Functional subdivision within a lobster motor unit

Summary A discrete middle band of tonic fibers in the claw closer muscles of lobsters functions as a sub-unit of the slow motor unit in maintaining dactyl posture at a low frequency of firing due to its synaptic properties and strategic location.Supported by National Institute of Health Grant to Dr A. G. Humes and the late Fred Lang.Supported by National Sciences and Engineering Research Council and Muscular Dystrophy Association of Canada.     

Visual cortical cells: How critical is focus?

Zusammenfassung Nachweis, dass rezeptive Kortexfelder der Kaninchen (70% der visuellen Zellen) auf Lichtstimuli bzw. Schärfe-Unschärfe-Änderung mit Amplitudenabfall reagieren.

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This work was supported by U.S.P.H.S. Grant No. EY00576.     

Morphological differences between Saturn's ultraviolet aurorae and those of Earth and Jupiter

It has often been stated that Saturn's magnetosphere and aurorae are intermediate between those of Earth, where the dominant processes are solar wind driven, and those of Jupiter, where processes are driven by a large source of internal plasma. But this view is based on information about Saturn that is far inferior to what is now available. Here we report ultraviolet images of Saturn, which, when combined with simultaneous Cassini measurements of the solar wind and Saturn kilometric radio emission, demonstrate that its aurorae differ morphologically from those of both Earth and Jupiter. Saturn's auroral emissions vary slowly; some features appear in partial corotation whereas others are fixed to the solar wind direction; the auroral oval shifts quickly in latitude; and the aurora is often not centred on the magnetic pole nor closed on itself. In response to a large increase in solar wind dynamic pressure Saturn's aurora brightened dramatically, the brightest auroral emissions moved to higher latitudes, and the dawn side polar regions were filled with intense emissions. The brightening is reminiscent of terrestrial aurorae, but the other two variations are not. Rather than being intermediate between the Earth and Jupiter, Saturn's auroral emissions behave fundamentally differently from those at the other planets.     

Disruption of Bardet-Biedl syndrome ciliary proteins perturbs planar cell polarity in vertebrates

The evolutionarily conserved planar cell polarity (PCP) pathway (or noncanonical Wnt pathway) drives several important cellular processes, including epithelial cell polarization, cell migration and mitotic spindle orientation. In vertebrates, PCP genes have a vital role in polarized convergent extension movements during gastrulation and neurulation. Here we show that mice with mutations in genes involved in Bardet-Biedl syndrome (BBS), a disorder associated with ciliary dysfunction, share phenotypes with PCP mutants including open eyelids, neural tube defects and disrupted cochlear stereociliary bundles. Furthermore, we identify genetic interactions between BBS genes and a PCP gene in both mouse (Ltap, also called Vangl2) and zebrafish (vangl2). In zebrafish, the augmented phenotype results from enhanced defective convergent extension movements. We also show that Vangl2 localizes to the basal body and axoneme of ciliated cells, a pattern reminiscent of that of the BBS proteins. These data suggest that cilia are intrinsically involved in PCP processes.     

A short gamma-ray burst apparently associated with an elliptical galaxy at redshift z = 0.225

Gamma-ray bursts (GRBs) come in two classes: long (> 2 s), soft-spectrum bursts and short, hard events. Most progress has been made on understanding the long GRBs, which are typically observed at high redshift (z approximately 1) and found in subluminous star-forming host galaxies. They are likely to be produced in core-collapse explosions of massive stars. In contrast, no short GRB had been accurately (< 10') and rapidly (minutes) located. Here we report the detection of the X-ray afterglow from--and the localization of--the short burst GRB 050509B. Its position on the sky is near a luminous, non-star-forming elliptical galaxy at a redshift of 0.225, which is the location one would expect if the origin of this GRB is through the merger of neutron-star or black-hole binaries. The X-ray afterglow was weak and faded below the detection limit within a few hours; no optical afterglow was detected to stringent limits, explaining the past difficulty in localizing short GRBs.     

At least two toxins are involved inEscherichia coli mastitis

Summary Culture filtrate ofEscherichia coli produces changes in the bovine udder identical to those seen in experimental infections with the same organism.E. coli endotoxin produces an acute inflammatory response but none of the cell damage induced by culture filtrate. It appears therefore that at least 2 toxins are involved in the disease.Acknowledgments. We are grateful to Mrs K. Wells, Miss H. Meads and Miss A. Ashford for technical assistance.     

Evolution and maintenance of cooperation via inheritance of neighborhood relationship

Cooperative behaviors are ubiquitous in nature and human society. It is very important to understand the internal mechanism of emergence and maintenance of cooperation. As we know now, the offsprings inherit not only the phenotype but also the neighborhood relationship of their parents. Some recent research results show that the interactions among individuals facilitate survival of cooperation through network reciprocity of clustering cooperators. This paper aims at introducing an inheritance mechanism of neighborhood relationship to explore the evolution of cooperation. In detail, a mathematical model is proposed to characterize the evolutionary process with the above inheritance mechanism. Theoretical analysis and numerical simulations indicate that high-level cooperation can emerge and be maintained for a wide variety of cost-to-benefit ratios, even if mutation happens during the evolving process.     

Opposing effects of polyglutamine expansion on native protein complexes contribute to SCA1

Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited neurodegenerative disease caused by expansion of a glutamine-encoding repeat in ataxin 1 (ATXN1). In all known polyglutamine diseases, the glutamine expansion confers toxic functions onto the protein; however, the mechanism by which this occurs remains enigmatic, in light of the fact that the mutant protein apparently maintains interactions with its usual partners. Here we show that the expanded polyglutamine tract differentially affects the function of the host protein in the context of different endogenous protein complexes. Polyglutamine expansion in ATXN1 favours the formation of a particular protein complex containing RBM17, contributing to SCA1 neuropathology by means of a gain-of-function mechanism. Concomitantly, polyglutamine expansion attenuates the formation and function of another protein complex containing ATXN1 and capicua, contributing to SCA1 through a partial loss-of-function mechanism. This model provides mechanistic insight into the molecular pathogenesis of SCA1 as well as other polyglutamine diseases.