A system reliability analysis for stand-by spares with non-zero unpowered failure rates

Equations which define the reliability of n-fold parallel systems with stand-by spares, and triply redundant, majority-voting systems with stand-by spares have been derived. The stand-by spares have been assumed to have a non-zero failure rate while in the stand-by mode. A Monte Carlo system simulation has been generated and the results compared to the theoretical reliability predictions. A comparison of these two stand-by configurations is also presented for three through six total units

Reconstructing aspects of human embryogenesis with pluripotent stem cells.

Understanding human development is of fundamental biological and clinical importance. Despite its significance, mechanisms behind human embryogenesis remain largely unknown. Here, we attempt to model human early embryo development with expanded pluripotent stem cells (EPSCs) in 3-dimensions. We define a protocol that allows us to generate self-organizing cystic structures from human EPSCs that display some hallmarks of human early embryogenesis. These structures mimic polarization and cavitation characteristic of pre-implantation development leading to blastocyst morphology formation and the transition to post-implantation-like organization upon extended culture. Single-cell RNA sequencing of these structures reveals subsets of cells bearing some resemblance to epiblast, hypoblast and trophectoderm lineages. Nevertheless, significant divergences from natural blastocysts persist in some key markers, and signalling pathways point towards ways in which morphology and transcriptional-level cell identities may diverge in stem cell models of the embryo. Thus, this stem cell platform provides insights into the design of stem cell models of embryogenesis

Wdpcp, a PCP Protein Required for Ciliogenesis, Regulates Directional Cell Migration and Cell Polarity by Direct Modulation of the Actin Cytoskeleton

Planar cell polarity (PCP) regulates cell alignment required for collective cell movement during embryonic development. This requires PCP/PCP effector proteins, some of which also play essential roles in ciliogenesis, highlighting the long-standing question of the role of the cilium in PCP. Wdpcp, a PCP effector, was recently shown to regulate both ciliogenesis and collective cell movement, but the underlying mechanism is unknown. Here we show Wdpcp can regulate PCP by direct modulation of the actin cytoskeleton. These studies were made possible by recovery of a Wdpcp mutant mouse model. Wdpcp-deficient mice exhibit phenotypes reminiscent of Bardet-Biedl/Meckel-Gruber ciliopathy syndromes, including cardiac outflow tract and cochlea defects associated with PCP perturbation. We observed Wdpcp is localized to the transition zone, and in Wdpcp-deficient cells, Sept2, Nphp1, and Mks1 were lost from the transition zone, indicating Wdpcp is required for recruitment of proteins essential for ciliogenesis. Wdpcp is also found in the cytoplasm, where it is localized in the actin cytoskeleton and in focal adhesions. Wdpcp interacts with Sept2 and is colocalized with Sept2 in actin filaments, but in Wdpcp-deficient cells, Sept2 was lost from the actin cytoskeleton, suggesting Wdpcp is required for Sept2 recruitment to actin filaments. Significantly, organization of the actin filaments and focal contacts were markedly changed in Wdpcp-deficient cells. This was associated with decreased membrane ruffling, failure to establish cell polarity, and loss of directional cell migration. These results suggest the PCP defects in Wdpcp mutants are not caused by loss of cilia, but by direct disruption of the actin cytoskeleton. Consistent with this, Wdpcp mutant cochlea has normal kinocilia and yet exhibits PCP defects. Together, these findings provide the first evidence, to our knowledge, that a PCP component required for ciliogenesis can directly modulate the actin cytoskeleton to regulate cell polarity and directional cell migration

The preservation of erythrocytes at liquid nitrogen temperatures with hydroxyethyl starch: the removal of hydroxyethyl starch from erythrocytes after thawing

Packed human erythrocytes were frozen in liquid nitrogen using hydroxyethyl starch as a cryoprotective agent. Upon thawing, the cells were washed with a balanced salt solution. The washed cells were stable when resuspended in 0.154 n NaCl. The postthaw saline stability approximated the total recovery after washing the cells. Intracellular potassium loss was 15% immediately postthaw, and an additional 15% loss occurred after washing. These results indicate that HES can be removed from frozen-thawed cells by washing, and that freezing erythrocytes protected by HES does not result in significant losses of intracellular potassium.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33516/1/0000014.pd

Developmental potential of aneuploid human embryos cultured beyond implantation

Funder: Weston Havens Foundation; doi: https://doi.org/10.13039/100011223Abstract: Aneuploidy, the presence of an abnormal number of chromosomes, is a major cause of early pregnancy loss in humans. Yet, the developmental consequences of specific aneuploidies remain unexplored. Here, we determine the extent of post-implantation development of human embryos bearing common aneuploidies using a recently established culture platform. We show that while trisomy 15 and trisomy 21 embryos develop similarly to euploid embryos, monosomy 21 embryos exhibit high rates of developmental arrest, and trisomy 16 embryos display a hypo-proliferation of the trophoblast, the tissue that forms the placenta. Using human trophoblast stem cells, we show that this phenotype can be mechanistically ascribed to increased levels of the cell adhesion protein E-CADHERIN, which lead to premature differentiation and cell cycle arrest. We identify three cases of mosaicism in embryos diagnosed as full aneuploid by pre-implantation genetic testing. Our results present the first detailed analysis of post-implantation development of aneuploid human embryos

ASEAN and the Dynamics of Resistance to Sovereignty Violation:The Case of the Third Indochina War (1978–1991)

This article investigates the history of ASEAN’s relationship to external intervention in regional affairs. It addresses a specific question: What was the basic cause of the success of ASEAN resistance to the Vietnamese challenge to ASEAN’s sovereignty from 1978-1991? ASEAN’s history is understood in terms of a realist theoretical logic, in terms of the relationship between an ASEAN state with the most compelling interests at stake in a given issue, which I call a ‘vanguard state,’ and selected external powers. Using the Third Indochina War (1978–1991) as a case study, this article contends that ASEAN’s ability to resist violations to the sovereignty of Thailand from a Soviet-backed Vietnam is a consequence of high interest convergence between Thailand, and a designated external power, China

Lrp4 Modulates Extracellular Integration of Cell Signaling Pathways in Development

The extent to which cell signaling is integrated outside the cell is not currently appreciated. We show that a member of the low-density receptor-related protein family, Lrp4 modulates and integrates Bmp and canonical Wnt signalling during tooth morphogenesis by binding the secreted Bmp antagonist protein Wise. Mouse mutants of Lrp4 and Wise exhibit identical tooth phenotypes that include supernumerary incisors and molars, and fused molars. We propose that the Lrp4/Wise interaction acts as an extracellular integrator of epithelial-mesenchymal cell signaling. Wise, secreted from mesenchyme cells binds to BMP's and also to Lrp4 that is expressed on epithelial cells. This binding then results in the modulation of Wnt activity in the epithelial cells. Thus in this context Wise acts as an extracellular signaling molecule linking two signaling pathways. We further show that a downstream mediator of this integration is the Shh signaling pathway

Meltrin β/ADAM19 Interacting with EphA4 in Developing Neural Cells Participates in Formation of the Neuromuscular Junction

BACKGROUND: Development of the neuromuscular junction (NMJ) is initiated by the formation of postsynaptic specializations in the central zones of muscles, followed by the arrival of motor nerve terminals opposite the postsynaptic regions. The post- and presynaptic components are then stabilized and modified to form mature synapses. Roles of ADAM (A Disintegrin And Metalloprotease) family proteins in the formation of the NMJ have not been reported previously. PRINCIPAL FINDINGS: We report here that Meltrin beta, ADAM19, participates in the formation of the NMJ. The zone of acetylcholine receptor alpha mRNA distribution was broader and excess sprouting of motor nerve terminals was more prominent in meltrin beta-deficient than in wild-type embryonic diaphragms. A microarray analysis revealed that the preferential distribution of ephrin-A5 mRNA in the synaptic region of muscles was aberrant in the meltrin beta-deficient muscles. Excess sprouting of motor nerve terminals was also found in ephrin-A5 knockout mice, which lead us to investigate a possible link between Meltrin beta and ephrin-A5-Eph signaling in the development of the NMJ. Meltrin beta and EphA4 interacted with each other in developing motor neurons, and both of these proteins localized in the NMJ. Coexpression of Meltrin beta and EphA4 strongly blocked vesicular internalization of ephrin-A5-EphA4 complexes without requiring the protease activity of Meltrin beta, suggesting a regulatory role of Meltrin beta in ephrin-A5-Eph signaling. CONCLUSION: Meltrin beta plays a regulatory role in formation of the NMJ. The endocytosis of ephrin-Eph complexes is required for efficient contact-dependent repulsion between ephrin and Eph. We propose that Meltrin beta stabilizes the interaction between ephrin-A5 and EphA4 by regulating endocytosis of the ephrinA5-EphA complex negatively, which would contribute to the fine-tuning of the NMJ during development

Isolation of Hox Cluster Genes from Insects Reveals an Accelerated Sequence Evolution Rate

Among gene families it is the Hox genes and among metazoan animals it is the insects (Hexapoda) that have attracted particular attention for studying the evolution of development. Surprisingly though, no Hox genes have been isolated from 26 out of 35 insect orders yet, and the existing sequences derive mainly from only two orders (61% from Hymenoptera and 22% from Diptera). We have designed insect specific primers and isolated 37 new partial homeobox sequences of Hox cluster genes (lab, pb, Hox3, ftz, Antp, Scr, abd-a, Abd-B, Dfd, and Ubx) from six insect orders, which are crucial to insect phylogenetics. These new gene sequences provide a first step towards comparative Hox gene studies in insects. Furthermore, comparative distance analyses of homeobox sequences reveal a correlation between gene divergence rate and species radiation success with insects showing the highest rate of homeobox sequence evolution