Search

MAGISTER EN ASTRONOMIA FONDECYT FONDECYT

In this thesis we study the necessary methods to perform a transit search for extrasolar planets. We apply these methods to search for planets in one of the fields of the LAIWO project: the Cygnus-Lyra field (Laiwo VI). We describe the problems that systematic effects can introduce for precise relative photometry at the millimagnitude level (~3mmag). Ways to minimize and quantify this correlated noise are also described. We test the weaknesses and strenghts of two transit detection algorithms (TDA) namely the Box fitting algorithm (BLS) and the TRUFAS algorithm using archive data from the OGLE project and simulations of the first year of the Pan-Planets survey. These projects are similar in terms of telescope size and field of view to the LAIWO survey. We have found that the main limitations of the BLS algorithm are the transit depth and correlated noise (Red Noise). The TRUFAS detection efficiency correlates with the number of points in transit and the number of transits present in the light curve, and, its detection efficiency is low (less than ~ 50%) for these type of ground-based observations. Finally, we create from the LAIWO data light curves which are suitable to detect planets among the stars brighter than R = 16.5 mag. We have found 31 eclipsing binaries and 18 light curves that have transits consistent with a planet. Of these detections, 3 eclipsing binaries and 8 planet candidates were independently found by the KEPLER survey. Of the 10 newly discovered transiting planets, 3 are promising to justify follow-up confirmation studies, which are always necessary to probe the planetary nature of a transiting companion.

En este trabajo se caracterizó la adenilil ciclasa TczAC. Se determinó que el gen que codifica para esta enzima se encuentra altamente conservado con los genes de adenilil ciclasas identificados en otros tripanosomátidos, es parte de una familia multigénica y se expresa en todos los estadios del ciclo de vida de T. cruzi. Se determinó que el producto de este gen es una enzima funcional capaz de complementar una cepa de levaduras carente de actividad adenilil ciclasa. Esta enzima es específica para AMPc, presenta una mayor actividad en presencia de Mn+2 que de Mg+2 y es inhibida por Zn+2 y el inhibidor del sitio P, 2'-deoxy-3'AMP. Por otro lado, el Ca+2 estimula la actividad de la misma manera independiente de calmodulina. Utilizando la técnica de doble híbrido en levaduras se demostró que TczAC dimeriza a través de su dominio catalítico y se identificaron 13 clones capaces de interaccionar específicamente con la misma. En particular se analizó la interacción de TczAC con el clon correspondiente a la proteína de flagelo paraflagellar rod. Asimismo, TczAC fire expresada en una cepa mutante de levaduras S. pombe. Los resultados obtenidos con estos experimentos sugieren que este sistema de expresión podría ser de gran utilidad para la búsqueda de inhibidores específicos. Por otra parte, se identificó y caracterizó el gen TczPDE que codifica para la primer fosfodiesterasa de AMPc de T. cruzi. Se determinó que este gen es parte de una familia multigénica y codifica para una proteína que presenta un posible péptido señal, dos dominios GAF de unión a GMPc y un dominio catalítico altamente conservado. La funcionalidad de esta proteína se confirmó por ensayos de complementación en levaduras carentes de actividad fosfodiesterasa. En dichas levaduras TczPDE se encontró asociada a la fracción particulada, mostró una alta afinidad por el AMPc y no fue capaz de hidrolizar GMPc. Por ensayos de Western blot se confirmó la asociación de TczPDE a la membrana de las levaduras y se observó que esta se encuentra fuertemente asociada a la misma. La localización subcelular de TczPDE en T. cruzi se estudió por fraccionamiento subcelular e inmunolocalización. Estos experimentos demostraron que TczPDE se encuentra localizada en la membrana plasmática del parásito y concentrada en el flagelo. In this work we have characterized TczAC adenylyl cyclase. The gene encodes an enzyme which is highly conserved with the adenylyl cyclase genes identified in other trypanosomatids, is part of a multigene family and is expressed in all the stages of T. cruzi life cycle. The product of this gene is a functional enzyme that can complement a yeast strain deficient in adenylyl cyclase activity. The enzyme is specific for cAMP, has a higher activity in the presence of Mn+2 instead of Mg 2+, and is inhibited by Zn+2 and the P-site inhibitor, 2'-deoxy-3 'AMP. On the other hand, Ca+2 stimulates its activity in a calmodulin independent manner. Using the yeast two-hybrid technique it was demonstrated that TczAC dimerizes through its catalytic domains, and 13 clones that interact with this protein were identified. In particular, the interaction of TczAC with the flagellar protein paraflagellar rod was analyzed. Besides, TczAC was expressed in a S. pombe mutant strain. The results obtain in these experiments suggest that this expression system could be useful for the identification of specific inhibitors. Apart from that, the gene TczPDE that codes for the first cAMP phosphodiesterase of T. cruzi was identified and characterized. It was found that this gene is part of a mutligene family and encodes a protein that presents a putative signal peptide, two GAF domains for cGMP binding and a highly conserved catalytic domain. The functionality of this protein was confirmed by complementation assays in yeasts lacking phosphodiesterase activity. In these yeasts TczPDE was found to be associated to the particulate fraction, showed a high affinity for CAMP and was not able to hydrolyze cGMP. By Western blot analysis, the association of TczPDE to the yeast membrane was confirmed, and it was observed that this enzyme is strongly associated to it. The subcellular localization of TczPDE in T. cruzi was studied by subcellular fractionation and immunolocalization. These experiments demonstrated that TczPDE is localized in the plasma membrane of the parasite and concentrated in the flagellum. Fil: D'Angelo, Maximiliano A.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Centrosomes are comprised of 2 orthogonally arranged centrioles surrounded by the pericentriolar material (PCM), which serves as the main microtubule organizing center of the animal cell. More importantly, centrosomes also control spindle polarity and orientation during mitosis. Recently, we and other investigators discovered that several nucleoporins play critical roles during cell division. Here, we show that nucleoporin Nup62 plays a novel role in centrosome integrity. Knockdown of Nup62 induced mitotic arrest in G 2/M phases and mitotic cell death. Depletion of Nup62 using RNA interference results in defective centrosome segregation and centriole maturation during the G 2 phase. Moreover, Nup62 depletion in human cells leads to the appearance of multinucleated cells and induces the formation of multipolar centrosomes, centriole synthesis defects, dramatic spindle orientation defects, and centrosome component rearrangements that impair cell bi-polarity. Our results also point to a potential role of Nup62 in targeting gamma-tubulin and SAS-6 to the centrioles.