End Of D2 Research Articles

Myonuclei Can Replicate DNA

Skeletal muscle is a heterogenous tissue composed of multinucleated muscle fibers and accompanying supporting cells like satellite cells (SCs). Myonuclei are believed to be post‐mitotic, arrested in G0 phase of the cell cycle and thus unable to proliferate. Consequently, it is hypothesized that growth of muscle is dependent on the donation of nuclei from SCs. Although some studies suggest that under certain conditions myonuclei can replicate, it has been difficult to address whether this replicative potential exists in vivo. We hypothesized that skeletal muscle resident myonuclei possess the ability to replicate in vivo. To test this hypothesis, we used the HSArtTA;Tet‐O‐H2B‐GFP (HSA‐H2B) mouse model, which uses doxycycline (DOX) treatment for temporal labeling (Tet‐ON) of residential myonuclei. After removing DOX, and thus turning off GFP‐labeling, we provided the stable isotope deuterium oxide (D2O) for 8 weeks to measure DNA synthesis. At the end of D2O labeling, muscles were harvested and GFP‐positive myonuclei were sorted using an antibody‐independent approach and a restrictive gating strategy. Both GFP+ (myonuclei) and GFP‐ (non‐myonuclei) fractions were then analyzed for D2O incorporation into DNA by GC‐QQQ. By our approach, DNA from GFP‐positive myonuclei was deuterium‐enriched and therefore deemed to be replicating. DNA replication occurred in at least one muscle of the 7 mice studied. We observed deuterium enrichment into DNA in 6 out of 7 plantaris (PLA), 4 out of 7 extensor digitorum longus (EDL), 4 out of 7 tibialis anterior (TA), 6 out of 7 gastrocnemius (GAS) and 7 out of 7 quadriceps (QUAD). The average fractional synthesis rates (FSR, %/day) of replicating myonuclei were: 0.0351 ± 0.017 in PLA, 0.0156 ± 0.015 in EDL, 0.0220 ± 0.018 in TA, 0.0223 ± 0.018 in GAS, and 0.02692 ± 0.043 in QUAD. These data are the first to unambiguously demonstrate that myonuclei replicate DNA in vivo. The proposed project challenges current dogma and might significantly impact skeletal muscle treatment to maintain muscle mass with age and disease.

No carbon “bet hedging” in pine seedlings under prolonged summer drought and elevated CO2

Abstract More frequent drought episodes are expected to cause higher mortality in isohydric tree species such as pines, because individuals close their stomata early during drought in order to maintain constant needle water potentials. It has been suggested that trees delay the ensuing carbon starvation by actively storing carbon at the expense of growth (“bet hedging”). Because such a strategy is only adaptive in drought‐prone regions, we hypothesise that the degree of carbon “bet hedging” should differ between ecotypes. We repeatedly measured the allocation of biomass, starch and soluble sugars to needles, stem and roots in seedlings of nine populations of Pinus sylvestris and Pinus nigra along a gradient from Central Europe to the Mediterranean. During two consecutive growing seasons, seedlings grown from seed were exposed to factorial combinations of 4 months of drought (D1, D2) and ambient/elevated CO2 (aCO2/eCO2). Drought‐stressed pine seedlings did neither increase starch concentrations, nor change biomass production or experience lower mortality under eCO2 compared to aCO2. By the end of D2, seedlings from drier origin had accumulated more starch but at the same time also more biomass than seedlings from wetter origin. Surprisingly, seedlings acclimatised to dry conditions after D1 so that mortality dropped to zero and drought effects on needle starch (P. sylvestris) and overall starch (P. nigra), respectively, disappeared after D2. Synthesis. The absence of a trade‐off between carbon storage (starch) and growth (biomass), and the patterns of mortality observed in seedlings growing under combined drought and eCO2 do not support the theory of carbon “bet hedging” in isohydric Pinus sylvestris and Pinus nigra. Results suggest that reduced growth and acclimatisation minimised seedling mortality in the second year. Acclimatisation might thus enable pine seedlings to resist a moderate increase in summer drought frequency expected in the future.

Dating brittle tectonic movements with cleft monazite: Fluid‐rock interaction and formation of REE minerals

AbstractTwo millimeter‐sized hydrothermal monazites from an open fissure (cleft) that developed late during a dextral transpressional deformation event in the Aar Massif, Switzerland, have been investigated using electron microprobe and ion probe. The monazites are characterized by high Th/U ratios typical of other hydrothermal monazites. Deformation events in the area have been subdivided into three phases: (D1) main thrusting including formation of a new schistosity, (D2) dextral transpression, and (D3) local crenulation including development of a new schistosity. The two younger deformational structures are related to a subvertically oriented intermediate stress axis, which is characteristic for strike slip deformation. The inferred stress environment is consistent with observed kinematics and the opening of such clefts. Therefore, the investigated monazite‐bearing cleft formed at the end of D2 and/or D3, and during dextral movements along NNW dipping planes. Interaction of cleft‐filling hydrothermal fluid with wall rock results in rare earth element (REE) mineral formation and alteration of the wall rock. The main newly formed REE minerals are Y‐Si, Y‐Nb‐Ti minerals, and monazite. Despite these mineralogical changes, the bulk chemistry of the system remains constant and thus these mineralogical changes require redistribution of elements via a fluid over short distances (centimeter). Low‐grade alteration enables local redistribution of REE, related to the stability of the accessory phases. This allows high precision isotope dating of cleft monazite. 232Th/208Pb ages are not affected by excess Pb and yield growth domain ages between 8.03 ± 0.22 and 6.25 ± 0.60 Ma. Monazite crystallization in brittle structures is coeval or younger than 8 Ma zircon fission track data and hence occurred below 280°C.

Features and controlling factors of epigenic karstification of the Ordovician carbonates in Akekule arch, Tarim Basin

Tabei (塔北) uplift is an area with the highest hydrocarbon enrichment in Tarim basin, and large oilfields have been found on Akekule (阿克库勒) arch at the middle section of Tabei uplift, with Ordovician carbonate reservoirs. Storage space of the Ordovician carbonate reservoirs in the Akekule arch are mainly caves, pores and fractures resulted from dissolution and/or karstification. The Ordovician carbonate reservoirs are affected and modified by the diagenetic process in penecontemporaneous, epigenetic and burial periods and the multi-stage karstification related with deep hydrothermal activities, among which the most significant effect is from the meteoric water karstification related to the tectonic uplift from the end of Middle Ordovician to the end of Late Ordovician (end of O2-end of O3) and at the end of Middle Devonian (end of D2). Varied palaeogeologic settings and tectonic features at different geologic periods lead to different fluid flowing patterns, karstification mechanisms and transformation features in different regions, which further influence the reservoir distribution. The paleo-uplifts at different periods, such as end of O2-end of O3 and end of D2, control the dominant development zones of karstification; the paleogeomorphology and faults resulted from tectonic uplift control the flowing depth of the karst fluid; and the lithology controls the position and extent of karst development.

Mutational Analysis Demonstrates That ClC-4 and ClC-5 Directly Mediate Plasma Membrane Currents

ClC-4 and ClC-5, together with ClC-3, form a distinct branch of the CLC chloride channel family. Although ClC-5 was shown to be mainly expressed in endocytotic vesicles, expression of ClC-5 in Xenopus oocytes elicited chloride currents. We now show that ClC-4 also gives rise to strongly outwardly rectifying anion currents when expressed in oocytes. They closely resemble ClC-5 currents with which they share a NO3- > Cl- > Br- > I- conductance sequence that differs from that reported for the highly homologous ClC-3. Both ClC-4 and ClC-5 currents are reduced by lowering extracellular pH. We could measure similar currents after expressing either channel in HEK293 cells. To demonstrate that these currents are directly mediated by the channel proteins, we introduced several point mutations that change channel characteristics. In ClC-5, several point mutations alter the kinetics of activation but leave macroscopic rectification and ion selectivity unchanged. A mutation (N565K) equivalent to a mutation reported to have profound effects on ClC-3 does not have similar effects on ClC-5. Moreover, a mutation at the end of D2 (S168T in ClC-5) changes ion selectivity, and a mutation at the end of D3 (E211A in ClC-5 and E224A in ClC-4) changes voltage dependence and ion selectivity. This shows that ClC-4 and ClC-5 can directly mediate plasma membrane currents.

Metamorphic and metasomatic evolution of the Snake Creek Anticline, Eastern Succession, Mt Isa Inlier

The Snake Creek Anticline is a regional D2 structure, with the overturning of the western limb and the curvature of the axial trace from north to east interpreted as an effect of D3, which produced folds and crenulations with shallowly dipping axial surfaces. Low‐pressure/high‐temperature metamorphism which affected the Mesoproterozoic Soldiers Cap Group reached its peak with the growth of sillimanite during intense foliation development during D2. However, microstructural studies have revealed multiple porphyroblast growth stages, namely: (i) pre‐ to early D1, (ii) late D1 to early D2, (iii) late to post‐D2, (iv) syn‐D3 and (v) syn‐D4. The kyanite/andalusite, sillimanite, and sillimanite/K‐feldspar isograds are D2‐related, whereas the garnet and andalusite/staurolite are composite isograds representing multiple growth events. To explain the occurrence of kyanite partially replaced by andalusite, and the replacement of early growth andalusite by staurolite + muscovite, it is suggested that the pressure‐temperature‐deformation path included a fall in temperature after D1, followed by a rise in both temperature and pressure by the end of D2. Quartz veining occurs throughout the evolution of the rocks, but the most notable events are: (i) an early (pre‐/syn‐D2) phase of albitite veining, (ii) syn‐D2 quartz (+ staurolite + andalusite + kyanite) veining, and (iii) late (syn‐/post‐D5) albitite veining. Preliminary fluid‐inclusion studies show that hypersaline fluids were dominant during at least some of this history. The Snake Creek Anticline and the Cloncurry Fault provided structural controls for the infiltration of the metasomatic fluids. Inferred to be initially of igneous origin. The fluids may have been important in the transfer of heat during D2.

Metamorphic P‐T paths from calcic pelitic schists from the Strafford Dome, Vermont, USA

ABSTRACTMetamorphism of the Gile Mountain Formation and Waits River Formation in the Strafford Dome and Townshend‐Brownington Syncline in east‐central Vermont records two nappe‐style events, D1 and D2, followed by doming. D1 formed a muscovite + biotite ± ilmenite schistosity subparallel to compositional layering, SO, and was followed by heating to garnet grade. The temperature and pressure at the end of D1 are estimated to be c. 450d̀ C and 6‐8 kbar. D2 variably crenulated and folded S1 during a nearly isothermal pressure increase of 1‐2 kbar, calculated from compositions of garnet, which have inclusions trails with progressive crenulation and rotation of the S1 fabric. Similar P‐T paths are computed for most of the area, suggesting that the later schistosity developed during emplacement of a regional nappe 3‐6 km thick. There is a general lack of D3 (dome‐stage) microstructures.Near the Strafford‐Willoughby Arch, staurolite and kyanite overgrew S2 in pelites, and plagioclase with increasing XAn overgrew S2 in calcic pelites, reflecting post‐D2 heating to a maximum of 550‐600d̀ C. Metamorphic pressures at the end of D2 are fairly constant on the west side of the dome, indicating minor dome‐stage uplift. In contrast, pressures at the thermal peak of metamorphism decrease by more than 4 kbar east of the dome. The observed pattern of isotherms and isobars is mainly the result of post‐metamorphic, differential uplift and unroofing.Finally, a minor, retrograde metamorphism produced the assemblage albite + epidote + K‐feldspar + muscovite + chlorite, with grade increasing east toward the Connecticut River.

Expression, characterization, and crystallization of oxygen-avid Ascaris hemoglobin domains.

The Ascaris perienteric hemoglobin is 10(4) times more oxygen-avid than mammalian hemoglobins. Inspection of its primary structure fails to explain this extraordinary association with oxygen. The Ascaris hemoglobin gene encodes a 40-kDa, two-domain globin; the two domains (D1 and D2) are 63% identical, and each is capable of binding a single heme. The native protein is an octamer. At the end of D2 is a highly charged carboxyl-terminal extension containing four direct repeats of HKEE. We have expressed the two domains separately in E. coli. Both individual domains are extremely oxygen-avid. D2, with attached COOH-terminal tail, is capable of multimerization, whereas D1 remains a monomer. Recombinant D1 readily forms diffractable, red, prismatic crystals. We conclude that: 1) the basis of the hemoglobin's oxygen avidity rests in an isolated heme pocket and does not involve inter-domain interactions and 2) multimerization is mediated through sequences in the second domain, most probably via the charged COOH-terminal tail.