Motor pattern control for increasing crushing force in the striped burrfish (Chilomycterus schoepfi)

The relationship between muscular force modulation and the underlying nervous system control signals has been difficult to quantify for in vivo animal systems. Our goal was to understand how animals alter muscle activation patterns to increase bite forces and to evaluate how accurate these patterns are in predicting crushing forces. We examined the relationship between commonly used measures of cranial muscle activity and force production during feeding events of the striped burrfish (Chilomycterus schoepfi), a mollusc crushing specialist. We quantified the force required to crush a common gastropod prey item (Littorina irrorata) of burrfish using a materials testing device. Burrfish were fed these calibrated prey items while we recorded electromyograms (EMGs) from the main jaw closing muscles (adductor mandibulae A1beta, A2alpha, and A2beta). We quantified EMG activity by measuring the burst duration, rectified integrated area, and then calculated the intensity of activity from these two variables. Least squares regressions relating force to crush (Fcrush) and all EMG variables were calculated for each fish. Multiple regression analyses were used to determine how much of the variation in Fcrush could be explained by muscle activation patterns. We found that 20 cm burrfish are capable of generating extremely high crushing forces (380 N peak force) primarily by increasing the duration of muscle activity. EMG variables explained 71% of the total variation in force production. After accounting for the inherent variation in Fcrush of snails, EMGs do a very good job of predicting bite forces for these fish.     

Functional morphology of extreme jaw protrusion in Neotropical cichlids

The New World cichlids Petenia splendida and Caquetaia spp. possess extraordinarily protrusible jaws. We investigated the feeding behavior of extreme (here defined as greater than 30% head length) and modest jaw-protruding Neotropical cichlids by comparing feeding kinematics, cranial morphology, and feeding performance. Digital high-speed video (500 fps) of P. splendida, C. spectabile, and Astronotus ocellatus feeding on live guppy prey was analyzed to generate kinematic and performance variables. All three cichlid taxa utilized cranial elevation, lower jaw depression, and rotation of the suspensorium to protrude the jaws during feeding experiments. Extreme anterior jaw protrusion in P. splendida and C. spectabile resulted from augmented lower jaw depression and anterior rotation of the suspensorium. Morphological comparisons among eight cichlid species revealed novel anterior and posterior points of flexion within the suspensorium of P. splendida and Caquetaia spp. The combination of anterior and posterior loosening within the suspensorium in P. splendida and Caquetaia spp. permitted considerable anterior rotation of the suspensorium and contributed to protrusion of the jaws. Petenia splendida and C. spectabile exhibited greater ram distance and higher ram velocities than did A. ocellatus, resulting primarily from increased jaw protrusion. Petenia splendida and C. spectabile exhibited lower suction feeding performance than A. ocellatus, as indicated by lower suction-induced prey movements and velocities. Thus, extreme jaw protrusion in these cichlids may represent an adaptation for capturing elusive prey by enhancing the ram velocity of the predator but does not enhance suction feeding performance.     

Microorganisms cultured from stratospheric air samples obtained at 41 km

Samples of air removed from the stratosphere, at an altitude of 41 km, were previously found to contain viable, but non-cultureable bacteria (cocci and rods). Here, we describe experiments aimed at growing these, together with any other organisms, present in these samples. Two bacteria (Bacillus simplex and Staphylococcus pasteuri) and a single fungus, Engyodontium album (Limber) de Hoog were isolated from the samples. Although the possibility of contamination can never be ruled out when space-derived samples are studied on earth, we are confident that the organisms originated from the stratosphere. Possible mechanisms by which these organisms could have attained such a height are discussed.     

HLA-F is a predominantly empty, intracellular, TAP-associated MHC class Ib protein with a restricted expression pattern

HLA-F is currently the most enigmatic of the human MHC-encoded class Ib genes. We have investigated the expression of HLA-F using a specific Ab raised against a synthetic peptide corresponding to amino acids 61-84 in the alpha1 domain of the predicted HLA-F protein. HLA-F is expressed as a beta2-microglobulin-associated, 42-kDa protein that shows a restricted tissue distribution. To date, we have detected this product only in peripheral blood B cells, B cell lines, and tissues containing B cells, in particular adult tonsil and fetal liver, a major site of B cell development. Thermostability assays suggest that HLA-F is expressed as an empty heterodimer devoid of peptide. Consistent with this, studies using endoglycosidase-H and cell surface immunoprecipitations also indicate that the overwhelming majority of HLA-F contains an immature oligosaccharide component and is expressed inside the cell. We have found that IFN-gamma treatment induces expression of HLA-F mRNA and HLA-F protein, but that this does not result in concomitant cell surface expression. HLA-F associates with at least two components of the conventional class I assembly pathway, calreticulin and TAP. The unusual characteristics of the predicted peptide-binding groove together with the predominantly intracellular localization raise the possibility that HLA-F may be capable of binding only a restricted set of peptides.     

A Model Based on Facilitated Passive Diffusion is Needed to Describe Root Water Entry through Aquaporins

Despite abundant evidence that water transfer from soil to xylem occurs along a pathway regulated by aquaporins (AQPs) water entry is still modeled using principles of ordinary passive diffusion. Problems with this model have been known for some time and include variable intrinsic properties of conductivity Lp, changing reflection coefficients, σ, and an inability to accurately resolve osmotic differentials between the soil and xylem. Here we propose a model of water entry based on principles of facilitated passive diffusion and following Michaelis-Menten formalism. If one accepts that water entry is controlled, at least in part, by AQPs, then a model of ordinary passive diffusion is precluded, as it does not allow for facilitation kinetics. By contrast, recognition of facilitated water entry through protein channels could explain shortcomings of ordinary passive diffusion, such as diurnal variability in conductivity which we have recently shown is directly correlated to diurnal changes in PsPIP2-1 mRNA levels in Pisum sativum.Key Words: aquaporins, root water entry, facilitated passive diffusion, simple passive diffusion, biophysical models