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Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 86-95). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 86-95). Also available on the Internet.

Silks from araneoid spiders have become an active area of research for material scientists, biochemists, and molecular biologists. Mechanical properties of spider silk such as elasticity, tensile strength, and toughness make the manufacturing of silk for medical sutures, body armor, ropes and other synthetic material applications great possibilities. The difficulties of having a black widow spider farm to harvest silk, due to their cannibalistic nature, make recombinant expression of silk proteins a fundamental goal of spider silk research. In order to express silk fibers, cDNAs encoding the corresponding silk fiber products must first be isolated and identified. One of the first steps in gene identification relies on the identification of the proteins in the silk fibers. No previous study has demonstrated the molecular constituents of gumfooted lines. In the course of this research, the core fibroins in the gumfooted lines were identified to be members of the Major Ampullate Spidroin family (MaSp), using mass spectrometry. This research was the first to identify the core fibroins of the gumfooted lines. Novel peptide fragments from solubilized gumfooted lines were acquired from manual de novo MSIMS sequencing after in-gel tryptic digestion. These peptide fragments showed post-translational modifications consistent with glycosylation, which aligns with the reported chemical properties of glue proteins. Novel peptide sequences were also acquired from the attachment discs as well as novel scanning electron microscopy images and reveal, for the first time, the physical attributes and molecular properties of threads attached to the surface of an immobilized structure. This study was the first to identify the molecular constituents of the attachment discs.

Spider silks are biological materials that have inspired the humankind since its beginning. From raising the interest of ancient philosophers to the practical outcomes in the societies, spider silks have always been part of our culture and, thus, of our scientific development. They are protein-based materials with exceptional mechanical and biological properties that from liquid solutions passes to the solid fibres once extruded from the body of the spiders. Spider silks have deeply been investigated in these decades for their possible outcomes in biomedical technology as a supporting material for drugs delivery or tissues regeneration. Furthermore, spiders build webs with the support of different types of silks to create mechanically efficient structures, which are currently under investigation as models for metamaterials and fabrics with superior mechanical properties. This diversity in materials and structures makes spider silks scientific outcomes potentially infinite. In this work, we present some of the outputs of these three years of PhD. We explored the properties of the native material across different aspects (different species and glands) and trying to find possible derived applications (tissue engineering). Then we explored the mechanical behaviour of the natural structures (such as orb webs or attachment discs) coupled with their biological functions. In order to develop to an industrial level this material, we tried to understand and improve the physical properties of artificial spider silk, which helps also in understanding the ones of the native materials.

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There is now considerable evidence that phobic responding is associated with a bias towards expecting aversive or traumatic outcomes following encounters with the phobic stimulus (e.g. Davey, 1995). In terms of conditioning contingencies, this can be described as a bias towards expecting an aversive or traumatic outcome (the unconditioned stimulus - UCS) following a phobic stimulus (the conditioned stimulus - CS). Research into the role of UCS expectancy biases in the development and maintenance of specific phobias has three basic requirements. First, it is not clear whether the ues expectancy biases evidenced in specific phobias represent a stimulus specific response or a more generalised associative phenomenon. Second, it is not clear what dispositional or state factors might contribute to the development and maintenance of such ues expectancy biases. Third, it is not clear what type of cognitive mechanisms might underlie UCS expectancy biases. This thesis uses a thought experiment version of a threat conditioning procedure to explore these requirements. The key findings indicate that spider phobics tend to overestimate the likelihood of aversive outcomes following phobic, but not other fear relevant stimuli, and tend to underestimate the likelihood of aversive outcomes following fear irrelevant stimuli in comparison to non-phobic controls. This dichotomous ues expectancy bias is mirrored both in the evaluation of stimuli in terms of dangerousness and valance, and in the generation of harm and safety cues with regards to these stimuli. Both positive and negative mood states, but not arousal states contributed to ues expectancy inflation, and in the case of revulsive animals induced state disgust also increased reported ues expectancies. The thesis concludes with an evaluation of the role of UCS'S expectancies in the development and maintenance of specific phobias, and a discussion of the implications of these findings for our understanding of the information processing mechanisms underlying the specific phobias.

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