Stark Tuning of the Silicon Vacancy in Silicon Carbide.

We present a versatile scheme dedicated to exerting strong electric fields up to 0.5 MV/cm on color centers in hexagonal silicon carbide, employing transparent epitaxial graphene electrodes. In both the axial and basal direction equally strong electric fields can be selectively controlled. Investigating the silicon vacancy (VSi) in ensemble photoluminescence experiments, we report Stark splitting of the V1' line of 3 meV by a basal electrical field and a Stark shift of the V1 line of 1 meV in an axial electric field. The spectral fine-tuning of the VSi, being an important candidate for realizing quantum networks, paves the way for truly indistinguishable single-photon sources.

A Polydimethylsiloxane (PDMS) Waveguide Sensor that Mimics a Neuromast to Measure Fluid Flow Velocity.

Accurate flow measurement is a ubiquitous task in fields such as industry, medical technology, or chemistry; it remains however challenging due to small measurement ranges or erosive flows. Inspiration for possible measurement methods can come from nature, for example from the lateral line organ of fish, which is comprised of hair cells embedded in a gelatinous cupula. When the cupula is deflected by water movement, the hair cells generate neural signals from which the fish gains an accurate representation of its environment. We built a flow sensor mimicking a hair cell, but coupled it with an optical detection method. Light is coupled into a PDMS waveguide that consists of a core and a cladding with a low refractive index contrast to ensure high bending sensitivity. Fluid flow bends the waveguide; this leads to a measurable light loss. The design of our sensory system allows flow measurement in opaque and corrosive fluids while keeping production costs low. To prove the measurement concept, we evaluated the light loss while (a) reproducibly bending the fiber with masses, and (b) exposing the fiber to air flow. The results demonstrate the applicability of an optical fiber as a flow sensor.

SIL1 mutations and clinical spectrum in patients with Marinesco-Sjogren syndrome.

Marinesco-Sjögren syndrome is a rare autosomal recessive multisystem disorder featuring cerebellar ataxia, early-onset cataracts, chronic myopathy, variable intellectual disability and delayed motor development. More recently, mutations in the SIL1 gene, which encodes an endoplasmic reticulum resident co-chaperone, were identified as the main cause of Marinesco-Sjögren syndrome. Here we describe the results of SIL1 mutation analysis in 62 patients presenting with early-onset ataxia, cataracts and myopathy or combinations of at least two of these. We obtained a mutation detection rate of 60% (15/25) among patients with the characteristic Marinesco-Sjögren syndrome triad (ataxia, cataracts, myopathy) whereas the detection rate in the group of patients with more variable phenotypic presentation was below 3% (1/37). We report 16 unrelated families with a total of 19 different SIL1 mutations. Among these mutations are 15 previously unreported changes, including single- and multi-exon deletions. Based on data from our screening cohort and data compiled from the literature we found that SIL1 mutations are invariably associated with the combination of a cerebellar syndrome and chronic myopathy. Cataracts were observed in all patients beyond the age of 7 years, but might be missing in infants. Six patients with SIL1 mutations had no intellectual disability, extending the known wide range of cognitive capabilities in Marinesco-Sjögren syndrome to include normal intelligence. Modestly constant features were somatic growth retardation, skeletal abnormalities and pyramidal tract signs. Examination of mutant SIL1 expression in cultured patient lymphoblasts suggested that SIL1 mutations result in severely reduced SIL1 protein levels irrespective of the type and position of mutations. Our data broaden the SIL1 mutation spectrum and confirm that SIL1 is the major Marinesco-Sjögren syndrome gene. SIL1 patients usually present with the characteristic triad but cataracts might be missing in young children. As cognitive impairment is not obligatory, patients without intellectual disability but a Marinesco-Sjögren syndrome-compatible phenotype should receive SIL1 mutation analysis. Despite allelic heterogeneity and many families with private mutations, the phenotype related to SIL1 mutations is relatively homogenous. Based on SIL1 expression studies we speculate that this may arise from a uniform effect of different mutations on protein expression.

Mutations in SIL1 cause Marinesco-Sjögren syndrome, a cerebellar ataxia with cataract and myopathy.

SIL1 (also called BAP) acts as a nucleotide exchange factor for the Hsp70 chaperone BiP (also called GRP78), which is a key regulator of the main functions of the endoplasmic reticulum. We found nine distinct mutations that would disrupt the SIL1 protein in individuals with Marinesco-Sjögren syndrome, an autosomal recessive cerebellar ataxia complicated by cataracts, developmental delay and myopathy. Identification of SIL1 mutations implicates Marinesco-Sjögren syndrome as a disease of endoplasmic reticulum dysfunction and suggests a role for this organelle in multisystem disorders.

Electrochemical etching strategy for shaping monolithic 3D structures from 4H-SiC wafers.

Silicon Carbide (SiC) is an outstanding material, not only for electronic applications, but also for projected functionalities in the realm of spin-based quantum technologies, nano-mechanical resonators and photonics-on-a-chip. For shaping 3D structures out of SiC wafers, predominantly dry-etching techniques are used. SiC is nearly inert with respect to wet etching, occasionally photoelectrochemical etching strategies have been applied. Here, we propose an electrochemical etching strategy that solely relies on defining etchable volumina by implantation of p-dopants. Together with the inertness of the n-doped regions, very sharp etching contrasts can be achieved. We present devices as different as monolithic cantilevers, disk-shaped optical resonators and membranes etched out of a single crystal wafer. The high quality of the resulting surfaces can even be enhanced by thermal treatment, with shape-stable devices up to and even beyond 1550°C. The versatility of our approach paves the way for new functionalities on SiC as high-performance multi-functional wafer platform.

Autosomal-dominant distal myopathy associated with a recurrent missense mutation in the gene encoding the nuclear matrix protein, matrin 3.

Distal myopathies represent a heterogeneous group of inherited skeletal muscle disorders. One type of adult-onset, progressive autosomal-dominant distal myopathy, frequently associated with dysphagia and dysphonia (vocal cord and pharyngeal weakness with distal myopathy [VCPDM]), has been mapped to chromosome 5q31 in a North American pedigree. Here, we report the identification of a second large VCPDM family of Bulgarian descent and fine mapping of the critical interval. Sequencing of positional candidate genes revealed precisely the same nonconservative S85C missense mutation affecting an interspecies conserved residue in the MATR3 gene in both families. MATR3 is expressed in skeletal muscle and encodes matrin 3, a component of the nuclear matrix, which is a proteinaceous network that extends throughout the nucleus. Different disease related haplotype signatures in the two families provided evidence that two independent mutational events at the same position in MATR3 cause VCPDM. Our data establish proof of principle that the nuclear matrix is crucial for normal skeletal muscle structure and function and put VCPDM on the growing list of monogenic disorders associated with the nuclear proteome.

Bottom-gated epitaxial graphene.

High-quality epitaxial graphene on silicon carbide (SiC) is today available in wafer size. Similar to exfoliated graphene, its charge carriers are governed by the Dirac-Weyl Hamiltonian and it shows excellent mobilities. For many experiments with graphene, in particular for surface science, a bottom gate is desirable. Commonly, exfoliated graphene flakes are placed on an oxidized silicon wafer that readily provides a bottom gate. However, this cannot be applied to epitaxial graphene as the SiC provides the source material out of which graphene grows. Here, we present a reliable scheme for the fabrication of bottom-gated epitaxial graphene devices, which is based on nitrogen (N) implantation into a SiC wafer and subsequent graphene growth. We demonstrate working devices in a broad temperature range from 6 to 300 K. Two gating regimes can be addressed, which opens a wide engineering space for tailored devices by controlling the doping of the gate structure.

The sandfish lizard's aerodynamic filtering system.

Particulate air pollution has an adverse effect on cardiovascular and respiratory health. Air filtration systems are therefore essential in closed indoor environments. While mechanical filtration is described as an efficient technology, particle filters may act as a source of pollution if not correctly installed and frequently maintained. The sandfish lizard, a sand swimmer that spends nearly its whole life in fine desert sand, inspired us to rethink traditional filtering systems due to its unique ability of filtering sand from its nasal cavity. During a slow, prolonged inhalation, strong cross-flow velocities develop in a certain region of the upper respiratory tract; these cross-flows enhance gravitational settling and force inhaled sand grains towards the wall where they adhere to mucus, which covers the walls in this region. During an intense, cough-like exhalation the particles are blasted out. In this work, the sandfish's aerodynamic filtering system was analyzed experimentally and by computational fluid dynamics simulations to study the flow profile and particle trajectories. Based on these findings, we discuss the development of a biomimetic filtering system, which could have the following advantages: due to the absence of a membrane, total pressure losses can be reduced. The mucus-covered surface would be mimicked by a specifically treated surface to trap particulate matter. Also, the device would contain a self-cleaning mechanism that simulates the lizard's exhalation. This biomimetic filtering system would therefore have an enhanced life-time and it would be low-maintenance and therefore economical and sustainable.

Native supercolonies of unrelated individuals in the invasive Argentine ant.

Kinship among group members has long been recognized as a main factor promoting the evolution of sociality and reproductive altruism, yet some ants have an extraordinary social organization, called unicoloniality, whereby individuals mix freely among physically separated nests. This type of social organization is not only a key attribute responsible for the ecological dominance of these ants, but also an evolutionary paradox because relatedness between nestmates is effectively zero. Recently, it has been proposed that, in the Argentine ant, unicoloniality is a derived trait that evolved after its introduction into new habitats. Here we test this basic assumption by conducting a detailed genetic analysis of four native and six introduced populations with five to 15 microsatellite loci and one mitochondrial gene. In contrast to the assumption that native populations consist of family-based colonies with related individuals who are aggressive toward members of other colonies, we found that native populations also form supercolonies, and are effectively unicolonial. Moreover, just as in introduced populations, the relatedness between nestmates is not distinguishable from zero in these native range supercolonies. Genetic differentiation between native supercolonies was very high for both nuclear and mitochondrial markers, indicating extremely limited gene flow between supercolonies. The only important difference between the native and introduced populations was that supercolonies were several orders of magnitude smaller in the native range (25-500 m). This size difference has important consequences for our understanding of the evolution and stability of unicolonial structures because the relatively small size of supercolonies in the native range implies that competition can occur between supercolonies, which can act as a break on the spread of selfish mutants by eliminating supercolonies harboring them.

Alternative genetic foundations for a key social polymorphism in fire ants.

Little is known about the genetic foundations of colony social organization. One rare example in which a single major gene is implicated in the expression of alternative social organizations involves the presumed odorant-binding protein gene Gp-9 in fire ants. Specific amino acid substitutions in this gene invariably are associated with the expression of monogyny (single queen per colony) or polygyny (multiple queens per colony) in fire ant species of the Solenopsis richteri clade. These substitutions are hypothesized to alter the abilities of workers to recognize queens and thereby regulate their numbers in a colony. We examined whether these same substitutions underlie the monogyny/polygyny social polymorphism in the distantly related fire ant S. geminata. We found that Gp-9 coding region sequences are identical in the polygyne and monogyne forms of this species, disproving our hypothesis that one or a few specific amino acid replacements in the protein are necessary to induce transitions in social organization in fire ants. On the other hand, polygyne S. geminata differs genetically from the monogyne form in ways not mirrored in the two forms of S. invicta, a well-studied member of the S. richteri clade, supporting the conclusion that polygyny did not evolve via analogous routes in the two lineages. Specifically, polygyne S. geminata has lower genetic diversity and different gene frequencies than the monogyne form, suggesting that the polygyne form originated via a founder event from a local monogyne population. These comparative data suggest an alternative route to polygyny in S. geminata in which loss of allelic variation at genes encoding recognition cues has led to a breakdown in discrimination abilities and the consequent acceptance of multiple queens in colonies.

Potential cause of lethality of an allele implicated in social evolution in fire ants.

The gene Gp-9 is believed to have a major effect on colony social organization in fire ants, with the presence of b-like alleles in a colony associated with multiple-queen (polygyne) organization. Queens and workers of polygyne Solenopsis invicta homozygous for the b-like allele designated b suffer reduced viability compared to other genotypes, and bb queens do not survive to become egg-layers. Thus, the b allele effectively acts as a recessive lethal. This allele differs from the remaining b-like alleles (designated b'), as well as all other Gp-9 alleles, by encoding a lysine at position 151 in the protein product, suggesting that this substitution is responsible for its deleterious effects. We tested this hypothesis by comparing frequencies of b'b' and bb homozygotes, first in queens of Solenopsis richteri and S. invicta, then in S. invicta workers from populations polymorphic for the two b-like alleles. We found that almost 20% of S. richteri queens were b'b' homozygotes, compared to the virtual absence of bb homozygotes among S. invicta queens, and that 5-18% of S. invicta workers bore genotype b'b', compared to the apparent lack of bb workers in the same populations. While we cannot entirely rule out involvement of other genes in complete gametic disequilibrium with Gp-9, our data are consistent with the hypothesis that the Lys(151) residue in GP-9 protein confers the deleterious effects of the b allele in homozygous condition, possibly by impairing the protein's function through interference with ligand binding/release or hindrance of dimer formation.

To b or not to b: a pheromone-binding protein regulates colony social organization in fire ants.

A major distinction in the social organization of ant societies is the number of reproductive queens that reside in a single colony. The fire ant Solenopsis invicta exists in two distinct social forms, one with colonies headed by a single reproductive queen and the other containing several to hundreds of egg-laying queens. This variation in social organization has been shown to be associated with genotypes at the gene Gp-9. Specifically, single-queen colonies have only the B allelic variant of this gene, whereas multiple-queen colonies always have the b variant as well. Subsequent studies revealed that Gp-9 shares the highest sequence similarity with genes encoding pheromone-binding proteins (PBPs). In other insects, PBPs serve as central molecular components in the process of chemical recognition of conspecifics. Fire ant workers regulate the number of egg-laying queens in a colony by accepting queens that produce appropriate chemical signals and destroying those that do not. The likely role of GP-9 in chemoreception suggests that the essential distinction in colony queen number between the single and multiple-queen form originates from differences in workers' abilities to recognize queens. Other, closely related fire ant species seem to regulate colony social organization in a similar fashion.

Molecular evolutionary analyses of the odorant-binding protein gene Gp-9 in fire ants and other Solenopsis species.

The fire ant Solenopsis invicta exists in two social forms, one with colonies headed by a single reproductive queen (monogyne form) and the other with colonies containing multiple queens (polygyne form). This variation in social organization is associated with variation at the gene Gp-9, with monogyne colonies harboring only the B allelic variant and polygyne colonies containing b-like variants as well. We generated new Gp-9 sequences from 15 Solenopsis species and combined these with previously published sequences to conduct a comprehensive, phylogenetically based study of the molecular evolution of this important gene. The exon/intron structure and the respective lengths of the five exons of Gp-9 are identical across all species examined, and we detected no evidence for intragenic recombination. These data conform to a previous suggestion that Gp-9 lies in a genomic region with low recombination, and they indicate that evolution of the coding region in Solenopsis has involved point substitutions only. Our results confirm a link between the presence of b-like alleles and the expression of polygyny in all South American fire ant species known to possess colonies of both social forms. Moreover, phylogenetic analyses show that b-like alleles comprise a derived clade of Gp-9 sequences within the socially polymorphic species, lending further support to the hypothesis that monogyny preceded polygyny in this group of fire ants. Site-specific maximum likelihood tests identified several amino acids that have experienced positive selection, two of which are adjacent to the inferred binding-pocket residues in the GP-9 protein. Four other binding-pocket residues are variable among fire ant species, although selection is not implicated in this variation. Branch-specific tests revealed strong positive selection on the stem lineage of the b-like allele clade, as expected if selection drove the amino acid replacements crucial to the expression of polygyne social organization. Such selection may have operated via the ligand-binding properties of GP-9, as one of the two amino acids uniquely shared by all b-like alleles is predicted to be a binding-pocket residue.

Identification of a major gene regulating complex social behavior.

Colony queen number, a major feature of social organization in fire ants, is associated with worker genotypes at the gene Gp-9. We sequenced Gp-9 and found that it encodes a pheromone-binding protein, a crucial molecular component in chemical recognition of conspecifics. This suggests that differences in worker Gp-9 genotypes between social forms may cause differences in workers' abilities to recognize queens and regulate their numbers. Analyses of sequence evolution indicate that regulation of social organization by Gp-9 is conserved in South American fire ant species exhibiting social polymorphism and suggest that positive selection has driven the divergence between the alleles associated with alternate social organizations. This study demonstrates that single genes of major effect can underlie the expression of complex behaviors important in social evolution.