Project description:Plant mitochondrial genomes are usually assembled and displayed as circular maps based on the widely-held view across the broad community of life scientists that circular genome-sized molecules are the primary form of plant mitochondrial DNA, despite the understanding by plant mitochondrial researchers that this is an inaccurate and outdated concept. Many plant mitochondrial genomes have one or more pairs of large repeats that can act as sites for inter- or intramolecular recombination, leading to multiple alternative arrangements (isoforms). Most mitochondrial genomes have been assembled using methods unable to capture the complete spectrum of isoforms within a species, leading to an incomplete inference of their structure and recombinational activity. To document and investigate underlying reasons for structural diversity in plant mitochondrial DNA, we used long-read (PacBio) and short-read (Illumina) sequencing data to assemble and compare mitochondrial genomes of domesticated (Lactuca sativa) and wild (L. saligna and L. serriola) lettuce species. We characterized a comprehensive, complex set of isoforms within each species and compared genome structures between species. Physical analysis of L. sativa mtDNA molecules by fluorescence microscopy revealed a variety of linear, branched, and circular structures. The mitochondrial genomes for L. sativa and L. serriola were identical in sequence and arrangement and differed substantially from L. saligna, indicating that the mitochondrial genome structure did not change during domestication. From the isoforms in our data, we infer that recombination occurs at repeats of all sizes at variable frequencies. The differences in genome structure between L. saligna and the two other Lactuca species can be largely explained by rare recombination events that rearranged the structure. Our data demonstrate that representations of plant mitochondrial genomes as simple, circular molecules are not accurate descriptions of their true nature and that in reality plant mitochondrial DNA is a complex, dynamic mixture of forms.
Project description:The appearance of heme, an organic ring surrounding an iron atom, in evolution forever changed the efficiency with which organisms were able to generate energy, utilize gasses and catalyze numerous reactions. Because of this, heme has become a near ubiquitous compound among living organisms. In this review we have attempted to assess the current state of heme synthesis and trafficking with a goal of identifying crucial missing information, and propose hypotheses related to trafficking that may generate discussion and research. The possibilities of spatially organized supramolecular enzyme complexes and organelle structures that facilitate efficient heme synthesis and subsequent trafficking are discussed and evaluated. Recently identified players in heme transport and trafficking are reviewed and placed in an organismal context. Additionally, older, well established data are reexamined in light of more recent studies on cellular organization and data available from newer model organisms. This article is part of a Special Issue entitled: Cell Biology of Metals.
Project description:From humble beginnings of a contaminated petri dish, β-lactam antibiotics have distinguished themselves among some of the most powerful drugs in human history. The devastating effects of antibiotic resistance have nevertheless led to an "arms race" with disquieting prospects. The emergence of multidrug resistant bacteria threatens an ever-dwindling antibiotic arsenal, calling for new discovery, rediscovery, and innovation in β-lactam research. Here the current state of β-lactam antibiotics from a structural perspective was reviewed.
Project description:Carbon nanorings are hoop-shaped, π-conjugated macrocycles that form the fundamental annular segments of single-walled carbon nanotubes (SWNTs). In a very recent report, the structures of chiral carbon nanorings (which may serve as chemical templates for synthesizing chiral nanotubes) were experimentally synthesized and characterized for the first time. Here in our Letter we show that the excited-state properties of these unique chiral nanorings exhibit anomalous and extremely interesting optoelectronic properties with excitation energies growing larger as a function of size (in contradiction with typical quantum confinement effects). Although the first electronic excitation in armchair nanorings is forbidden with a weak oscillator strength, we find that the same excitation in chiral nanorings is allowed because of a strong geometric symmetry breaking. Most importantly, among all the possible nanorings synthesized in this fashion, we show that only one ring, corresponding to a SWNT with chiral indices (n+3,n+1), is extremely special with large photoinduced transitions that are most readily observable in spectroscopic experiments.
Project description:The exclusive expression of single sensory receptors in individual neurons (the ‘one-neuron-one receptor’ rule) is essential for vision and other sensory systems. Here, we show that the transcriptional corepressor Samd7 enforces this rule in vertebrate red cones and acts in other photoreceptor types to maintain cell identity. In the zebrafish samd7-/- retina, red cones are transformed to hybrid red/UV-sensitive cones, green cones are transfated to blue cones, and the number of rods is greatly reduced. In the mouse Samd7-/- retina, dorsal M-cones are transformed to hybrid M/S-cones—analogous to the transformation of red to red/UV cones that occurs in zebrafish—and rods aberrantly express cone genes including S-opsin. Altogether, Samd7 acts to repress short-wavelength cone gene expression in long-wavelength-sensitive cones, thereby sustaining the mutually exclusive patterns of opsin expression and cone identity required for color vision.
Project description:BackgroundThe SPFH protein superfamily is a diverse family of proteins whose eukaryotic members are involved in the scaffolding of detergent-resistant microdomains. Recently the origin of the SPFH proteins has been questioned. Instead, convergent evolution has been proposed. However, an independent, convergent evolution of three large prokaryotic and three eukaryotic families is highly unlikely, especially when other mechanisms such as lateral gene transfer which could also explain their distribution pattern have not yet been considered.To gain better insight into this very diverse protein family, we have analyzed the genomes of 497 microorganisms and investigated the pattern of occurrence as well as the genomic vicinity of the prokaryotic SPFH members.ResultsAccording to sequence and operon structure, a clear division into 12 subfamilies was evident. Three subfamilies (SPFH1, SPFH2 and SPFH5) show a conserved operon structure and two additional subfamilies are linked to those three through functional aspects (SPFH1, SPFH3, SPFH4: interaction with FtsH protease). Therefore these subgroups most likely share common ancestry. The complex pattern of occurrence among the different phyla is indicative of lateral gene transfer. Organisms that do not possess a single SPFH protein are almost exclusively endosymbionts or endoparasites.ConclusionThe conserved operon structure and functional similarities suggest that at least 5 subfamilies that encompass almost 75% of all prokaryotic SPFH members share a common origin. Their similarity to the different eukaryotic SPFH families, as well as functional similarities, suggests that the eukaryotic SPFH families originated from different prokaryotic SPFH families rather than one. This explains the difficulties in obtaining a consistent phylogenetic tree of the eukaryotic SPFH members. Phylogenetic evidence points towards lateral gene transfer as one source of the very diverse patterns of occurrence in bacterial species.
Project description:In the last decade, genomics data have been largely adopted to sketch, study and better understand the complex mechanisms that underlie biological processes. The amount of publicly available data sources has grown accordingly, and several types of regulatory interactions have been collected and documented in literature. Unfortunately, often these efforts do not follow any data naming/interoperability/formatting standards, resulting in high-quality but often uninteroperable heterogeneous data repositories. To efficiently take advantage of the large amount of available data and integrate these heterogeneous sources of information, we built the RING (Regulatory Interaction Graph), an integrative standardized multilevel database of biological interactions able to provide a comprehensive and unmatched high-level perspective on several phenomena that take place in the regulatory cascade and that researchers can use to easily build regulatory networks around entities of interest.
Project description:The exclusive expression of single sensory receptors in individual neurons (the ‘one-neuron-one receptor’ rule) is essential for vision and other sensory systems. Here, we show that the transcriptional corepressor Samd7 enforces this rule in vertebrate red cones and acts in other photoreceptor types to maintain cell identity. In the zebrafish samd7-/- retina, red cones are transformed to hybrid red/UV-sensitive cones, green cones are transfated to blue cones, and the number of rods is greatly reduced. In the mouse Samd7-/- retina, dorsal M-cones are transformed to hybrid M/S-cones—analogous to the transformation of red to red/UV cones that occurs in zebrafish—and rods aberrantly express cone genes including S-opsin. Altogether, Samd7 acts to repress short-wavelength cone gene expression in long-wavelength-sensitive cones, thereby sustaining the mutually exclusive patterns of opsin expression and cone identity required for color vision.
Project description:The exclusive expression of single sensory receptors in individual neurons (the ‘one-neuron-one receptor’ rule) is essential for vision and other sensory systems. Here, we show that the transcriptional corepressor Samd7 enforces this rule in vertebrate red cones and acts in other photoreceptor types to maintain cell identity. In the zebrafish samd7-/- retina, red cones are transformed to hybrid red/UV-sensitive cones, green cones are transfated to blue cones, and the number of rods is greatly reduced. In the mouse Samd7-/- retina, dorsal M-cones are transformed to hybrid M/S-cones—analogous to the transformation of red to red/UV cones that occurs in zebrafish—and rods aberrantly express cone genes including S-opsin. Altogether, Samd7 acts to repress short-wavelength cone gene expression in long-wavelength-sensitive cones, thereby sustaining the mutually exclusive patterns of opsin expression and cone identity required for color vision.