Limpet Shells from the Aterian Level 8 of El Harhoura 2 Cave (Témara, Morocco): Preservation State of Crossed-Foliated Layers

International audienceThe exploitation of mollusks by the first anatomically modern humans is a central question for archaeologists. This paper focuses on level 8 (dated around * 100 ka BP) of El Har-houra 2 Cave, located along the coastline in the Rabat-Témara region (Morocco). The large quantity of Patella sp. shells found in this level highlights questions regarding their origin and preservation. This study presents an estimation of the preservation status of these shells. We focus here on the diagenetic evolution of both the microstructural patterns and organic components of crossed-foliated shell layers, in order to assess the viability of further investigations based on shell layer minor elements, isotopic or biochemical compositions. The results show that the shells seem to be well conserved, with microstructural patterns preserved down to sub-micrometric scales, and that some organic components are still present in situ. But faint taphonomic degradations affecting both mineral and organic components are nonetheless evidenced, such as the disappearance of organic envelopes surrounding crossed-foliated lamellae, combined with a partial recrystallization of the lamellae. Our results provide a solid case-study of the early stages of the diagenetic evolution of crossed-foliated shell layers. Moreover, they highlight the fact that extreme caution must be taken before using fossil shells for palaeoenvironmental or geochronological reconstructions. Without thorough investigation, the alteration patterns illustrated here would easily have gone unnoticed. However, these degradations are liable to bias any proxy based on the elemental, isotopic or biochemical composition of the shells. This study also provides significant data concerning human subsistence behavior: the presence of notches and the good preservation state of limpet shells (no dissolution/recrystallization, no bioerosion and no abrasion/fragmentation aspects) would attest that limpets were gathered alive with tools by Middle Palaeolithic (Aterian) populations in North Africa for consumption

Pseudomorphic transformation of Ca/Mg carbonates into phosphates with focus on dolomite conversion

Hydrothermal conversion of single crystals of calcite, CaCO3, dolomite, CaMg(CO3)2, and magnesite, MgCO3, was carried out in ammonium phosphate buffer solution. While calcite easily forms a pseudomorph of hydroxylapatite, Ca5(PO4)3OH, it takes several weeks to convert magnesite into pseudomorphic dittmarite, (NH4)Mg(PO4)·H2O. The conversion of dolomite, as the compositional intermediate, also proceeded slowly, but yielded a biphasic pseudomorph composed of whitlockite, Ca9Mg(PO4)6(PO3OH), and dittmarite. To our knowledge, this is the first description of a biphasic pseudomorph with chemically and structurally different phases. Near the surface, the two phases formed a porous layered structure, while towards the core of the single crystal a fine-grained mixture of both minerals precipitated. The initially sequential pattern of precipitation of Ca-rich whitlockite followed by Mg-rich dittmarite can be explained by dissolved Mg ions being adsorbed onto the dolomite surface or incorporated into hydrated magnesium complexes, retarding crystallization of dittmarite. Surface adsorbed Mg ions impeding further dissolution of dolomite also partly accounts for the observed lower reaction rates of dolomite and magnesite, as compared to calcite. An additional factor decreasing the reaction rates of dolomite and magnesite is a considerable increase in molar volume upon conversion, which restricts the formation of porosity and, hence, ion transport to the reaction front

Temperature dependent properties of silicon containing diamondlike carbon films prepared by plasma source ion implantation

Silicon containing diamondlike carbon (Si-DLC) films were prepared on silicon wafer substrates by a plasma source ion implantation method with negative pulses superposed on a negative dc voltage. A mixture of acetylene and tetramethylsilane gas was introduced into the discharge chamber as working gases for plasma formation. Ions produced in the plasma are accelerated toward a substrate holder because of the negative voltage applied directly to it. After deposition, the films were annealed for 0.5 h in ambient air at temperatures up to 923 K in order to evaluate the thermal stability of the Si-DLC films. The films were analyzed by x-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy, and Raman spectroscopy. The surface morphology of the films and the film thickness were observed by atomic force microscopy and scanning electron microscopy. The mechanical and tribological properties were investigated by an indentation method and a ball-on-disk test. The results show the silicon containing DLC films were amorphous and the surface roughness of the Si containing DLC films was very smooth and no special structure was observed. Integrated intensity ratios ID/IG of Raman spectroscopy of the Si containing DLC films decreased with Si content. The Raman spectra showed that the structure of the Si-free DLC film changed to a graphitelike structure with increasing annealing temperature, whereas that of the 24 at. % Si containing DLC films did not change at the maximum temperature used in this study. A very low friction coefficient was obtained for the 13 at. % Si containing DLC film. The surface roughness and the hardness of the films changed with increasing annealing temperature. The formation of Si oxide in a near surface layer was confirmed by XPS and it prevents further oxidation of the inside of the film. Heat resistivity of DLC films can be improved by Si addition into the DLC films

M.(phi)BssHII, a novel cytosine-C5-DNA-methyltransferase with target-recognizing domains at separated locations of the enzyme.

In all cytosine-C5-DNA-methyltransferases (MTases) from prokaryotes and eukaryotes, remarkably conserved amino acid sequence elements responsible for general enzymatic functions are arranged in the same canonical order. In addition, one variable region, which includes the target-recognizing domain(s) (TRDs) characteristic for each enzyme, has been localized in one region between the same blocks of these conserved elements. This conservation in the order of conserved and variable sequences suggests stringent structural constraints in the primary structure to obtain the correct folding of the enzymes. Here we report the characterization of a new type of a multispecific MTase, M.(phiphi)BssHII, which is expressed as two isoforms. Isoform I is an entirely novel type of MTase which has, in addition to the TRDs at the conventional location, one TRD located at a non-canonical position at its N-terminus. Isoform II is represented by the same MTase, but without the N-terminal TRD. The N-terminal TRD provides HaeII methylation specificity to isoform I. The TRD is fully functional when engineered into either the conventional variable region of M.(phiphi)BssHII or the related monospecific M.phi3TII MTase. The implications of this structural plasticity with respect to the evolution of MTases are discussed

Reduction in left ventricular messenger RNA for transforming growth factor beta(1) attenuates left ventricular fibrosis and improves survival without lowering blood pressure in the hypertensive TGR(mRen2)27 rat

Angiotensin TI recruits transforming growth factor beta (1) (TGF beta (1)) and is related to left ventricular fibrosis, However, it is unclear whether chronic in vivo reduction in left ventricular TGF beta (1), expression blunts fibrosis and improves outcome in angiotensin II-dependent hypertension. Four week-old male hypertensive TGR(mRen2)27 (Ren2) rats received either normal food, low-dose losartan (0.5 mg.kg(-1).d(-1)), or tranilast (a nonspecific TGF beta inhibitor; 400 mg.kg(-1).d(-1)) (n = 10 For each group) for 12 weeks and were compared with Sprague-Dawley control rats. The effect of tranilast on survival was evaluated in 34 additional untreated homozygous Ren2 rats. Tranilast or low-dose losartan did not lower blood pressure. However, the increase in left ventricular weight (Ren2 versus SD 3.1 +/- 0.16 versus 2.1 +/- 0.06 mg/g body wt; P <0,05) was significantly (P <0,05) blunted by both tranilast (2.7 +/- 0.05) and losartan (2,7 +/- 0.07), Both drugs prevented the increase in left ventricular TGF beta (1), mRNA and fibronectin mRNA and blunted the increase in hydroxyproline content and the increase in perivascular fibrosis, The perivascular fibrosis score correlated significantly with the level of expression of TGF beta (1), (r = 0.62; P = 0,019), In situ hybridization demonstrated increases in TGF beta (1), mRNA, predominantly in perivascular and nonmyocyte areas. Both drugs did not prevent the decrease in systolic or diastolic dP/dt, but tranilast significantly improved the survival of untreated Ren2 rats (P = 0,029). In conclusion, TGF beta (1), mRNA expression is increased predominantly in nonmyocyte regions in the hypertrophied left ventricle in this angiotensin II-dependent model of hypertension. This increase is probably due to high angiotensin II levels rather than to hypertension. This is the first study to suggest that chronic inhibition of TGF beta (1), expression attenuates left ventricular hypertrophy and fibrosis, even without lowering blood pressure

Transformation mechanism of amorphous calcium carbonate into calcite in the sea urchin larval spicule

Sea urchin larval spicules transform amorphous calcium carbonate (ACC) into calcite single crystals. The mechanism of transformation is enigmatic: the transforming spicule displays both amorphous and crystalline properties, with no defined crystallization front. Here, we use X-ray photoelectron emission spectromicroscopy with probing size of 40–200 nm. We resolve 3 distinct mineral phases: An initial short-lived, presumably hydrated ACC phase, followed by an intermediate transient form of ACC, and finally the biogenic crystalline calcite phase. The amorphous and crystalline phases are juxtaposed, often appearing in adjacent sites at a scale of tens of nanometers. We propose that the amorphous-crystal transformation propagates in a tortuous path through preexisting 40- to 100-nm amorphous units, via a secondary nucleation mechanism