The coral-inhabiting snail Coralliophila violacea is a common species in the Indo-Pacific coral reefs and it usually lives on the surface of its host, Porites spp. In this study, field survey on the distribution of C. violacea on poritid corals, Porites spp. among sites were conducted. And the influence of flow rate on the distribution of snails was also examined through a simulation model. The sampling sites were northeastern of Taiwan, Taitung, Penghu, Lutao, Hsiao-liu-chiu and Lanyu. The presence of spatial variability in the relative abundance of C. violacea on porited corals has been observed. The highest percentage of corals with snails was in northeastern Taiwan, i.e. 45% and the lowest ones were in Lutao and Lanyu, i.e. 12%. The distribution of snails among sites were heterogeneous (X2-test of independence; p<0.001). Significant differences of shell length in snails among sites were also found. Among them, the distribution pattern of shell length in snails from Lutao and Lanyu was not normal. Difference in the age-distribution of snails among sites was present. In general, five and six years old snails were most abundant. A lack of snails under two years old had been found in Lutao, Lanyu and Penghu. Based on the simulated downward trajectory of snail larvae, it was indicated that a minimum substratum for larval settlement varied with flow rates and depth of water.

The procerebrum of terrestrial molluscs is an important processing centre for olfaction. While the physiology of the procerebrum is relatively well characterized, the procerebrum's structure and organization has not been previously investigated in detail. The goal of this thesis is to better characterize the structural organization of the procerebrum and to understand how it compares with other olfactory systems. / The morphology of the procerebral neurons in the snail Helix aspersa was investigated through intracellular injections of biocytin. The population of cells is heterogeneous, but no formal categorization of neuronal types was possible. The main difference among cells lies in the placement of the cells' neurites. Furthermore, contradicting previous results, certain neurons were found to have neurite projections outside the procerebrum, travelling as far as the contralateral cerebral ganglion. / To investigate if differences in sites of arborization represent functional differences, the distribution of synaptic contacts on labelled cells was studied using serial sections and electron microscopy. Neurons with different sites of arborization have distinct patterns of synapse distribution. Cells with arborizations in the procerebrum but not in the internal mass have large varicosities specialized for output. Cells that arborize in the internal mass or outside the procerebrum have mostly input synapses proximal to the soma and mostly output synapses in the terminal region of the neurites. These latter cells appear to transmit information from the procerebral cell body mass to other brain regions. The implications of these data are, firstly, that the procerebrum directly distributes processed information throughout the nervous system. Secondly, the procerebral neuron population may be divisible into two subgroups: intrinsically arborizing interneurons and projection neurons. / These results suggest a novel mechanism by which compartmentalization could be achieved in the procerebrum. Compartmentalization is believed to be important for processing olfactory information, is present in most olfactory centres but has not previously been described in the molluscan olfactory system. I propose that varicosities on the local interneurons generate foci of activity in the procerebrum which, in turn, activate specific subsets of output neurons, similar to what happens in other olfactory systems.

The morphology of C3, a motoneuron mediating the tentacle withdrawal reflex, was investigated in the snail Helix aspersa by intracellular injections of the tracers Neurobiotin and biocytin. Axonal projections were identified in the optic nerve, the olfactory nerve, the internal peritentacular nerve, the external peritentacular nerve, the cerebral-pedal connective and the cerebral commissure. A rare characteristic of the cell was the multibranching of axons in the neuropil and the exiting of this bundle of fibres into the cerebral-pedal connective. Dendritic arborizations were observed branching from the cell body, the axon hillock and the dorsal main axon. In addition, tufts of dendrites were seen to branch from the ventral axon. Based on its morphology, C3 is probably a central component in the avoidance behaviour, receiving sensory input at extensive dendritic sites and sending axons to a number of key effector sites to co-ordinate the chain of reactions that constitutes the snail's avoidance behaviour.

Cell death is an integral part of oogenesis in the fruit fly, Drosophila melanogaster. When the fly is starved of protein, some pre-vitellogenic egg chambers die apoptotically. As egg chambers mature, excess germline cells die via a non-apoptotic, developmentally programmed death. Overexpression of the transcription factor escargot was found to block both death events in the ovary, which is very unusual. escargot overexpression blocked starvation-dependent death upstream of caspases, but still needed a death signal to produce undead egg chambers. In maturing egg chambers, escargot overexpression blocked death more effectively than disrupting both apoptosis and autophagy, indicating that it must affect non-apoptotic, non-autophagic death mechanisms. RNA-Seq and a genetic modifier screen were used to identify potential escargot targets that inhibit cell death. Studies were also undertaken to characterize the loss-of-function phenotype of escargot in the ovary. escargot is a member of the Snail family of transcription factors that play integral roles in development and gene regulation throughout Bilaterian organisms. In Drosophila melanogaster, the genes snail, escargot, and worniu are critical for stem cells in neuroblasts, gut, and testis, but a role in the ovary had not been shown. To analyze Snail family function in the ovary, I made a triple deficiency that removed the three Snail family members, called ΔSF. Surprisingly, ΔSF homozygous follicle stem cells are rapidly lost. Follicle stem cell loss was rescued by the expression of escargot or worniu but not snail, indicating that there is shared capability between genes. Moreover, follicle stem cells did not linger in the germarium, and their loss was not prevented by blocking apoptosis, indicating that the ΔSF defect is a failure of stem cell maintenance. Together, the results described in this dissertation show that Snail genes are needed for the normal function of the Drosophila ovary, and that escargot can regulate multiple kinds of cell death. Understanding Snail family genes is particularly important for the study of cancer, as they are implicated in mechanisms underlying the cancer stem cell state. Analysis of the highly conserved Snail family genes in Drosophila illuminates their function and dysfunction in human health and disease.

L’hypoxie tumorale par l’intermédiaire d’une de ses cibles HIF-1α, est associée à la transition épithélio-mésenchymateuse (TEM) dans de nombreuses tumeurs solides. La TEM a été associée aux résistances à la chimiothérapie et aux métastases dans de nombreux cancers. Dans ce travail, nous avons montré que l’hypoxie tumorale définit un pronostic péjoratif après chirurgie d’un cancer bronchique non à petites cellules (CBNPC). Nous avons également montré sur des lignées cellulaires de CBNPC présentant des mutations activatrices de l’EGFR, que l’hypoxie via HIF-1α, induit la TEM, avec activation de différents facteurs de transcription dépendant du statut mutationnel des lignées : induction de SNAIL-1/SNAIL-2 dans la lignée H1650 ayant une deletion de l’exon 19 et induction de SNAIL-1/ZEB-1 dans la lignée H1975 ayant la mutation L858R de l’exon 21 et T790M de l’exon 20. En considérant l’ensemble de ces données, il apparaît que HIF-1α peut être une nouvelle cible thérapeutique. / Tumoral hypoxia, and his target HIF-1α, are linked to the epithelial to mesenchymal transition (EMT) in various solid tumors. EMT has been linked to chemotherapy resistance and metastases in many cancers. In this work, we have shown that tumoral hypoxia may help to define a worst prognosis in case of hypoxia after non-small cell lung cancer surgery (NSCLC). We have also shown that on NSCLC cell lines harboring activating EGFR mutations, hypoxia trough expression of HIF-1α, was able to induce EMT, with activation of different transcription factors according to cell mutational status: induction of SNAIL-1/SNAIL-2 in H1650 cell line harboring exon 19 deletion, induction of SNAIL-1/ZEB-1 in H1975 cell line harboring both exon 21 L858R and exon 20 T790M mutations. Considering all these data, it appears that HIF-1α may be considered a a new therapeutic target.

Marstonia lustrica is a poorly understood aquatic snail, relatively rare throughout its range and listed in the State of Massachusetts as Endangered (MNHESP 2010, Hershler et. al 1987). It is the northern-most cold temperate species of its genus, with other members of the genus occurring along the southern edge of its range and in the southeastern United States (Thompson 1977). The current range of M. lustrica appears to follow the maximum extent of the Laurentide Glacier (20–25 kya), extending from Minnesota to western Massachusetts. Research regarding the distribution, ecology, and phylogeny of M. lustrica in the State of Massachusetts and eastern New York raised the possible role of glaciers and pro-glacial lakes in the establishment and distribution of the snail, leading to the hypothesis that its distribution and evolution may be dependent upon glacial processes. A full range survey was completed in 2007 and 2008, with populations identified in 20 water bodies from Minnesota to Massachusetts, and Ohio to Ontario, Canada. Fifty-seven specimens from the 20 populations were sequenced for two mtDNA markers (COI and NDI), developing both phylogenetic trees and haplotype networks. Here I present those trees and networks, and correlate the distribution of these populations and their representative haplotypes with both glacial events and contemporary watersheds, using AMOVAs and Mantel tests to examine several v phylogeographic models. In addition to the results for M. lustrica, the unexpected occurrence of several other species of Marstonia spp. found across the range of M. lustrica are presented, including M. pachyta, M. comalensis, and M. hershleri.

No description available.

<p>Geometric morphometrics (GM) provides a complementary method for studying morphology. Snails have been analyzed in the field of morphometrics since the 1960s because their shells serve to record information about their life histories and environmental habitats. In this thesis, we present an annotated bibliography for advancements in GM, using applications to snail shells as a representative case study. We categorize 30 publications into four fields, morphology, ecology, taxonomy and evolution, and show that developments have been unequal among them. We conclude by predicting that GM applications on snail shells will increase, especially in hybrid fields, such as, ecotoxicology, which currently are underrepresented. As a demonstration, we describe an experiment wherein we applied GM as a complementary morphological method to study the garden snail species Cepea nemoralis in an organophosphatepesticide, ecotoxicological setting. We conclude by showing that GM reveals subtle morphological differences among treatment groups with no relation to pesticide dosage.</p> / Master of Science (MSc)

Understanding the ecological processes that impact parasite abundance and distribution is critically important for epidemiology and predicting how infectious disease dynamics may respond to future disturbance. Digenean trematodes (Platyhelminthes: Trematoda) are parasitic flatworms with complex, multi-host life cycles that include snail first-intermediate hosts and vertebrate definitive hosts. Trematodes cause numerous diseases of humans (e.g. schistosomiasis) and livestock (e.g. fascioliasis), and impact the ecology of wildlife systems. Identifying the ecological mechanisms that regulate these complex, multi-host interactions will advance both our understanding of parasitism and the dynamics of infectious disease. By examining patterns of infection in Elimia (= Oxytrema = Goniobasis) proxima snails, my dissertation research investigated the environmental factors and ecological processes that structure trematode communities in streams. First, I examined temporal variation in trematode infection of snails in five headwater streams. Over a three year period, I found no consistent seasonal patterns of trematode infection. There was consistency across sites in trematode prevalence, as sites with high prevalence at the beginning of the study tended to remain sites of high infection, relative to lower prevalence sites. Second, I examined landscape level variation in trematode infection by characterizing the regional distribution, abundance and diversity of E. proxima infections in 20 headwater streams. I found a broad scale spatial pattern in trematode communities due to regional turnover in dominant species. This pattern was correlated with elevation, but there were no significant relationships with other environmental variables. Additionally, molecular characterization of trematodes indicated the presence of cryptic (morphologically indistinguishable) species complexes within this system, and variation in genetic diversity among trematode types may reflect differences in host dispersal abilities. Third, I examined trematode infection within a single stream network across multiple headwaters and the mainstem. I found a decreasing downstream gradient of trematode prevalence related to several environmental variables including elevation, snail density, conductivity, and stream depth. Additionally, headwater communities were nested subsets of the communities found in the mainstem. By combining approaches at different temporal and spatial scales, my dissertation research increases our understanding of the processes that impact the abundance and distribution of parasites. / Ph. D.

L'engagement des cellules vers un destin donné, ou détermination cellulaire, est un processus clé du développement. Quels sont les mécanismes qui sous-tendent la détermination cellulaire ? Pour aborder cette question, nous utilisons le lignage des soies mécanosensorielles de la drosophile. Dans ce lignage, la diversité des cellules résulte de l'activation différentielle de la voie Notch ainsi que la ségrégation asymétrique de déterminants cellulaire à chaque division. Cependant, comment la répétition d’un même mécanisme peut-elle être à l’origine des destins cellulaires différents ? D'autres facteurs doivent être impliqués dans ce processus. Afin des les identifier, mon intérêt s’est porté sur les facteurs de transcription de la superfamille Snail, connus pour être impliqués dans la détermination cellulaire au cours du développement de la drosophile.Deux membres de cette superfamille, Escargot (Esg) et Scratch (Scrt) sont exprimés dans le lignage des soies, en particulier dans les cellules neurales et leurs précurseurs. Des analyses de perte et de gain de fonction indiquent qu’Esg et Scrt, agissant de manière redondante, sont nécessaires pour le maintien de l'identité du précurseur secondaire neural. Des tests d’interaction génétique ont montré que ces facteurs agissent en interaction avec la voie Notch, probablement via la répression de l’expression des gènes cibles de la voie. De plus, Esg, mais pas Scrt, a un rôle supplémentaire lors de la formation du lignage des soies. La perte de fonction de ce facteur provoque un défaut de l’arborisation et de la croissance axonales. En outre, l'expression des gènes impliqués dans la différenciation neuronale, tels que Elav et Prospero, est altérée dans ce contexte, suggérant qu’Esg contrôle la différenciation neuronale en régulant l'expression de gènes clés de l’identité neuronale.Ensemble, mes résultats ont montré qu’Esg et Scrt participent à la mise en place de la diversité cellulaire dans le lignage des soies de la drosophile. / The commitment of cells to a given fate, or cell fate determination, is a key process in development. Cell type diversity arises from variations in this process. What are the mechanisms underlying cell determination and how is cell diversity achieved? In order to approach these questions, we use the Drosophila mechanosensory bristle lineage. In this lineage, cell diversity arises from the differential activation of the Notch pathway as well as the asymmetric segregation of cell fate determinants at each division. However, how does the repetition of the same mechanism trigger different cell fates? Other factors might be involved in cell fate commitment. In order to identify such factors, I focused my interest on the transcription factor of the Snail superfamily, known to be involved in cell determination during Drosophila development.Two members of this superfamily, escargot (esg) and scratch (scrt) are expressed in the bristle lineage, specifically in the inner neural cells and their precursor cells. Loss and gain of function analysis indicate that Esg and Scrt, acting redundantly, are necessary for the maintenance of the neural secondary precursor cell identity. A genetics interaction test showed that this role is achieved in interaction with the Notch pathway, probably through the repression of Notch target genes expression. Moreover, Esg, but not Scrt, has an additional role during the inner bristle cell formation. Loss of function of this factor induces a defect in neuronal differentiation, specifically axon growth and patterning. Moreover, the expression of genes involved in neuronal differentiation, such as elav and prospero, is impaired in this context. Altogether, these data suggests that Esg is involved in neuronal differentiation by regulating the expression of key neuronal genes.Together, my results showed that Esg and Scrt participate to the establishment of cell diversity in Drosophila bristle cell lineage.