Separate to operate: the centriole-free inner core of the centrosome regulates the assembly of the intranuclear spindle in Toxoplasma gondii

Centrosomes are the main microtubule-organizing center of the cell. They are normally formed by two centrioles, embedded in a cloud of proteins known as pericentriolar material. The PCM ascribes centrioles with their microtubule nucleation capacity. Toxoplasma gondii, the causative agent of toxoplasmosis, divides by endodyogeny. Successful cell division is critical for pathogenesis. The centrosome, plays central roles in orchestrating the temporal and physical coordination of major organelle segregation and daughter cell formation. The T. gondii centrosome is formed by two domains; an outer core, distal from the nucleus, and an inner core, proximal to the nucleus. This dual organization has been proposed to underlie T. gondii’s cell division plasticity. However, the role of the inner core remains undeciphered. Here, we focus on the role of its only known molecular marker; TgCEP250L1. We show that upon conditional degradation of TgCEP250L1, parasites exhibit nuclear segregation defects, whilst normally forming daughter cells. In addition, the centrioles, disconnect from the nucleus. We explore the structural defects underlying these phenotypes by high resolution microscopy. We show that TgCEP250L1’s location is dynamic and encompasses the formation of the mitotic spindle. Moreover, we show that in the absence of TgCEP250L1, the microtubule binding protein TgEB1, fails to translocate from the nucleus to the mitotic spindle, while polyploid nuclei accumulate. Overall, our data supports a model in which the inner core of the T. gondii centrosome critically participates in cell division by directly impacting the formation or stability of the mitotic spindle.

Rapid Variations of Earth’s Core Magnetic Field

Evidence of fast variations in the Earth’s core field are seen both in magnetic observatory and satellite records. We present here how they have been identified at the Earth’s surface from ground-based observatory records and how their spatio-temporal structure is now characterised by satellite data. It is shown how their properties at the core mantle boundary are extracted through localised and global modelling processes, paying particular attention to their time scales. Finally are listed possible types of waves in the liquid outer core, together with their main properties, that may give rise to these observed fast variations.

Thermal conductivity of Fe-Si alloys and thermal stratification in Earth’s core

Light elements in Earth’s core play a key role in driving convection and influencing geodynamics, both of which are crucial to the geodynamo. However, the thermal transport properties of iron alloys at high-pressure and -temperature conditions remain uncertain. Here we investigate the transport properties of solid hexagonal close-packed and liquid Fe-Si alloys with 4.3 and 9.0 wt % Si at high pressure and temperature using laser-heated diamond anvil cell experiments and first-principles molecular dynamics and dynamical mean field theory calculations. In contrast to the case of Fe, Si impurity scattering gradually dominates the total scattering in Fe-Si alloys with increasing Si concentration, leading to temperature independence of the resistivity and less electron–electron contribution to the conductivity in Fe-9Si. Our results show a thermal conductivity of ∼100 to 110 W⋅m−1⋅K−1 for liquid Fe-9Si near the topmost outer core. If Earth’s core consists of a large amount of silicon (e.g., > 4.3 wt %) with such a high thermal conductivity, a subadiabatic heat flow across the core–mantle boundary is likely, leaving a 400- to 500-km-deep thermally stratified layer below the core–mantle boundary, and challenges proposed thermal convection in Fe-Si liquid outer core.

Can NASA’s Gravity Satellites Detect Motions in Earth’s Core?

Measurements of our planet’s gravitational field could expose processes in the fluid outer core—if scientists can decipher the signals.

Association of major earthquakes (magnitude >= 6 Richter scale) with geomagnetic activity index KP during the period 2001-2007

A critical study of variation of geomagnetic activity index Kp for the period 2001-2007 have been made and its close association with major earthquakes (magnitude >= 6 Richter scale) is presented. From statistical analysis it is confirmed that when Kp touches 0 or 0+ values, major earthquakes take place within 48 hours. This is also explained considering the motion of the molten metal inside the outer core of earth.

Shear Properties of Earth's Inner Core

Understanding how Earth's inner core (IC) develops and evolves, including fine details of its structure and energy exchange across the boundary with the liquid outer core, helps us constrain its age, relationship with the planetary differentiation, and other significant global events throughout Earth's history, as well as the changing magnetic field. Since its discovery in 1936 and the solidity hypothesis in 1940, Earth's IC has never ceased to inspire geoscientists. However, while there are many seismological observations of compressional waves and normal modes sensitive to the IC's compressional and shear structure, the shear waves that provide direct evidence for the IC's solidity have remained elusive and have been reported in only a few publications. Further advances in the emerging correlation-wavefield paradigm, which explores waveform similarities, may hold the keys to refined measurements of all inner-core shear properties, informing dynamical models and strengthening interpretations of the IC's anisotropic structure and viscosity. ▪ What are the shear properties of the inner core, such as the shear-wave speed, shear modulus, shear attenuation, and shear-wave anisotropy? Can the shear properties be measured seismologically and confirmed experimentally? Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 50 is May 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Phylogenomics of two ST1 antibiotic-susceptible non-clinical Acinetobacter baumannii strains reveals multiple lineages and complex evolutionary history in global clone 1

Acinetobacter baumannii is an opportunistic pathogen that is difficult to treat due to its resistance to extreme conditions, including desiccation and antibiotics. Most strains causing outbreaks around the world belong to two main global lineages, namely global clones 1 and 2 (GC1 and GC2). Here, we used a combination of Illumina short read and MinION (Oxford Nanopore) long-read sequence data with a hybrid assembly approach to complete the genome sequence of two antibiotic-sensitive GC1 strains, Ex003 and Ax270, recovered in Lebanon from water and a rectal swab of a cat, respectively. Phylogenetic analysis of Ax270 and Ex003 with 186 publicly available GC1 genomes revealed two major clades, including five main lineages (L1–L5), and four single-isolate lineages outside of the two clades. Ax270 and Ex003, along with AB307-0294 and MRSN7213 (both predicted antibiotic-susceptible isolates) represent these individual lineages. Antibiotic resistance islands and transposons interrupting the comM gene remain important features in L1–L5, with L1 associated with the AbaR-type resistance islands, L2 with AbaR4, L3 strains containing either AbaR4 or its variants as well as Tn6022::ISAba42, and L4 and L5 associated with Tn6022 or its variants. Analysis of the capsule (KL) and outer core (OCL) polysaccharide loci further revealed a complex evolutionary history probably involving many recombination events. As more genomes become available, more GC1 lineages continue to emerge. However, genome sequence data from more diverse geographical regions are needed to draw a more accurate population structure of this globally distributed clone.