[Differential expressions of seminal plasma piRNAs in men and its significance].

OBJECTIVE: To study the differential expressions of piRNAs in the seminal plasma of men and the role of piRNAs in spermatogenesis. METHODS: We sequenced the seminal plasma samples collected from 187 male infertility patients and 58 normal healthy men, obtained differentially expressed piRNAs, and detected the relative expressions of piRNAs in different types of sperm by RT-qPCR to explore their significance in the diagnosis of male infertility. Using histopathology, RNA-protein pull-down and Western blot, we investigated the action mechanism of piRNAs in spermatogenesis in the mouse model. RESULTS: RT-qPCR of the seminal plasma samples revealed a high expression of hsa_piR_000478 in teratozoospermia and ROC curve analysis showed an auxiliary significance of hsa_piR_000478 in the diagnosis of the disease (AUC = 0.7549). Transfection of hsa_piR_000478 and its homologous sequence piR_mmu_54800729 into the seminiferous tubules of the mouse model significantly decreased sperm motility, increased the percentage of morphologically abnormal sperm and destroyed the testicular structure. Molecular biological experiments exhibited a close correlation between piRNAs and the energy metabolism-related pathway, which elevated the level of cell glycolysis and interfered with normal spermatogenesis. CONCLUSION: hsa_piR_000478 has an auxiliary significance in the diagnosis of male infertility, and piRNAs may interfere with spermatogenesis by affecting the glycolysis-related pathway in the spermatogenic microenvironment of the testis.

Low dinosaur biodiversity in central China 2 million years prior to the end-Cretaceous mass extinction.

Whether or not nonavian dinosaur biodiversity declined prior to the end-Cretaceous mass extinction remains controversial as the result of sampling biases in the fossil record, differences in the analytical approaches used, and the rarity of high-precision geochronological dating of dinosaur fossils. Using magnetostratigraphy, cyclostratigraphy, and biostratigraphy, we establish a high-resolution geochronological framework for the fossil-rich Late Cretaceous sedimentary sequence in the Shanyang Basin of central China. We have found only three dinosaurian eggshell taxa (Macroolithus yaotunensis, Elongatoolithus elongatus, and Stromatoolithus pinglingensis) representing two clades (Oviraptoridae and Hadrosauridae) in sediments deposited between ∼68.2 and ∼66.4 million y ago, indicating sustained low dinosaur biodiversity, and that assessment is consistent with the known skeletal remains in the Shanyang and surrounding basins of central China. Along with the dinosaur eggshell records from eastern and southern China, we find a decline in dinosaur biodiversity from the Campanian to the Maastrichtian. Our results support a long-term decline in global dinosaur biodiversity prior to 66 million y ago, which likely set the stage for the end-Cretaceous nonavian dinosaur mass extinction.

The end of the lunar dynamo.

Magnetic measurements of the lunar crust and Apollo samples indicate that the Moon generated a dynamo magnetic field lasting from at least 4.2 until <2.5 billion years (Ga) ago. However, it has been unclear when the dynamo ceased. Here, we report paleomagnetic and 40Ar/39Ar studies showing that two lunar breccias cooled in a near-zero magnetic field (<0.1 µT) at 0.44 ± 0.01 and 0.91 ± 0.11 Ga ago, respectively. Combined with previous paleointensity estimates, this indicates that the lunar dynamo likely ceased sometime between ~1.92 and ~0.80 Ga ago. The protracted lifetime of the lunar magnetic field indicates that the late dynamo was likely powered by crystallization of the lunar core.

A two-billion-year history for the lunar dynamo.

Magnetic studies of lunar rocks indicate that the Moon generated a core dynamo with surface field intensities of ~20 to 110 µT between at least 4.25 and 3.56 billion years ago (Ga). The field subsequently declined to <~4 µT by 3.19 Ga, but it has been unclear whether the dynamo had terminated by this time or just greatly weakened in intensity. We present analyses that demonstrate that the melt glass matrix of a young regolith breccia was magnetized in a ~5 ± 2 µT dynamo field at ~1 to ~2.5 Ga. These data extend the known lifetime of the lunar dynamo by at least 1 billion years. Such a protracted history requires an extraordinarily long-lived power source like core crystallization or precession. No single dynamo mechanism proposed thus far can explain the strong fields inferred for the period before 3.56 Ga while also allowing the dynamo to persist in such a weakened state beyond ~2.5 Ga. Therefore, our results suggest that the dynamo was powered by at least two distinct mechanisms operating during early and late lunar history.

Lifetime of the solar nebula constrained by meteorite paleomagnetism.

A key stage in planet formation is the evolution of a gaseous and magnetized solar nebula. However, the lifetime of the nebular magnetic field and nebula are poorly constrained. We present paleomagnetic analyses of volcanic angrites demonstrating that they formed in a near-zero magnetic field (<0.6 microtesla) at 4563.5 ± 0.1 million years ago, ~3.8 million years after solar system formation. This indicates that the solar nebula field, and likely the nebular gas, had dispersed by this time. This sets the time scale for formation of the gas giants and planet migration. Furthermore, it supports formation of chondrules after 4563.5 million years ago by non-nebular processes like planetesimal collisions. The core dynamo on the angrite parent body did not initiate until about 4 to 11 million years after solar system formation.

Weaker axially dipolar time-averaged paleomagnetic field based on multidomain-corrected paleointensities from Galapagos lavas.

The geomagnetic field is predominantly dipolar today, and high-fidelity paleomagnetic mean directions from all over the globe strongly support the geocentric axial dipole (GAD) hypothesis for the past few million years. However, the bulk of paleointensity data fails to coincide with the axial dipole prediction of a factor-of-2 equator-to-pole increase in mean field strength, leaving the core dynamo process an enigma. Here, we obtain a multidomain-corrected Pliocene-Pleistocene average paleointensity of 21.6 ± 11.0 µT recorded by 27 lava flows from the Galapagos Archipelago near the Equator. Our new result in conjunction with a published comprehensive study of single-domain-behaved paleointensities from Antarctica (33.4 ± 13.9 µT) that also correspond to GAD directions suggests that the overall average paleomagnetic field over the past few million years has indeed been dominantly dipolar in intensity yet only ∼ 60% of the present-day field strength, with a long-term average virtual axial dipole magnetic moment of the Earth of only 4.9 ± 2.4 × 10(22) A ⋅ m(2).

Quantified abundance of magnetofossils at the Paleocene-Eocene boundary from synchrotron-based transmission X-ray microscopy.

The Paleocene-Eocene boundary (∼55.8 million years ago) is marked by an abrupt negative carbon isotope excursion (CIE) that coincides with an oxygen isotope decrease interpreted as the Paleocene-Eocene thermal maximum. Biogenic magnetite (Fe3O4) in the form of giant (micron-sized) spearhead-like and spindle-like magnetofossils, as well as nano-sized magnetotactic bacteria magnetosome chains, have been reported in clay-rich sediments in the New Jersey Atlantic Coastal Plain and were thought to account for the distinctive single-domain magnetic properties of these sediments. Uncalibrated strong field magnet extraction techniques have been typically used to provide material for scanning and transmission electron microscopic imaging of these magnetic particles, whose concentration in the natural sediment is thus difficult to quantify. In this study, we use a recently developed ultrahigh-resolution, synchrotron-based, full-field transmission X-ray microscope to study the iron-rich minerals within the clay sediment in their bulk state. We are able to estimate the total magnetization concentration of the giant biogenic magnetofossils to be only ∼10% of whole sediment. Along with previous rock magnetic studies on the CIE clay, we suggest that most of the magnetite in the clay occurs as isolated, near-equidimensional nanoparticles, a suggestion that points to a nonbiogenic origin, such as comet impact plume condensates in what may be very rapidly deposited CIE clays.

Paleomagnetism. Solar nebula magnetic fields recorded in the Semarkona meteorite.

Magnetic fields are proposed to have played a critical role in some of the most enigmatic processes of planetary formation by mediating the rapid accretion of disk material onto the central star and the formation of the first solids. However, there have been no experimental constraints on the intensity of these fields. Here we show that dusty olivine-bearing chondrules from the Semarkona meteorite were magnetized in a nebular field of 54 ± 21 microteslas. This intensity supports chondrule formation by nebular shocks or planetesimal collisions rather than by electric currents, the x-wind, or other mechanisms near the Sun. This implies that background magnetic fields in the terrestrial planet-forming region were likely 5 to 54 microteslas, which is sufficient to account for measured rates of mass and angular momentum transport in protoplanetary disks.

Evidence for abundant isolated magnetic nanoparticles at the Paleocene-Eocene boundary.

New rock magnetic results (thermal fluctuation tomography, high-resolution first-order reversal curves and low temperature measurements) for samples from the Paleocene-Eocene thermal maximum and carbon isotope excursion in cored sections at Ancora and Wilson Lake on the Atlantic Coastal Plain of New Jersey indicate the presence of predominantly isolated, near-equidimensional single-domain magnetic particles rather than the chain patterns observed in a cultured magnetotactic bacteria sample or magnetofossils in extracts. The various published results can be reconciled with the recognition that chain magnetosomes tend to be preferentially extracted in the magnetic separation process but, as we show, may represent only a small fraction of the overall magnetic assemblage that accounts for the greatly enhanced magnetization of the carbon isotope excursion sediment but whose origin is thus unclear.