Modulation of the asymmetry of sea urchin sperm flagellar bending by calmodulin

Sea urchin spermatozoa demembranated with Triton X-100 in the presence of EGTA, termed potentially asymmetric, generate asymmetric bending waves in reactivation solutions containing EGTA. After they are converted to the potentially symmetric condition by extraction with Triton and millimolar Ca++, they generate symmetric bending waves in reactivation solutions containing EGTA. In the presence of EGTA, their asymmetry can be restored by addition of brain calmodulin or the concentrated supernatant obtained from extraction with Triton and millimolar Ca++. These extracts contain calmodulin, as assayed by gel electrophoresis, radioimmunoassay, activation of brain phosphodiesterase, and Ca++-dependent binding of asymmetry-restoring activity to a trifluorophenothiazine-affinity resin. Conversion to the potentially symmetric condition can also be achieved with trifluoperazine substituted for Triton during the exposure to millimolar Ca++, which suggests that the calmodulin-binding activity of Triton is important for this conversion. These observations suggest that the conversion to the potentially symmetric condition is the result of removal of some of the axonemal calmodulin and provide additional evidence for axonemal calmodulin as a mediator of the effect of Ca++ on the asymmetry of flagellar bending

Effects of antibodies against dynein and tubulin on the stiffness of flagellar axonemes

Antidynein antibodies, previously shown to inhibit flagellar oscillation and active sliding of axonemal microtubules, increase the bending resistance of axonemes measured under relaxing conditions, but not the bending resistance of axonemes measured under rigor conditions. These observations suggest that antidynein antibodies can stabilize rigor cross-bridges between outer-doublet microtubules, by interfering with ATP-induced cross-bridge detachment. Stabilization of a small number of cross-bridge appears to be sufficient to cause substantial inhibition of the frequency of flagellar oscillation. Antitubulin antibodies, previously shown to inhibit flagellar oscillation without inhibiting active sliding of axonemal microtubules, do not increase the static bending resistance of axonemes. However, we observed a viscoelastic effect, corresponding to a large increase in the immediate bending resistance. This immediate bending resistance increase may be sufficient to explain inhibition of flagellar oscillation; but several alternative explanations cannot yet be excluded

Phylogeny and floral character evolution of Mentzelia section Bicuspidaria (Loasaceae)

Mentzelia section Bicuspidaria (Loasaceae) is a monophyletic group of desert ephemerals that inhabit the complex, heterogeneous landscapes of the southwestern United States and northwestern Mexico. To investigate species circumscriptions and evolutionary relationships in M. sect. Bicuspidaria, we employed phylogeny reconstructions based on DNA sequences from the plastid trnL-trnF, trnS-trnfM, ndhF-rpl32, and rpl32-trnL regions and the nuclear ribosomal ITS and ETS regions. Due to evidence of discordant relationships reconstructed from the plastid and nuclear partitions, we used coalescent-based methods in addition to concatenated data sets to estimate the species tree. Maximum likelihood reconstructions based on the combined plastid and nuclear data and coalescent-based reconstructions inferred congruent, fully-resolved species-level phylogenies of M. sect. Bicuspidaria. A monophyletic M. sect. Bicuspidaria was composed of two main clades, which corresponded to a clade of species endemic to the United States composed of M. reflexa, M. tricuspis, and M. tridentata that was sister to a clade of species at least partially distributed in Mexico, composed of M. hirsutissima and M. involucrata. Despite the unusual floral morphology of M. reflexa, molecular reconstructions placed M. reflexa sister to M. tridentata. All species of M. sect. Bicuspidaria were monophyletic, except for M. hirsutissima, which was composed of two distinct lineages and paraphyletic with respect to M. involucrata. The northern clade of M. hirsutissima from California and Baja California was sister to M. involucrata, and both, in turn, were sister to a geographically disjunct southern clade of M. hirsutissima from Baja California Sur and Cedros Island. These phylogeny reconstructions provide evidence for the inclusion of five species in M. sect. Bicuspidaria and have uncovered cryptic diversity that has been largely unrecognized. Character state reconstructions based on the phylogeny of M. sect. Bicuspidaria suggest innovative and, at times, homoplasious floral evolution

Rapid changes in shape and number of MHC class II expressing cells in rat airways after Mycoplasma pulmonis infection

This article is made available for unrestricted research re-use and secondary analysis in any form or by any means with acknowledgement of the original source. These permissions are granted for the duration of the World Health Organization (WHO) declaration of COVID-19 as a global pandemic.Mycoplasma pulmonis infection in rodents causes a chronic inflammatory airway disease with a strong immunological component, leading to mucosal remodeling and angiogenesis. We sought to determine the effect of this infection on the shape and number of dendritic cells and other major histocompatibility complex (MHC) class II expressing cells in the airway mucosa of Wistar rats. Changes in the shape of subepithelial OX6 (anti-MHC class II)-immunoreactive cells were evident in the tracheal mucosa 2 days after intranasal inoculation with M. pulmonis. By 1 week, the shape of the cells had changed from stellate to rounded (mean shape index increased from 0.42 to 0.77). The number of OX6-positive cells was increased 6-fold at 1 week and 16-fold at 4 weeks. Coincident with these changes, many columnar epithelial cells developed OX6 immunoreactivity, which was still present at 4 weeks. We conclude that M. pulmonis infection creates a potent immunologic stimulus that augments and transforms the OX6-immunoreactive cell population in the airways by changing the functional state of airway dendritic cells, initiating an influx of MHC class II expressing cells, and activating expression of MHC class II molecules by airway epithelial cells

Mentzelia pectinata var. chrysopetala (Loasaceae), a yellow-petaled race from west-central California

Mentzelia pectinata Kellogg var. chrysopetala Keil & Brokaw, var. nov., is a yellow-petaled race of the otherwise orange-petaled M. pectinata, a species endemic to central California. The yellow-and orange-petaled varieties are largely allopatric, with var. chrysopetala nearly restricted to San Luis Obispo County, whereas var. pectinata extends eastward into the dry hills and mountains around the southern end of the San Joaquin Valley, including eastern portions of San Luis Obispo County. Petals of var. chrysopetala are golden yellow, usually with orange bases, unlike the petals of var. pectinata, which are coppery orange with red-orange bases. We designate a neotype for M. pectinata because original material, which presumably was in CAS, apparently is no longer extant; the holotype was probably destroyed in the 1906 San Francisco earthquake and fire. Mentzelia pectinata Kellogg is an annual species endemic to the southern part of California\u27s San Joaquin Valley and the surrounding hills and mountains of the South Coast Range, Transverse Range, and foothills of the southern Sierra Nevada. In spring growing seasons with abundant rainfall, these plants often form large populations, and the mass displays of their flowers form conspicuous splashes of color across the landscape. The species exhibits two strikingly different flower color forms. Plants from a large part of its range have coppery-orange petals with red-orange bases. Plants from the southern Diablo Range through central San Luis Obispo County and south-central Monterey County have golden yellow petals, usually with orange bases. Taxonomic treatments of these plants have varied. Kellogg (1863) originally described Mentzelia pectinata with flowers of a shining golden color, with a lustrous metallic hue. shading from a deep, vivid orange to a burnt carmine center. Jepson (1925, 1936) treated M. pectinata as part of a broadly defined M. gracilenta Torr. & A.Gray, describing the petals of the species as yellow with orange base. Munz (1959) recognized M. pectinata and described the petals as orange above, coppery-red toward base. Hoover (1970) treated the orange-flowered plants as M. pectinata and the yellow-flowered plants as M. gracilenta. He noted that that flower color appears to be the only reliable differentiation between the two kinds of plants, but that they are distinct ecologically, geographically, and apparently genetically. Brokaw (2016) distinguished diploid M. pectinata from tetraploid M. gracilenta using several characters, including (1) orange petals (in most collections of M. pectinata, absent in M. gracilenta), (2) bracts with white bases (in most collections of M. gracilenta, absent in M. pectinata), and (3) elevation/habitat (M. pectinata occurs at lower elevations than M. gracilenta where the ranges overlap in San Luis Obispo County)

Physical Aspects of Axonemal Beating and Swimming

We discuss a two-dimensional model for the dynamics of axonemal deformations driven by internally generated forces of molecular motors. Our model consists of an elastic filament pair connected by active elements. We derive the dynamic equations for this system in presence of internal forces. In the limit of small deformations, a perturbative approach allows us to calculate filament shapes and the tension profile. We demonstrate that periodic filament motion can be generated via a self-organization of elastic filaments and molecular motors. Oscillatory motion and the propagation of bending waves can occur for an initially non-moving state via an instability termed Hopf bifurcation. Close to this instability, the behavior of the system is shown to be independent of microscopic details of the axoneme and the force-generating mechanism. The oscillation frequency however does depend on properties of the molecular motors. We calculate the oscillation frequency at the bifurcation point and show that a large frequency range is accessible by varying the axonemal length between 1 and 50$\mu$m. We calculate the velocity of swimming of a flagellum and discuss the effects of boundary conditions and externally applied forces on the axonemal oscillations.Comment: 14 pages, 8 figures, REVTE

Does Attending a Regional Medical Campus Influence the Training Outcomes of Family Medicine Residents?

Introduction: Indiana University School of Medicine (IUSM) is the largest medical school in the nation, with its main campus located in Indianapolis and eight regional medical campuses (RMC) distributed across the state. In this study, we compared the survey responses of family medicine residents who had attended medical school at the main campus in Indianapolis versus an RMC to see if there were any noticeable differences in their residency training outcomes. Methods: From 2012 to 2017, in the spring of each year, a cross-sectional survey was administered to all final-year family medicine residents graduating from the eleven family medicine residency programs in Indiana. A total of 519 out of 520 residents completed the survey. Of whom, 132 respondents indicated they had graduated from IUSM; 45 reported they had attended the Indianapolis campus and 87 had attended one of the RMCs in the state. Our dataset for this study was comprised of these 132 respondents. Chi-square test or Fisher’s exact test were used to compare responses between groups. P-values ≤ 0.05 were considered statistically significant. Results: In the ACGME competency areas, the residents who attended an RMC versus the Indianapolis campus were significantly more likely to report being fully competent in Medical Knowledge (90% vs. 76%, p = 0.032) and Systems-Based Practice (83% vs. 64%, p = 0.019). Additionally, the residents who attended an RMC compared to their Indianapolis counterparts reported significantly higher rates of being trained to serve rural populations (73% vs. 52%, p = 0.017) as well as being fully competent to serve rural populations (69% vs. 42%, p = 0.003). However, the residents who attended an RMC were no more likely to establish a practice in a rural area than were the residents who attended Indianapolis (18% vs. 17%, p = 0.845). Conclusions: Based on these self-reported data, the family medicine residents who attended an RMC may perceive themselves to be better-prepared in a few core competency areas, as well as in serving rural populations, compared to those who attended the Indianapolis campus. These findings suggest that IUSM’s complex statewide system of medical education may offer some unique advantages in preparing students for residency, especially in family medicine

Self-organized Beating and Swimming of Internally Driven Filaments

We study a simple two-dimensional model for motion of an elastic filament subject to internally generated stresses and show that wave-like propagating shapes which can propel the filament can be induced by a self-organized mechanism via a dynamic instability. The resulting patterns of motion do not depend on the microscopic mechanism of the instability but only of the filament rigidity and hydrodynamic friction. Our results suggest that simplified systems, consisting only of molecular motors and filaments could be able to show beating motion and self-propulsion.Comment: 8 pages, 2 figures, REVTe

The optimal elastic flagellum

Motile eukaryotic cells propel themselves in viscous fluids by passing waves of bending deformation down their flagella. An infinitely long flagellum achieves a hydrodynamically optimal low-Reynolds number locomotion when the angle between its local tangent and the swimming direction remains constant along its length. Optimal flagella therefore adopt the shape of a helix in three dimensions (smooth) and that of a sawtooth in two dimensions (non-smooth). Physically, biological organisms (or engineered micro-swimmers) must expend internal energy in order to produce the waves of deformation responsible for the motion. Here we propose a physically-motivated derivation of the optimal flagellum shape. We determine analytically and numerically the shape of the flagellar wave which leads to the fastest swimming while minimizing an appropriately-defined energetic expenditure. Our novel approach is to define an energy which includes not only the work against the surrounding fluid, but also (1) the energy stored elastically in the bending of the flagellum, (2) the energy stored elastically in the internal sliding of the polymeric filaments which are responsible for the generation of the bending waves (microtubules), and (3) the viscous dissipation due to the presence of an internal fluid. This approach regularizes the optimal sawtooth shape for two-dimensional deformation at the expense of a small loss in hydrodynamic efficiency. The optimal waveforms of finite-size flagella are shown to depend upon a competition between rotational motions and bending costs, and we observe a surprising bias towards half-integer wave-numbers. Their final hydrodynamic efficiencies are above 6%, significantly larger than those of swimming cells, therefore indicating available room for further biological tuning

Metachronal wave and hydrodynamic interaction for deterministic switching rowers

We employ a model system, called rowers, as a generic physical framework to define the problem of the coordinated motion of cilia (the metachronal wave) as a far from equilibrium process. Rowers are active (two-state) oscillators interacting solely through forces of hydrodynamic origin. In this work, we consider the case of fully deterministic dynamics, find analytical solutions of the equation of motion in the long wavelength (continuum) limit, and investigate numerically the short wavelength limit. We prove the existence of metachronal waves below a characteristic wavelength. Such waves are unstable and become stable only if the sign of the coupling is reversed. We also find that with normal hydrodynamic interaction the metachronal pattern has the form of stable trains of traveling wave packets sustained by the onset of anti-coordinated beating of consecutive rowers.Comment: 11 pages, 7 figure