Habituation to environmental enrichment in captive sloth bears—effect on stereotypies

The benefits to captive animals of environmental enrichment (EE) are widely recognized. Few studies have, however, studied how to maximise the effect of EE. One issue with EE programs seems to be habituation to the enrichment device. To study the effect of habituation to EE, 14 captive sloth bears (Melursus ursinus) were subjected to two different EE treatments. Treatment one presented EE (logs with honey containing holes) for five consecutive days, whereas treatment two presented EE on intermittent days for five days. Intermittent presentations tended to reduce habituation toward the EE. Both consecutive and intermittent presentations significantly reduced stereotypies; however, the consecutive presentations had a longer‐lasting effect. Explorative behaviors increased in both treatments, consistent with earlier findings that EE increase levels of natural behaviors. Other behaviors were unaffected by the EE presentations. The results show that intermittent presentation of EE objects may secure the interest of the animals, but continuous access to enrichment may be more efficient in reducing stereotypies in the long run. Zoo Biol 29:705–714, 2010. © 2010 Wiley‐Liss, Inc.     

Light-dependent orientation responses in animals can be explained by a model of compass cue integration

The magnetic compass sense of animals is currently thought to be based on light-dependent processes like the proposed radical pair mechanism. In accordance, many animals show orientation responses that depend on light. However, the orientation responses depend on the wavelength and irradiance of monochromatic light in rather complex ways that cannot be explained directly by the radical pair mechanism. Here, a radically different model is presented that can explain a vast majority of the complex observed light-dependent responses. The model put forward an integration process consisting of simple lateral inhibition between a normal functioning, light-independent magnetic compass (e.g. magnetite based) and a vision based skylight color gradient compass that misperceives compass cues in monochromatic light. Integration of the misperceived color compass cue and the normal magnetic compass not only explains most of the categorically different light-dependent orientation responses, but also shows a surprisingly good fit to how well the animals are oriented (r-values) under light of different wavelength and irradiance. The model parsimoniously suggests the existence of a single magnetic sense in birds (probably based on magnetic crystals).     

Membrane Curvature Induction and Tubulation Are Common Features of Synucleins and Apolipoproteins

Synucleins and apolipoproteins have been implicated in a number of membrane and lipid trafficking events. Lipid interaction for both types of proteins is mediated by 11 amino acid repeats that form amphipathic helices. This similarity suggests that synucleins and apolipoproteins might have comparable effects on lipid membranes, but this has not been shown directly. Here, we find that α-synuclein, β-synuclein, and apolipoprotein A-1 have the conserved functional ability to induce membrane curvature and to convert large vesicles into highly curved membrane tubules and vesicles. The resulting structures are morphologically similar to those generated by amphiphysin, a curvature-inducing protein involved in endocytosis. Unlike amphiphysin, however, synucleins and apolipoproteins do not require any scaffolding domains and curvature induction is mediated by the membrane insertion and wedging of amphipathic helices alone. Moreover, we frequently observed that α-synuclein caused membrane structures that had the appearance of nascent budding vesicles. The ability to function as a minimal machinery for vesicle budding agrees well with recent findings that α-synuclein plays a role in vesicle trafficking and enhances endocytosis. Induction of membrane curvature must be under strict regulation in vivo; however, as we find it can also cause disruption of membrane integrity. Because the degree of membrane curvature induction depends on the concerted action of multiple proteins, controlling the local protein density of tubulating proteins may be important. How cellular safeguarding mechanisms prevent such potentially toxic events and whether they go awry in disease remains to be determined.     

The Trypanosoma brucei Life Cycle Switch TbPTP1 Is Structurally Conserved and Dephosphorylates the Nucleolar Protein NOPP44/46

Trypanosoma brucei adapts to changing environments as it cycles through arrested and proliferating stages in the human and tsetse fly hosts. Changes in protein tyrosine phosphorylation of several proteins, including NOPP44/46, accompany T. brucei development. Moreover, inactivation of T. brucei protein-tyrosine phosphatase 1 (TbPTP1) triggers differentiation of bloodstream stumpy forms into tsetse procyclic forms through unknown downstream effects. Here, we link these events by showing that NOPP44/46 is a major substrate of TbPTP1. TbPTP1 substrate-trapping mutants selectively enrich NOPP44/46 from procyclic stage cell lysates, and TbPTP1 efficiently and selectively dephosphorylates NOPP44/46 in vitro. To provide insights into the mechanism of NOPP44/46 recognition, we determined the crystal structure of TbPTP1. The TbPTP1 structure, the first of a kinetoplastid protein-tyrosine phosphatase (PTP), emphasizes the conservation of the PTP fold, extending to one of the most diverged eukaryotes. The structure reveals surfaces that may mediate substrate specificity and affords a template for the design of selective inhibitors to interfere with T. brucei transmission.     

Specimen dimensions influence the measurement of material properties in tendon fascicles

Stress, strain and modulus are regularly used to characterize material properties of tissue samples. However, when comparing results from different studies it is evident the reported material properties, particularly failure strains, vary hugely. The aim of our study was to characterize how and why specimen length and cross-sectional area (CSA) appear to influence failure stress, strain and modulus in fascicles from two functionally different tendons. Fascicles were dissected from five rat tails and five bovine foot extensors, their diameters determined by a laser micrometer, and loaded to failure at a range of grip-to-grip lengths. Strain to failure significantly decreased with increasing in specimen length in both rat and bovine fascicles, while modulus increased. Specimen length did not influence failure stress in rat tail fascicles, although in bovine fascicles it was significantly lower in the longer 40 mm specimens compared to 5 and 10 mm specimens. The variations in failure strain and modulus with sample length could be predominantly explained by end-effects. However, it was also evident that strain fields along the sample length were highly variable and notably larger towards the ends of the sample than the mid-section even at distances in excess of 5 mm from the gripping points. Failure strain, stress and modulus correlated significantly with CSA at certain specimen lengths. Our findings have implications for the mechanical testing of tendon tissue: while it is not always possible to control for fascicle length and/or CSA, these parameters have to be taken into account when comparing samples of different dimensions.     

Phosphorylation of Lte1 by Cdk prevents polarized growth during mitotic arrest in S. cerevisiae

Lte1 is known as a regulator of mitotic progression in budding yeast. Here we demonstrate phosphorylation-dependent inhibition of polarized bud growth during G2/M by Lte1. Cla4 activity first localizes Lte1 to the polarity cap and thus specifically to the bud. This localization is a prerequisite for subsequent Clb-Cdk-dependent phosphorylation of Lte1 and its relocalization to the entire bud cortex. There, Lte1 interferes with activation of the small GTPases, Ras and Bud1. The inhibition of Bud1 prevents untimely polarization until mitosis is completed and Cdc14 phosphatase is released. Inhibition of Bud1 and Ras depends on Lte1's GEF-like domain, which unexpectedly inhibits these small G proteins. Thus, Lte1 has dual functions for regulation of mitotic progression: it both induces mitotic exit and prevents polarized growth during mitotic arrest, thereby coupling cell cycle progression and morphological development.