromosome synapsis to the formation of crossover-specific recombination complexes. Selective localization of RNF212 to a subset of recombination sites is shown to be a key early step in the crossover designation process. RNF212 acts at these sites to stabilize meiosis-specific recombination factors, including the MutSγ complex (MSH4-MSH5). We infer that selective stabilization of key recombination proteins is a fundamental feature of meiotic crossover control. Haploinsufficiency indicates that RNF212 is a limiting factor for crossover control and raises the possibility that human alleles may alter the amount or stability of RNF212 and be risk factors for aneuploid conditions.

Crossover recombination facilitates accurate segregation of homologous chromosomes during meiosis1,2. In mammals, poorly characterized regulatory processes ensure every pair of chromosomes obtains at least one crossover, even though the majority of recombination sites yield non-crossovers3. Designation of crossovers involves selective localization of SUMO-ligase RNF212 to a minority of recombination sites where it stabilizes pertinent factors, such as MutSγ4. Here we show ubiquitin-ligase HEI10/CCNB1IP15,6 is essential for this crossover/non-crossover differentiation process. In Hei10 mutant mice, RNF212 localizes to most recombination sites and dissociation of RNF212 and MutSγ from chromosomes is blocked. Consequently, recombination is impeded and crossing-over fails. In wild-type mice, HEI10 accumulates at designated crossover sites suggesting a late role to implement crossing-over. Like RNF212, dosage-sensitivity indicates HEI10 is a limiting factor for crossing-over. We suggest SUMO and ubiquitin play antagonistic roles during meiotic recombination that are balanced to effect differential stabilization of recombination factors at crossover and non-crossover sites.

Meiosis produces haploid gametes through a succession of chromosomal events, including pairing, synapsis, and recombination. Mechanisms that orchestrate these events remain poorly understood. We found that the SUMO (small ubiquitin-like modifier)–modification and ubiquitin-proteasome systems regulate the major events of meiotic prophase in mouse. Interdependent localization of SUMO, ubiquitin, and proteasomes along chromosome axes was mediated largely by RNF212 and HEI10, two E3 ligases that are also essential for crossover recombination. RNF212-dependent SUMO conjugation effected a checkpointlike process that stalls recombination by rendering the turnover of a subset of recombination factors dependent on HEI10-mediated ubiquitylation. We propose that SUMO conjugation establishes a precondition for designating crossover sites via selective protein stabilization. Thus, meiotic chromosome axes are hubs for regulated proteolysis via SUMO-dependent control of the ubiquitin-proteasome system.

The intimate synapsis of homologous chromosome pairs (homologs) by synaptonemal complexes (SCs) is an essential feature of meiosis. In many organisms, synapsis and homologous recombination are interdependent: recombination promotes SC formation and SCs are required for crossing-over. Moreover, several studies indicate that initiation of SC assembly occurs at sites where crossovers will subsequently form. However, recent analyses in budding yeast and fruit fly imply a special role for centromeres in the initiation of SC formation. In addition, in budding yeast, persistent SC–dependent centromere-association facilitates the disjunction of chromosomes that have failed to become connected by crossovers. Here, we examine the interplay between SCs, recombination, and centromeres in a mammal. In mouse spermatocytes, centromeres do not serve as SC initiation sites and are invariably the last regions to synapse. However, centromeres are refractory to de-synapsis during diplonema and remain associated by short SC fragments. Since SC–dependent centromere association is lost before diakinesis, a direct role in homolog segregation seems unlikely. However, post–SC disassembly, we find evidence of inter-centromeric connections that could play a more direct role in promoting homolog biorientation and disjunction. A second class of persistent SC fragments is shown to be crossover-dependent. Super-resolution structured-illumination microscopy (SIM) reveals that these structures initially connect separate homolog axes and progressively diminish as chiasmata form. Thus, DNA crossing-over (which occurs during pachynema) and axis remodeling appear to be temporally distinct aspects of chiasma formation. SIM analysis of the synapsis and crossover-defective mutant Sycp1−/− implies that SCs prevent unregulated fusion of homolog axes. We propose that SC fragments retained during diplonema stabilize nascent bivalents and help orchestrate local chromosome reorganization that promotes centromere and chiasma function.

Single-nucleotide substitutions and small in-frame insertions or deletions identified in human breast cancer susceptibility genes BRCA1 and BRCA2 are frequently classified as variants of unknown clinical significance (VUS) due to the availability of very limited information about their functional consequences. Such variants can most reliably be classified as pathogenic or non-pathogenic based on the data of their co-segregation with breast cancer in affected families and/or their co-occurrence with a pathogenic mutation. Biological assays that examine the effect of variants on protein function can provide important information that can be used in conjunction with available familial data to determine the pathogenicity of VUS. In this report, we have used a previously described mouse embryonic stem (mES) cell-based functional assay to characterize eight BRCA2 VUS that affect highly conserved amino acid residues and map to the N-terminal PALB2-binding or the C-terminal DNA-binding domains. For several of these variants, very limited co-segregation information is available, making it difficult to determine their pathogenicity. Based on their ability to rescue the lethality of Brca2-deficient mES cells and their effect on sensitivity to DNA-damaging agents, homologous recombination and genomic integrity, we have classified these variants as pathogenic or non-pathogenic. In addition, we have used homology-based modeling as a predictive tool to assess the effect of some of these variants on the structural integrity of the C-terminal DNA-binding domain and also generated a knock-in mouse model to analyze the physiological significance of a residue reported to be essential for the interaction of BRCA2 with meiosis-specific recombinase, DMC1.

Objective Nonmotor symptoms (NMS) are critical players in the patients' quality of life in Parkinson disease (PD). Vesicular monoamine transporter type 2 (VMAT2) has been reported owing to a role in affecting dopamine neurons in the striatum. Therefore, this study set out to characterize the relationship between VMAT2 distribution in the striatum in relation to the NMS in PD. Methods Totally, 21 age-matched normal controls and 37 patients with PD in the moderate stages were included, followed by examination using 18F-DTBZ (18F-AV133) PET/CT. The specific uptake ratio (SUR) of each striatal subregion was then determined with the occipital cortex as the reference background region. The overall NMSs of each individual patient were evaluated. Finally, the role of the striatal SURs in the clinical symptom scores were evaluated through the application of a Spearman correlation analysis as well as a multivariable stepwise regression analysis. Results Patients with PD, particularly those at a more advanced stage, exhibited a more pronounced reduction in SURs in the bilateral putamen and caudate nucleus (P < 0.05, vs healthy controls). Meanwhile, patients at more advanced PD stages were found to have significantly worse scores in NMS except cognitive function. The Spearman correlation analysis demonstrated that NMS scores, with the exception of cognition scores, were correlated with striatal SURs (P < 0.05). Conclusion The key findings of the study identified a correlation between decreased striatal VMAT2 with a broad spectrum of NMS in patients with PD, highlighting the association between diminished dopamine supply and the development of NMS in PD.

Introduction This paper reports the synthesis and labeling of 18F alanine derivatives. We also investigate their biological characteristics as potential tumor imaging agents mediated by alanine-serine-cysteine preferring (ASC) transporter system. Methods Three new 18F alanine derivatives were prepared from corresponding tosylate-precursors through a two-step labelling reaction. In vitro uptake studies to evaluate and to compare these three analogs were carried out in 9L glioma and PC-3 prostate cancer cell lines. Potential transport mechanisms, protein incorporation and stability of 3-(1-[18F]fluoromethyl)-L-alanine (L[18F]FMA) were investigated in 9L glioma cells. Its biodistribution was determined in a rat-bearing 9L tumor model. PET imaging studies were performed on rat bearing 9L glioma tumors and transgenic mouse carrying spontaneous generated M/tomND tumor (mammary gland adenocarcinoma). Results New 18F alanine derivatives were prepared with 7–34% uncorrected radiochemical yields, excellent enantiomeric purity (>99%) and good radiochemical purity (>99%). In vitro uptake of the L-[18F]FMA in 9L glioma and PC-3 prostate cancer cells was higher than those observed for other two alanine derivatives and [18F]FDG in first 1 h. Inhibition of cell uptake studies suggested that L-[18F]FMA uptake in 9L glioma was predominantly via transport system ASC. After entering into cells, L-[18F]FMA remained stable and was not incorporated into protein within 2 h. In vivo biodistribution studies demonstrated that L-[18F]FMA had relatively high uptake in liver and kidney. Tumor uptake was fast, reaching a maximum within 30 min. The tumor-to-muscle, tumor-to-blood and tumor-to-brain ratios at 60 min post injection were 2.2, 1.9 and 3.0, respectively. In PET imaging studies, tumors were visualized with L-[18F]FMA in both 9L rat and transgenic mouse. Conclusion L-[18F]FMA showed promising properties as a PET imaging agent for up-regulated ASC transporter associated with tumor proliferation.

SUMMARY Oocyte quality control culls eggs with defects in meiosis. In mouse, oocyte death can be triggered by defects in chromosome synapsis and recombination, which involve repair of DNA double-strand breaks (DSBs) between homologous chromosomes. We show that RNF212, a SUMO ligase required for crossing over, also mediates oocyte quality control. Both physiological apoptosis and wholesale oocyte elimination in meiotic mutants require RNF212. RNF212 sensitizes oocytes to DSB-induced apoptosis within a narrow window as chromosomes desynapse and cells transition into quiescence. Analysis of DNA damage during this transition implies that RNF212 impedes DSB repair. Consistently, RNF212 is required for HORMAD1, a negative regulator of inter-sister recombination, to associate with desynapsing chromosomes. We infer that oocytes impede repair of residual DSBs to retain a “memory” of meiotic defects that enables quality control processes. These results define the logic of oocyte quality control and suggest RNF212 variants may influence transmission of defective genomes.