Thesis (Ph.D.) -- University of Adelaide, Dept. of Genetics, 2000? / Bibliography: p. 75-84.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009. / Title from title screen (site viewed January 12, 2010). PDF text: v, 131 p. : ill. ; 3 Mb. UMI publication number: AAT 3360086. Includes bibliographical references. Also available in microfilm and microfiche formats.

There has recently been renewed interest concerning the location of the major loci responsible for the Segregation Distortion phenomenon in Drosophila melanogaster. Hartl (1974) has shown that two major sites are involved: Sd and Rsp. Rsp confers insensitivity to SD chromosomes, while Sd is considered to be the major locus that initiates distortion, Sd is located to the left of Rsp and both are located between Tft and cn. Ganetzky (1977) has extended these findings by showing that just distal to pr there is a locus that, if deleted on a SD chromosome, eliminates distortion and he argues that this is the Sd site. Ganetzky (1977) also uncovered another important locus, in or near the heterochromatin of 2L, that, if deleted from a SD chromosome, greatly reduces the ability of that chromosome to distort and he argued that this site is an enhancer of SD, E(SD). Ganetzky (1977) , also suggests that Rsp might be located very close to the centromere in the proximal heterochromatin of 2R. The results presented here demonstrate the presence of an important component of SD located within the proximal heterochromatin of 2L. These results also show that there is another important site located just distal to pr. However, when this site is removed by recombination from a SD chromosome, a certain level of residual distortion remains. It is argued that the site that Ganetzky (1977) called E(SD) is likely responsible for this residual distortion in the absence of the site just distal to pr. Thus the site near pr is called Sd₁ and the site near 1t is called Sd₂,. Loss of either site results in a large reduction, but not complete elimination, of the distorting ability of a SD chromosome. Other data are presented that, on the whole, agree with Ganetzky's (1977) proposal that Rsp is located in the centromeric heterochromatin of 2R, very close to the centromere. Miklos and Smith-White (1971) have suggested that k (the segregation ratio observed from a given mating) is a deceptive measure of the degree of distortion and they have proposed another method of measuring distortion based on their model of sperm dysfunction. Some of the weak assumptions of this model are discussed and a simpler alternative is presented. The alternative model assumes that the potential segregation ratios of a population of SD males follow a truncated normal distribution. Data are presented that are not necessarily inconsistent with this assumption. The same data show that it is likely that certain SJJ chromosomes differ in their susceptibility to modifiers of It is concluded that at present k provides the clearest measure of distortion. / Science, Faculty of / Zoology, Department of / Graduate

Includes bibliographies. / {59} leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The Polycomblike gene of Drosophila melanogaster is required for the correct spatial expression of the homeotic genes of Antenapaedia and Bithorax Complexes. This thesis describes the isolation and molecular characterization of the Polycomblike gene. / Thesis (Ph.D.)--University of Adelaide, Dept. of Biochemistry, 1995

Bibliography: p. 75-84. / 84 p., [20] leaves, [36] leaves of plates : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Identifies key interactions between Polycomblike and other members of the Polycomb group and suggests a model for the role of Polycomblike within the group. / Thesis (Ph.D.)--University of Adelaide, Dept. of Genetics, 2000?

Bibliography: p. 75-84. / 84 p., [20] leaves, [36] leaves of plates : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Identifies key interactions between Polycomblike and other members of the Polycomb group and suggests a model for the role of Polycomblike within the group. / Thesis (Ph.D.)--University of Adelaide, Dept. of Genetics, 2000?

Bibliography: p. 75-84. Identifies key interactions between Polycomblike and other members of the Polycomb group and suggests a model for the role of Polycomblike within the group.

Bibliography: p. 96-108. / 108, [31] p., [9] leaves of plates : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The major aim of this thesis is the identification and characterisation of Polycomblike (PCL) protein interactors. The study analyses the ability of PCL to bind directly to DNA anchoring the Pc-G complex to the genes which they repress. / Thesis (Ph.D.)--University of Adelaide, Dept. of Genetics, 1997

This thesis was done in collaboration with Sorbonne University as part of a double degree Cotutelle. / During development, cell differentiation frequently occurs upon signaling from concentration or activity gradients of molecules called morphogens. These molecules control in a dose-dependent manner the expression of sets of target genes that determine cell identity. A simple paradigm to study morphogens is the Bicoid gradient, which determines antero-posterior patterning in fruit fly embryos. The Bicoid transcription factor allows the rapid step-like expression of its major target gene hunchback, expressed only in the anterior half of the embryo. The general goal of my thesis was to understand how the information contained in the Bicoid morphogen gradient is rapidly interpreted to provide the precise expression pattern of its target. Using the MS2 system to fluorescently tag specific RNA in living embryos, we were able to show that the ongoing transcription process at the hunchback promoter is bursty and likely functions according to a two-state model. At each nuclear interphase, transcription is first observed in the anterior and it rapidly spreads towards the posterior, as expected for a Bicoid dose-dependent activation process. Surprisingly, it takes only 3 minutes from the first hints of transcription at the anterior to reach steady state with the setting of a sharp expression border in the middle of the embryo. Using modeling taking into account this very fast dynamics, we show that the presence of only 6 Bicoid binding sites (known number of sites in the hunchback promoter) in the promoter, is not sufficient to explain the establishment of a sharp expression border in such a short time. Thus, either more Bicoid binding sites or inputs from other transcription factors could help reconcile the model to the data. To better understand the role of transcription factors other than Bicoid in this process, I used a two-pronged strategy involving synthetic MS2 reporters combined with the analysis of the hunchback MS2 reporter in various mutant backgrounds. I show that the pioneer factor Zelda and the Hunchback protein itself are also critical for hunchback expression, maternal Hunchback acting at nuclear cycle 11-12, while zygotic Hunchback is acting later at nuclear cycle 13-14. The synthetic reporter approach indicate that in contrast to Hunchback and Caudal, Bicoid is able to activate transcription on its own when bound to the promoter. However, the presence of 6 Bicoid binding sites only leads to stochastic activation of the target loci. Interestingly, the binding of Hunchback to the Bicoid-dependent promoter reduces this stochasticity while Caudal might act as a posterior repressor gradient. Confronting these experimental data to theoretical models is ongoing and should allow to better understand the role of transcription factors, other than Bicoid, in hunchback expression at the mechanistic level. / Thesis / Doctor of Philosophy (PhD) / Have you ever wondered how a single cell can become a full grown organism? Well it starts when an egg and sperm fuse together. As time passes this single cell divides over and over again until an organism is formed. During this developmental process, somehow the cells know exactly where they are and what they need to become so that they form the organism. However, we don’t fully understand this process and this is what we hope to answer with our research: How do the cells know where they are and what they need to become during development? We study this process in the fruit fly. Although fruit flies might not look a lot like us, during early embryonic development we are quite similar, so we can try to answer these questions in fruit flies and what we find might be relevant to other organisms like us. During development, the first element that an embryo needs to know is the orientation of its body, where the head and tail, the left and right and the back and front of the body will be. We concentrate on studying how the head to tail axis, which we call the anterior-posterior axis, is formed. To know where the head is going to be, the embryo releases proteins called morphogens that broadcast instructions to other genes so that cells know where they are and what they should become. We study a morphogen called Bicoid. Its concentration is high in the anterior, the region that will become the head of the embryo, and lower as you move towards the posterior where the tail will form. Bicoid activates a gene called hunchback, which ends up dividing the embryo in two large parts, the top and the bottom. However, Bicoid’s message fades away during each cell division and needs to be read again at the beginning of each new nuclear cycle. So how is the message read and how long does this process take? This last question is particularly critical during the period of very fast cell division. My thesis tries to answer this question. We found out that it takes 3 minutes for a nuclei to read the Bicoid concentration, activate hunchback and express it correctly. However, in contrast to what was believed before, or namely, that only Bicoid was involved in this process, we found out that other players are involved in helping relay this message. This way hunchback can accurately divide the body in two parts exactly in the middle and without mistake in such a short period of time.

Au cours de ma thèse j’ai étudié les néprilysines (Nep), des protéinases connues pour dégrader de petits neuropeptides, en particulier les peptides amyloïdes (Aβ). Lors de la maladie d’Alzheimer, les peptides Aβ s’agrègent pour former des plaques toxiques. Il a été montré que l’expression des Nep module l’effet toxique d’Aβ sur la mémoire chez les modèles murins. Néanmoins, le rôle des Nep dans la mémoire dans des conditions physiologiques reste à ce jour inconnu.La drosophile exprime 4 Nep dans le système nerveux central adulte. Nous avons analysé leur rôle dans la mémoire olfactive. Les 4 Nep sont requises pour 2 phases spécifiques de mémoire: à moyen terme (MTM) et à long terme (LTM). De plus, nous avons identifié les neurones dans lesquels elles sont requises : les Mushroom Bodies (MB) ainsi qu’une paire de neurones afférents, les Dorsal Paired Medial neurons (DPM). Nous avons ensuite cherché à savoir si Aβ était l’une des cibles des Nep. Nous avons montré que l’expression d’Aβ dans les DPM n’altère la MTM que lorsque l’expression de Nep1 est inhibée. De plus, le défaut de LTM de drosophiles exprimant Aβ dans les DPM est sauvé par la surexpression de Nep1. En conclusion, nos résultats suggèrent qu’Aβ est dégradé par Nep1 au cours des processus de mémorisation, et qu’Aβ est une cible de Nep1 en conditions non pathologiques.Enfin, nous nous sommes intéressés au neuropeptide amnesiac, décrit comme étant requis pour la mémoire dans les DPM. Nos travaux démontrent qu’amnesiac est en fait requis dans les DPM pour leur développement, et chez l’adulte dans les MB pour activer l’adénylate cyclase responsable de la détection de coïncidence permettant la formation de la MTM. / During my PhD, I studied neprilysins, proteinases known to degrade small neuropeptides, in particular mammalian amyloid-β peptides (Aβ). During Alzheimer’s disease, Aβ peptides aggregate to form toxic plaques. It has been shown that neprilysins expression modulates toxic effects of Aβ on memory in murine models of the disease. However, the role of neprilysins in memory under physiological conditions is still unknown. Drosophila expresses 4 neprilysins in the adult central nervous system. First we have analyzed their role in olfactive memory. We have shown that all of them are required for 2 specific memory phases: Middle-Term Memory (MTM) and Long-Term Memory (LTM). We also have identified the neurons in which they are required: the Mushroom Bodies (MB) and a pair of afferent neurons, the Dorsal Paired Medial (DPM) neurons. Then we investigated whether Aβ peptides could be one of the neprilysins’ targets. We have shown that Aβ expression in DPM neurons alters MTM only when Nep1 expression is inhibited. Furthermore, the LTM deficit of flies expressing Aβ in DPM neurons is rescued by Nep1 overexpression. To conclude, our results suggest that Nep1 degrades endogenous Aβ peptides during memory processes, and that Aβ is a physiological target for Nep1 under non-pathological condition.Finally, we became interested in the amnesiac neuropeptide, described as being required for memory in DPM neurons. Our work shows that amnesiac is actually required in DPM neurons for their development, and in the MB of adult flies in order to activate the adenylate cyclase responsible for coincidence detection leading to MTM formation.