Pathway to Totipotency: Lessons from Germ Cells

Oocytes and sperm are some of the most differentiated cells in our bodies, yet they generate all cell types after fertilization. Accumulating evidence suggests that this extraordinary potential is conferred to germ cells from the time of their formation during embryogenesis. In this Review, we describe common themes emerging from the study of germ cells in vertebrates and invertebrates. Transcriptional repression, chromatin remodeling, and an emphasis on posttranscriptional gene regulation preserve the totipotent genome of germ cells through generations

Regulation of the MEX-5 Gradient by a Spatially Segregated Kinase/Phosphatase Cycle

SummaryProtein concentration gradients encode spatial information across cells and tissues and often depend on spatially localized protein synthesis. Here, we report that a different mechanism underlies the MEX-5 gradient. MEX-5 is an RNA-binding protein that becomes distributed in a cytoplasmic gradient along the anterior-to-posterior axis of the one-cell C. elegans embryo. We demonstrate that the MEX-5 gradient is a direct consequence of an underlying gradient in MEX-5 diffusivity. The MEX-5 diffusion gradient arises when the PAR-1 kinase stimulates the release of MEX-5 from slow-diffusive, RNA-containing complexes in the posterior cytoplasm. PAR-1 directly phosphorylates MEX-5 and is antagonized by the spatially uniform phosphatase PP2A. Mathematical modeling and in vivo observations demonstrate that spatially segregated phosphorylation and dephosphorylation reactions are sufficient to generate stable protein concentration gradients in the cytoplasm. The principles demonstrated here apply to any spatially segregated modification cycle that affects protein diffusion and do not require protein synthesis or degradation

Nanoscale resetting of the Th/Pb system in an isotopically-closed monazite grain: A combined atom probe and transmission electron microscopy study

© 2018 China University of Geosciences (Beijing) and Peking University Understanding the mechanisms of parent-daughter isotopic mobility at the nanoscale is key to rigorous interpretation of U–Th–Pb data and associated dating. Until now, all nanoscale geochronological studies on geological samples have relied on either Transmission Electron Microscope (TEM) or Atom Probe Microscopy (APM) characterizations alone, thus suffering from the respective weaknesses of each technique. Here we focus on monazite crystals from a ~1 Ga, ultrahigh temperature granulite from Rogaland (Norway). This sample has recorded concordant U–Pb dates (measured by LA-ICP-MS) that range over 100 My, with the three domains yielding distinct isotopic U–Pb ages of 1034 ± 6 Ma (D1; S-rich core), 1005 ± 7 Ma (D2), and 935 ± 7 Ma (D3), respectively. Combined APM and TEM characterization of these monazite crystals reveal phase separation that led to the isolation of two different radiogenic Pb (Pb*) reservoirs at the nanoscale. The S-rich core of these monazite crystals contains Ca–S-rich clusters, 5–10 nm in size, homogenously distributed within the monazite matrix with a mean inter-particle distance of 40–60 nm. The clusters acted as a sink for radiogenic Pb (Pb*) produced in the monazite matrix, which was reset at the nanoscale via Pb diffusion while the grain remained closed at the micro-scale. Compared to the concordant ages given by conventional micro-scale dating of the grain, the apparent nano-scale age of the monazite matrix in between clusters is about 100 Myr younger, which compares remarkably well to the duration of the metamorphic event. This study highlights the capabilities of combined APM-TEM nano-structural and nano-isotopic characterizations in dating and timing of geological events, allowing the detection of processes untraceable with conventional dating methods

Pulmonary delivery of cationic gold nanoparticles boost antigen-specific CD4+ T Cell Proliferation

To address how surface charge affects the fate of potential nanocarriers in the lung, gold nanoparticles (AuNPs) coated with polyvinyl alcohol containing either positively (NH2) or negatively (COOH) charged functional groups were intra-nasally instilled in mice, and their uptake by antigen presenting cell populations (APC) in broncho-alveolar lavage (BAL) fluid, trachea, and lung parenchyma, as well as trafficking to the lung draining lymph nodes (LDLNs) was assessed by flow cytometry. Furthermore, CD4+ T cell proliferation in LDLNs was investigated following instillation. All APC subpopulations preferentially captured positively-charged AuNPs compared to their negatively-charged counterparts. Uptake of AuNPs up-regulated expression of co-stimulatory molecules on all APC populations. Furthermore, positively-charged AuNPs induced enhanced OVA-specific CD4+ T cell stimulation in LDLNs compared to negatively-charged AuNPs, or polymer alone. Our findings demonstrate surface charge as a key parameter determining particle uptake by APC, and down-stream immune responses depend on the presence of particle core-bound polymer

The contribution of Swiss scientists to the assessment of energy metabolism

Although Switzerland is considered a small country, it has its share in discoveries, inventions and developments for the assessment of energy metabolism. This includes seminal contributions to respiratory and metabolic physiology and to devices for measuring energy expenditure by direct and indirect calorimetry in vivo in humans and small animals (as well as in vitro in organs/tissues), for the purpose of evaluating the basic nutritional requirements. A strong momentum came during World War II when it was necessary to evaluate the energy requirements of soldiers protecting the country by assessing their energy expenditure, as well as to determine the nutritional needs of the Swiss civil population in time of war when food rationing was necessary to ensure national neutrality and independence. A further impetus came in the 1970s at the start of the obesity epidemics, toward a better understanding of the metabolic basis of obesity, ranging from the development of whole-body concepts to molecular mechanisms. In a trip down memory lane, this review focuses on some of the earlier leading Swiss scientists who have contributed to a better understanding of the field

Hemolysis following coil embolization of a patent ductus arteriosus

We describe the development of hemolysis from moderate residual shunting across a patent ductus arteriosus following coil embolization. The fall in hemoglobin levels from 11.6 to 6.0 gm/dl necessitated a second coil procedure which resulted in complete closure of the residual shunting and resolution of hemolysis. Therefore, appearance of anemia following coil embolization of patent ductus arteriosus should be monitored closely; however, repeat coil embolization with elimination of residual shunt will lead to prompt recovery of normal hemoglobin levels. © 1996 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38225/1/17_ftp.pd

"Case files from the University of Florida: When an Earache is more than an Earache": A case report

Brain abscess is not a common diagnosis as there are only approximately 2000 cases reported each year in the United States. There are three main routes of access to the brain including contiguous infection from the oropharynx, direct implantation and hematogenously. We present a case of brain abscess in a child who had multiple visits for ear pain to various physicians including pediatricians and to emergency departments. Additionally, the microbiology of brain abscesses is briefly discussed, as is treatment

Selective inhibition of anti-MAG IgM autoantibody binding to myelin by an antigen-specific glycopolymer.

Anti-myelin-associated glycoprotein (MAG) neuropathy is a disabling autoimmune peripheral neuropathy that is caused by circulating monoclonal IgM autoantibodies directed against the human natural killer-1 (HNK-1) epitope. This carbohydrate epitope is highly expressed on adhesion molecules such as MAG, a glycoprotein present in myelinated nerves. We previously showed the therapeutic potential of the glycopolymer poly(phenyl disodium 3-O-sulfo-β-d-glucopyranuronate)-(1→3)-β-d-galactopyranoside (PPSGG) in selectively neutralizing anti-MAG IgM antibodies in an immunological mouse model and ex vivo with sera from anti-MAG neuropathy patients. PPSGG is composed of a biodegradable backbone that multivalently presents a mimetic of the HNK-1 epitope. In this study, we further explored the pharmacodynamic properties of the glycopolymer and its ability to inhibit the binding of anti-MAG IgM to peripheral nerves. The polymer selectively bound anti-MAG IgM autoantibodies and prevented the binding of patients' anti-MAG IgM antibodies to myelin of non-human primate sciatic nerves. Upon PPSGG treatment, neither activation nor inhibition of human and murine peripheral blood mononuclear cells nor alteration of systemic inflammatory markers was observed in mice or ex vivo in human peripheral blood mononuclear cells. Intravenous injections of PPSGG to mice immunized against the HNK-1 epitope removed anti-MAG IgM antibodies within less than 1 hr, indicating a fast and efficient mechanism of action as compared to a B-cell depletion with anti-CD20. In conclusion, these observations corroborate the therapeutic potential of PPSGG for an antigen-specific treatment of anti-MAG neuropathy. Read the Editorial Highlight for this article on page 465

Impaired photoprotection in Phaeodactylum tricornutum KEA3 mutants reveals the proton regulatory circuit of diatoms light acclimation

International audienceDiatoms are successful phytoplankton clades able to acclimate to changing environmental conditions, including e.g. variable light intensity. Diatoms are outstanding at dissipating light energy exceeding the maximum photosynthetic electron transfer (PET) capacity via the nonphotochemical quenching (NPQ) process. While the molecular effectors of NPQ as well as the involvement of the proton motive force (PMF) in its regulation are known, the regulators of the PET/PMF relationship remain unidentified in diatoms. We generated mutants of the H$^+$ /K$^+$ antiporter KEA3 in the model diatom $Phaeodactylum\ tricornutum$. Loss of KEA3 activity affects the PET/PMF coupling and NPQ responses at the onset of illumination, during transients and in steady-state conditions. Thus, this antiporter is a main regulator of the PET/PMF coupling. Consistent with this conclusion, a parsimonious model including only two free components, KEA3 and the diadinoxanthin de-epoxidase, describes most of the feedback loops between PET and NPQ. This simple regulatory system allows for efficient responses to fast (minutes) or slow (e.g. diel) changes in light environment, thanks to the presence of a regulatory calcium ion (Ca$^{2+}$ )-binding domain in KEA3 modulating its activity. This circuit is likely tuned by the NPQ-effector proteins, LHCXs, providing diatoms with the required flexibility to thrive in different ocean provinces

Nucleologenesis in the Caenorhabditis elegans Embryo

In the Caenorhabditis elegans nematode, the oocyte nucleolus disappears prior to fertilization. We have now investigated the re-formation of the nucleolus in the early embryo of this model organism by immunostaining for fibrillarin and DAO-5, a putative NOLC1/Nopp140 homolog involved in ribosome assembly. We find that labeled nucleoli first appear in somatic cells at around the 8-cell stage, at a time when transcription of the embryonic genome begins. Quantitative analysis of radial positioning showed the nucleolus to be localized at the nuclear periphery in a majority of early embryonic nuclei. At the ultrastructural level, the embryonic nucleolus appears to be composed of a relatively homogenous core surrounded by a crescent-shaped granular structure. Prior to embryonic genome activation, fibrillarin and DAO-5 staining is seen in numerous small nucleoplasmic foci. This staining pattern persists in the germline up to the ∼100-cell stage, until the P4 germ cell divides to give rise to the Z2/Z3 primordial germ cells and embryonic transcription is activated in this lineage. In the ncl-1 mutant, which is characterized by increased transcription of rDNA, DAO-5-labeled nucleoli are already present at the 2-cell stage. Our results suggest a link between the activation of transcription and the initial formation of nucleoli in the C. elegans embryo