U-Pb memory behavior in Chicxulub's peak ring - Applying U-Pb depth profiling to shocked zircon

The zircon U-Pb system is one of the most robust geochronometers, but during an impact event individual crystals can be affected differently by the passage of the shock wave and impact generated heat. Unraveling the potentially complex thermal history recorded by zircon crystals that experienced variable levels of shock and heating, as well as additioanl pre- and post-impact thermal events, has been difficult using classical geochronological methods. The existing high-precision 40Ar/39Ar age constraints for the K-Pg Chicxulub event, and the previous U-Pb dating of the basement rocks from the impact site, make Chicxulub an ideal location to study impact-induced effects on the zircon U-Pb systematics and to evaluate potential 'memory effects' of pre-impact U-Pb signatures preserved within those individual zircon crystals. Recent IODP-ICDP drilling of the Chicxulub impact structure recovered 580 m of uplifted shocked granitoid and 130 m of melt and suevite, providing an unprecedented opportunity to study zircon crystals subjected to a range of shock pressures, thermal, and deformational histories. Zircon morphologies were classified using scanning electron microscopy (SEM) imaging and then samples were depth profiled using laser ablation inductively coupled plasma mass-spectrometry (LA-ICP-MS) to document the range of preserved age domains from rim-to-center within individual crystals. The results show U-Pb ages range from 66 to 472 Ma, which are consistent with both inherited Carboniferous and Late Paleozoic basement ages as well as Pb loss ages in response to the K-Pg impact event. While the bulk of the zircon grains preserve Paleozoic ages, high U (metamict) zones within fractured zircon crystals exhibited an age within uncertainty (66 ± 6.2 Ma) of the impact age (66.038 ± 0.049 Ma), indicating that inherited intragrain U-Pb kinetics and/or hydrothermal fluid flow may have controlled age resetting those zircon crystals rather than impact-induced shock and heating alone. Moreover, the calculated α-decay doses suggest that the zircon crystals experienced Stage 1 or early Stage 2 radiation damage accumulation. Therefore, we suggest that the lowered crystal annealing temperature in crystals that previoulsy experienced radiation damage make the zircon U-Pb clock either more susceptible to the relatively short heat pulse of the impact event, the moderate pressure and temperature conditions in the peak ring, and/or to hot-fluid flow in the long-lasting post impact hydrothermal system

The CD34-Related Molecule Podocalyxin Is a Potent Inducer of Microvillus Formation

BACKGROUND: Podocalyxin is a CD34-related transmembrane protein involved in hematopoietic cell homing, kidney morphogenesis, breast cancer progression, and epithelial cell polarization. Although this sialomucin has been shown to block cell adhesion, the mechanisms involved remain enigmatic. It has, however, been postulated that the adaptor proteins NHERF-1 and 2 could regulate apical targeting of Podocalyxin by linking it to the actin cytoskeleton. PRINCIPAL FINDINGS: Here, in contrast, we find that full-length Podocalyxin acts to recruit NHERF-1 to the apical domain. Moreover, we show that ectopic expression of Podocalyxin in epithelial cells leads to microvillus formation along an expanded apical domain that extends laterally to the junctional complexes. Removal of the C-terminal PDZ-binding domain of Podocalyxin abolishes NHERF-1 recruitment but, surprisingly, has no effect on the formation of microvilli. Instead, we find that the extracellular domain and transmembrane region of Podocalyxin are sufficient to direct recruitment of filamentous actin and ezrin to the plasma membrane and induce microvillus formation. CONCLUSIONS/SIGNIFICANCE: Our data suggest that this single molecule can modulate NHERF localization and, independently, act as a key orchestrator of apical cell morphology, thereby lending mechanistic insights into its multiple roles as a polarity regulator, tumor progression marker, and anti-adhesin

Keratan sulphate in the tumour environment

Keratan sulphate (KS) is a bioactive glycosaminoglycan (GAG) of some complexity composed of the repeat disaccharide D-galactose β1→4 glycosidically linked to N-acetyl glucosamine. During the biosynthesis of KS, a family of glycosyltransferase and sulphotransferase enzymes act sequentially and in a coordinated fashion to add D-galactose (D-Gal) then N-acetyl glucosamine (GlcNAc) to a GlcNAc acceptor residue at the reducing terminus of a nascent KS chain to effect chain elongation. D-Gal and GlcNAc can both undergo sulphation at C6 but this occurs more frequently on GlcNAc than D-Gal. Sulphation along the developing KS chain is not uniform and contains regions of variable length where no sulphation occurs, regions which are monosulphated mainly on GlcNAc and further regions of high sulphation where both of the repeat disaccharides are sulphated. Each of these respective regions in the KS chain can be of variable length leading to KS complexity in terms of chain length and charge localization along the KS chain. Like other GAGs, it is these variably sulphated regions in KS which define its interactive properties with ligands such as growth factors, morphogens and cytokines and which determine the functional properties of tissues containing KS. Further adding to KS complexity is the identification of three different linkage structures in KS to asparagine (N-linked) or to threonine or serine residues (O-linked) in proteoglycan core proteins which has allowed the categorization of KS into three types, namely KS-I (corneal KS, N-linked), KS-II (skeletal KS, O-linked) or KS-III (brain KS, O-linked). KS-I to -III are also subject to variable addition of L-fucose and sialic acid groups. Furthermore, the GlcNAc residues of some members of the mucin-like glycoprotein family can also act as acceptor molecules for the addition of D-Gal and GlcNAc residues which can also be sulphated leading to small low sulphation glycoforms of KS. These differ from the more heavily sulphated KS chains found on proteoglycans. Like other GAGs, KS has evolved molecular recognition and information transfer properties over hundreds of millions of years of vertebrate and invertebrate evolution which equips them with cell mediatory properties in normal cellular processes and in aberrant pathological situations such as in tumourogenesis. Two KS-proteoglycans in particular, podocalyxin and lumican, are cell membrane, intracellular or stromal tissue–associated components with roles in the promotion or regulation of tumour development, mucin-like KS glycoproteins may also contribute to tumourogenesis. A greater understanding of the biology of KS may allow better methodology to be developed to more effectively combat tumourogenic processes

Magnetic Clouds seen at different locations in the Heliosphere

We analyze two magnetic clouds (MCs) observed in different points of the heliosphere. The main aim of the present study is to provide a link between the different aspects of this phenomenon, starting with information on the origins of the MCs at the Sun and following by the analysis of in-situ observations at 1 AU and at Ulysses. The candidate source regions were identified in SOHO/EIT and SOHO/MDI observations. They were correlated with H-± images that were obtained from ground-based observatories. Hints on the internal magnetic field configuration of the associated coronal mass ejections are obtained from LASCO C2 images. In interplanetary space, magnetic and plasma moments of the distribution function of plasma species (ACE/Ulysses) were analyzed together with information on the plasma composition, and the results were compared between both spacecraft in order to understand how these structures interact and evolve in their cruise from the Sun to 5 AU. Additionally, estimates of global magnitudes of magnetic fluxes and helicity were obtained from magnetic field models applied to the data in interplanetary space. We have found that these magnetic characteristics were well kept from their solar source, up to 5 AU where Ulysses provided valuable information which, together with that obtained from ACE, can help to reinforce the correct matching of solar events and their interplanetary counterparts.status: publishe