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  • Proceedings of the National Academy of Sciences  (181)
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  • Proceedings of the National Academy of Sciences  (181)
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  • 1
    Online Resource
    Online Resource
    Evidence for indigenous nitrogen in sedimentary and aeolian deposits from the Curiosity rover investigations at Gale crater, Mars
    Proceedings of the National Academy of Sciences ; 2015
    In:  Proceedings of the National Academy of Sciences Vol. 112, No. 14 ( 2015-04-07), p. 4245-4250
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 112, No. 14 ( 2015-04-07), p. 4245-4250
    Abstract: The Sample Analysis at Mars (SAM) investigation on the Mars Science Laboratory (MSL) Curiosity rover has detected oxidized nitrogen-bearing compounds during pyrolysis of scooped aeolian sediments and drilled sedimentary deposits within Gale crater. Total N concentrations ranged from 20 to 250 nmol N per sample. After subtraction of known N sources in SAM, our results support the equivalent of 110–300 ppm of nitrate in the Rocknest (RN) aeolian samples, and 70–260 and 330–1,100 ppm nitrate in John Klein (JK) and Cumberland (CB) mudstone deposits, respectively. Discovery of indigenous martian nitrogen in Mars surface materials has important implications for habitability and, specifically, for the potential evolution of a nitrogen cycle at some point in martian history. The detection of nitrate in both wind-drifted fines (RN) and in mudstone (JK, CB) is likely a result of N 2 fixation to nitrate generated by thermal shock from impact or volcanic plume lightning on ancient Mars. Fixed nitrogen could have facilitated the development of a primitive nitrogen cycle on the surface of ancient Mars, potentially providing a biochemically accessible source of nitrogen.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1420932112
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2015
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  • 2
    Online Resource
    Online Resource
    TMEM161B regulates cerebral cortical gyration, Sonic Hedgehog signaling, and ciliary structure in the developing central nervous system
    Proceedings of the National Academy of Sciences ; 2023
    In:  Proceedings of the National Academy of Sciences Vol. 120, No. 4 ( 2023-01-24)
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 120, No. 4 ( 2023-01-24)
    Abstract: Sonic hedgehog signaling regulates processes of embryonic development across multiple tissues, yet factors regulating context-specific Shh signaling remain poorly understood. Exome sequencing of families with polymicrogyria (disordered cortical folding) revealed multiple individuals with biallelic deleterious variants in TMEM161B , which encodes a multi-pass transmembrane protein of unknown function. Tmem161b null mice demonstrated holoprosencephaly, craniofacial midline defects, eye defects, and spinal cord patterning changes consistent with impaired Shh signaling, but were without limb defects, suggesting a CNS-specific role of Tmem161b. Tmem161b depletion impaired the response to Smoothened activation in vitro and disrupted cortical histogenesis in vivo in both mouse and ferret models, including leading to abnormal gyration in the ferret model. Tmem161b localizes non-exclusively to the primary cilium, and scanning electron microscopy revealed shortened, dysmorphic, and ballooned ventricular zone cilia in the Tmem161b null mouse, suggesting that the Shh-related phenotypes may reflect ciliary dysfunction. Our data identify TMEM161B as a regulator of cerebral cortical gyration, as involved in primary ciliary structure, as a regulator of Shh signaling, and further implicate Shh signaling in human gyral development.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.2209964120
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2023
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
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  • 3
    Online Resource
    Online Resource
    A Pleistocene legacy structures variation in modern seagrass ecosystems
    Proceedings of the National Academy of Sciences ; 2022
    In:  Proceedings of the National Academy of Sciences Vol. 119, No. 32 ( 2022-08-09)
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 119, No. 32 ( 2022-08-09)
    Abstract: Distribution of Earth’s biomes is structured by the match between climate and plant traits, which in turn shape associated communities and ecosystem processes and services. However, that climate–trait match can be disrupted by historical events, with lasting ecosystem impacts. As Earth’s environment changes faster than at any time in human history, critical questions are whether and how organismal traits and ecosystems can adjust to altered conditions. We quantified the relative importance of current environmental forcing versus evolutionary history in shaping the growth form (stature and biomass) and associated community of eelgrass ( Zostera marina ), a widespread foundation plant of marine ecosystems along Northern Hemisphere coastlines, which experienced major shifts in distribution and genetic composition during the Pleistocene. We found that eelgrass stature and biomass retain a legacy of the Pleistocene colonization of the Atlantic from the ancestral Pacific range and of more recent within-basin bottlenecks and genetic differentiation. This evolutionary legacy in turn influences the biomass of associated algae and invertebrates that fuel coastal food webs, with effects comparable to or stronger than effects of current environmental forcing. Such historical lags in phenotypic acclimatization may constrain ecosystem adjustments to rapid anthropogenic climate change, thus altering predictions about the future functioning of ecosystems.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.2121425119
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2022
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  • 4
    Online Resource
    Online Resource
    Climate drives the geography of marine consumption by changing predator communities
    Proceedings of the National Academy of Sciences ; 2020
    In:  Proceedings of the National Academy of Sciences Vol. 117, No. 45 ( 2020-11-10), p. 28160-28166
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 117, No. 45 ( 2020-11-10), p. 28160-28166
    Abstract: The global distribution of primary production and consumption by humans (fisheries) is well-documented, but we have no map linking the central ecological process of consumption within food webs to temperature and other ecological drivers. Using standardized assays that span 105° of latitude on four continents, we show that rates of bait consumption by generalist predators in shallow marine ecosystems are tightly linked to both temperature and the composition of consumer assemblages. Unexpectedly, rates of consumption peaked at midlatitudes (25 to 35°) in both Northern and Southern Hemispheres across both seagrass and unvegetated sediment habitats. This pattern contrasts with terrestrial systems, where biotic interactions reportedly weaken away from the equator, but it parallels an emerging pattern of a subtropical peak in marine biodiversity. The higher consumption at midlatitudes was closely related to the type of consumers present, which explained rates of consumption better than consumer density, biomass, species diversity, or habitat. Indeed, the apparent effect of temperature on consumption was mostly driven by temperature-associated turnover in consumer community composition. Our findings reinforce the key influence of climate warming on altered species composition and highlight its implications for the functioning of Earth’s ecosystems.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.2005255117
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2020
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    detail.hit.zdb_id: 1461794-8
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  • 5
    Online Resource
    Online Resource
    Robust paths to net greenhouse gas mitigation and negative emissions via advanced biofuels
    Proceedings of the National Academy of Sciences ; 2020
    In:  Proceedings of the National Academy of Sciences Vol. 117, No. 36 ( 2020-09-08), p. 21968-21977
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 117, No. 36 ( 2020-09-08), p. 21968-21977
    Abstract: Biofuel and bioenergy systems are integral to most climate stabilization scenarios for displacement of transport sector fossil fuel use and for producing negative emissions via carbon capture and storage (CCS). However, the net greenhouse gas mitigation benefit of such pathways is controversial due to concerns around ecosystem carbon losses from land use change and foregone sequestration benefits from alternative land uses. Here, we couple bottom-up ecosystem simulation with models of cellulosic biofuel production and CCS in order to track ecosystem and supply chain carbon flows for current and future biofuel systems, with comparison to competing land-based biological mitigation schemes. Analyzing three contrasting US case study sites, we show that on land transitioning out of crops or pasture, switchgrass cultivation for cellulosic ethanol production has per-hectare mitigation potential comparable to reforestation and severalfold greater than grassland restoration. In contrast, harvesting and converting existing secondary forest at those sites incurs large initial carbon debt requiring long payback periods. We also highlight how plausible future improvements in energy crop yields and biorefining technology together with CCS would achieve mitigation potential 4 and 15 times greater than forest and grassland restoration, respectively. Finally, we show that recent estimates of induced land use change are small relative to the opportunities for improving system performance that we quantify here. While climate and other ecosystem service benefits cannot be taken for granted from cellulosic biofuel deployment, our scenarios illustrate how conventional and carbon-negative biofuel systems could make a near-term, robust, and distinctive contribution to the climate challenge.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1920877117
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2020
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
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  • 6
    Online Resource
    Online Resource
    Bidirectional communication between oocytes and ovarian follicular somatic cells is required for meiotic arrest of mammalian oocytes
    Proceedings of the National Academy of Sciences ; 2013
    In:  Proceedings of the National Academy of Sciences Vol. 110, No. 39 ( 2013-09-24)
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 110, No. 39 ( 2013-09-24)
    Abstract: Coordinated regulation of oocyte and ovarian follicular development is essential for fertility. In particular, the progression of meiosis, a germ cell-specific cell division that reduces the number of chromosomes from diploid to haploid, must be arrested until just before ovulation. Follicular somatic cells are well-known to impose this arrest, which is essential for oocyte–follicle developmental synchrony. Follicular somatic cells sustain meiotic arrest via the natriuretic peptide C/natriuretic peptide receptor 2 (NPPC/NPR2) system, and possibly also via high levels of the purine hypoxanthine in the follicular fluid. Upon activation by the ligand NPPC, NPR2, the predominant guanylyl cyclase in follicular somatic cells, produces cyclic guanosine monophosphate (cGMP), which maintains meiotic arrest after transfer to the oocyte via gap junctions. Here we report that both the NPPC/NPR2 system and hypoxanthine require the activity of inosine monophosphate dehydrogenase (IMPDH), the rate-limiting enzyme required for the production of guanylyl metabolites and cGMP. Furthermore, oocyte-derived paracrine factors, particularly the growth differentiation factor 9–bone morphogenetic protein 15 heterodimer, promote expression of Impdh and Npr2 and elevate cGMP levels in cumulus cells. Thus, although the somatic compartment of ovarian follicles plays an essential role in the maintenance of oocyte meiotic arrest, as has been known for many years, this function of the somatic cells is surprisingly regulated by signals from the oocyte itself.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1314829110
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2013
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  • 7
    Online Resource
    Online Resource
    Efficient targeted gene disruption in the soma and germ line of the frog Xenopus tropicalis using engineered zinc-finger nucleases
    Proceedings of the National Academy of Sciences ; 2011
    In:  Proceedings of the National Academy of Sciences Vol. 108, No. 17 ( 2011-04-26), p. 7052-7057
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 108, No. 17 ( 2011-04-26), p. 7052-7057
    Abstract: The frog Xenopus , an important research organism in cell and developmental biology, currently lacks tools for targeted mutagenesis. Here, we address this problem by genome editing with zinc-finger nucleases (ZFNs). ZFNs directed against an eGFP transgene in Xenopus tropicalis induced mutations consistent with nonhomologous end joining at the target site, resulting in mosaic loss of the fluorescence phenotype at high frequencies. ZFNs directed against the noggin gene produced tadpoles and adult animals carrying up to 47% disrupted alleles, and founder animals yielded progeny carrying insertions and deletions in the noggin gene with no indication of off-target effects. Furthermore, functional tests demonstrated an allelic series of activity between three germ-line mutant alleles. Because ZFNs can be designed against any locus, our data provide a generally applicable protocol for gene disruption in Xenopus .
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1102030108
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2011
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  • 8
    Online Resource
    Online Resource
    Development of bat flight: Morphologic and molecular evolution of bat wing digits
    Proceedings of the National Academy of Sciences ; 2006
    In:  Proceedings of the National Academy of Sciences Vol. 103, No. 17 ( 2006-04-25), p. 6581-6586
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 103, No. 17 ( 2006-04-25), p. 6581-6586
    Abstract: The earliest fossil bats resemble their modern counterparts in possessing greatly elongated digits to support the wing membrane, which is an anatomical hallmark of powered flight. To quantitatively confirm these similarities, we performed a morphometric analysis of wing bones from fossil and modern bats. We found that the lengths of the third, fourth, and fifth digits (the primary supportive elements of the wing) have remained constant relative to body size over the last 50 million years. This absence of transitional forms in the fossil record led us to look elsewhere to understand bat wing evolution. Investigating embryonic development, we found that the digits in bats ( Carollia perspicillata ) are initially similar in size to those of mice ( Mus musculus ) but that, subsequently, bat digits greatly lengthen. The developmental timing of the change in wing digit length points to a change in longitudinal cartilage growth, a process that depends on the relative proliferation and differentiation of chondrocytes. We found that bat forelimb digits exhibit relatively high rates of chondrocyte proliferation and differentiation. We show that bone morphogenetic protein 2 (Bmp2) can stimulate cartilage proliferation and differentiation and increase digit length in the bat embryonic forelimb. Also, we show that Bmp2 expression and Bmp signaling are increased in bat forelimb embryonic digits relative to mouse or bat hind limb digits. Together, our results suggest that an up-regulation of the Bmp pathway is one of the major factors in the developmental elongation of bat forelimb digits, and it is potentially a key mechanism in their evolutionary elongation as well.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.0509716103
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2006
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
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  • 9
    Online Resource
    Online Resource
    Stromal response to Hedgehog signaling restrains pancreatic cancer progression
    Proceedings of the National Academy of Sciences ; 2014
    In:  Proceedings of the National Academy of Sciences Vol. 111, No. 30 ( 2014-07-29)
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 111, No. 30 ( 2014-07-29)
    Abstract: Pancreatic ductal adenocarcinoma (PDA) is the most lethal of common human malignancies, with no truly effective therapies for advanced disease. Preclinical studies have suggested a therapeutic benefit of targeting the Hedgehog (Hh) signaling pathway, which is activated throughout the course of PDA progression by expression of Hh ligands in the neoplastic epithelium and paracrine response in the stromal fibroblasts. Clinical trials to test this possibility, however, have yielded disappointing results. To further investigate the role of Hh signaling in the formation of PDA and its precursor lesion, pancreatic intraepithelial neoplasia (PanIN), we examined the effects of genetic or pharmacologic inhibition of Hh pathway activity in three distinct genetically engineered mouse models and found that Hh pathway inhibition accelerates rather than delays progression of oncogenic Kras-driven disease. Notably, pharmacologic inhibition of Hh pathway activity affected the balance between epithelial and stromal elements, suppressing stromal desmoplasia but also causing accelerated growth of the PanIN epithelium. In striking contrast, pathway activation using a small molecule agonist caused stromal hyperplasia and reduced epithelial proliferation. These results indicate that stromal response to Hh signaling is protective against PDA and that pharmacologic activation of pathway response can slow tumorigenesis. Our results provide evidence for a restraining role of stroma in PDA progression, suggesting an explanation for the failure of Hh inhibitors in clinical trials and pointing to the possibility of a novel type of therapeutic intervention.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1411679111
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2014
    detail.hit.zdb_id: 209104-5
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  • 10
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    Online Resource
    Virstatin inhibits dimerization of the transcriptional activator ToxT
    Proceedings of the National Academy of Sciences ; 2007
    In:  Proceedings of the National Academy of Sciences Vol. 104, No. 7 ( 2007-02-13), p. 2372-2377
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 104, No. 7 ( 2007-02-13), p. 2372-2377
    Abstract: The development of antimicrobials is critical in this time of increasing antibiotic resistance of most clinically relevant bacteria. To date, all current antibiotics focus on inhibiting crucial enzymatic activities of their protein targets (i.e., trimethoprim for dihydrofolate reductase), thus disrupting in vitro essential gene functions. In contrast, we have previously reported the identification of virstatin, a small molecule that inhibits virulence regulation in Vibrio cholerae , thereby preventing intestinal colonization in an infant mouse model for cholera. Virstatin prevents expression of the two major V. cholerae virulence factors, cholera toxin (CT) and the toxin coregulated pilus, by inhibiting the virulence transcriptional activator ToxT. It has previously been described that the N-terminal domain of ToxT has the ability to form homodimers. We now demonstrate that virstatin inhibits ToxT dimerization, thus demonstrating that it further falls into a unique class of inhibitors that works by disrupting protein-protein interactions, particularly homodimerization. Using virstatin, truncation mutants of ToxT, and a virstatin-resistant mutant, we show that dimerization is required for ToxT activation of the ctx promoter. In contrast, ToxT dimerization does not appear to be required at all of the other ToxT-regulated promoters, suggesting multiple mechanisms may exist for its transcriptional activity.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.0611643104
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2007
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
    SSG: 11
    SSG: 12
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