Measurement of the Excitation Spectrum of a Dipolar Gas in the Macrodroplet Regime.

The excitation spectrum of a cigar-shaped strongly dipolar quantum gas at the crossover from a Bose-Einstein condensate to a trapped macrodroplet is predicted to exhibit peculiar features-a strong upward shift of low momentum excitation energies together with a strong multiband response for high momenta. By performing Bragg spectroscopy over a wide range of momenta, we observe both key elements and also confirm the predicted stiffening of excitation modes when approaching the macrodroplet regime. Our measurements are in good agreement with numerical calculations taking into account finite size effects.

Quantum Droplet States of a Binary Magnetic Gas.

Quantum droplets can emerge in bosonic binary magnetic gases (BMGs) from the interplay of short- and long-ranged interactions, and quantum fluctuations. We develop an extended mean field theory for this system and use it to predict equilibrium and dynamical properties of BMG droplets. We present a phase diagram and characterize miscible and immiscible droplet states. We also show that a single-component self-bound droplet can bind another magnetic component, which is not in the droplet regime, due to the interspecies dipole-dipole interactions. Our results should be realizable in experiments with mixtures of highly magnetic lanthanide atoms.

Droplet Crystal Ground States of a Dipolar Bose Gas.

We show that the ground state of a dipolar Bose gas in a cylindrically symmetric harmonic trap has a rich phase diagram, including droplet crystal states in which a set of droplets arrange into a lattice pattern that breaks the rotational symmetry. An analytic model for small droplet crystals is developed and used to obtain a zero temperature phase diagram that is numerically validated. We show that in certain regimes a coherent low-density halo surrounds the droplet crystal, giving rise to a novel phase with localized and extended features.

Collective Excitations of Self-Bound Droplets of a Dipolar Quantum Fluid.

We calculate the collective excitations of a dipolar Bose-Einstein condensate in the regime where it self-binds into droplets stabilized by quantum fluctuations. We show that the filament-shaped droplets act as a quasi-one-dimensional waveguide along which low-angular-momentum phonons propagate. The evaporation (unbinding) threshold occurring as the atom number N is reduced to the critical value N_{c} is associated with a monopolelike excitation going soft as ε_{0}∼(N-N_{c})^{1/4}. Considering the system in the presence of a trapping potential, we quantify the crossover from a trap-bound condensate to a self-bound droplet.

Number fluctuations of a dipolar condensate: anisotropy and slow approach to the thermodynamic regime.

We present a theory for the number fluctuations of a quasi-two-dimensional (quasi-2D) dipolar Bose-Einstein condensate measured with finite resolution cells. We show that when the dipoles are tilted to have a component parallel to the plane of the trap, the number fluctuations become anisotropic, i.e., depend on the in-plane orientation of the measurement cell. We develop analytic results for the quantum and thermal fluctuations applicable to the cell sizes accessible in experiments. We show that as cell size is increased the thermodynamic fluctuation result is approached much more slowly than in condensates with short range interactions, so experiments would not require high numerical aperture imaging to observe the predicted effect.

LET-413 is a basolateral protein required for the assembly of adherens junctions in Caenorhabditis elegans.

Epithelial cells are polarized, with apical and basal compartments demarcated by tight and adherens junctions. Proper establishment of these subapical junctions is critical for normal development and histogenesis. We report the characterization of the gene let-413 which has a critical role in assembling adherens junctions in Caenorhabditis elegans. In let-413 mutants, adherens junctions are abnormal and mislocalized to more basolateral positions, epithelial cell polarity is affected and the actin cytoskeleton is disorganized. The LET-413 protein contains one PDZ domain and 16 leucine-rich repeats with high homology to proteins known to interact with small GTPases. Strikingly, LET-413 localizes to the basolateral membrane. We suggest that LET-413 acts as an adaptor protein involved in polarizing protein trafficking in epithelial cells.

UNC-60B, an ADF/cofilin family protein, is required for proper assembly of actin into myofibrils in Caenorhabditis elegans body wall muscle.

The Caenorhabditis elegans unc-60 gene encodes two functionally distinct isoforms of ADF/cofilin that are implicated in myofibril assembly. Here, we show that one of the gene products, UNC-60B, is specifically required for proper assembly of actin into myofibrils. We found that all homozygous viable unc-60 mutations resided in the unc-60B coding region, indicating that UNC-60B is responsible for the Unc-60 phenotype. Wild-type UNC-60B had F-actin binding, partial actin depolymerizing, and weak F-actin severing activities in vitro. However, mutations in UNC-60B caused various alterations in these activities. Three missense mutations resulted in weaker F-actin binding and actin depolymerizing activities and complete loss of severing activity. The r398 mutation truncated three residues from the COOH terminus and resulted in the loss of severing activity and greater actin depolymerizing activity. The s1307 mutation in a putative actin-binding helix caused greater activity in actin-depolymerizing and severing. Using a specific antibody for UNC-60B, we found varying protein levels of UNC-60B in mutant animals, and that UNC-60B was expressed in embryonic muscles. Regardless of these various molecular phenotypes, actin was not properly assembled into embryonic myofibrils in all unc-60 mutants to similar extents. We conclude that precise control of actin filament dynamics by UNC-60B is required for proper integration of actin into myofibrils.

MUP-4 is a novel transmembrane protein with functions in epithelial cell adhesion in Caenorhabditis elegans.

Tissue functions and mechanical coupling of cells must be integrated throughout development. A striking example of this coupling is the interactions of body wall muscle and hypodermal cells in Caenorhabditis elegans. These tissues are intimately associated in development and their interactions generate structures that provide a continuous mechanical link to transmit muscle forces across the hypodermis to the cuticle. Previously, we established that mup-4 is essential in embryonic epithelial (hypodermal) morphogenesis and maintenance of muscle position. Here, we report that mup-4 encodes a novel transmembrane protein that is required for attachments between the apical epithelial surface and the cuticular matrix. Its extracellular domain includes epidermal growth factor-like repeats, a von Willebrand factor A domain, and two sea urchin enterokinase modules. Its intracellular domain is homologous to filaggrin, an intermediate filament (IF)-associated protein that regulates IF compaction and that has not previously been reported as part of a junctional complex. MUP-4 colocalizes with epithelial hemidesmosomes overlying body wall muscles, beginning at the time of embryonic cuticle maturation, as well as with other sites of mechanical coupling. These findings support that MUP-4 is a junctional protein that functions in IF tethering, cell-matrix adherence, and mechanical coupling of tissues.

Description of International Caenorhabditis elegans Experiment first flight (ICE-FIRST).

Traveling, living and working in space is now a reality. The number of people and length of time in space is increasing. With new horizons for exploration it becomes more important to fully understand and provide countermeasures to the effects of the space environment on the human body. In addition, space provides a unique laboratory to study how life and physiologic functions adapt from the cellular level to that of the entire organism. Caenorhabditis elegans is a genetic model organism used to study physiology on Earth. Here we provide a description of the rationale, design, methods, and space culture validation of the ICE-FIRST payload, which engaged C. elegans researchers from four nations. Here we also show C. elegans growth and development proceeds essentially normally in a chemically defined liquid medium on board the International Space Station (10.9 day round trip). By setting flight constraints first and bringing together established C. elegans researchers second, we were able to use minimal stowage space to successfully return a total of 53 independent samples, each containing more than a hundred individual animals, to investigators within one year of experiment concept. We believe that in the future, bringing together individuals with knowledge of flight experiment operations, flight hardware, space biology, and genetic model organisms should yield similarly successful payloads.

THE CAENORHABDITIS ELEGANS GENOME: A Guide in The Post Genomics Age.

The completion of the entire genome sequence of the free-living nematode, Caenorhabditis elegans is a tremendous milestone in modern biology. Not only will scientists be poring over data mined from this resource, but techniques and methodologies developed along the way have changed the way we can approach biological questions. The completion of the C. elegans genomic sequence will be of particular importance to scientists working on parasitic nematodes. In many cases, these nematode species present intractable challenges to those interested in their biology and genetics. The data already compared from parasites to the C. elegans database reveals a wealth of opportunities for parasite biologists. It is likely that many of the same genes will be present in parasites and that these genes will have similar functions. Additional information regarding differences between free-living and parasitic species will provide insight into the evolution and nature of parasitism. Finally, genetic and genomic approaches to the study of parasitic nematodes now have a clearly marked path to follow.

Minimal skin dose increase in longitudinal rotating biplanar linac-MR systems: examination of radiation energy and flattening filter design.

The magnetic fields of linac-MR systems modify the path of contaminant electrons in photon beams, which alters patient entrance skin dose. Also, the increased SSD of linac-MR systems reduces the maximum achievable dose rate. To accurately quantify the changes in entrance skin dose, the authors use EGSnrc Monte Carlo calculations that incorporate 3D magnetic field of the Alberta 0.5 T longitudinal linac-MR system. The Varian 600C linac head geometry assembled on the MRI components is used in the BEAMnrc simulations for 6 MV and 10 MV beam models and skin doses are calculated at an average depth of 70 µm using DOSXYZnrc. 3D modeling shows that magnetic fringe fields decay rapidly and are small at the linac head. SSDs between 100 and 120 cm result in skin-dose increases of between ~6%-19% and ~1%-9% for the 6 and 10 MV beams, respectively. For 6 MV, skin dose increases from ~10.5% to ~1.5% for field-size increases of 5 × 5 cm(2) to 20 × 20 cm(2). For 10 MV, skin dose increases by ~6% for a 5 × 5 cm(2) field, and decreases by ~1.5% for a 20 × 20 cm(2) field. Furthermore, the proposed reshaped flattening filter increases the dose rate from the current 355 MU min(-1) to 529 MU min(-1) (6 MV) or 604 MU min(-1) (10 MV), while the skin-dose increases by only an additional ~2.6% (all percent increases in skin dose are relative to D max). This study suggests that there is minimal increase in the entrance skin dose and minimal/no decrease in the dose rate of the Alberta longitudinal linac-MR system. The even lower skin dose increase at 10 MV offers further advantages in future designs of linac-MR prototypes.

let-756, a C. elegans fgf essential for worm development.

In vertebrates, Fibroblast Growth Factors (FGFs) and their receptors are involved in various developmental and pathological processes, including neoplasia. The number of FGFs and their large range of activities have made the understanding of their precise functions difficult. Investigating their biology in other species might be enlightening. A sequence encoding a putative protein presenting 30-40% identity with the conserved core of vertebrate FGFs has been identified by the C. elegans sequencing consortium. We show here that this gene is transcribed and encodes a putative protein of 425 amino acids (aa). The gene is expressed at all stages of development beyond late embryogenesis, peaking at the larval stages. Loss-of-function mutants of the let-756 gene are rescued by the wild type fgf gene in germline transformation experiments. Two partial loss-of-function alleles, s2613 and s2809, have a mutation that replaces aa 317 by a stop. The truncated protein retains the FGF core but lacks a C-termins portion. These worms are small and develop slowly into clear and scrawny, yet viable and fertile adults. A third allele, s2887, is inactivated by an inversion that disrupts the first exon. It causes a developmental arrest early in the larval stages. Thus, in contrast to the other nematode fgf gene egl-17, let-756/fgf is essential for worm development.

The genetic analysis of a reciprocal translocation, eT1(III; V), in Caenorhabditis elegans.

The Caenorhabditis elegans mutation e873, which results in a recessive uncoordinated phenotype (formerly named Unc-72) and which had been isolated after 32P treatment (Brenner 1974), has now been found to act as a crossover suppressor and to be associated with a translocation between linkage groups (LG's) III and V. The translocation has been named, eT1(III; V); eT1 acts as a dominant crossover suppressor for both the right half of LGIII and the left half of LGV, providing a balancer for a total of 39 map units. The uncoordinated e873 phenotype has been shown to be a consequence of an inactive unc-36III gene. It was possible to demonstrate that, in translocation heterozygotes, eT1 chromosomes marked with either sma-3 or dpy-11 segregate from normal LGIII, while those marked with bli-5, sma-2 or unc-42 segregate from normal LGV. Since bli-5 and sma-2 are normally on LGIII, and dpy-11 is normally on LGV, it is concluded that: (a) eT1 is a reciprocal translocation; (b) there is a breakpoint between sma-3 and sma-2 in LGIII (the region containing unc-36) and one between dpy-11 and unc-42 in LGV; (c) there is no dominant centromere between sma-2 and bli-5 on LGIII, since in eT1 these genes are not linked to a LGIII centromere. Similarly, it is highly unlikely that there is a centromere to the left of dpy-11 on LGV. The new gene order in eT1 was determined by measuring recombination rates between markers in eT1 homozygotes. It is concluded that the new order is: dpy-1 sma-3 (break) dpy-11 unc-60, and bli-5 sma-2 (break) unc-42 unc-51.--This is the first analysis of a C. elegans translocation with respect to reciprocity, breakpoints and new gene order.

Genetic organization of the region around UNC-15 (I), a gene affecting paramyosin in Caenorhabditis elegans.

In the nematode Caenorhabditis elegans mutants in the gene unc-15 (I) affect the muscle protein paramyosin (Waterston, Fishpool and Brenner 1977). We have characterized 20 ethyl methanesulfonate-induced mutations in essential genes closely linked to unc-15. These lethals defined 16 new complementation groups. In the 0.65 map-unit interval around unc-15 defined by dpy-14 and unc-56, seven newly identified genes have been mapped relative to five existing genes. At present, the average distance between genes in this region is approximately 0.05 map units. Two genes, unc-15 and unc-13, are only 0.025 map units apart. Partial fine-structures maps of alleles of these two genes have been constructed. This analysis of unc-15 and genes adjacent to it is the first in a series of genetic and biochemical studies directed towards understanding the control of unc-15 expression.

Genetic Organization in CAENORHABDITIS ELEGANS: Fine-Structure Analysis of the unc-22 Gene.

Fine-structure analysis of the unc-22 gene of Caenorhabditis elegans has revealed a number of sites that are separable by recombination. Eight new ethyl methanesulfonate-induced recessive mutations of the unc-22 gene have been isolated. Using these new alleles, as well as e66, a number of separable sites have been identified and positioned relative to one another. The map distances obtained are found to be comparable to those associated with intragenic recombination in Drosophila melanogaster, indicating that genetic fine-structure analysis is feasible in Caenorhabditis elegans. Evidence of possible gene conversion is presented. A preliminary estimate of the unc-22 gene size is 2.4 x 10(-2) map units.

The Effect of Temperature and Parental Age on Recombination and Nondisjunction in CAENORHABDITIS ELEGANS.

The effect of temperature and parental age on recombination frequency in C. elegans was studied between pairs of closely linked markers on linkage groups I and V. In the regions studied, recombination frequency varied three-fold over the temperature range 13.5 degrees to 26 degrees . Temperature-shift experiments indicated that a temperature-sensitive recombination event occurs approximately 50 oocytes prior to fertilization. Recombination frequency was observed to decrease with maternal age. The greatest decrease was observed in the first 24 hours of egg production. The frequency of male progeny, a measure of X-chromosome nondisjunction was also studied. This frequency increased with elevated temperature and age of the parent.

Genetic analysis of a major segment [LGV(left)] of the genome of Caenorhabditis elegans.

From 10,900 F1 progeny of ethyl methanesulfonate (EMS)-mutagenized Caenorhabditis elegans nematodes, we isolated 194 lethal mutations on the left arm of LGV, a region balanced by the reciprocal translocation of eT1. The analysis of 166 of those mutations resulted in the identification of one deficiency and alleles of 78 genes including 38 new genes, thus increasing the number of identified essential genes to 101. We estimate that there are a minimum of 120 essential genes in this region, which comprises approximately 7% of the recombinational distance, although only about 4.2% of the genes, in C. elegans. We calculate that there are a minimum of 2850 essential genes in the genome. The left arm of LGV has two recombinational gene clusters separated by a high-recombination and/or essential gene-sparse region. One gene in this region, let-330, is the largest EMS target on the left arm of LGV, with twice as many alleles (16) as the next most EMS-mutable genes, let-332 and rol-3. Another gene in the sparse region, lin-40, and the region near lin-40 are major targets for Tc1 mobilization-induced mutagenesis. The analysis of essential genes in large regions should help to define C. elegans in terms of all its genes and aid in the understanding of the relationship of genome structure to genome function.

Mutagenesis in Caenorhabditis elegans. II. A spectrum of mutational events induced with 1500 r of gamma-radiation.

We previously established a gamma-ray dose-response curve for recessive lethal events (lethals) captured over the eT1 balancer. In this paper we analyze the nature of lethal events produced, with a frequency of 0.04 per eT1 region, at a dose of 1500 r. To do so, we developed a protocol that, in the absence of cytogenetics, allows balanced lethals to be analyzed for associated chromosomal rearrangements. A set of 35 lethal strains was chosen for the analysis. Although the dosage was relatively low, a large number of multiple-break events were observed. The fraction of lethals associated with rearrangements was found to be 0.76. Currently most X- and gamma-ray dosages used for mutagenesis in C. elegans are 6000-8000 r. From our data we conservatively estimated that 43% of rearrangements induced with 8000 r would be accompanied by additional chromosome breaks in the genome. With 1500 r the value was 5%. The 35 lethals studied were derived from 875 screened F1's. Among these lethals there were (1) at least two unc-36 duplications, (2) at least four translocations, (3) at least six deficiencies of chromosome V (these delete about 90% of the unc-60 to unc-42 region) and (4) several unanalyzed rearrangements. Thus, it is possible to recover desired rearrangements at reasonable rates with a dose of only 1500 r. We suggest that the levels of ionizing radiation employed in most published C. elegans studies are excessive and efforts should be made to use reduced levels in the future.

Essential genes and deficiencies in the unc-22 IV region of Caenorhabditis elegans.

Five formaldehyde-induced deficiencies that uncover unc-22 IV, a gene affecting muscle structure in the nematode Caenorhabditis elegans were isolated and positioned. The largest deficiency, sDf2, extends in both directions from unc-22 and is approximately 1.0-2.0 map units in length. The other four deficiencies, sDf7, sDf8, sDf9 and sDf10, are all smaller than sDf2 and are located within the region uncovered by this deficiency. Thirty-seven ethyl methane-sulfonate-induced lethal and sterile mutations linked to unc-22 were isolated and tested for complementation with sDf2. Nineteen lethal mutations failed to complement sDf2. Sixteen of these were further positioned by recombination mapping and also by deficiency mapping with sDf7, sDf8, sDf9 and sDf10. These sixteen mutations define 11 new essential genes in this region. Eight of the genes lie in a 0.9-map unit interval to the left of unc-22, whereas the three remaining genes lie in a region of about 0.2 map units to the right of unc-22. We believe that two of the essential genes identified in this study, let-56 and let-52, are the adjacent genes on either side of unc-22. The lethal mutations exhibit a wide range of terminal phenotypes: from first stage larva to sterile adult.

Pairing for recombination in LGV of Caenorhabditis elegans: a model based on recombination in deficiency heterozygotes.

The effect of deficiencies on recombination was studied in Caenorhabditis elegans. Heterozygous deficiencies in the left half of linkage group V [LGV(left)] were shown to inhibit recombination to their right. Fourteen deficiencies, all to the left of unc-46, were analyzed for their effect on recombination along LGV. The deficiencies fell into two groups: 10 "major inhibitors" which reduce recombination to less than 11% of the expected rate between themselves and unc-46; and four "minor inhibitors" which reduce recombination, but to a much lesser extent. All four minor inhibitors delete the left-most known gene on the chromosome, while six of the ten major inhibitors do not (i.e., these are "internal" deficiencies). Where recombination could be measured on both sides of a deficiency, recombination was inhibited to the right but not to the left. In order to explain these results we have erected a model for the manner in which pairing for recombination takes place. In doing so, we identify a new region of LGV, near the left terminus, that is important for the pairing process.