Hypopigmentation is a characteristic of several diseases associated with vesicle traffic defects, like the Hermansky-Pudlak, Chediak-Higashi, and Griscelli syndromes. Hypopigmentation is also a characteristic of the zebrafish mutant vps18(hi2499A), which is affected in the gene vps18, a component of the homotypic fusion and protein sorting complex that is involved in tethering during vesicular traffic. Vps18, as part of this complex, participates in the formation of early endosomes, late endosomes, and lysosomes. Here, we show that Vps18 is also involved in the formation of melanosomes. In the zebrafish mutant vps18(hi2499A) the retroviral insertion located at exon 4 of vps18, leads to the formation of two abnormal splicing variants lacking the coding sequence for the clathrin repeat and the RING finger conserved domains. A deficiency of Vps18 in zebrafish larvae results in hepatomegaly and skin hypopigmentation. We also observed a drastic reduction in the number of melanosomes in the eye's retinal pigmented epithelium along with the accumulation of immature melanosomes. A significant reduction in the vps18(hi2499A) larvae visual system capacity was found using the optokinetic response assay. We propose that the insertional mutant vps18(hi2499A) can be used as a model for studying hypopigmentation diseases in which vesicle traffic problems exist.

In S. cerevisiae, K + transport relies principally on two structurally related membrane proteins, known as Trk1p and Trk2p. Direct involvement in cation movements has been demonstrated for Trk1p, which is a high-affinity K + transporter. Initially described as a low-affinity K + transporter, Trk2p seems to play a minor role in K + transport, since its activity is only apparent under very specific conditions, such as in a ∆sin3 background. Here we show that growth of a ∆trk1∆sin3 double mutant, under K + -limiting conditions or at low pH, is Trk2p-dependent, and by Northern blot analysis we demonstrate that deletion of SIN3 results in transcriptional derepression of TRK2. In addition, we show that heterologous overexpression of TRK2 with the inducible GAL1 promoter bypasses Sin3p repression in a ∆trk1∆trk2 double mutant and fully restores growth under non-permissive conditions. Furthermore, kinetic experiments in a ∆trk1∆sin3 double mutant revealed a K + transporter with an apparent high affinity and a moderate capacity. Taken together, these results indicate that TRK2 encodes a functional K + transporter that, under our experimental conditions, displays distinctive kinetic characteristics.

The effects of ketoconazole and miconazole uptake on K(+) transport and the internal pH of Saccharomyces cerevisiae were studied. The uptake of both drugs was very fast, linear with concentration and not dependent on glucose, indicating entrance by diffusion and concentrating inside. Low (5.0μM) to intermediate concentrations (40μM) of both drugs produced a glucose-dependent K(+) efflux; higher ones also produced a small influx of protons, probably through a K(+)/H(+) exchanger, resulting in a decrease of the internal pH of the cells and the efflux of material absorbing at 260nm and phosphate. The cell membrane was not permeabilized. The K(+) efflux with miconazole was dependent directly on the medium pH. This efflux results in an increased membrane potential, responsible for an increased Ca(2+) uptake and other effects. These effects were not observed with two triazolic antifungals. A decrease of the Zeta (ζ) potential was observed at low concentrations of miconazole. Although the main effect of these antifungals is the inhibition of ergosterol synthesis, K(+) efflux is an important additional effect to be considered in their therapeutic use. Under certain conditions, the use of single mutants of several transporters involved in the movements of K(+) allowed to identify the participation of several antiporters in the efflux of the cation.

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Introducción: El proceso de regeneración puede ocurrir en múltiples niveles de la organización biológica y la habilidad de los diferentes organismos para regenerar partes faltantes es altamente variable. El gen Nanog es un factor de transcripción en células madre embrionarias; se cree que es clave en el mantenimiento de la pluripotencia. Objetivo: Determinar la filogenia de la inactivación de los genes Nanog postembrionario en comparación con el Ambystoma mexicanum. Materiales y métodos: Se utilizó un diseño cualitativo, basado en la revisión y recolección de las secuencias genómicas con datos del Genbank, donde se compararon las secuencias de nucleótidos por BLAST, se trabajó con el software de alineamiento genético MEGA, para alinear las secuencias y se construyeron dendogramas de Neighbor Joining. Resultados: Se observó que las especies con mayor similitud con el Ambystoma mexicanum son las aves, al contar con una distancia evolutiva menos amplia que la del Homo sapiens, entre las que encontraron Taeniopygia guttata, Zonotrichia albicollis, una especie en particular es el Ornithorhynchus anatinus. Conclusión: El Ambystoma mexicanum y el Homo sapiens presentan un alto grado de distancia genética por ser pocas las secuencias genómicas del gen Nanog que comparten, en comparación con otras especies que comparten más secuencias genómicas. Se cree que para inducir la regeneración en humanos lo mejor sería poder reproducir los procesos que la naturaleza nos muestra en animales como la salamandra. Este proceso parece bloquear la formación del blastema. En principio, los genes o moléculas que atenúan la inflamación o que bloquean la remodelación de la matriz podrían favorecer una respuesta regenerativa al impedir la cicatrización.