<p> In the past two decades or so. microsatellites have become a very widely used genetic tool in many disciplines of biology. Their major downfalL however. is that they often need to be isolated de novo before they can be applied to molecular studies. Traditional shotgun cloning can be successfuL but it is often overly costly and time consuming. Compounding this downfall, isolating microsatellites from some taxa has been shown to be difficult. For example. on average only 0.46% of all clones screened using avian genomes will yield positive clones. This is thought to be a result of a smaller avian genome, a requirement for flight. Several alternative methods have been developed for isolating microsatellites, but the choice as to which isolation method to use is often arbitrary. To address this. four species of birds. the smooth-billed ani (Crotophaga ani). herring gull (Larus argentatus), yellow-bellied elaenia (Elaenia flavogaster), and pukeko (Porphyria porphyria), representing four different orders were used to compare two alternative isolation methods. Enrichment via selective hybridization versus cloning with Lambda Zap phage vector were compared in terms of monetary requirements (total startup cost as well as per isolation attempt cost). and time requirements (total time from start to finish and hands-on experimentation time). No significant difference was detected in terms of number of polymorphic microsatellite loci isolated by each method (p = 0.57), with enrichment yielding more for the anis and elaenias, Lambda Zap yielding more for herring gulls. and both methods isolating equal numbers for pukekos. Nor was any difference found between the methods for dollars spent per sequence with repeat (SWR) using the startup cost (p = 0.30). Enrichment. however. proved to be significantly more effective in terms of dollars per SWR isolated using the per use cost (p = 0.004) as well as hands-on minutes per SWR (p = 0.01) and total minutes per SWR (p < 0.01 ). Based on these tindings. selective hybridization is the better choice for microsatellite isolation. </p> / Thesis / Master of Science (MSc)

The demand for treatment strategies of musculoskeletal tissues is continuously growing, especially considering the increasing number of elderly people with degenerative diseases of the skeletal system. Despite major strides in the field of bone regenerative medicine during the years, current therapies, such as bone grafts, still have several limitations. Multipotent stem cells, such as mesenchymal stem cells (MSCs) are promising candidates for tissue repair because of their differentiation potential and their capacity to undergo extensive replication. However, isolating a homogeneous population of MSCs from multiple sources is an area that needs to be addressed. Also, the knowledge regarding the mechanisms and pathways that lead to the final osteogenic differentiation is still scarce. The following research is a feasibility study on a new isolation technique developed by our lab. The major focus of the research will be the isolation and characterization of mesenchymal stem cells from both adult bone marrow and umbilical cord blood using a novel isolation method based on immunodepletion. Furthermore we will look at the potential of these isolated MSCs to differentiate into mature, bone producing osteoblasts. The results of the studies showed that our novel isolation method allowed proliferation of a homogeneous MSC population. Our irnrnunodepleted MSCs were 99% double positive for antibodies CD44 and CD105 which are highly specific for multipotent MSCs while cells isolated using the plastic adherence method were only 43% double positive for the two MSC-specific markers. Homogeneous MSCs were derived from both adult bone marrow and umbilical cord blood using our isolation method. Utilizing the techniques of confocal microscopy, von Kossa staining, and RTPCR we also show that MSCs, upon stimulation with osteogenic supplements, differentiate into osteoblasts capable of being used for bone tissue engineering applications.

Lorsque le système visuel est confronté à un nouvel environnement, un nombre trop important d’informations lui parvient en même temps. De façon précoce, avant tout mouvement oculaire, l’attention explore automatiquement la scène pour sélectionner les éléments d’intérêt. Des recherches récentes ont montré que cette exploration du champ visuel ne se faisait pas aléatoirement, mais se basait sur la saillance des éléments visuels. La saillance est une caractéristique qui émerge de la comparaison des éléments visuels entre eux, par exemple une fleur jaune dans un jardin de fleurs rouges va être considérée comme plus saillante que son voisinage. En permanence et de façon continue, une hiérarchie des éléments est établie à un niveau préattentif ; ils sont triés du plus au moins saillant, et l’attention se base sur cet organisation pour progresser dans le champ visuel. Les recherches présentées dans ce document avaient pour objectif d’investiguer les mécanismes de ce phénomène : quels sont les mécanismes cognitifs impliqués dans la progression de l’attention sur la base de la hiérarchie de la saillance ? Le présent document regroupe des articles qui cherchent à répondre à cette question grâce à des travaux en Psychologie expérimentale. Par ailleurs, de nombreux travaux de Psychologie, Neurophysiologie et Neuroimagerie se sont penchés sur le substrat neural de l’attention visuelle et ont révélé un ensemble de structures clés qui sous-tendraient les mécanismes responsables des fonctions attentionnelles. Cependant, vis-à-vis de la progression de l’attention sur la base de la saillance, seule une étude récente a pu apporter des indices quant au rôle de certaines voies visuelles. Les recherches présentées ici avaient donc également pour objectif de définir ces voies visuelles et les structures corticales et sous-corticales qui les composent, pour investiguer leurs rôles dans la hiérarchie de la saillance et la progression de l’attention. Le présent document regroupe des travaux qui ont exploré ces aspects par le biais de l’approche Psychophysique et Electroencéphalographique. / When confronted to a new environment, the visual system faces too much information intake and cannot process it all at once. Before any eye movement, early automatic attention explores the visual scene in order to select relevant items.Recent research revealed that the exploration of the visual scene is not a random process, but is based on the respective saliency of the items in the field. Salience is not a characteristic of an item per se but is emerging as a result of the comparison between an item and its visual neighborhood. For instance, a yellow flower in a garden of red flowers will be considered as more salient than the others in its visual neighborhood. Thus, a hierarchical ordering of the items is continuously established in a preattentive stage, and consists in a sorting of every element from the most to the least salient. Attention, then, relies on this hierarchy to progress in the visual field. The present dissertation had for objective to investigate the cognitive mechanisms involved in this phenomenon: what mechanisms support the salience-based progression of visual attention? Several papers are reported here and explored this question with experimental Psychology.Moreover, numerous works in Psychology, Neurophysiology and Neuroimaging took interest in the neural substrate of visual attention and revealed several key-structures that would subtend the mechanisms involved in attentional functions. However, when it comes to the salience-based progression of attention, only one study could bring cues of the involvement of certain visual pathways in this phenomenon. Another objective of the present dissertation was to define the cortical and sub-cortical structures that constitute those pathways, in order to explore their roles in the salience-base progression of attention. Several papers in the present report are investigating this aspect through Psychophysics and Electroencephalography studies.