Meiotic spindle assembly checkpoint and aneuploidy in males versus females

The production of gametes (sperm and eggs in mammals) involves two sequential cell divisions, meiosis I and meiosis II. In meiosis I, homologous chromosomes segregate to different daughter cells, and meiosis II resembles mitotic divisions in that sister chromatids separate. While in principle the process is identical in males and females, the time frame and susceptibility to chromosomal defects, including achiasmy and cohesion weakening, and the response to mis-segregating chromosomes are not. In this review, we compare and contrast meiotic spindle assembly checkpoint function and aneuploidy in the two sexes.Peer reviewe

Time to go functional! Determining tumors' DNA repair capacity ex vivo.

n.a.Non peer reviewe

Mlh1 heterozygosity and promoter methylation associates with microsatellite instability in mouse sperm

DNA mismatch repair (MMR) proteins play an important role in maintaining genome stability, both in somatic and in germline cells. Loss of MLH1, a central MMR protein, leads to infertility and to microsatellite instability (MSI) in spermatocytes, however, the effect of Mlh1 heterozygosity on germline genome stability remains unexplored. To test the effect of Mlh1 heterozygosity on MSI in mature sperm, we combined mouse genetics with single-molecule PCR that detects allelic changes at unstable microsatellites. We discovered 4.5% and 5.9% MSI in sperm of 4- and 12-month-old Mlh1(+/-) mice, respectively, and that Mlh1 promoter methylation in Mlh1(+/-) sperm correlated with higher MSI. No such elevated MSI was seen in non-proliferating somatic cells. Additionally, we show contrasting dynamics of deletions versus insertions at unstable microsatellites (mononucleotide repeats) in sperm.Peer reviewe

Single-Cell Sequencing of Mouse Thymocytes Reveals Mutational Landscape Shaped by Replication Errors, Mismatch Repair, and H3K36me3

DNA mismatch repair (MMR) corrects replication errors and is recruited by the histone mark H3K36me3, enriched in exons of transcriptionally active genes. To dissect in vivo the mutational landscape shaped by these processes, we employed single-cell exome sequencing on T cells of wild-type andMMR-deficient (Mlh1(-/-)) mice. Within active genes, we uncovered a spatial bias in MMR efficiency: 3' exons, often H3K36me3-enriched, acquire significantly fewer MMR-dependent mutations compared with 5' exons. Huwe1 and Mcm7 genes, both active during lymphocyte development, stood out as mutational hotspots in MMR-deficient cells, demonstrating their intrinsic vulnerability to replication error in this cell type. Both genes are H3K36me3-enriched, which can explain MMR-mediated elimination of replication errors in wild-type cells. Thus, H3K36me3 can boost MMR in transcriptionally active regions, both locally and globally. This offers an attractive concept of thriftyMMR targeting, where critical genes in each cell type enjoy preferential shielding against de novo mutations.Peer reviewe

Tissue-specific reduction in MLH1 expression induces microsatellite instability in intestine of Mlh1+/- mice

Tumors of Lynch syndrome (LS) patients display high levels of microsatellite instability (MSI), which results from complete loss of DNA mismatch repair (MMR), in line with Knudson’s two-hit hypothesis. Why some organs, in particular those of the gastrointestinal (GI) tract, are prone to tumorigenesis in LS remains unknown. We hypothesized that MMR is haploinsufficient in certain tissues, compromising microsatellite stability in a tissue-specific manner before tumorigenesis. Using mouse genetics, we tested how levels of MLH1, a central MMR protein, affect age- and tissue-specific microsatellite stability in vivo and whether elevated MSI is detectable prior to loss of MMR function and to neoplastic growth. To assess putative tissue-specific MMR haploinsufficiency, we determined relevant molecular phenotypes (MSI, Mlh1 promoter methylation status, MLH1 protein and RNA levels) in jejuna of Mlh1+/− mice and compared them to those in spleen, as well as to MMR-proficient and -deficient controls (Mlh1+/+ and Mlh1−/− mice). While spleen MLH1 levels of Mlh1+/− mice were, as expected, approximately 50 % compared to wildtype mice, MLH1 levels in jejunum varied substantially between individual Mlh1+/− mice and moreover, decreased with age. Mlh1+/− mice with soma-wide Mlh1 promoter methylation often displayed severe MLH1 depletion in jejunum. Reduced (but still detectable) MLH1 levels correlated with elevated MSI in Mlh1+/− jejunum. MSI in jejunum increased with age, while in spleens of the same mice, MLH1 levels and microsatellites remained stable. Thus, MLH1 expression levels are particularly labile in intestine of Mlh1+/− mice, giving rise to tissue-specific MSI long before neoplasia. A similar mechanism likely also operates also in the human GI epithelium and could explain the wide range in age-of-onset of LS-associated tumorigenesis.Peer reviewe

Detection of Retrotransposition Activity of Hot LINE-1s by Long-Distance Inverse PCR

Long interspersed nuclear elements 1 (LINE-1s) are the only family of mobile genetic elements in the human genome that can move autonomously. They do so by a process called retrotransposition wherein they transcribe to form an mRNA intermediate which is then consequently inserted into the genome by reverse transcription. Despite being silent in normal cells, LINE-1s are highly active in different epithelial tumors. De novo LINE-1 insertions can potentially drive tumorigenesis, and hence it is important to systematically study LINE-1 retrotransposition in cancer. Out of similar to 150 retrotransposition-competent LINE-1s present in the human genome, only a handful of LINE-1 loci, also referred to as "hot" LINE-1s, account for the majority of de novo LINE-1 insertion in different cancer types. We have developed a simple polymerase chain reaction (PCR)-based method to monitor retrotransposition activity of these hot LINE-1s. This method, based on long-distance inverse (LDI)-PCR, takes advantage of 3 ' transduction, a mechanism by which a LINE-1 mobilizes its flanking non-repetitive region, which can subsequently be used to identify de novo LINE-1 3 ' transduction events stemming from a particular hot LINE-1.Peer reviewe

Single-Cell Mononucleotide Microsatellite Analysis Reveals Differential Insertion-Deletion Dynamics in Mouse T Cells

Microsatellite sequences are particularly prone to slippage during DNA replication, forming insertion-deletion loops that, if left unrepaired, result in de novo mutations (expansions or contractions of the repeat array). Mismatch repair (MMR) is a critical DNA repair mechanism that corrects these insertion-deletion loops, thereby maintaining microsatellite stability. MMR deficiency gives rise to the molecular phenotype known as microsatellite instability (MSI). By sequencing MMR-proficient and -deficient (Mlh1(+/+) and Mlh1(-/-)) single-cell exomes from mouse T cells, we reveal here several previously unrecognized features of in vivo MSI. Specifically, mutational dynamics of insertions and deletions were different on multiple levels. Factors that associated with propensity of mononucleotide microsatellites to insertions versus deletions were: microsatellite length, nucleotide composition of the mononucleotide tract, gene length and transcriptional status, as well replication timing. Here, we show on a single-cell level that deletions - the predominant MSI type in MMR-deficient cells - are preferentially associated with longer A/T tracts, long or transcribed genes and later-replicating genes.Peer reviewe

Time-resolved classification of dog brain signals reveals early processing of faces, species and emotion

Dogs process faces and emotional expressions much like humans, but the time windows important for face processing in dogs are largely unknown. By combining our non-invasive electroencephalography (EEG) protocol on dogs with machine-learning algorithms, we show category-specific dog brain responses to pictures of human and dog facial expressions, objects, and phase-scrambled faces. We trained a support vector machine classifier with spatiotemporal EEG data to discriminate between responses to pairs of images. The classification accuracy was highest for humans or dogs vs. scrambled images, with most informative time intervals of 100-140 ms and 240-280 ms. We also detected a response sensitive to threatening dog faces at 30-40 ms; generally, responses differentiating emotional expressions were found at 130-170 ms, and differentiation of faces from objects occurred at 120-130 ms. The cortical sources underlying the highest-amplitude EEG signals were localized to the dog visual cortex.Peer reviewe

Suljettujen ja hylättyjen kaivosten kaivannaisjätealueiden jatkokartoitus (KAJAK II)

Suomessa kartoitettiin vuosina 2011–2013 EU:n kaivannaisjätedirektiivin mukaiset suljettujen ja hylättyjen vakavaa ympäristön pilaantumista tai ympäristölle mahdollista vaaraa aiheuttavat kaivannaisjätealueet. Hankkeen loppuraportissa esitettiin 30 kaivoksen kaivannaisjätealueelle jatkotoimenpidetarpeet. Tässä jatkohankkeessa (KAJAK II) keskityttiin pääasiallisesti näiden 30 kaivoskohteen ja esille nousseiden kahden lisäkaivoskohteen nykytilan ja jatkotoimenpidetarpeiden selvittämiseen. Raporttiin on koottu tietoa tutkittavien kohteiden kaivostoiminnasta ja kaivannaisjätteistä, läjitysalueiden sijainnista ja tiedossa olevista ympäristövaikutuksista, hankkeen aikana toteutetusta maastotarkastuksista ja kenttämittauksista sekä kaivostoimintaan liittyvistä luvista ja valvonnasta sekä alueen mahdollisesta kaavoituksesta. Lupa-asioihin ja valvontaan liittyvässä kohdassa keskityttiin lähtökohtaisesti ympäristönsuojelu- ja vesilainsäädäntöihin. Raportissa kuvataan kaivosalueen vaikutusta maankäyttöön ja esitetään suosituksia jatkotoimenpiteiksi. Tämän selvitysten perusteella kaivosalueet ryhmiteltiin ympäristökuormituksen ja -vaikutusten mukaan: 1. happamia valumavesiä tuottavat kaivosalueet, 2. neutraaleja/lähes neutraaleja metallipitoisia vesiä tuottavat kaivosalueet, 3. kaivosalueet, joiden ympäristökuormituksesta on saatavilla vain vähän tutkittua tietoa, 4a. kohteet, joissa on voimassa kaivospiiri tai kunnostus käynnissä ja kunnostukselle ympäristölupa, 4b. kaivosalueet, joiden ympäristökuormitus oli pientä käytössä olleen aineiston perusteella. Raportissa tuodaan myös esille vanhojen ja/tai konkurssiin joutuneiden ja varattomaksi päätyneiden kaivosalueiden kunnostamisen ongelmallisuutta ja esitetään selvennettäväksi näiden kaivosalueiden nykytilaselvityksen, kunnostamisen ja ympäristön tilan tarkkailun toteuttamisen vastuuta