No abstract

Sister-chromatid separation at the metaphase-anaphase transition is regulated by a proteolytic cascade. Destruction of the securin Pds1p liberates the Esp1p separase, which ultimately targets the mitotic cohesin Mcd1p/Scc1p for destruction. Pds1p stabilization by the spindle or DNA damage checkpoints prevents sister-chromatid separation while mutants lacking PDS1 (pds1D) are temperature sensitive for growth due to elevated chromosome loss. This report examined the role of the budding yeast Pds1p in meiotic progression using genetic, cytological, and biochemical assays. Similar to its mitotic function, Pds1p destruction is required for metaphase I-anaphase I transition. However, even at the permissive temperature for growth, pds1D mutants arrest with prophase I spindle and nuclear characteristics. This arrest was partially suppressed by preventing recombination initiation or by inactivating a subset of recombination checkpoint components. Further studies revealed that Pds1p is required for recombination in both double-strand-break formation and synaptonemal complex assembly. Although deleting PDS1 did not affect the degradation of the meiotic cohesin Rec8p, Mcd1p was precociously destroyed as cells entered the meiotic program. This role is meiosis specific as Mcd1p destruction is not altered in vegetative pds1D cultures. These results define a previously undescribed role for Pds1p in cohesin maintenance, recombination, and meiotic progression. M EIOSIS generates haploid gametes through a specialized cell division process that consists of one round of DNA replication followed by two nuclear divisions. The first meiotic division is unique to meiosis for two reasons. First, during the extended prophase I, homologous chromosomes synapse and undergo high levels of genetic recombination that is essential for the correct chromosome alignment at metaphase I (Kupiec et al. 1997). Second, following resolution of the recombination intermediates, the spindle makes monopolar attachments to the sister chromatids permitting the execution of meiosis I or the reductional division. Meiosis II resembles mitosis in that the replicated sister chromatids segregate to opposite poles.Meiotic recombination establishes chromosome alignment essential for accurate segregation during the first meiotic division. It follows therefore that the first step in this process, i.e., the formation of doublestrand breaks (DSBs), is also a critical event (Keeney et al. 1997). To date, in budding yeast, at least 10 proteins are required for this process (reviewed in Baudat and Keeney 2001;Arora et al. 2004;Borde 2007). Some of these proteins are meiosis specific whereas others also have roles in mitotically dividing cells. Significantly, apart from Spo11p, which initiates DSB formation (Keeney et al. 1997), little is known about the biochemical function of the individual components of this complex and how they are regulated.The proper execution of recombination and other meiotic landmark events is governed by several checkpoint pathways (reviewe...

Aims To develop an automated method for bloodpool segmentation and imaging plane re-slicing of cardiac CT via deep learning (DL) for clinical use in coronary artery disease (CAD) wall motion assessment and reproducible longitudinal imaging. Methods and Results 100 patients who underwent clinically indicated cardiac CT scans with manually segmented left ventricle (LV) and left atrial (LA) chambers were used for training. For each patient, long-axis (LAX) and short-axis (SAX) planes were manually defined by an imaging expert. A DL model was trained to predict bloodpool segmentations and imaging planes. DL bloodpool segmentations showed close agreement with manual LV (median Dice: 0.91, Hausdorff distance: 6.18mm) and LA (Dice: 0.93, HD: 7.35mm) segmentations and strong correlation with manual EF (Pearson r: 0.95 LV, 0.92 LA). Predicted planes had low median location (6.96mm) and angular orientation (7.96 °) errors which were comparable to inter-reader differences (p > 0.71). 84 – 97% of DL-prescribed LAX planes correctly intersected American Heart Association (AHA) segments, which was comparable (p > 0.05) to manual slicing. In a test cohort of 144 patients, we evaluated the ability of the DL approach to provide diagnostic imaging planes. Visual scoring by two blinded experts determined ≥94% of DL-predicted planes to be diagnostically adequate. Further, DL enabled visualization of LV wall motion abnormalities due to CAD and provided reproducible planes upon repeat imaging. Conclusion A volumetric, DL approach provides multiple chamber segmentations and can re-slice the imaging volume along standardized cardiac imaging planes for reproducible wall motion abnormality and functional assessment.

No abstract