Tetraploid cells from cytokinesis failure induce aneuploidy and spontaneous transformation of mouse ovarian surface epithelial cells

Most ovarian cancers originate from the ovarian surface epithelium and are characterized by aneuploid karyotypes. Aneuploidy, a consequence of chromosome instability, is an early event during the development of ovarian cancers. However, how aneuploid cells are evolved from normal diploid cells in ovarian cancers remains unknown. In the present study, cytogenetic analyses of a mouse syngeneic ovarian cancer model revealed that diploid mouse ovarian surface epithelial cells (MOSECs) experienced an intermediate tetraploid cell stage, before evolving to aneuploid (mainly near-tetraploid) cells. Using long-term live-cell imaging followed by fluorescence in situ hybridization (FISH), we demonstrated that tetraploid cells originally arose from cytokinesis failure of bipolar mitosis in diploid cells, and gave rise to aneuploid cells through chromosome mis-segregation during both bipolar and multipolar mitoses. Injection of the late passage aneuploid MOSECs resulted in tumor formation in C57BL/6 mice. Therefore, we reveal a pathway for the evolution of diploid to aneuploid MOSECs and elucidate a mechanism for the development of near-tetraploid ovarian cancer cells.     

DNA replication is required for the checkpoint response to damaged DNA in Xenopus egg extracts

Alkylating agents, such as methyl methanesulfonate (MMS), damage DNA and activate the DNA damage checkpoint. Although many of the checkpoint proteins that transduce damage signals have been identified and characterized, the mechanism that senses the damage and activates the checkpoint is not yet understood. To address this issue for alkylation damage, we have reconstituted the checkpoint response to MMS in Xenopus egg extracts. Using four different indicators for checkpoint activation (delay on entrance into mitosis, slowing of DNA replication, phosphorylation of the Chk1 protein, and physical association of the Rad17 checkpoint protein with damaged DNA), we report that MMS-induced checkpoint activation is dependent upon entrance into S phase. Additionally, we show that the replication of damaged double-stranded DNA, and not replication of damaged single-stranded DNA, is the molecular event that activates the checkpoint. Therefore, these data provide direct evidence that replication forks are an obligate intermediate in the activation of the DNA damage checkpoint.     

Proteomic analysis of the potato tuber life cycle

The tuber of potato (Solanum tuberosum) is commonly used as a model for underground storage organs. In this study, changes in the proteome were followed from tuberization, through tuber development and storage into the sprouting phase. Data interrogation using principal component analysis was able to clearly discriminate between the various stages of the tuber life cycle. Moreover, five well-defined protein expression patterns were found by hierarchical clustering. Altogether 150 proteins showing highly significant differences in abundance between specific stages in the life cycle were highlighted; 59 of these were identified. In addition, 50 proteins with smaller changes in abundance were identified, including several novel proteins. Most noticeably, the development process was characterized by the accumulation of the major storage protein patatin isoforms and enzymes involved in disease and defense reactions. Furthermore, enzymes involved in carbohydrate and energy metabolism and protein processing were associated with development but decreased during tuber maturation. These results represent the first comprehensive picture of many proteins involved in the tuber development and physiology.     

ERp27, a new non-catalytic endoplasmic reticulum-located human protein disulfide isomerase family member, interacts with ERp57

Protein folding and quality control in the endoplasmic reticulum are critical processes for which our current understanding is far from complete. Here we describe the functional characterization of a new human 27.7-kDa protein (ERp27). We show that ERp27 is a two-domain protein located in the endoplasmic reticulum that is homologous to the non-catalytic b and b' domains of protein disulfide isomerase. ERp27 was shown to bind Delta-somatostatin, the standard test peptide for protein disulfide isomerase-substrate binding, and this ability was localized to the second domain of ERp27. An alignment of human ERp27 and human protein disulfide isomerase allowed for the putative identification of the peptide binding site of ERp27 indicating conservation of the location of the primary substrate binding site within the protein disulfide isomerase family. NMR studies revealed a significant conformational change in the b'-like domain of ERp27 upon substrate binding, which was not just localized to the substrate binding site. In addition, we report that ERp27 is bound by ERp57 both in vitro and in vivo by a similar mechanism by which ERp57 binds calreticulin.     

SPORE GERMINATION AND DEVELOPMENT OF THE YOUNG GAMETOPHYTE OF THE OSTRICH FERN (MATTEUCCIA STRUTHIOPTERIS)

Light is required for the germination of spores of Matteuccia struthiopteris. Histochemical studies show that dormant spores contain no starch, but have an abundance of storage protein granules. Starch accumulates in the numerous chloroplasts of the spore on exposure to light and becomes gradually more extensive. Protein granules disappear as germination progresses. Following this, the centrally located nucleus migrates toward the proximal spore face. Concomitant with the nuclear migration, an increase of cytoplasmic RNA surrounding the nucleus occurs. An equal nuclear division and unequal cell division give rise to a 2-celled gametophyte consisting of a large prothallial cell and smaller rhizoidal cell. A new peripheral wall forms around the entire protoplast at the time of nuclear migration, while a transverse wall forms after nuclear division. The rhizoid emerges through the split raphe along the proximal spore face; it is rich in cytoplasmic RNA but contains very few chloroplasts and little starch. Electron microscopy of the 2-celled stage revealed a greater concentration of mitochondria, Golgi bodies, and a more extensive endoplasmic reticulum in the rhizoid than was found in the prothallial cell, which, however, was far richer in chloroplasts and lipid bodies. As the rhizoid elongates and becomes more vacuolated, cytoplasmic RNA decreases as cytoplasmic protein increases. The rhizoid undergoes no cell divisions, while the prothallial cell retains the potential for further cell division. The possible significance of the distribution of storage products, cell organelles, and other cell components were considered in relation to the non-equational cell division and differentiation of the 2 cells.     

Lithiation‐Induced Dilation Mapping in a Lithium‐Ion Battery Electrode by 3D X‐Ray Microscopy and Digital Volume Correlation

Recent advances in high‐resolution 3D X‐ray computed tomography (CT) allow detailed, non‐destructive 3D structural mapping of a complete lithium‐ion battery. By repeated 3D image acquisition (time lapse CT imaging) these investigations of material microstructure are extended into the fourth dimension (time) to study structural changes of the device in operando. By digital volume correlation (DVC) of successive 3D images the dimensional changes taking place during charge cycling are quantified at the electrode level and at the Mn₂O₄ particle scale. After battery discharging, the extent of lithiation of the manganese (III/IV) oxide grains in the electrode is found to be a function of the distance from the battery terminal with grains closest to the electrode/current collector interface having the greatest expansion (≈30%) and grains furthest from the current collector and closest to the counter electrode showing negligible dilation. This implies that the discharge is limited by electrical conductivity. This new CT+DVC technique is widely applicable to the 3D exploration of the microstructural degradation processes for a range of energy materials including fuel cells, capacitors, catalysts, and ceramics.     

THE MAINTENANCE OF SEX BY PARASITISM AND MUTATION ACCUMULATION UNDER EPISTATIC FITNESS FUNCTIONS

The mutation accumulation hypothesis predicts that sex functions to reduce the population mutational load, while the Red Queen hypothesis holds that sex is adaptive as a defense against coevolving pathogens. We used computer simulations to examine the combined and separate effects of selection against deleterious mutations and host-parasite coevolution on the spread of a clone into an outcrossing sexual population. The results suggest that the two processes operating simultaneously may select for sex independent of the exact shape of the function that maps mutation number onto host fitness.     

Pair approximations and the inclusion of indirect transmission: theory and application to between farm transmission of Salmonella

The spatial-temporal dynamics of farm animal diseases depend both on disease specific processes and the underlying contact network between farms. Indirect transmission via free-living bacteria in the environment is an important transmission route and contributes significantly to the dynamics. The pair-wise model has been developed to include both direct transmission and indirect transmission via free stages. The model is compared with stochastic simulations of epidemics on contact networks. The network framework is applied to the investigation of the epidemiological dynamics of between-herd transmission of Salmonella spp. The main results help to explain differences in observed epidemiological patterns and to identify possible causes for different strains of Salmonella developing so much variation in their infection dynamics in UK dairy herds. Numerical results show that shorter infectious period, more persistent immune response and more rapid removal of faeces result in a lower prevalence of infection and a greater tendency for (damped) oscillation. A possible control strategy is consequently suggested. Furthermore, the effect of network structure on long-term dynamics is examined.