Next Issue
Previous Issue

Table of Contents

Life, Volume 4, Issue 2 (June 2014), Pages 117-280

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
View options order results:
result details:
Displaying articles 1-11
Export citation of selected articles as:

Editorial

Jump to: Research, Review, Other

Open AccessEditorial Opening up Peer Review in Life: Towards a Transparent and Reliable Process
Life 2014, 4(2), 225-226; doi:10.3390/life4020225
Received: 12 May 2014 / Accepted: 12 May 2014 / Published: 16 May 2014
Cited by 2 | PDF Full-text (127 KB) | HTML Full-text | XML Full-text
Abstract
As an advocate of the transparency on the peer review process, during the last months, I’ve been working with MDPI to implant a new system of open peer review, under which the peer-review reports and authors’ responses are published as an integral part
[...] Read more.
As an advocate of the transparency on the peer review process, during the last months, I’ve been working with MDPI to implant a new system of open peer review, under which the peer-review reports and authors’ responses are published as an integral part of the final version of each article. This new model of publishing associated with the open access platform of MDPI result in one of the most transparent, unbiased, democratic and reliable assessment of research currently available. Life is the first MDPI journal to make this courageous step towards open peer-review in order to demonstrate the rigorous, fair and efficient standard of our editorial work. The first paper published under this new policy was a manuscript written by a Nobelist and reviewed by three experts in the field, as highlighted in this editorial. Full article

Research

Jump to: Editorial, Review, Other

Open AccessArticle Disk Evolution, Element Abundances and Cloud Properties of Young Gas Giant Planets
Life 2014, 4(2), 142-173; doi:10.3390/life4020142
Received: 31 October 2013 / Revised: 13 March 2014 / Accepted: 18 March 2014 / Published: 14 April 2014
Cited by 17 | PDF Full-text (831 KB) | HTML Full-text | XML Full-text
Abstract
We discuss the chemical pre-conditions for planet formation, in terms of gas and ice abundances in a protoplanetary disk, as function of time and position, and the resulting chemical composition and cloud properties in the atmosphere when young gas giant planets form, in
[...] Read more.
We discuss the chemical pre-conditions for planet formation, in terms of gas and ice abundances in a protoplanetary disk, as function of time and position, and the resulting chemical composition and cloud properties in the atmosphere when young gas giant planets form, in particular discussing the effects of unusual, non-solar carbon and oxygen abundances. Large deviations between the abundances of the host star and its gas giants seem likely to occur if the planet formation follows the core-accretion scenario. These deviations stem from the separate evolution of gas and dust in the disk, where the dust forms the planet cores, followed by the final run-away accretion of the left-over gas. This gas will contain only traces of elements like C, N and O, because those elements have frozen out as ices. PRODIMO protoplanetary disk models are used to predict the chemical evolution of gas and ice in the midplane. We find that cosmic rays play a crucial role in slowly un-blocking the CO, where the liberated oxygen forms water, which then freezes out quickly. Therefore, the C/O ratio in the gas phase is found to gradually increase with time, in a region bracketed by the water and CO ice-lines. In this regions, C/O is found to approach unity after about 5 Myrs, scaling with the cosmic ray ionization rate assumed. We then explore how the atmospheric chemistry and cloud properties in young gas giants are affected when the non-solar C/O ratios predicted by the disk models are assumed. The DRIFT cloud formation model is applied to study the formation of atmospheric clouds under the influence of varying premordial element abundances and its feedback onto the local gas. We demonstrate that element depletion by cloud formation plays a crucial role in converting an oxygen-rich atmosphere gas into carbon-rich gas when non-solar, premordial element abundances are considered as suggested by disk models. Full article
(This article belongs to the Special Issue Planet Formation and the Rise of Life)
Open AccessArticle Cineradiographic Analysis of Mouse Postural Response to Alteration of Gravity and Jerk (Gravity Deceleration Rate)
Life 2014, 4(2), 174-188; doi:10.3390/life4020174
Received: 14 January 2014 / Revised: 14 April 2014 / Accepted: 15 April 2014 / Published: 24 April 2014
Cited by 1 | PDF Full-text (1446 KB) | HTML Full-text | XML Full-text
Abstract
The ability to maintain the body relative to the external environment is important for adaptation to altered gravity. However, the physiological limits for adaptation or the disruption of body orientation are not known. In this study, we analyzed postural changes in mice upon
[...] Read more.
The ability to maintain the body relative to the external environment is important for adaptation to altered gravity. However, the physiological limits for adaptation or the disruption of body orientation are not known. In this study, we analyzed postural changes in mice upon exposure to various low gravities. Male C57BL6/J mice (n = 6) were exposed to various gravity-deceleration conditions by customized parabolic flight-maneuvers targeting the partial-gravity levels of 0.60, 0.30, 0.15 and μ g (<0.001 g). Video recordings of postural responses were analyzed frame-by-frame by high-definition cineradiography and with exact instantaneous values of gravity and jerk. As a result, the coordinated extension of the neck, spine and hindlimbs was observed during the initial phase of gravity deceleration. Joint angles widened to 120%–200% of the reference g level, and the magnitude of the thoracic-curvature stretching was correlated with gravity and jerk, i.e., the gravity deceleration rate. A certain range of jerk facilitated mouse skeletal stretching efficiently, and a jerk of −0.3~−0.4 j (g/s) induced the maximum extension of the thoracic-curvature. The postural response of animals to low gravity may undergo differential regulation by gravity and jerk. Full article
(This article belongs to the Special Issue Response of Terrestrial Life to Space Conditions)
Open AccessCommunication Effects of the Extraterrestrial Environment on Plants: Recommendations for Future Space Experiments for the MELiSSA Higher Plant Compartment
Life 2014, 4(2), 189-204; doi:10.3390/life4020189
Received: 17 February 2014 / Revised: 3 April 2014 / Accepted: 28 April 2014 / Published: 5 May 2014
Cited by 4 | PDF Full-text (453 KB) | HTML Full-text | XML Full-text
Abstract
Due to logistical challenges, long-term human space exploration missions require a life support system capable of regenerating all the essentials for survival. Higher plants can be utilized to provide a continuous supply of fresh food, atmosphere revitalization, and clean water for humans. Plants
[...] Read more.
Due to logistical challenges, long-term human space exploration missions require a life support system capable of regenerating all the essentials for survival. Higher plants can be utilized to provide a continuous supply of fresh food, atmosphere revitalization, and clean water for humans. Plants can adapt to extreme environments on Earth, and model plants have been shown to grow and develop through a full life cycle in microgravity. However, more knowledge about the long term effects of the extraterrestrial environment on plant growth and development is necessary. The European Space Agency (ESA) has developed the Micro-Ecological Life Support System Alternative (MELiSSA) program to develop a closed regenerative life support system, based on micro-organisms and higher plant processes, with continuous recycling of resources. In this context, a literature review to analyze the impact of the space environments on higher plants, with focus on gravity levels, magnetic fields and radiation, has been performed. This communication presents a roadmap giving directions for future scientific activities within space plant cultivation. The roadmap aims to identify the research activities required before higher plants can be included in regenerative life support systems in space. Full article
(This article belongs to the Special Issue Response of Terrestrial Life to Space Conditions)
Open AccessArticle The Evolution of the Ribosome and the Genetic Code
Life 2014, 4(2), 227-249; doi:10.3390/life4020227
Received: 30 January 2014 / Revised: 23 April 2014 / Accepted: 25 April 2014 / Published: 20 May 2014
Cited by 6 | PDF Full-text (709 KB) | HTML Full-text | XML Full-text
Abstract
The evolution of the genetic code is mapped out starting with the aminoacyl tRNA-synthetases and their interaction with the operational code in the tRNA acceptor arm. Combining this operational code with a metric based on the biosynthesis of amino acids from the Citric
[...] Read more.
The evolution of the genetic code is mapped out starting with the aminoacyl tRNA-synthetases and their interaction with the operational code in the tRNA acceptor arm. Combining this operational code with a metric based on the biosynthesis of amino acids from the Citric acid, we come to the conclusion that the earliest genetic code was a Guanine Cytosine (GC) code. This has implications for the likely earliest positively charged amino acids. The progression from this pure GC code to the extant one is traced out in the evolution of the Large Ribosomal Subunit, LSU, and its proteins; in particular those associated with the Peptidyl Transfer Center (PTC) and the nascent peptide exit tunnel. This progression has implications for the earliest encoded peptides and their evolutionary progression into full complex proteins. Full article
(This article belongs to the Special Issue The Origins and Early Evolution of RNA)

Review

Jump to: Editorial, Research, Other

Open AccessReview The Role of Mechanical Stimulation in Recovery of Bone Loss—High versus Low Magnitude and Frequency of Force
Life 2014, 4(2), 117-130; doi:10.3390/life4020117
Received: 19 February 2014 / Revised: 25 March 2014 / Accepted: 25 March 2014 / Published: 2 April 2014
Cited by 3 | PDF Full-text (128 KB) | HTML Full-text | XML Full-text
Abstract
Musculoskeletal pathologies associated with decreased bone mass, including osteoporosis and disuse-induced bone loss, affect millions of Americans annually. Microgravity-induced bone loss presents a similar concern for astronauts during space missions. Many pharmaceutical treatments have slowed osteoporosis, and recent data shows promise for countermeasures
[...] Read more.
Musculoskeletal pathologies associated with decreased bone mass, including osteoporosis and disuse-induced bone loss, affect millions of Americans annually. Microgravity-induced bone loss presents a similar concern for astronauts during space missions. Many pharmaceutical treatments have slowed osteoporosis, and recent data shows promise for countermeasures for bone loss observed in astronauts. Additionally, high magnitude and low frequency impact such as running has been recognized to increase bone and muscle mass under normal but not microgravity conditions. However, a low magnitude and high frequency (LMHF) mechanical load experienced in activities such as postural control, has also been shown to be anabolic to bone. While several clinical trials have demonstrated that LMHF mechanical loading normalizes bone loss in vivo, the target tissues and cells of the mechanical load and underlying mechanisms mediating the responses are unknown. In this review, we provide an overview of bone adaptation under a variety of loading profiles and the potential for a low magnitude loading as a way to counteract bone loss as experienced by astronauts. Full article
(This article belongs to the Special Issue Response of Terrestrial Life to Space Conditions)
Open AccessReview Plant Growth and Morphogenesis under Different Gravity Conditions: Relevance to Plant Life in Space
Life 2014, 4(2), 205-216; doi:10.3390/life4020205
Received: 13 March 2014 / Revised: 18 April 2014 / Accepted: 12 May 2014 / Published: 16 May 2014
Cited by 4 | PDF Full-text (725 KB) | HTML Full-text | XML Full-text
Abstract
The growth and morphogenesis of plants are entirely dependent on the gravitational acceleration of earth. Under microgravity conditions in space, these processes are greatly modified. Recent space experiments, in combination with ground-based studies, have shown that elongation growth is stimulated and lateral expansion
[...] Read more.
The growth and morphogenesis of plants are entirely dependent on the gravitational acceleration of earth. Under microgravity conditions in space, these processes are greatly modified. Recent space experiments, in combination with ground-based studies, have shown that elongation growth is stimulated and lateral expansion suppressed in various shoot organs and roots under microgravity conditions. Plant organs also show automorphogenesis in space, which consists of altered growth direction and spontaneous curvature in the dorsiventral (back and front) directions. Changes in cell wall properties are responsible for these modifications of growth and morphogenesis under microgravity conditions. Plants live in space with interesting new sizes and forms. Full article
(This article belongs to the Special Issue Response of Terrestrial Life to Space Conditions)
Figures

Open AccessReview Horizontal Gene Transfer among Bacteria and Its Role in Biological Evolution
Life 2014, 4(2), 217-224; doi:10.3390/life4020217
Received: 19 February 2014 / Revised: 22 April 2014 / Accepted: 23 April 2014 / Published: 16 May 2014
Cited by 5 | PDF Full-text (652 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This is a contribution to the history of scientific advance in the past 70 years concerning the identification of genetic information, its molecular structure, the identification of its functions and the molecular mechanisms of its evolution. Particular attention is thereby given to horizontal
[...] Read more.
This is a contribution to the history of scientific advance in the past 70 years concerning the identification of genetic information, its molecular structure, the identification of its functions and the molecular mechanisms of its evolution. Particular attention is thereby given to horizontal gene transfer among microorganisms, as well as to biosafety considerations with regard to beneficial applications of acquired scientific knowledge. Full article
(This article belongs to the Special Issue Horizontal Gene Transfer and the Last Universal Common Ancestor)
Open AccessReview Host-Microbe Interactions in Microgravity: Assessment and Implications
Life 2014, 4(2), 250-266; doi:10.3390/life4020250
Received: 8 February 2014 / Revised: 14 May 2014 / Accepted: 20 May 2014 / Published: 26 May 2014
Cited by 2 | PDF Full-text (818 KB) | HTML Full-text | XML Full-text
Abstract
Spaceflight imposes several unique stresses on biological life that together can have a profound impact on the homeostasis between eukaryotes and their associated microbes. One such stressor, microgravity, has been shown to alter host-microbe interactions at the genetic and physiological levels. Recent sequencing
[...] Read more.
Spaceflight imposes several unique stresses on biological life that together can have a profound impact on the homeostasis between eukaryotes and their associated microbes. One such stressor, microgravity, has been shown to alter host-microbe interactions at the genetic and physiological levels. Recent sequencing of the microbiomes associated with plants and animals have shown that these interactions are essential for maintaining host health through the regulation of several metabolic and immune responses. Disruptions to various environmental parameters or community characteristics may impact the resiliency of the microbiome, thus potentially driving host-microbe associations towards disease. In this review, we discuss our current understanding of host-microbe interactions in microgravity and assess the impact of this unique environmental stress on the normal physiological and genetic responses of both pathogenic and mutualistic associations. As humans move beyond our biosphere and undergo longer duration space flights, it will be essential to more fully understand microbial fitness in microgravity conditions in order to maintain a healthy homeostasis between humans, plants and their respective microbiomes. Full article
(This article belongs to the Special Issue Response of Terrestrial Life to Space Conditions)
Open AccessReview Stem Cells toward the Future: The Space Challenge
Life 2014, 4(2), 267-280; doi:10.3390/life4020267
Received: 30 March 2014 / Revised: 17 May 2014 / Accepted: 20 May 2014 / Published: 30 May 2014
Cited by 4 | PDF Full-text (600 KB) | HTML Full-text | XML Full-text
Abstract
Astronauts experience weightlessness-induced bone loss due to an unbalanced process of bone remodeling that involves bone mesenchymal stem cells (bMSCs), as well as osteoblasts, osteocytes, and osteoclasts. The effects of microgravity on osteo-cells have been extensively studied, but it is only recently that
[...] Read more.
Astronauts experience weightlessness-induced bone loss due to an unbalanced process of bone remodeling that involves bone mesenchymal stem cells (bMSCs), as well as osteoblasts, osteocytes, and osteoclasts. The effects of microgravity on osteo-cells have been extensively studied, but it is only recently that consideration has been given to the role of bone MSCs. These live in adult bone marrow niches, are characterized by their self-renewal and multipotent differentiation capacities, and the published data indicate that they may lead to interesting returns in the biomedical/bioengineering fields. This review describes the published findings concerning bMSCs exposed to simulated/real microgravity, mainly concentrating on how mechanosignaling, mechanotransduction and oxygen influence their proliferation, senescence and differentiation. A comprehensive understanding of bMSC behavior in microgravity and their role in preventing bone loss will be essential for entering the future age of long-lasting, manned space exploration. Full article
(This article belongs to the Special Issue Response of Terrestrial Life to Space Conditions)

Other

Jump to: Editorial, Research, Review

Open AccessHypothesis RNA Catalysis, Thermodynamics and the Origin of Life
Life 2014, 4(2), 131-141; doi:10.3390/life4020131
Received: 27 February 2014 / Revised: 28 March 2014 / Accepted: 31 March 2014 / Published: 10 April 2014
Cited by 5 | PDF Full-text (804 KB) | HTML Full-text | XML Full-text
Abstract
The RNA World Hypothesis posits that the first self-replicating molecules were RNAs. RNA self-replicases are, in general, assumed to have employed nucleotide 5ʹ-polyphosphates (or their analogues) as substrates for RNA polymerization. The mechanism by which these substrates might be synthesized with sufficient abundance
[...] Read more.
The RNA World Hypothesis posits that the first self-replicating molecules were RNAs. RNA self-replicases are, in general, assumed to have employed nucleotide 5ʹ-polyphosphates (or their analogues) as substrates for RNA polymerization. The mechanism by which these substrates might be synthesized with sufficient abundance to supply a growing and evolving population of RNAs is problematic for evolutionary hypotheses because non-enzymatic synthesis and assembly of nucleotide 5ʹ-triphosphates (or other analogously activated phosphodiester species) is inherently difficult. However, nucleotide 2ʹ,3ʹ-cyclic phosphates are also phosphodiesters, and are the natural and abundant products of RNA degradation. These have previously been dismissed as viable substrates for prebiotic RNA synthesis. We propose that the arguments for their dismissal are based on a flawed assumption, and that nucleotide 2ʹ,3ʹ-cyclic phosphates in fact possess several significant, advantageous properties that indeed make them particularly viable substrates for prebiotic RNA synthesis. An RNA World hypothesis based upon the polymerization of nucleotide 2ʹ,3ʹ-cyclic phosphates possesses additional explanatory power in that it accounts for the observed ribozyme “fossil record”, suggests a viable mechanism for substrate transport across lipid vesicle boundaries of primordial proto-cells, circumvents the problems of substrate scarcity and implausible synthetic pathways, provides for a primitive but effective RNA replicase editing mechanism, and definitively explains why RNA, rather than DNA, must have been the original catalyst. Finally, our analysis compels us to propose that a fundamental and universal property that drives the evolution of living systems, as well as pre-biotic replicating molecules (be they composed of RNA or protein), is that they exploit chemical reactions that already possess competing kinetically-preferred and thermodynamically-preferred pathways in a manner that optimizes the balance between the two types of pathways. Full article
(This article belongs to the Special Issue The Origins and Early Evolution of RNA)
Figures

Journal Contact

MDPI AG
Life Editorial Office
St. Alban-Anlage 66, 4052 Basel, Switzerland
life@mdpi.com
Tel. +41 61 683 77 34
Fax: +41 61 302 89 18
Editorial Board
Contact Details Submit to Life
Back to Top