Till disassembly do us part: a happy marriage of nuclear envelope and chromatin

A characteristic feature of eukaryotic cells is the presence of nuclear envelope (NE) which separates genomic DNA from cytoplasm. NE is composed of inner nuclear membrane (INM), which interacts with chromatin, and outer nuclear membrane, which is connected to endoplasmic reticulum. Nuclear pore complexes are inserted into NE to form transport channels between nucleus and cytoplasm. In metazoan cells, an intermediate filament-based meshwork called as nuclear lamina exists between INM and chromatin. Sophisticated collaboration of these molecular machineries is necessary for the structure and functions of NE. Recent research advances have revealed that NE dynamically communicates with chromatin and cytoskeleton to control multiple nuclear functions. In this mini review, I briefly summarize the basic concepts and current topics of functional relationships between NE and chromatin.     

Together until separin do us part

Loss of sister-chromatid cohesion triggers chromosome segregation. Several recent reports show that the protease Esp1 cleaves the cohesin subunit Scc1/Mcd1 to induce sister-chromatid segregation in yeast and vertebrates. This finding indicates that cohesin cleavage may control sister-chromatid separation in all vertebrates.     

'Til cell death do us part: nitric oxide and mechanisms of hepatotoxicity

Like many juggernauts in biology, the elusive nature of nitric oxide (NO) sprints through the fields, sometimes the savior, at other times the scimitar. In the liver, which is the metabolic center of the organism, hepatocytes and immune cells trade blows using the reactive diatomic molecule NO to induce cellular damage under toxic conditions. In response, hepatocytes can utilize several mechanisms of NO to their protective advantage by prohibiting the activation of programmed cell death, a.k.a. apoptosis. The balance of these effects in this reactive milieu set the stage for the homeostatic response to cellular injury that determines whether hepatocytes will live, die, or regenerate. Insights that we and others have gained from the liver under pathologic conditions of stress can be applied to the understanding of cellular death mechanisms in other organs and tissues.     

Neuronal polarity: until GSK-3 do us part

Specification of the axon and dendrites is a critical step in the development of a neuron. Two new studies have shed light on the molecular pathway that controls the establishment of neuronal polarity.     

Drought until death do us part: a case study of the desiccation-tolerance of a tropical moist forest seedling-tree,Licania platypus (Hemsl.) Fritsch

Studies of the desiccation tolerance of 15-month-old Licania platypus (Hemsl.) Fritsch seedlings were performed on potted plants. Pots were watered to field capacity and then dehydrated for 23-46 d to reach various visible wilting stages from slightly-wilted to dead. Root hydraulic conductance, k(r), was measured with a high-pressure flow meter and whole-stem hydraulic conductance, k(ws), was measured by a vacuum chamber method. Leaf punches were harvested for measurement of leaf water potential by a thermocouple psychrometer and for measurement of fresh- and dry-weight. L. platypus was surprisingly desiccation-tolerant, suggesting that most species of central Panama may be well adapted to the seasonality of rainfall in the region. The slightly-wilted stage corresponded to leaf water potentials and relative water contents of -2.7 MPa and 0.85, respectively, but plants did not die until these values fell to -7.5 MPa and 0.14, respectively. As desiccation proceeded k(r) and k(ws) declined relative to irrigated controls, but k(ws) was more sensitive to desiccation than k(r). Values of k(ws) declined by 70-85% in slightly-wilted to dead plants, respectively. By comparison, k(r) showed no significant change in slightly-wilted plants and fell by about 50% in plants having severely-wilted to dead shoots.     

>For better or worse, till death us do part<--spousal age gap and differential longevity: evidence from historical demography

Based on a set of 2,371 family related entries dating from 1688 to 1921, the current study tried to verify longevity differentials due to interspousal age difference. For the purpose of the analysis, age-heterogamy was operationalized in terms of sample-specific marital age gap (3.2 years) with a standard deviation of 6.1 years. Based on this, five marriage groups were isolated. Female mean age at marriage experienced a slight increase over time, while the male mean at marriage decreased. This led to an appreciable narrowing of the spousal age gap. Age-homogamous unions were most prevalent in the lower socio-economic class (day-laborers, industrial workers) (p<0.01). In both husband-older and wife-older unions, the interspousal gap increased with marriage order. In accord with previous studies, mean age at death varied significantly by marriage group. Females, who married younger men, died later than females, who married older men. In contrast, male longevity was most depressed within age-similar marriages, while those who married older or younger wives displayed higher life spans. Overall, marriage to a younger spouse seemed to increase longevity prospects (p<0.05). These differentials were not exclusively a function of the marital age gap, but were affected by diverse confounders such as reproductive output and socio-economic status.     

Nuclear envelope-limited chromatin sheets are part of mitotic death

Nuclear envelope-limited chromatin sheets (ELCS) are enigmatic membranous structures of uncertain function. This study describes the induction of ELCS in p53 mutated Burkitt's lymphoma cell lines after treatment with irradiation or the microtubule inhibitor, SK&F 96365. Both treatments evoked similar mitotic death, involving metaphase arrest followed by extensive endopolyploidisation and delayed apoptosis, although the kinetics were different. We found that induction of ELCS and nuclear segmentation correlated with the amount and kinetics of M-phase arrest, mitosis restitution and delayed apoptosis of endopolyploid cells. In metaphases undergoing restitution, ELCS are seen participating in the restoration of the nuclear envelope, mediating the attachment of peripheral chromatin to it. In interphase cells, ELCS join nuclear segments, ectopically linking and fusing with heterochromatin regions. In cells with segmented nuclei, continued DNA replication was observed, along with activation and redistribution of Ku70, suggestive of non-homologous DNA end-joining. Induction of ELCS also parallels the induction of cytoplasmic stacked membrane structures, such as confronting cisternae and annulate lamellae, which participate in the turnover and degeneration of ELCS. The results suggest that arrest at a spindle checkpoint and the uncoupling of mitosis from DNA replication lead to the emergence of ELCS in the resulting endopolyploid cells.     

Q & A: Till Roenneberg

Till Roenneberg is Professor of Chronobiology at the University of Munich. He studies the circadian clock from its cellular/molecular mechanisms up to the consequences of shift work. He received his education in Munich and London, and worked in the 1980s with Woody Hastings at Harvard. Since then, he has built up the Centre for Chronobiology at the Munich Medical School. For many years, he has coordinated circadian research and education in Germany and in Europe. He is also involved in reforming the University curriculum, incorporating problem-based approaches. He has received international prizes for both his research and his teaching.     

Legal status of brain death in Japan: why many Japanese do not accept "brain death" as a definition of death

Several speculations on the reasoning for the lack of performance of organ transplants from brain-dead donors in Japan for the last 8 months since the official acceptance of the recent Final Report will be presented. Such obstinate reluctance shown by the Japanese population against organ transplantation from brain-dead donors is certainly an unusual situation. There must be definitely some serious reasons underlying it. No one seems, however, to be able to pinpoint them, although there have been several speculations. The main purpose of my paper today concerns "Why many Japanese do not accept 'brain death' as a definition of death of a person".