Reproductive axis´ response to food restriction in the cichlid fish Cichlasoma dimerus

La mayoría de los peces teleósteos pueden atravesar largos períodos sin alimentarse, ya seapor una eventual ausencia de alimento en sus nichos ecológicos o como consecuencia de sucomportamiento durante el cuidado parental o la reproducción. En esta Tesis se estudió el efecto dela restricción alimentaria sobre el eje reproductivo del pez cíclido Cichlasoma dimerus incluyendo enel análisis a leptina, hormona ampliamente estudiada en mamíferos por su relación entre el estadonutricional y la reproducción. Se analizó la histología gonadal, la expresión génica de distintashormonas del eje reproductivo y los niveles plasmáticos de esteroides sexuales en animalesalimentados versus animales sometidos a restricción alimentaria. En hembras, no se observó efecto del hambreado sobre el eje reproductivo, ya que lamaduración folicular y la expresión génica de las distintas hormonas analizadas no mostrarondiferencias con respecto a los controles. Sin embargo, en machos, la restricción alimentaria tuvo unefecto estimulatorio en el eje reproductivo, lo que se reflejó en un mayor número deespermatozoides en sus lóbulos seminíferos y en el ducto espermático, un aumento de la expresiónde la hormona folículo estimulante y una disminución de la expresión del factor de crecimiento tipoinsulina 1 y de los niveles plasmáticos de 11-ceto testosterona. Teniendo en cuenta la acción de leptina en mamíferos, se propuso también estudiar larespuesta de esta hormona frente a la restricción alimentaria en C. dimerus. En primer lugar, secaracterizaron los transcriptos de leptina y de su receptor y se llevaron a cabo distintos estudiosbioinformáticos. Se identificaron dos parálogos de leptina con expresión diferencial en los distintosórganos y un único receptor ampliamente distribuido. Luego, se evaluaron los niveles de leptina ydel receptor en condiciones de restricción alimentaria. De los resultados obtenidos se puededestacar la disminución de la expresión de leptina hepática en animales hambreados, lo que sugiereque en esta especie esta hormona tendría un efecto similar al reportado en mamíferos. Por último, en esta Tesis también se secuenció la variante de la hormona liberadora degonadotrofinas 1 (gnrh1) y se analizó la secuencia de las tres variantes de Gnrh presentes en estaespecie y, al igual que con leptina, se llevaron a cabo estudios bioinformáticos. De los mismossurgieron nuevas preguntas acerca del péptido asociado a GnRH (GAP), inicialmente postuladocomo un factor inhibidor de prolactina en mamíferos. Considerando que la estructuratridimensional (3D) de una proteína se relaciona con su función, se evaluó si ésta se encontrabafilogenéticamente conservada en los vertebrados, a pesar de la baja identidad en su secuencia aminoacídica entre los distintos grupos. Se observó que la estructura 3D del GAP asociado a GnRH1se encuentra altamente conservada y presenta una estructura típica de hélice-loop-hélice,característica de algunos factores de transcripción. Estos resultados infieren una presión deselección en el mantenimiento de la estructura 3D de GAP a lo largo del linaje de los vertebrados,sugiriendo una posible función hipofisiotrópica de la misma.Most teleost fishes can go through long periods without feeding, either due to an eventuallack of food in their ecological niches or as a consequence of their behavior during parental care orreproduction. In this Thesis, the effect of food restriction on the reproductive axis of the cichlid fish Cichlasoma dimerus was studied. The analysis included leptin, a hormone widely studied inmammals for its relationship between the nutritional status and reproduction. Specifically, gonadalhistology, gene expression of different hormones of the reproductive axis and sex steroids plasmalevels were evaluated in fed deprived vs. control animals. Food restriction did not affect the reproductive axis in females, since follicular maturationand gene expression of the different hormones analyzed did not show differences with respect tothe controls. However, in males, food restriction showed a stimulatory effect on the reproductiveaxis, which was reflected in a greater number of spermatozoa in their seminiferous lobes andspermatic ducts, an increase in the expression of the follicle stimulating hormone, a decreased inexpression of insulin-like growth factor 1, and a decrease in the plasmatic levels of 11-ketotestosterone. Considering leptin actions in mammals, the response of this hormone to foodrestriction also was evaluated. First, the transcripts of leptin and its receptor were characterized anddifferent bioinformatic studies were performed. Two leptin paralogs with differential expression inthe different organs and a single widely distributed receptor were identified. Then, leptin andreceptor levels were evaluated under food restriction conditions. From the results obtained, it canbe highlighted that the expression of hepatic leptin in unfed animals decreased, which suggeststhat, in this species, this hormone would have a similar effect to that of the reported in mammals. Finally, in this Thesis, the variant of the gonadotropin-releasing hormone 1 (gnrh1)was also sequenced, and the sequences of the three variants of Gnrh present in this species wereanalyzed and, as with leptin, bioinformatic studies were performed. Because of these, newquestions arose about the peptide associated with GnRH (GAP), initially postulated as a prolactininhibiting factor in mammals. Considering that the tridimensional structure of a protein is related toits function, it was evaluated if it was phylogenetically conserved among vertebrates, despite the lowidentity in its amino acid sequence between the different groups. It was observed that the 3Dstructure of GAP associated with GnRH1 is highly conserved and presents a typical helix-loop-helixstructure, characteristic of some transcription factors. These results infer a selection pressure in the maintenance of the 3D structure of GAP along the vertebrate´s lineage, suggesting a possiblehypophysiotropic function.Fil: Pérez Sirkin, Daniela Irina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Nanopore gatesviareversible crosslinking of polymer brushes: a theoretical study

Polymer-brush-modified nanopores are synthetic structures inspired by the gated transport exhibited by their biological counterparts. This work theoretically analyzes how the reversible crosslinking of a polymer network by soluble species can be used to control transport through nanochannels and pores. The study was performed with a molecular theory that allows inhomogeneities in the three spatial dimensions and explicitly takes into account the size, shape and conformations of all molecular species, considers the intermolecular interactions between the polymers and the soluble crosslinkers and includes the presence of a translocating particle inside the pore. It is shown than increasing the concentration of the soluble crosslinkers in bulk solution leads to a gradual increase of its number within the pore until a critical bulk concentration is reached. At the critical concentration, the number of crosslinkers inside the pore increases abruptly. For long chains, this sudden transition triggers the collapse of the polymer brush to the center of the nanopore. The resulting structure increases the free-energy barrier that a translocating particle has to surmount to go across the pore and modifies the route of translocation from the axis of the pore to its walls. On the other hand, for short polymer chains the crosslinkers trigger the collapse of the brush to the pore walls, which reduces the translocation barrier.Fil: Pérez Sirkin, Yamila Anahí. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Tagliazucchi, Mario Eugenio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Szleifer, Igal. Northwestern University; Estados Unido

Mechanisms of Nucleation and Stationary States of Electrochemically Generated Nanobubbles

Gas evolving reactions are ubiquitous in the operation of electrochemical devices. Recent studies of individual gas bubbles on nanoelectrodes have resulted in unprecedented control and insights on their formation. The experiments, however, lack the spatial resolution to elucidate the molecular pathway of nucleation of nanobubbles and their stationary size and shape. Here we use molecular simulations with an algorithm that mimics the electrochemical formation of gas, to investigate the mechanisms of nucleation of gas bubbles on nanoelectrodes, and characterize their stationary states. The simulations reproduce the experimental currents in the induction and stationary stages, and indicate that surface nanobubbles nucleate through a classical mechanism. We identify three distinct regimes for bubble nucleation, depending on the binding free energy per area of bubble to the electrode, ΔΓbind. If ΔΓbind is negative, the nucleation is heterogeneous and the nanobubble remains bound to the electrode, resulting in a low-current stationary state. For very negative ΔΓ, the bubble fully wets the electrode, forming a one-layer-thick micropancake that nucleates without supersaturation. On the other hand, when ΔΓbind > 0 the nanobubble nucleates homogeneously close to the electrode, but never attaches to it. We conclude that all surface nanobubbles must nucleate heterogeneously. The simulations reveal that the size and contact angle of stationary nanobubbles increase with the reaction driving force, although their residual current is invariant. The myriad of driven nonequilibrium stationary states with the same rate of production of gas, but distinct bubble properties, suggests that these dissipative systems have attractors that control the stationary current.Fil: Pérez Sirkin, Yamila Anahí. University of Utah; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Gadea, Esteban David. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Scherlis Perel, Damian Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Molinero, Valeria. University of Utah; Estados Unido

Electrochemically Generated Nanobubbles: Invariance of the Current with Respect to Electrode Size and Potential

Gas-producing electrochemical reactions are key to energy conversion and generation technologies. Bubble formation dramatically decreases gas-production rates on nanoelectrodes, by confining the reaction to the electrode boundary. This results in the collapse of the current to a stationary value independent of the potential. Startlingly, these residual currents also appear to be insensitive to the nanoelectrode diameter in the 5 to 500 nm range. These results are counterintuitive, as it may be expected that the current be proportional to the circumference of the electrode, i.e., the length of the three-phase line where the reaction occurs. Here, we use molecular simulations and a kinetic model to elucidate the origin of current insensitivity with respect to the potential and establish its relationship to the size of nanoelectrodes. We provide critical insights for the design and operation of nanoscale electrochemical devices and demonstrate that nanoelectrode arrays maximize conversion rates compared to macroscopic electrodes with same total area.Fil: Gadea, Esteban David. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Pérez Sirkin, Yamila Anahí. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Molinero, Valeria. University of Utah; Estados UnidosFil: Scherlis Perel, Damian Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentin

Vapor pressure of aqueous solutions of electrolytes reproduced with coarse-grained models without electrostatics

The vapor pressure of water is a key property in a large class of applications from the design of membranes for fuel cells and separations to the prediction of the mixing state of atmospheric aerosols. Molecular simulations have been used to compute vapor pressures, and a few studies on liquid mixtures and solutions have been reported on the basis of the Gibbs Ensemble Monte Carlo method in combination with atomistic force fields. These simulations are costly, making them impractical for the prediction of the vapor pressure of complex materials. The goal of the present work is twofold: (1) to demonstrate the use of the grand canonical screening approach (Factorovich, M. H. et al. J. Chem. Phys. 2014, 140, 064111) to compute the vapor pressure of solutions and to extend the methodology for the treatment of systems without a liquid−vapor interface and (2) to investigate the ability of computationally efficient high-resolution coarse-grained models based on the mW monatomic water potential and ions described exclusively with short-range interactions to reproduce the relative vapor pressure of aqueous solutions. We find that coarse-grained models of LiCl and NaCl solutions faithfully reproduce the experimental relative pressures up to high salt concentrations, despite the inability of these models to predict cohesive energies of the solutions or the salts. A thermodynamic analysis reveals that the coarse-grained models achieve the experimental activity coefficients of water in solution through a compensation of severely underestimated hydration and vaporization free energies of the salts. Our results suggest that coarse-grained models developed to replicate the hydration structure and the effective ion−ion attraction in solution may lead to this compensation. Moreover, they suggest an avenue for the design of coarse-grained models that accurately reproduce the activity coefficients of solutions.Fil: Pérez Sirkin, Yamila Anahí. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Factorovich, Matias Hector. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Molinero, Valeria. University of Utah; Estados UnidosFil: Scherlis Perel, Damian Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentin

Inter-individual variability in reproductive success and somatic growth in Cichlasoma dimerus (Heckel, 1840)

Environmental factors and social interactions are known to affect somatic growth and reproduction in teleost fish. It has been described for Cichlasoma dimerus that only one pair is formed under a wide range of laboratory conditions. However, this was not observed in tanks composed of three males and three females, where multiple pair formation occurred. Thus, our objective was to evaluate somatic growth and reproductive performance in C. dimerus under this particular condition, in which more than one pair is expected to be formed. A clear sexual growth dimorphism, with males growing faster than females, and multiple pair formation, sometimes simultaneously, were observed. Both features were absent in previous studies with other aquaria structures. Additionally, there was a significant association between reproductive events and body size, where the bigger the fish, both male and female, the higher the number of reproductive events. Despite the sexual growth dimorphism, no differences were observed between males and females in IGF-I and GHR2 mRNA levels. The results obtained for this social species show a high inter-individual variability in the aquaria in regard to reproductive success and growth. This may have implications on experimental design, where a low level of heterogeneity between fish is desirable. If this variability is not taken into account, possible treatment effects may not be detected.Fil: Delgadin, Tomás Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; ArgentinaFil: Pérez Sirkin, Daniela Irina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; ArgentinaFil: Karp, Paola Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; ArgentinaFil: Fossati, Mariana. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental. Laboratorio de Neuroendocrinología del Crecimiento y la Reproducción; ArgentinaFil: Vissio, Paula Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentin

Growth hormone, luteinizing hormone, and follicle-stimulating hormone regulation by neuropeptide Y in both sexes of the cichlid fish, Cichlasoma dimerus

Neuropeptide Y (NPY) is considered the most potent orexigenic peptide, increasing before meal time and during fasting. In teleost, most studies on NPY action upon growth hormone (GH) and luteinizing hormone (LH) were conducted in females or group of animals without sex discrimination. The aim of this study was to evaluate whether NPY modulates the expression and release of GH and gonadotropins in both sexes of Cichlasoma dimerus. By double-label immunofluorescence, we first determined the association between NPY fibers and pituitary cells. In addition, we performed in vitro studies to evaluate the effect of NPY on GH and gonadotropins expression by real-time PCR, and release by Western blot, in males and females separately. Contacts between NPY fibers and GH and follicle-stimulating hormone (FSH)-producing cells were detected, indicating possible functional relationships. We observed an increase in GH release in the culture medium at 2 nM for males (p = 0.043) and 20 nM for females (p = 0.028). Pituitary FSH release was stimulated at 20 nM (p = 0.026) and 200 nM (p = 0.033) for males and females, respectively. Finally, NPY only increased β-LH mRNA expression at 20 nM in females (p = 0.028) and its release at 2 nM (p = 0.049) and 200 nM for males (p = 0.005) and 200 nM for females (p = 0.018). In conclusion, NPY acts as a GH-, LH- and FSH-releasing factor, in a dose- and sex-dependent way.Fil: Di Yorio, María Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; ArgentinaFil: Delgadin, Tomás Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; ArgentinaFil: Pérez Sirkin, Daniela Irina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; ArgentinaFil: Vissio, Paula Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentin

Pore condensation and freezing is responsible for ice formation below water saturation for porous particles

Ice nucleation in the atmosphere influences cloud properties, altering precipitation and the radiative balance, ultimately regulating Earth’s climate. An accepted ice nucleation pathway, known as deposition nucleation, assumes a direct transition of water from the vapor to the ice phase, without an intermediate liquid phase. However, studies have shown that nucleation occurs through a liquid phase in porous particles with narrow cracks or surface imperfections where the condensation of liquid below water saturation can occur, questioning the validity of deposition nucleation. We show that deposition nucleation cannot explain the strongly enhanced ice nucleation efficiency of porous compared with nonporous particles at temperatures below −40 °C and the absence of ice nucleation below water saturation at −35 °C. Using classical nucleation theory (CNT) and molecular dynamics simulations (MDS), we show that a network of closely spaced pores is necessary to overcome the barrier for macroscopic ice-crystal growth from narrow cylindrical pores. In the absence of pores, CNT predicts that the nucleation barrier is insurmountable, consistent with the absence of ice formation in MDS. Our results confirm that pore condensation and freezing (PCF), i.e., a mechanism of ice formation that proceeds via liquid water condensation in pores, is a dominant pathway for atmospheric ice nucleation below water saturation. We conclude that the ice nucleation activity of particles in the cirrus regime is determined by the porosity and wettability of pores. PCF represents a mechanism by which porous particles like dust could impact cloud radiative forcing and, thus, the climate via ice cloud formation.Fil: David, Robert O.. Institute for Atmospheric and Climate Science; SuizaFil: Marcolli, Claudia. Institute for Atmospheric and Climate Science; SuizaFil: Fahrni, Jonas. Zurich University of Applied Sciences; SuizaFil: Qiu, Yuqing. University of Utah; Estados UnidosFil: Pérez Sirkin, Yamila Anahí. University of Utah; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Molinero, Valeria. University of Utah; Estados UnidosFil: Mahrt, Fabian. Institute for Atmospheric and Climate Science; SuizaFil: Brühwiler, Dominik. University of Applied Sciences; SuizaFil: Lohmann, Ulrike. Institute for Atmospheric and Climate Science; SuizaFil: Kanji, Zamin A.. Institute for Atmospheric and Climate Science; Suiz

Reproductive axis´ response to food restriction in the cichlid fish Cichlasoma dimerus

La mayoría de los peces teleósteos pueden atravesar largos períodos sin alimentarse, ya seapor una eventual ausencia de alimento en sus nichos ecológicos o como consecuencia de sucomportamiento durante el cuidado parental o la reproducción. En esta Tesis se estudió el efecto dela restricción alimentaria sobre el eje reproductivo del pez cíclido Cichlasoma dimerus incluyendo enel análisis a leptina, hormona ampliamente estudiada en mamíferos por su relación entre el estadonutricional y la reproducción. Se analizó la histología gonadal, la expresión génica de distintashormonas del eje reproductivo y los niveles plasmáticos de esteroides sexuales en animalesalimentados versus animales sometidos a restricción alimentaria. En hembras, no se observó efecto del hambreado sobre el eje reproductivo, ya que lamaduración folicular y la expresión génica de las distintas hormonas analizadas no mostrarondiferencias con respecto a los controles. Sin embargo, en machos, la restricción alimentaria tuvo unefecto estimulatorio en el eje reproductivo, lo que se reflejó en un mayor número deespermatozoides en sus lóbulos seminíferos y en el ducto espermático, un aumento de la expresiónde la hormona folículo estimulante y una disminución de la expresión del factor de crecimiento tipoinsulina 1 y de los niveles plasmáticos de 11-ceto testosterona. Teniendo en cuenta la acción de leptina en mamíferos, se propuso también estudiar larespuesta de esta hormona frente a la restricción alimentaria en C. dimerus. En primer lugar, secaracterizaron los transcriptos de leptina y de su receptor y se llevaron a cabo distintos estudiosbioinformáticos. Se identificaron dos parálogos de leptina con expresión diferencial en los distintosórganos y un único receptor ampliamente distribuido. Luego, se evaluaron los niveles de leptina ydel receptor en condiciones de restricción alimentaria. De los resultados obtenidos se puededestacar la disminución de la expresión de leptina hepática en animales hambreados, lo que sugiereque en esta especie esta hormona tendría un efecto similar al reportado en mamíferos. Por último, en esta Tesis también se secuenció la variante de la hormona liberadora degonadotrofinas 1 (gnrh1) y se analizó la secuencia de las tres variantes de Gnrh presentes en estaespecie y, al igual que con leptina, se llevaron a cabo estudios bioinformáticos. De los mismossurgieron nuevas preguntas acerca del péptido asociado a GnRH (GAP), inicialmente postuladocomo un factor inhibidor de prolactina en mamíferos. Considerando que la estructuratridimensional (3D) de una proteína se relaciona con su función, se evaluó si ésta se encontrabafilogenéticamente conservada en los vertebrados, a pesar de la baja identidad en su secuencia aminoacídica entre los distintos grupos. Se observó que la estructura 3D del GAP asociado a GnRH1se encuentra altamente conservada y presenta una estructura típica de hélice-loop-hélice,característica de algunos factores de transcripción. Estos resultados infieren una presión deselección en el mantenimiento de la estructura 3D de GAP a lo largo del linaje de los vertebrados,sugiriendo una posible función hipofisiotrópica de la misma.Most teleost fishes can go through long periods without feeding, either due to an eventuallack of food in their ecological niches or as a consequence of their behavior during parental care orreproduction. In this Thesis, the effect of food restriction on the reproductive axis of the cichlid fish Cichlasoma dimerus was studied. The analysis included leptin, a hormone widely studied inmammals for its relationship between the nutritional status and reproduction. Specifically, gonadalhistology, gene expression of different hormones of the reproductive axis and sex steroids plasmalevels were evaluated in fed deprived vs. control animals. Food restriction did not affect the reproductive axis in females, since follicular maturationand gene expression of the different hormones analyzed did not show differences with respect tothe controls. However, in males, food restriction showed a stimulatory effect on the reproductiveaxis, which was reflected in a greater number of spermatozoa in their seminiferous lobes andspermatic ducts, an increase in the expression of the follicle stimulating hormone, a decreased inexpression of insulin-like growth factor 1, and a decrease in the plasmatic levels of 11-ketotestosterone. Considering leptin actions in mammals, the response of this hormone to foodrestriction also was evaluated. First, the transcripts of leptin and its receptor were characterized anddifferent bioinformatic studies were performed. Two leptin paralogs with differential expression inthe different organs and a single widely distributed receptor were identified. Then, leptin andreceptor levels were evaluated under food restriction conditions. From the results obtained, it canbe highlighted that the expression of hepatic leptin in unfed animals decreased, which suggeststhat, in this species, this hormone would have a similar effect to that of the reported in mammals. Finally, in this Thesis, the variant of the gonadotropin-releasing hormone 1 (gnrh1)was also sequenced, and the sequences of the three variants of Gnrh present in this species wereanalyzed and, as with leptin, bioinformatic studies were performed. Because of these, newquestions arose about the peptide associated with GnRH (GAP), initially postulated as a prolactininhibiting factor in mammals. Considering that the tridimensional structure of a protein is related toits function, it was evaluated if it was phylogenetically conserved among vertebrates, despite the lowidentity in its amino acid sequence between the different groups. It was observed that the 3Dstructure of GAP associated with GnRH1 is highly conserved and presents a typical helix-loop-helixstructure, characteristic of some transcription factors. These results infer a selection pressure in the maintenance of the 3D structure of GAP along the vertebrate´s lineage, suggesting a possiblehypophysiotropic function.Fil: Pérez Sirkin, Daniela Irina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Thermodynamic properties of aqueous systems in the nanoscopic scale

Thermodynamic properties of aqueous systems in nanoscopic scaleIn the present thesis, the thermodynamical properties of aqueous systems in the nanos-cale regime were investigated. In particular, the following phenomena were analyzed: i)the vapor pressure of water-ions systems, from the macroscopic scale to aggregates ofonly a few particles. ii) The nucleation of bubbles on nanoelectrodes. iii) The effect ofconfinement on the water dissociation constant.The GCS (Grand Canonical Screening) methodology, which has been developed in ourgroup before this thesis, allows us to obtain the vapor pressure of systems that havea liquid-vapor interface. In the present thesis, this methodology has been modified inorder to study the vapor pressure of systems without an interface, with the purpose ofapplying it to more complex systems, like fuel cells. The effect of electrolytes on thevapor pressure of water has been studied from both the experimental and theoreticalpoints of view in the case of bulk systems, however the resolution of the experiments fornanoaggregate does not allow a description on the microscopic scale, and is the cause ofone of the greatest uncertainties in atmospheric predictions. In this context, we studythe ability of different models, both atomistic and coarse-grained, to predict the vaporpressure of systems of just a few molecules.The nucleation of nanobubbles on nanoscopic electrodes has been frequently studiedin recent decades, not only for its relevance from a chemical-physics standpoint, whichleaves many open questions regarding the nucleation mechanism and the stability, butalso because of its importance in the design and optimization of electrocatalytic tech-nologies. In this thesis, this phenomenon has been studied through molecular dynamicssimulations with coarse-grained models in collaboration with an experimental group atThe University of Utah.Different authors have speculated on how confinement can affect the autodissociation ofwater, but this question has not yet been answered through experiments, and has beenscarcely addressed from simulations. Recent studies suggest an increase of the dissocia-tion constant in bidimiensional nanometric pores. In the present thesis, this effect hasbeen studied under a more extreme confinement, in particular in a (6,6) carbon nano-tube, where the opposite effect was observed.To study these problems, this thesis has used different classical, quantum, and QM-MMsimulation schemes, including the following open source software: LAMMPS, MCCCS-Towhee and Quantum Espresso. It has often been necessary to implement new featureswithin these programs, as well as different tools for data analysis .In the present thesis, the thermodynamical properties of aqueous systems in the nanoscale regime were investigated. In particular, the following phenomena were analyzed: i) the vapor pressure of water-ions systems, from the macroscopic scale to aggregates of only a few particles. ii) The nucleation of bubbles on nanoelectrodes. iii) The effect of confinement on the water dissociation constant. The GCS (Grand Canonical Screening) methodology, which has been developed in our group before this thesis, allows us to obtain the vapor pressure of systems that have a liquid-vapor interface. In the present thesis, this methodology has been modified in order to study the vapor pressure of systems without an interface, with the purpose of applying it to more complex systems, like fuel cells. The effect of electrolytes on the vapor pressure of water has been studied from both the experimental and theoretical points of view in the case of bulk systems, however the resolution of the experiments for nanoaggregate does not allow a description on the microscopic scale, and is the cause of one of the greatest uncertainties in atmospheric predictions. In this context, we study the ability of different models, both atomistic and coarse-grained, to predict the vapor pressure of systems of just a few molecules. The nucleation of nanobubbles on nanoscopic electrodes has been frequently studied in recent decades, not only for its relevance from a chemical-physics standpoint, which leaves many open questions regarding the nucleation mechanism and the stability, but also because of its importance in the design and optimization of electrocatalytic technologies. In this thesis, this phenomenon has been studied through molecular dynamics simulations with coarse-grained models in collaboration with an experimental group at The University of Utah. Different authors have speculated on how confinement can affect the autodissociation of water, but this question has not yet been answered through experiments, and has been scarcely addressed from simulations. Recent studies suggest an increase of the dissociation constant in bidimiensional nanometric pores. In the present thesis, this effect has been studied under a more extreme confinement, in particular in a (6,6) carbon nanotube, where the opposite effect was observed. To study these problems, this thesis has used different classical, quantum, and QM-MM simulation schemes, including the following open source software: LAMMPS, MCCCSTowhee and Quantum Espresso. It has often been necessary to implement new features within these programs, as well as different tools for data analysis .Fil: Pérez Sirkin, Yamila Anahí. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentin