Synaptonemal Complex Components Persist at Centromeres and Are Required for Homologous Centromere Pairing in Mouse Spermatocytes

Recent studies in simple model organisms have shown that centromere pairing is important for ensuring high-fidelity meiotic chromosome segregation. However, this process and the mechanisms regulating it in higher eukaryotes are unknown. Here we present the first detailed study of meiotic centromere pairing in mouse spermatogenesis and link it with key events of the G2/metaphase I transition. In mouse we observed no evidence of the persistent coupling of centromeres that has been observed in several model organisms. We do however find that telomeres associate in non-homologous pairs or small groups in B type spermatogonia and pre-leptotene spermatocytes, and this association is disrupted by deletion of the synaptonemal complex component SYCP3. Intriguingly, we found that, in mid prophase, chromosome synapsis is not initiated at centromeres, and centromeric regions are the last to pair in the zygotene-pachytene transition. In late prophase, we first identified the proteins that reside at paired centromeres. We found that components of the central and lateral element and transverse filaments of the synaptonemal complex are retained at paired centromeres after disassembly of the synaptonemal complex along diplotene chromosome arms. The absence of SYCP1 prevents centromere pairing in knockout mouse spermatocytes. The localization dynamics of SYCP1 and SYCP3 suggest that they play different roles in promoting homologous centromere pairing. SYCP1 remains only at paired centromeres coincident with the time at which some kinetochore proteins begin loading at centromeres, consistent with a role in assembly of meiosis-specific kinetochores. After removal of SYCP1 from centromeres, SYCP3 then accumulates at paired centromeres where it may promote bi-orientation of homologous centromeres. We propose that, in addition to their roles as synaptonemal complex components, SYCP1 and SYCP3 act at the centromeres to promote the establishment and/or maintenance of centromere pairing and, by doing so, improve the segregation fidelity of mammalian meiotic chromosomes

High density of REC8 constrains sister chromatid axes and prevents illegitimate synaptonemal complex formation

During meiosis, cohesin complexes mediate sister chromatid cohesion (SCC), synaptonemal complex (SC) assembly and synapsis. Here, using super-resolution microscopy, we imaged sister chromatid axes in mouse meiocytes that have normal or reduced levels of cohesin complexes, assessing the relationship between localization of cohesin complexes, SCC and SC formation. We show that REC8 foci are separated from each other by a distance smaller than 15% of the total chromosome axis length in wild-type meiocytes. Reduced levels of cohesin complexes result in a local separation of sister chromatid axial elements (LSAEs), as well as illegitimate SC formation at these sites. REC8 but not RAD21 or RAD21L cohesin complexes flank sites of LSAEs, whereas RAD21 and RAD21L appear predominantly along the separated sister-chromatid axes. Based on these observations and a quantitative distribution analysis of REC8 along sister chromatid axes, we propose that the high density of randomly distributed REC8 cohesin complexes promotes SCC and prevents illegitimate SC formation.European Union's Horizon 2020 research and innovation programme, 634113 GermAgeSwedish Cancer SocietySwedish Research CouncilKarolinska InstitutetScience for Life LaboratoryAccepte

Human disease locus discovery and mapping to molecular pathways through phylogenetic profiling

Genes with common profiles of the presence and absence in disparate genomes tend to function in the same pathway. By mapping all human genes into about 1000 clusters of genes with similar patterns of conservation across eukaryotic phylogeny, we determined that sets of genes associated with particular diseases have similar phylogenetic profiles. By focusing on those human phylogenetic gene clusters that significantly overlap some of the thousands of human gene sets defined by their coexpression or annotation to pathways or other molecular attributes, we reveal the evolutionary map that connects molecular pathways and human diseases. The other genes in the phylogenetic clusters enriched for particular known disease genes or molecular pathways identify candidate genes for roles in those same disorders and pathways. Focusing on proteins coevolved with the microphthalmia-associated transcription factor (MITF), we identified the Notch pathway suppressor of hairless (RBP-Jk/SuH) transcription factor, and showed that RBP-Jk functions as an MITF cofactor

Meiosis in Mice without a Synaptonemal Complex

The synaptonemal complex (SC) promotes fusion of the homologous chromosomes (synapsis) and crossover recombination events during meiosis. The SC displays an extensive structural conservation between species; however, a few organisms lack SC and execute meiotic process in a SC-independent manner. To clarify the SC function in mammals, we have generated a mutant mouse strain (Sycp1−/−Sycp3−/−, here called SC-null) in which all known SC proteins have been displaced from meiotic chromosomes. While transmission electron microscopy failed to identify any remnants of the SC in SC-null spermatocytes, neither formation of the cohesion axes nor attachment of the chromosomes to the nuclear membrane was perturbed. Furthermore, the meiotic chromosomes in SC-null meiocytes achieved pre-synaptic pairing, underwent early homologous recombination events and sustained a residual crossover formation. In contrast, in SC-null meiocytes synapsis and MLH1-MLH3-dependent crossovers maturation were abolished, whereas the structural integrity of chromosomes was drastically impaired. The variable consequences that SC inactivation has on the meiotic process in different organisms, together with the absence of SC in some unrelated species, imply that the SC could have originated independently in different taxonomic groups

The sterility of the instrument table

Bakgrund: Postoperativa infektioner är ett allvarligt patientsäkerhetsproblem och drabbar ca 3 % av alla patienter som genomgår en operation. Konsekvenserna av detta blir förlängda vårdtider, höga samhällskostnader, ökad användning av antibiotika och försämrad livskvalité för patienten. Det har visat sig att postoperativa infektioner kan orsakas av kontamination redan i operationssalen. Idag vet man att det förekommer växt av mikroorganismer på instrumentbordets ovansida, men forskningen är bristfällig gällande instrumentbordets kanter. Syfte: Undersöka om sterildraperingen på instrumentbordets kanter är sterila efter avslutad operation. Metod: Kontaktplattor har tryckts på strategiskt utvalda ytor på sterildraperingens ovansida och kanter. I pilotstudien togs totalt 51 odlingar i slutet av tre operationer som varade i minst tre timmar. Resultat: Växt på sterildraperingens kanter och ovansida påvisades. Den vanligast förekommande bakterien var koagulasnegativa staphylokocker följt av difteroida stavar och bacillus. Resultatet visar en negativ korrelation mellan operationstid och CFU (Colony forming units). Diskussion: Denna studie har indikerat att sterildraperingens kanter och ovansida är kontaminerade. Detta kan innebära en potentiell källa till vårdrelaterade infektioner.Background: Postoperative infections are a serious patient safety problem and affects about 3 % of all patients undergoing surgery. The consequences are prolonged hospital stays, high social costs, increased use of antibiotics and impaired quality of life for the patient. It has been shown that postoperative infections may be caused by contamination already in the operating room. Today we know that there is growth of microorganisms on the instrument table´s top, but there is a research gap about the instrument table's edges. Aim: To examine if the sterile drape on the instrument table´s edges are sterile after finished surgery. Method: Contact plates are printed on strategically selected areas on the sterile drapes top and edges. In the pilot study, a total of 51 cultures were taken at the end of three operations which lasted over three hours. Results: Growth on the top surface and the edges of the sterile drape were detected. The most frequent bacteria were coagulase-negative staphylococci, followed by difteroid rods and bacillus. The results show a negative correlation between operative time and CFU (Colony forming units). Discussion: This study has indicated that the sterile drape´s edges and the top is contaminated. This may constitute a potential source of surgical site infections

Blunda inte för sorg - sjuksköterskans stöd till patienter i sorg

Sjuksköterskor möter ofta sorg i sitt arbete, därför är kunskaper om sorgprocessen och sorgreaktioner viktiga för att sjuksköterskor ska kunna ge bra stöd till sörjande patienter. Syftet med studien var att belysa sjuksköterskans stöd till patienter i sorg. Studien har genomförts som en litteraturstudie med resultat som visar på att många sörjande ansåg att stödet från vårdpersonalen var otillfredsställande eller otillräckligt. De sörjande ansåg att mest negativt var vårdpersonalens brist på medkänsla, empati, ärlighet och intresse för den sörjandes känslor. Det viktigaste i stödet visade sig vara när vårdpersonalen bara var där och lyssnade på de sörjande och lät dem uttrycka sina känslor. En del sörjande ansåg att många sjuksköterskor gav intryck av att vara obekväma i att ge stöd till patienter i sorg. Många sjuksköterskor som medverkat i studierna ansåg att de behövde mer kunskap och erfarenhet i att ge stöd till sörjande patienter. Det visade sig vara viktigt att ha kunskap om att individer inte sörjer på samma sätt och att därför ta hänsyn till individuella skillnader och behov. Ett mycket utforskat område är sorg vid perinatal förlust, däremot behövs mer forskning inom sorg som orsakats av andra sorters förluster

A system for inducible mitochondria-specific protein degradation in vivo

Abstract Targeted protein degradation systems developed for eukaryotes employ cytoplasmic machineries to perform proteolysis. This has prevented mitochondria-specific analysis of proteins that localize to multiple locations, for example, the mitochondria and the nucleus. Here, we present an inducible mitochondria-specific protein degradation system in Saccharomyces cerevisiae based on the Mesoplasma florum Lon (mf-Lon) protease and its corresponding ssrA tag (called PDT). We show that mitochondrially targeted mf-Lon protease efficiently and selectively degrades a PDT-tagged reporter protein localized to the mitochondrial matrix. The degradation can be induced by depleting adenine from the medium, and tuned by altering the promoter strength of the MF-LON gene. We furthermore demonstrate that mf-Lon specifically degrades endogenous, PDT-tagged mitochondrial proteins. Finally, we show that mf-Lon-dependent PDT degradation can also be achieved in human mitochondria. In summary, this system provides an efficient tool to selectively analyze the mitochondrial function of dually localized proteins

Temporal expression of RAD51 and DMC1 in wild-type and SC-null oocytes.

<p>Oocytes at different stages of meiotic prophase were labeled with antisera to RAD51 or DMC1 (red). The chromosomal axes were visualized by STAG3 protein labeling (blue). The RAD51 and DMC1 recombination-related proteins disappear from the chromosomal axes in wild-type oocytes by late pachytene. In SC-null oocytes DMC1 show a pattern similar to that seen in wild-type oocytes, while RAD51 foci persist until the diplotene stage. Bar, 10 µm.</p

The recombination process in SC-null oocytes stops prior to the formation of recombination structures that contain MLH1 or MLH3.

<p>The chromosomal axes were labeled by STAG3 (blue), and centromeres by CREST (blue). MLH1 (red)/MLH3 (green) axis-associated complexes are absent in SC-null oocytes at the pachytene stage. Bars, 10 µm.</p