In order to maintain a multicellular organism cells need to interact and communicate with each other. Signalling cascades such as the Bone Morphogenic Protein (BMP) and Hedgehog (Hh) signalling pathways therefore play essential roles in development and disease. Intercellular signalling also underlies the function of stem cell niches, signalling microenvironments that regulate behaviour of associated stem cells. Range and intensity of the niche signal controls stem cell proliferation and differentation and must therefore be strictly regulated. The testis and ovary of the fruit fly Drosophila melanogaster are established models of stem cell niche biology. In the apical tip of the testis, germ line stem cell (GSCs) and somatic cyst stem cells (CySCs) are arranged around a group of postmitotic somatic cells termed hub. While it is clear which signals regulate GSC maintenance it is unclear how these signals are spatially regulated. Here I show that BMP signalling is specifically activated at the interface of niche and stem cells. This local activation is possible because the transport of signalling and adhesion molecules is coupled and directed towards contact sites between niche and stem cells. I further show that the generation of the BMP signal in the wing disc follows the same mechanism. Hh signalling controls somatic stem cell populations in the Drosophila ovary and the mammalian testis. However, it was unknown what role Hh might play in the fly testis, where the components of this signalling cascade are also expressed. Here I show that overactivation of Hh signalling leads to an increased proliferation and an expansion of the cyst stem cell compartment. Finally, while the major components of the Hh signalling pathway are known, detailed knowledge of how signal transduction is implemented at the cell biological level is still lacking. Here, I show that localisation of the key signal transducer Smo to the plasma membrane is sufficient for phosphorylation of its cytoplasmic tail and downstream pathway activation. Using advanced, microscopy based biophysical methods I further demonstrate that Smo clustering is, in contrast to the textbook model, independent of phosphorylation.

A oxidação cíclica é um fenômeno que pode trazer problemas a diversas indústrias e, apesar de estudada em grande medida para materiais de alto desempenho, como superligas, pesquisas em materiais menos nobres são incipientes. Essa tese teve como objetivo investigar as propriedades de oxidação cíclica de materiais ferrosos de baixo custo e compará-las com as do aço inoxidável fundido ASTM A 297 grau HH modificado. A motivação surgiu de uma análise de falha de componente feito com aço HH e da possibilidade de pesquisar materiais com melhor relação custo-benefício em aplicações onde a principal solicitação seja a de resistência à oxidação cíclica. Seis ligas ferrosas com teores de cromo e níquel menores que o do aço HH, ou sem esses elementos, compuseram o estudo. Nestas ligas, os elementos silício e alumínio (1 liga) foram utilizados como alternativa para resistir à oxidação. As composições das ligas (% em peso) foram aproximadamente Fe-15Al-1,1C, Fe-14,5Si-4Cr-0,75C, Fe-5Si-5Cr-V-C, Fe-5Si-5Cr-4Ni-Nb-C, Fe-17Mn-5Si-10Cr-4Ni-V-C e Fe-12Mn-5Si-10Cr-4Ni-Nb-C, além do aço HH modificado (HH-mod). Foram realizados ensaios de oxidação cíclica nas temperaturas de 800, 900 e 1000 ºC e ensaios de dureza, tração e impacto. As ligas mostraram fragilidade, com exceção das ligas com alto teor de manganês que superaram o aço HH-mod em tenacidade. Em oxidação cíclica, as ligas apresentaram boa resistência, com taxas de variação de massa pequenas ou moderadas, e quando houve destacamento, este foi menor que o apresentado pelo aço HH-mod. Camadas oxidadas foram caracterizadas por técnicas de microscopia eletrônica de varredura (MEV), espectroscopia por dispersão de energia de raios-X (EDX) e difração de raios-X (DRX). Foi possível verificar a formação de óxidos protetores de Si, Cr ou Al, mas também de Fe, Cu e principalmente Mn. Por fim, a determinação das cinéticas de ganho de massa e destacamento mostrou que apesar de algumas ligas apresentarem kp maiores que os do aço HH-mod, todas sofreram menores destacamentos, o que ocorreu para o aço HH-mod nas três temperaturas, devido à diferença entre coeficientes de expansão térmica da matriz austenítica e dos óxidos. Dentre as demais ligas, Fe-15Al-1,1C e Fe-5Si-5Cr-4Ni-Nb-C não sofreram destacamentos e apresentaram baixo ganho de massa, devido às finas camadas de óxido e assim apresentando os melhores resultados. / The cyclic oxidation phenomenon can cause problems to several industries. Although studied in high performance materials, as superalloys, researches on less noble materials are incipient. The aim of this thesis was investigate the cyclic oxidation properties of low cost iron-based alloys and compare them with a cast stainless steel ASTM A 297 HH modified grade. The motivation was a failure analysis on a component made of HH and the possibility of research materials with a better cost-benefit ratio for applications where the main solicitation is the cyclic oxidation resistance. Six alloys with less chromium and nickel amount than HH steel, or without these elements, constituted the study. In these alloys, silicon and aluminum (1 alloy) were used to improve the oxidation resistance. The alloy compositions (weight %) were nearly Fe-15Al-1,1C, Fe-14,5Si-4Cr-0,75C, Fe-5Si-5Cr-V-C, Fe-5Si-5Cr-4Ni-Nb-C, Fe-17Mn-5Si-10Cr-4Ni-V-C and Fe-12Mn-5Si-10Cr-4Ni-Nb-C, and the HH steel modified (HH-mod). Cyclic oxidation tests were performed at 800, 900 and 1000 ºC and also hardness, impact and tensile tests. The alloys studied presented brittleness, and only the high Mn alloys had better mechanical properties than HH-mod steel. The alloys presented good results on cyclic oxidation, with low or moderate oxidation rates and when suffering spallation, it was less than HH-mod steel. Oxidized scales were characterized by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-Ray diffraction (XRD). The formation of protective oxide of Si, Cr or Al was noticed, but also Fe, Cu and Mn oxides were found. Finally, the mass gain and spallation kinetics was determined, and spite the fact of some alloys having higher kp values than HH-mod, no alloys suffered more spallation than HH steel. The austenitic matrix was considered the responsible of this behavior in all temperatures, due to the high thermal expansion coefficient compared with oxides. The better results were found to Fe-15Al-1,1C and Fe-5Si-5Cr-4Ni-Nb-C alloy, with low mass gain and without spalling, on account of the thin oxide scales formed.

A oxidação cíclica é um fenômeno que pode trazer problemas a diversas indústrias e, apesar de estudada em grande medida para materiais de alto desempenho, como superligas, pesquisas em materiais menos nobres são incipientes. Essa tese teve como objetivo investigar as propriedades de oxidação cíclica de materiais ferrosos de baixo custo e compará-las com as do aço inoxidável fundido ASTM A 297 grau HH modificado. A motivação surgiu de uma análise de falha de componente feito com aço HH e da possibilidade de pesquisar materiais com melhor relação custo-benefício em aplicações onde a principal solicitação seja a de resistência à oxidação cíclica. Seis ligas ferrosas com teores de cromo e níquel menores que o do aço HH, ou sem esses elementos, compuseram o estudo. Nestas ligas, os elementos silício e alumínio (1 liga) foram utilizados como alternativa para resistir à oxidação. As composições das ligas (% em peso) foram aproximadamente Fe-15Al-1,1C, Fe-14,5Si-4Cr-0,75C, Fe-5Si-5Cr-V-C, Fe-5Si-5Cr-4Ni-Nb-C, Fe-17Mn-5Si-10Cr-4Ni-V-C e Fe-12Mn-5Si-10Cr-4Ni-Nb-C, além do aço HH modificado (HH-mod). Foram realizados ensaios de oxidação cíclica nas temperaturas de 800, 900 e 1000 ºC e ensaios de dureza, tração e impacto. As ligas mostraram fragilidade, com exceção das ligas com alto teor de manganês que superaram o aço HH-mod em tenacidade. Em oxidação cíclica, as ligas apresentaram boa resistência, com taxas de variação de massa pequenas ou moderadas, e quando houve destacamento, este foi menor que o apresentado pelo aço HH-mod. Camadas oxidadas foram caracterizadas por técnicas de microscopia eletrônica de varredura (MEV), espectroscopia por dispersão de energia de raios-X (EDX) e difração de raios-X (DRX). Foi possível verificar a formação de óxidos protetores de Si, Cr ou Al, mas também de Fe, Cu e principalmente Mn. Por fim, a determinação das cinéticas de ganho de massa e destacamento mostrou que apesar de algumas ligas apresentarem kp maiores que os do aço HH-mod, todas sofreram menores destacamentos, o que ocorreu para o aço HH-mod nas três temperaturas, devido à diferença entre coeficientes de expansão térmica da matriz austenítica e dos óxidos. Dentre as demais ligas, Fe-15Al-1,1C e Fe-5Si-5Cr-4Ni-Nb-C não sofreram destacamentos e apresentaram baixo ganho de massa, devido às finas camadas de óxido e assim apresentando os melhores resultados. / The cyclic oxidation phenomenon can cause problems to several industries. Although studied in high performance materials, as superalloys, researches on less noble materials are incipient. The aim of this thesis was investigate the cyclic oxidation properties of low cost iron-based alloys and compare them with a cast stainless steel ASTM A 297 HH modified grade. The motivation was a failure analysis on a component made of HH and the possibility of research materials with a better cost-benefit ratio for applications where the main solicitation is the cyclic oxidation resistance. Six alloys with less chromium and nickel amount than HH steel, or without these elements, constituted the study. In these alloys, silicon and aluminum (1 alloy) were used to improve the oxidation resistance. The alloy compositions (weight %) were nearly Fe-15Al-1,1C, Fe-14,5Si-4Cr-0,75C, Fe-5Si-5Cr-V-C, Fe-5Si-5Cr-4Ni-Nb-C, Fe-17Mn-5Si-10Cr-4Ni-V-C and Fe-12Mn-5Si-10Cr-4Ni-Nb-C, and the HH steel modified (HH-mod). Cyclic oxidation tests were performed at 800, 900 and 1000 ºC and also hardness, impact and tensile tests. The alloys studied presented brittleness, and only the high Mn alloys had better mechanical properties than HH-mod steel. The alloys presented good results on cyclic oxidation, with low or moderate oxidation rates and when suffering spallation, it was less than HH-mod steel. Oxidized scales were characterized by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-Ray diffraction (XRD). The formation of protective oxide of Si, Cr or Al was noticed, but also Fe, Cu and Mn oxides were found. Finally, the mass gain and spallation kinetics was determined, and spite the fact of some alloys having higher kp values than HH-mod, no alloys suffered more spallation than HH steel. The austenitic matrix was considered the responsible of this behavior in all temperatures, due to the high thermal expansion coefficient compared with oxides. The better results were found to Fe-15Al-1,1C and Fe-5Si-5Cr-4Ni-Nb-C alloy, with low mass gain and without spalling, on account of the thin oxide scales formed.

In order to maintain a multicellular organism cells need to interact and communicate with each other. Signalling cascades such as the Bone Morphogenic Protein (BMP) and Hedgehog (Hh) signalling pathways therefore play essential roles in development and disease. Intercellular signalling also underlies the function of stem cell niches, signalling microenvironments that regulate behaviour of associated stem cells. Range and intensity of the niche signal controls stem cell proliferation and differentation and must therefore be strictly regulated. The testis and ovary of the fruit fly Drosophila melanogaster are established models of stem cell niche biology. In the apical tip of the testis, germ line stem cell (GSCs) and somatic cyst stem cells (CySCs) are arranged around a group of postmitotic somatic cells termed hub. While it is clear which signals regulate GSC maintenance it is unclear how these signals are spatially regulated. Here I show that BMP signalling is specifically activated at the interface of niche and stem cells. This local activation is possible because the transport of signalling and adhesion molecules is coupled and directed towards contact sites between niche and stem cells. I further show that the generation of the BMP signal in the wing disc follows the same mechanism. Hh signalling controls somatic stem cell populations in the Drosophila ovary and the mammalian testis. However, it was unknown what role Hh might play in the fly testis, where the components of this signalling cascade are also expressed. Here I show that overactivation of Hh signalling leads to an increased proliferation and an expansion of the cyst stem cell compartment. Finally, while the major components of the Hh signalling pathway are known, detailed knowledge of how signal transduction is implemented at the cell biological level is still lacking. Here, I show that localisation of the key signal transducer Smo to the plasma membrane is sufficient for phosphorylation of its cytoplasmic tail and downstream pathway activation. Using advanced, microscopy based biophysical methods I further demonstrate that Smo clustering is, in contrast to the textbook model, independent of phosphorylation.:Summary 1 List of publications 3 1 Introduction 9 Aims of the thesis 15 2 Generation of a local BMP signal in testis and wing disc 17 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.1.1 Stem cells and stem cell niches . . . . . . . . . . . . . . 19 2.1.2 The Drosophila testis stem cell niche . . . . . . . . . . 20 2.1.3 BMP signalling in the fly . . . . . . . . . . . . . . . . . 23 2.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.2.1 The BMP niche signal is transduced locally at adherens junctions 25 2.2.2 Generation of the local BMP niche signal . . . . . . . . 30 2.2.3 Exocyst involvement in long-range BMP signalling . . 34 2.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3 Hedgehog pathway overactivation in the testicular niche 41 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.1.1 The role of Hedgehog in the fly . . . . . . . . . . . . . 43 3.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.2.1 Overexpression of Hh increases the CySC number and expands their range 45 3.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 4 Visualization of Smo phosphorylation and biophysical detection of Smo clustering 49 4.1 Introduction (part I) . . . . . . . . . . . . . . . . . . . . . . . 51 4.1.1 Hedgehog signalling in the fly . . . . . . . . . . . . . . 51 4.1.2 Reception and transduction of the Hh signal by Ptc and Smo 54 4.2 Results (part I) . . . . . . . . . . . . . . . . . . . . . . . . . . 56 4.2.1 A fluorescent reporter for Drosophila Smo tail phosphorylation 56 4.2.2 Smo phosphorylation and localisation in the salivary gland 61 4.2.3 Smo localisation in cultured insect cells . . . . . . . . . 63 4.2.4 Smo membrane localisation and phosphorylation . . . . 65 4.3 Introduction (part II) . . . . . . . . . . . . . . . . . . . . . . . 67 4.3.1 Fluorescence correlation spectroscopy (FCS) . . . . . . 67 4.3.2 Dual-color fluorescence cross-correlation spectroscopy (FCCS) 72 4.3.3 Artefacts in FCS/FCCS . . . . . . . . . . . . . . . . . 73 4.4 Results (part II) . . . . . . . . . . . . . . . . . . . . . . . . . . 79 4.4.1 Smo clustering measured by FCCS . . . . . . . . . . . 79 4.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

Bakgrund Medicinska gaser är kalla och torra, därav behövs de befuktas och värmas för att inte åsamka skador på lungorna hos patienter som behandlas i respirator. De vanligaste metoderna är aktiv och passiv befuktning, så kallad heated humidification (HH) och heat and moisture exchanger (HME filter). Syfte Att sammanfatta befintlig forskning om för- och nackdelar samt skillnader som framkommit med aktiv respektive passiv befuktning i respirationsvård på intensivvårdsavdelning. Metod En systematiskt genomförd litteraturstudie med narrativ summering. Sökningar gjordes i databaserna CINAHL, PubMed samt Cochrane. Nio vetenskapliga artiklar med kvantitativ ansats mellan tidsintervallet 2012–2022 inkluderades utifrån PICO. Kvalitetsgranskning utfördes med validerade granskningsmallar från Joanna Briggs Institute. Huvudresultat HH tillförde mindre mekaniskt dead space för intuberade som gav bättre PaCO2 värden, vilket är specifikt fördelaktigt för patienter med acidos. Den metoden är dock mer kostsam och fungerar ej lika effektivt vid stigande rumstemperatur och direkt solljus på apparaturen. Den kräver därav mer kontroller samt tillsyn vid dessa förhållanden. Vid non-invasiv behandling och tracheostomi i respirator ger HME filter inte sämre PaCO2 värden eftersom det större mekaniska dead space den tillför inte har samma negativa effekt vid dessa behandlingar och tillstånd. Den inkrementella kostnaden är bättre för HME filter, men huruvida den ger upphov till fler incidenser av tubocklusion är ej klarlagt. Slutsats Båda befuktningsmetoderna har klara fördelar och nackdelar, därav är det fördelaktigt att ha tillgång till båda metoderna på intensivvårdsavdelningar tillsammans med en tydlig rutin om när metoderna skall användas till patienten. / Background Medical gases are cold and dry, therefore the need for adding humid and heat is highly important, otherwise they can cause damage at the lungs in patients undergoing mechanical ventilation. The most common methods are active and passive humidification so called heated humidification (HH) and heat and moisture exchanger (HME). Aim Summarize existing research on advantages, drawbacks and differences that have emerged with active and passive humidification in respiratory care in the intensive care unit. Method A systematic conducted literature review with a narrative summary to compile the results. Searches were made on the databases CINAHL, PubMed and Cochrane. Nine scientific articles with a quantitative approach between 2012-2022 were included based on PICO. Quality review was performed with validated review templates from Joanna Briggs Institute. Results HH provided less mechanical dead space for intubated patients which provided better PaCO2 values, specifically beneficial for patients with acidosis. However, this method is more expensive and does not work as effectively with increasing room temperature and direct sunlight on the equipment. It therefore requires more controls and supervision in presence of these conditions. In patients undergoing non-invasive mechanical ventilation and in patients with tracheostomy who are mechanically ventilated, HME filters do not give higher PaCO2 values. ​​The increased mechanical dead space it adds does not have the same negative effect in these treatments and conditions. The incremental cost is better for HME filters, but whether it gives rise to more incidences of tube occlusion is not clear. Conclusion Both humidification methods have clear advantages and drawbacks, hence it is advantageous to have access to both methods at intensive care units together with a clear routine about when the methods should be used.

The region GGD 27, located in Sagittarius at a distance of 1.7 kpc, is an active star forming region. The most well-known observational signature of this region, the HH 80/81/80N jet, is one of the largest collimated jet system known so far, spanning over a total length of about 5 pc. Ahead of the Herbig-Haro object HH 80N, assumed to be the northern head of the jet, there is a dense core of 0.3 pc in size and mass of 20 M (HH 80N core) that exhibits peculiar chemistry, possibly induced by the UV radiation incoming from the HH object. In addition, the HH 80N core has star forming signatures, namely a bipolar molecular outflow and supersonic infall velocity (0.6 km s(-1)), which differs from what standard contracting core models predict. This rises the question whether the HH 80/81/80N jet has triggered or sped up the star formation process in this core. VLA cm continuum observations carried out as a preliminary part of this thesis show that the jet could expand further away than HH 80N. This makes possible the cause-and-effect relationship between the jet and the star forming signatures of the core. In this thesis we study the possible influence of the HH 80/81/80N jet on the properties of the HH 80N core in several approaches. We first derive the physical and chemical properties of the large envelope of the HH 80N core using data obtained with the BIMA and IRAM 30m telescopes. All the detected BIMA molecular species arise in a ring-like structure contracting at 0.6 km s(-1). This morphology is likely the result of strong molecular depletion occurring at the inner part of the core (r < 0.1 pc), when the gas reaches densities > 10(5) cm(-3), as derived from a multi-transition analysis of CS and SO lines observed with IRAM 30m. Despite the overall morphology and kinematic similarity between the different species, there is significant molecular differentiation along the ring-like structure. Part of this differentiation may be caused by the UV irradiation of the nearby HH 80N object that illuminates the part of the core facing HH 80N, which results in an abundance enhancement of some species. Given the peculiar kinematic properties of the HH 80N core, we analyze the continuum emission of the core using self-consistent standard models of protostellar collapse to see if the dynamical evolution of this core departs from the predictions of classic models of star formation. We find that a young protostar (IRS1) surrounded by a slowly rotating collapsing envelope plus a circumstellar disk provide a good fit to our data observed at several bands. However, this model implies that the core has a static envelope at radii > 1.5 x10(4) AU, apparently in contradiction with the contracting ring-like structure that has 10(6) AU of radius. Besides, the continuum maps at 350 m and 3.5 mm reveal additional clumps independent from the main continuum peak at IRS 1. Therefore, we propose a scenario where IRS1 has infall motions with no connection with the kinematics of the large envelope of the HH 80N core. The later is possibly affected by the HH 80/81/80N jet and exhibits fragmentation that may lead to the formation of several protostars. In order to disentangle the gas motions belonging to the protostellar collapse of IRS1 from those associated to large scale kinematics we analyze high-density tracers (NH(3), HN(13)C, NH(2)D), observed at high angular resolution with VLA and PdBI, aiming to recover kinematic information in parts of the HH 80N core where other molecules are depleted. The results question the scenario of the contracting molecular ring. Instead, the velocity gradients seen with high density tracers suggest that part of the core is being swept by the HH 80/81/80N jet in the process of dissipating energy (e.g. though generation of magneto hydrodynamic waves in the medium). Future simulations of the events occurring in the HH 80N region are paramount to confirm whether the formation of IRS1 was caused by the interaction of the HH 80N core with the HH 80/81/80N outflow. / La font amb formació estel_lar per davant d'HH 80N: estudi de la seva interacció amb un jet a escala de parsecs Josep-Maria Masqué Saumell - Universitat de Barcelona L'objecte Herbig-Haro HH 80N representa l'extrem nord del sistema HH 80/81/80N, el jet estel.lar més llarg i col.limat conegut fins ara, que es troba a 1.7 kpc de distància a la regió de Sagitari. Observacions al voltant d'HH 80N revelen que a 0.3 pc de l'objecte HH hi ha un nucli dens (font d'HH 80N) de 0.3 pc de grandària i de massa 20 M, que mostra una química i cinemàtica peculiars i, a més, té un protoestel embegut al seu interior (IRS1). Donades aquestes característiques existeix la possibilitat de que les propietats de la font d'HH 80N hagin estat alterades pel jet d'HH 80/81/80N. L'objectiu d'aquesta tesi és l'estudi de la influència dels jets protoestel_lars centrant-nos en el cas particular de la regió d'HH 80N. Primer, trobem que la radiació ultraviolada provinent d'HH 80N és capaç d'alterar la química de la part de la font més exposada a l'objecte HH. Segon, malgrat una possible influència dinàmica del jet a la font d'HH 80N, el procés de col.lapse d'IRS1 es pot explicar dins el marc clàssic de formació estel.lar. No obstant, trobem que gran part del material de la font d'HH 80N constitueix un embolcall independent d'IRS1, el qual es fragmenta en vàries condensacions de gas. Possiblement, el gas d'aquest embolcall extens ha estat parcialment escombrat per ones magneto-hidrodinàmiques produïdes pel pas del jet. Aquest tipus d'interacció podria provocar inestabilitats a la font d'HH 80N donant lloc al naixement induït d'estels. Concloem que futures simulacions magneto-hidrodinàmiques són necessàries per confirmar que la formació d'IRS1 ha estat provocada per la interacció del jet HH 80/81/80N amb la font d'HH

We present Magellan adaptive optics Ha imaging of HH 508, which has the highest surface brightness among protostellar jets in the Orion Nebula. We find that HH 508 actually has a shorter component to the west, and a longer and knotty component to the east. The east component has a kink at 0.'' 3 from the jet-driving star theta(1) Ori B-2, so it may have been deflected by the wind/radiation from the nearby theta(1) Ori B1B5. The origin of both components is unclear, but if each of them is a separate jet, then theta(1) Ori B-2 may be a tight binary. Alternatively, HH 508 may be a slow-moving outflow, and each component represents an illuminated cavity wall. The ionization front surrounding theta(1) Ori B2B3 does not directly face theta(1) Ori B1B5, suggesting that the EUV radiation from theta(1) Ori C plays a dominant role in affecting the morphology of proplyds even in the vicinity of theta(1) Ori B1B5. Finally, we report an Ha blob that might be ejected by the binary proplyd LV 1.

No description available.

Au cours de ma thèse, mes projets de recherche ont visé à mieux comprendre les mécanismes moléculaires contrôlant la prolifération et la spécification des cellules progénitrices dans la rétine du xénope à travers trois projets principaux. Le réseau de régulation qui contrôle la spécification des cellules progénitrices vers les sous-types neuronaux est à ce jour très peu connu. C’est dans ce contexte que j’ai étudié le rôle du facteur de transcription à domaine bHLH, Ascl1, dans la détermination des sous-types rétiniens au cours du développement. Par des approches in vivo de gain et perte de fonction d’Ascl1, des expériences d’épistasie et la recherche de ses cibles transcriptionnelles, j’ai pu mettre en évidence qu’Ascl1 (i) est impliqué dans la genèse des neurones GABAergiques rétiniens, (ii) qu’il est épistatique sur des facteurs glutamatergiques tels que Neurog2, NeuroD1 ou Atoh7, (iii) que son activité GABAergique est conférée par son domaine basique de liaison à l’ADN et (iv) que cette activité implique la régulation directe du facteur de transcription Ptf1a. Ces données ajoutent donc une nouvelle pièce au réseau transcriptionnel gouvernant la spécification des sous-types GABAergiques au cours du développement de la rétine. La mise en place correcte des types et sous-types cellulaires de la rétine nécessite une coordination avec le moment de sortie du cycle cellulaire des progéniteurs rétiniens. Dans ce contexte, j’ai contribué à l’avancée d’un projet visant à étudier le réseau de signalisation contrôlant la prolifération des précurseurs de la rétine. Par des approches in vivo, génétiques et pharmacologiques, cette étude a montré que les voies Wnt et Hedgehog s’antagonisent pour réguler l’activité proliférative des cellules souches et progénitrices rétiniennes. Nos données préliminaires suggèrent que ces voies agissent de façon opposée à la fois sur la sortie et sur la cinétique du cycle cellulaire. Ce travail nous a conduit à proposer un modèle selon lequel ces voies Wnt et Hedgehog réguleraient la balance entre prolifération et différenciation dans la rétine post-embryonnaire. Enfin, dans le but d’élargir nos connaissances sur les réseaux de signalisation et les réseaux transcriptionnels impliqués dans le contrôle de la prolifération et de la détermination cellulaire dans la rétine, j’ai également contribué à la recherche de nouveaux marqueurs spécifiques des différentes populations cellulaires rétiniennes au travers d’un crible à grande échelle par hybridation in situ. De nombreux gènes spécifiquement exprimés dans les cellules souches ou les cellules progénitrices constituent des gènes candidats pour de futures approches fonctionnelles. / My thesis research work aimed to better understand the molecular mechanisms underlying proliferation and specification of retinal progenitors in Xenopus through three main projects. As the mechanisms governing specification of retinal progenitors towards the different neuronal subtypes are still poorly understood, I focused my work on the role of Ascl1, a bHLH transcription factor, in cell-subtype determination during retinogenesis. Using in vivo gain- and loss-of-function experiments, I have investigated Ascl1’s epistatic relationships with other bHLH factors and identified its transcriptional targets. My results indicate that Ascl1 (i) is implicated in the genesis of retinal GABAergic neurons (ii) is epistatic to glutamatergic factors such as Neurog2, NeuroD1 and Atoh7 (iii) that its basic DNA-biding domain is sufficient for its GABAergic-inducing activity (iv) and that this activity involves a direct regulation of the Ptf1a transcription factor. The correct order of neural cell types and subtypes formation is tightly coordinated with the timing of cell-cycle exit of retinal progenitors. Ongoing work in the laboratory, to which I have contributed, was therefore investigating the role of signaling pathways controlling retinal precursor proliferation in this process. Using in vivo genetic and pharmacological tools, we have shown that an antagonistic cross-regulation between Wnt and Hedgehog signaling governs stem cell and progenitor proliferation in post-embryonic retina. Preliminary data shows that Wnt and Hedgehog have opposite effects on both cell cycle exit and kinetics and may therefore regulate the proliferation/differentiation balance in the post-embryonic retina. Lastly, in order to broaden our knowledge on the transcriptional and signaling networks which govern proliferation and cell fate determination in the retina, I have participated in a large scale screen by in situ hybridization aiming to identify new molecular markers of different retinal cell population. Many genes that are exclusively expressed in retinal stem cells or progenitors are promising candidates for future functional studies.

La presente tesis posee un enfoque cuantitativo, mientras que su diseño de investigación fue no experimental transversal, cuyo tipo fue exploratorio, descriptivo y correlacional. El problema a resolver fue ¿En qué medida un estudio de productividad influye en la planificación de una obra, enfocado en la mano de obra?, para lo cual se planteó como objetivo principal elaborar un estudio de productividad en obra de un edificio multifamiliar para mejorar la planificación de obra. Para su desarrollo se utilizó la metodología de recolección de datos a través de la observación estructurada, con las herramientas de Carta Balance y Registro de Avance. Del estudio se determinó los factores que perjudican el avance de los trabajadores, que generaban los flujos no contributorios y desgaste de los trenes de actividad, los cuales fueron el inadecuado uso de la mano de obra y distribución del trabajo, así como la falta coordinación y supervisión perenne. This thesis has a quantitative approach, while its research design was not experimental cross, whose type was exploratory, descriptive and correlational. The problem to solve was what extent a productivity study influences the planning of a work focused on labor?, for which he was raised as main objective to develop a study of productivity in a multifamily building work to improve planning work. The data collection methodology used through structured observation for development, tools and Registration Card Balance Forward. Study the factors that hinder the advancement of workers, non-contributory generating flows and wear activity trains, which were the inappropriate use of labor and distribution of work and the lack of coordination was determined and perennial supervision.