Reconstruction of the kinetochore: a prelude to meiosis

In eukaryotic organisms, chromosomes are spatially organized within the nucleus. Such nuclear architecture provides a physical framework for the genetic activities of chromosomes, and changes its functional organization as the cell moves through the phases of the cell cycle. The fission yeast Schizosaccharomyces pombe provides a striking example of nuclear reorganization during the transition from mitosis to meiosis. In this organism, centromeres remain clustered at the spindle-pole body (SPB; a centrosome-equivalent structure in fungi) during mitotic interphase. In contrast, during meiotic prophase, centromeres dissociate from the SPB and telomeres cluster to the SPB. Recent studies revealed that this repositioning of chromosomes is regulated by mating pheromone signaling. Some centromere proteins disappear from the centromere in response to mating pheromone, leading to dissociation of centromeres from the SPB. Interestingly, mating pheromone signaling is also required for monopolar orientation of the kinetochore which is crucial for proper segregation of sister chromatids during meiosis. When meiosis is induced in the absence of mating pheromone signaling, aberrant chromosome behaviors are observed: the centromere proteins remain at the centromere; the centromere remains associated with the SPB; and sister chromatids segregate precociously in the first meiotic division. These aberrant chromosome behaviors are all normalized by activating the mating pheromone signaling pathway. Thus, action of mating pheromone on the centromere is important for coherent behavior of chromosomes in meiosis. Here we discuss repositioning and reconstruction of the centromere during the transition from mitosis to meiosis, and highlight its significance for proper progression of meiosis

Harry Lenas

Taha Toros Arşivi, Dosya No: 112-Pastahaneler, Bozacılar, Gazozcular, Börekçiler, Turşucular, Sucularİstanbul Kalkınma Ajansı (TR10/14/YEN/0033) İstanbul Development Agency (TR10/14/YEN/0033

Characterization of rec15 , an early meiotic recombination gene in Schizosaccharomyces pombe

In S. pombe strains mutant for rec15 aberrant ascus morphology, reduced spore viability and severe reduction of meiotic recombination was detected. Genetic and cytological analysis identified frequent interruption of meiosis after the first division, and nondisjunction I, as the main segregation errors in the mutant. Chromosome segregation at meiosis I was not random in rec15, suggesting the presence of a backup system for correct segregation of achiasmate chromosomes. The analysis of meiotic progression in time-course experiments revealed that the major meiotic events, such as the onset of premeiotic DNA synthesis, of horse-tail nuclear movement, and of the first meiotic division occurred earlier in rec15 than in wild-type. The early onset of meiotic events is a novel observation for an early recombination mutant and implies a function of rec15 protein already at or before DNA synthesi

A locally-induced increase in intracellular Ca2+ propagates cell-to-cell in the presence of plasma membrane Ca2+ ATPase inhibitors in non-excitable cells

AbstractIntercellular Ca2+ waves are commonly observed in many cell types. In non-excitable cells, intercellular Ca2+ waves are mediated by gap junctional diffusion of a Ca2+ mobilizing messenger such as IP3. Since Ca2+ is heavily buffered in the cytosolic environment, it has been hypothesized that the contribution of the diffusion of Ca2+ to intercellular Ca2+ waves is limited. Here, we report that in the presence of plasma membrane Ca2+ ATPase inhibitors, locally-released Ca2+ from the flash-photolysis of caged-Ca2+ appeared to induce further Ca2+ release and were propagated from one cell to another, indicating that Ca2+ was self-amplified to mediate intercellular Ca2+ waves. Our findings support the notion that non-excitable cells can establish a highly excitable medium to communicate local responses with distant cells

Spindle checkpoint activation at meiosis I advances anaphase II onset via meiosis-specific APC/C regulation

During mitosis, the spindle assembly checkpoint (SAC) inhibits the Cdc20-activated anaphase-promoting complex/cyclosome (APC/CCdc20), which promotes protein degradation, and delays anaphase onset to ensure accurate chromosome segregation. However, the SAC function in meiotic anaphase regulation is poorly understood. Here, we examined the SAC function in fission yeast meiosis. As in mitosis, a SAC factor, Mad2, delayed anaphase onset via Slp1 (fission yeast Cdc20) when chromosomes attach to the spindle improperly. However, when the SAC delayed anaphase I, the interval between meiosis I and II shortened. Furthermore, anaphase onset was advanced and the SAC effect was reduced at meiosis II. The advancement of anaphase onset depended on a meiosis-specific, Cdc20-related factor, Fzr1/Mfr1, which contributed to anaphase cyclin decline and anaphase onset and was inefficiently inhibited by the SAC. Our findings show that impacts of SAC activation are not confined to a single division at meiosis due to meiosis-specific APC/C regulation, which has probably been evolved for execution of two meiotic divisions

Chromosome Scaffold is a Double-Stranded Assembly of Scaffold Proteins

Poonperm, R., Takata, H., Hamano, T. et al. Chromosome Scaffold is a Double-Stranded Assembly of Scaffold Proteins. Sci Rep 5, 11916 (2015). https://doi.org/10.1038/srep11916

Overexpression of the human MNB/DYRK1A gene induces formation of multinucleate cells through overduplication of the centrosome

BACKGROUND: Previously we cloned the human MNB/DYRK1A gene from the "Down syndrome critical region" on chromosome 21. This gene encodes a dual specificity protein kinase that catalyzes its autophosphorylation on serine/threonine and tyrosine residues. But, the functions of the MNB/DYRK1A gene in cellular processes are unknown. RESULTS: In this study, we examined HeLa cells transfected with cDNA encoding a green fluorescent protein (GFP)-MNB/DYRK1A fusion protein and found 2 patterns of expression: In one group of transfected cells, GFP-MNB/DYRK1A was localized as dots within the nucleus; and in the other group, it was overexpressed and had accumulated all over the nucleus. In the cells overexpressing GFP-MNB/DYRK1A, multinucleation was clearly observed; whereas in those with the nuclear dots, such aberrant nuclei were not found. Furthermore, in the latter cells, essential processes such as mitosis and cytokinesis occurred normally. Multinucleation was dependent on the kinase activity of MNB/DYRK1A, because it was not observed in cells overexpressing kinase activity-negative mutants, GFP-MNB/DYRK1A (K179R) and GFP-MNB/DYRK1A (Y310F/Y312F). Immunostaining of GFP-MNB/DYRK1A-overexpressing cells with specific antibodies against α- and γ-tubulin revealed that multiple copies of centrosomes and aberrant multipolar spindles were generated in these cells. CONCLUSIONS: These results indicate that overexpression of MNB/DYRK1A induces multinucleation in HeLa cells through overduplication of the centrosome during interphase and production of aberrant spindles and missegregation of chromosomes during mitosis

Histologic Transformation from Follicular Lymphoma to Diffuse Large B-cell Lymphoma Detected during Colonoscopy

A 77-year-old Japanese woman who had been treated for follicular lymphoma for 8 years developed abdominal pain and intra-abdominal lymphadenopathies. Colonoscopy revealed an elevated lesion in the rectum, which presented as two humps with erosions. A diagnosis of histologic transformation of follicular lymphoma to diffuse large B-cell lymphoma was made by endoscopic biopsy. This case underscores the importance of endoscopy examinations and biopsy of newly emerged gastrointestinal lesions for the prompt diagnosis of histologic transformation, since salvage chemotherapy must be initiated quickly in such cases