Codium fragile (Suringar) Harlot (Chlorophyta, Codiales) is a siphonous marine alga of extensive distribution and varied habitat. Ordinarily It is described as reproducing sexually, by fusion of anisogamous gametes produced on separate individuals. However, there are populations reported which consist exclusively of female plants reproducing by parthenogenetic germination of female gametes. Three aspects of the biology of a population of Codium fragile from Vancouver Island, British Columbia, were studied. (1) Zygotes and germlings were obtained in cultures in the laboratory and their growth and early development were observed. No utricles were produced by young germlings, even after three to four months in culture; the existence of a "juvenile filamentous stage" without utricles is suggested. The possibility of parthenogenetic development of female gametes was investigated and it was found that, in the material studied, zygotes and germlings are produced only in the presence of both male and female plants. (2) Apical segments of C. fragile 2.5, 3.5 and 4.5 cm in length were treated with 5 mg/l IAA. IAA-treated 4.5 cm segments showed a slight but significant increase in growth over controls. No such increase was found in IAA-treated 2.5 and 3.5 cm segments. (3) The mitotic cycle and the periodicity of mitosis in germlings in culture were investigated. In most respects mitosis in C. fragile resembles "normal" mitosis. However, a persistent nucleolus-like body was observed during all stages of division. Attempts to ascertain the chemical nature of this body were unsuccessful. Experiments on the periodicity of mitosis disclosed a series of peaks of mitotic activity which appear to be unrelated to the time of onset of light or darkness. Mitosis within any one germling is asynchronous. / Science, Faculty of / Botany, Department of / Graduate

Thèse (M.Sc.) -- Université Laval, 1998. / Bibliogr.: f. [107]-125. Publié aussi en version électronique.

Thèse (M.Sc.) -- Université Laval, 1997. / Bibliogr.: f. 89-99. Publ. aussi en version électronique.

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Digital watermarking algorithms based on wavelet transforms provide increased performance and perceptual quality. This thesis proposes two wavelet-based schemes: one robust and one fragile. Robust watermarks should withstand attacks, such as compression, while maintaining the data integrity. The first approach presented is an algorithm which implements image watermarking in the domain of an overcomplete, or redundant, wavelet transform. Alternately, fragile watermarks are intended for use in applications wherein any loss of image quality is not acceptable. In the second approach presented, data embedding in the domain of an integer wavelet transform is considered. An algorithm is proposed that uses a bilevel image coder to compress a chosen bitplane, thereby providing space in which to store a payload while guaranteeing perfect image recovery.

The loss of expression of the fragile X mental retardation protein (FMRP) leads to fragile X syndrome. Fragile X syndrome is the most prevalent inheritable mental retardation. FMRP has two types of RNA binding domains, two K-homology domains and an arginine-glycine-glycine box domain, and is proposed to act as a translation regulator of specific mRNA. Despite extensive research, the mechanism by which FMRP loss leads to the fragile X syndrome remains unclear. Thus, there is high interest to produce sufficient quantities of pure recombinant FMRP for biochemical and biophysical studies of the protein function. However, the recombinant bacterial expression of FMRP has had limited success, and subsequent recombinant eukaryotic and in vitro systems may produce FMRP which is posttranslationally modified, as phosphorylation and arginine methylation have been shown to occur on FMRP. In this study, we have successfully isolated the conditions for recombinant expression, purification and dialysis of full-length FMRP using Escherichia coli, with a high yield. The expression of FMRP using E. coli renders the protein devoid of the posttranslational modifications of phosphorylation and arginine methylation, allowing for the further study of the direct effects of these modifications individually and simultaneously. Additionally, FMRP has been shown to undergo alternative splicing, with one of the splicing sites in close proximity to the FMRP domain shown to be involved in binding G quadruplex mRNA with high affinity and specificity. We have analyzed how naturally occurring truncations in the FMRP sequence affect its RNA binding affinity, by applying the expression, purification and dialysis process to the second and third longest FMRP isoforms, followed by subsequent analysis of the G quadruplex mRNA binding properties by fluorescence spectroscopy. Our results show that as FMRP gets truncated by alternative splicing, its mRNA binding affinity increases. To test a model we proposed for FMRP translation regulation activity, we developed a luciferase reporter gene construct that contains the G quadruplex structure in the mRNA 5���-untranslated region. Using luminescence spectroscopy to analyze luciferase translation, we showed that low levels of full-length FMRP reduces luciferase translation, and as the concentration of full-length FMRP increases the luciferase translation increases. / Bayer School of Natural and Environmental Sciences / Chemistry and Biochemistry; / PhD; / Dissertation;

Le syndrome de l’X-fragile est la forme la plus fréquente de déficience intellectuelle héréditaire liée au chromosome X. Cette maladie résulte de la mutation du gène FMR1 localisé sur le chromosome X. La protéine correspondante, FMRP, est absente chez les patients atteints de la maladie. Il faut noter ici qu’il existe un modèle murin mimant la pathologie humaine. Ainsi dans ces animaux qui n’expriment pas la protéine FMRP, les neurones présentent des anomalies architecturales de la synapse entraînant d’importants dysfonctionnements dans la transmission et la plasticité synaptique qui sont à l’origine des déficits intellectuels observés chez les patients atteints du syndrome de l’X-fragile. FMRP joue donc un rôle majeur dans la genèse et la maturation des épines dendritiques. Une des fonctions de FMRP est de lier de nombreux ARNm, de les transporter et d’inhiber leur traduction jusqu’à la synapse. Pour accomplir ses fonctions, FMRP interagit avec de nombreux partenaires cellulaires et ses interactions sont finement régulées par différentes modifications post-traductionnelles. Nous avons montré in vivo que la protéine FMRP est un substrat d’une nouvelle modification, la sumoylation. Nous avons également montré que la sumoylation de FMRP est impliquée dans le maintien de l’architecture synaptique et participe à la régulation de la transmission synaptique. Et enfin, nous avons montré que la sumoylation de FMRP permet sa dissociation avec ses partenaires protéiques au sein des complexes ribonucléoprotéiques se trouvant à la base des épines dendritiques. Les ARNm réprimés par FMRP au sein de ces complexes sont ainsi libérés puis traduits. / Fragile X Syndrome is the most frequent inherited cause of intellectual disability in children and is caused by the lack of the mRNA-binding Fragile-X Mental Retardation Protein (FMRP) expression. FMRP plays a role in the activity-dependent targeting and translation of specific mRNAs in dendrites. The absence of FMRP expression in neurons leads to an abnormal neuronal morphology with increased spine length and density. FMRP is therefore playing key roles both in neuronal development and synaptic plasticity. However, the molecular mechanisms underlying the functional regulation of FMRP-mediated mRNA trafficking, translation and subsequent protein synthesis are still largely unknown. My host laboratory has recently discovered that FMRP is sumoylated in vivo. Sumoylation is a post-translational modification that consists in the covalent conjugation of the protein SUMO to specific lysine residues of target proteins. To start unraveling the functional consequences of FMRP sumoylation, I studied first the spine morphology of the WT and FMRP Knock Out mice that recapitulated the human disease. Morphological analysis of fmr1-KO neurons transfected with the WT form of FMRP restores the correct mature spine morphology whereas the non-sumoylatable protein failed to do so. Moreover the non-sumoylatable form of FMRP acts as a dominant negative on WT neurons so confirming the important role of FMRP sumoylation in its function. We report here that FMRP sumoylation is required for the control of spine morphology.

Fragile X Syndrome is the most common form of heritable cognitive disability. It is caused by a genetic mutation that leads to a lack of protein from the FMR1 gene. This protein (FMRP) is used to regulate the translation of many other proteins, thereby leading to a wide range of effects. Because the origin of this disease is based on the lack of a single protein, an animal model with construct validity can be used to investigate the potential effects leading to the symptoms of the disease. Many studies have investigated the synaptic plasticity differences of CA1 pyramidal neurons between a mouse model of fragile X syndrome (KO) and a wild type mouse (WT). This study investigates the differences in firing properties of a CA1 pyramidal neuron between the KO and WT. Specifically, contributions of two ion channels are investigated: the Ca2+ and voltage activated potassium channel (BK) and the potassium channel (M) inhibited by the muscarinic acetylcholine receptor. This study finds some differences that warrant further investigation, including differences in spike timing, spike width and the initial rate of rise of an action potential. However, several areas of investigation yield subtle or confounding results, which may indicate that the CA1 pyramidal neurons affected by the lack of FMRP may make up more than one population. / text

Faces provide important information necessary for social communication. The current study aimed to evaluate Event-Related Brain Potentials (ERPs) as a method of exploring face processing abilities in fragile X syndrome (FXS), a genetic disorder where social deficits lie at the core of the cognitive phenotype. Neural changes were investigated in three children with FXS across various conditions such as upright vs. inverted faces, intact faces vs. faces with no eyes as well as faces vs. cars. Relative to chronological age matched controls, children with FXS displayed greater N170 amplitudes and shorter latency peaks across conditions. In addition, the FXS group showed right hemispheric specialization for both face and non-face stimuli. Heightened electrophysiological responses in FXS are discussed in the context of reported hyper-sensitivity and arousal.

A series of empirical studies is presented that examine the contribution of Fragile X Mental Retardation 1 (FMR1) gene expression to the structure and function of the visual system. This contribution is documented using a histological approach in human and nonhuman primate tissue in conjunction with psychophysical testing of Fragile X Syndrome affected patients who are lacking FMR1 expression. / In the first set of experiments, immunohistological studies of unaffected human and primate brain tissue were carried out to reveal the staining pattern for Fragile X Mental Retardation Protein (FMRP), the protein product of the FMR1 gene, within the two main subcortical pathways at the level of the lateral geniculate nucleus (LGN). FMRP is expressed in significantly greater quantity within the magnocellular (M) neurons of the LGN when compared to levels obtained from the parvocellular (P) neurons. This finding suggests that M neurons depend on FMRP to greater extent than P neurons for determining their normal structure and function. A subsequent histological analysis of the LGN from a FXS affected individual revealed atypical LGN composed of small-sized neurons that were more P- than M-like. This result supports the notion that with the lack of FMR1 expression as occurs in FXS, the impact is greatest to M neuron morphology. / A second set of experiments explored the idea that the M neuron pathology in FXS results in a functional deficit for processing of visual information carried by this pathway. Detection thresholds for stimuli known to probe either M or P-pathway integrity were obtained from individuals affected by FXS as well as age- and developmental-matched control participants. In support of this hypothesis, FXS affected individuals displayed significantly elevated thresholds for M-but not P-specific achromatic visual stimuli. The selectivity of this deficit was verified in a consequent experiment that evaluated colour vision, a visual attribute known to be exclusively processed by the P-pathway. Affected individuals did not differ significantly from developmental-matched control participants in their ability to detect chromatic stimuli. Finally, the effect of the M pathway deficit on cortical visual function was assessed. Results of these experiments reveal that the thresholds for detection of coherent motion, but not form, are significantly elevated in the FXS group. This finding suggests that the parietal (dorsal) visual stream, the major cortical recipient of input from the M pathway, is detrimentally affected in FXS. / A third experiment examines the extent to which the M pathway deficit impacts on cortical visual functioning by employing stimuli of varying complexity that probe the parietal (dorsal) and temporal (ventral) visual streams separately. Results suggest that FXS affected individuals have a pervasive deficit in their ability to detect both simple and more complex forms of motion. In contrast, these same individuals have normal detection thresholds for simple form stimuli. However, with more complex form stimuli affected individuals have significant elevations in threshold. Taken together these results support the notion that the M pathway deficit is amplified at higher levels of visual processing and further, that FXS affected individuals have difficulties integrating all early visual information.