Actin polymerization drives polar growth in Arabidopsis root hair cells.

In plants, the actin cytoskeleton is a prime regulator of cell polarity, growth, and cytoplasmic streaming. Tip growth, as observed in root hairs, caulonema, and pollen tubes, is governed by many factors, including calcium gradients, exocytosis and endocytosis, reactive oxygen species, and the cytoskeleton. Several studies indicate that the polymerization of G-actin into F-actin also contributes to tip growth. The structure and function of F-actin within the apical dome is variable, ranging from a dense meshwork to sparse single filaments. The presence of multiple F-actin structures in the elongating apices of tip-growing cells suggests that this cytoskeletal array is tightly regulated. We recently reported that sublethal concentrations of fluorescently labeled cytochalasin could be used to visualize the distribution of microfilament plus ends using fluorescence microscopy, and found that the tip region of the growing root hair cells of a legume plant exhibits a clear response to the nodulation factors secreted by Rhizobium. (1) In this current work, we expanded our analysis using confocal microscopy and demonstrated the existence of highly dynamic fluorescent foci along Arabidopsis root hair cells. Furthermore, we show that the strongest fluorescence signal accumulates in the tip dome of the growing root hair and seems to be in close proximity to the apical plasma membrane. Based on these findings, we propose that actin polymerization within the dome of growing root hair cells regulates polar growth.

Enteroparasitosis en indígenas de la comunidad Japrería estado Zulia Venezuela / Enteroparasites in indigenous individuals from the Japreria community Zulia state Venezuela

Las enfermedades parasitarias representan un problema médico, económico y social, afectando a todas las clases sociales, pero principalmente a los estratos socioeconómicos más bajos. Para determinar la prevalencia de enteroparásitos en la comunidad indígena Japrer¡a, ubicada en la Sierra de Perijá, Estado Zulia, Venezuela, se procesaron 191 muestras fecales correspondientes a individuos de ambos sexos con edades comprendidas entre 1 mes y 86 años. Las muestras fueron analizadas a través de los métodos coproparasitológico directo y por la técnica de concentración formol-éter. Se encontró una elevada prevalencia de enteroparásitos (82,20 por ciento) y un predominio del poliparasitismo (78,98 por ciento), con asociaciones entre especies comensales y patógenas. No se observó diferencia significativa de susceptibilidad entre la prevalencia de parásitos y el sexo (p>0,05). En cuanto al grupo etario, el estrato más afectado resultó ser el de adultos jóvenes (20-39 años; 25,48 por ciento). Las especies de protozoarios mas frecuentes fueron Blastocystis hominis (46,07 por ciento), Entamoeba coli (42,93 por ciento) y el complejo Entamoeba histolytica/Entamoeba dispar (34,0 por ciento). Entre los helmintos, Ancylostomideos (30,89 por ciento), Ascaris lumbricoides (9,95 por ciento) e Hymenolepis nana (4,19 por ciento) ocuparon los primeros lugares. La presencia incrementada de enteroparásitos se relaciona con el escaso saneamiento ambiental en esta comunidad indígena, por lo que los resultados avalan la importancia de diseñar programas de control específicos para disminuir los factores condicionantes presentes, lo cual tendr¡a impacto en el descenso de las infecciones parasitarias.

Silencing the morphogenesis of rotavirus.

The morphogenesis of rotaviruses follows a unique pathway in which immature double-layered particles (DLPs) assembled in the cytoplasm bud across the membrane of the endoplasmic reticulum (ER), acquiring during this process a transient lipid membrane which is modified with the ER resident viral glycoproteins NSP4 and VP7; these enveloped particles also contain VP4. As the particles move towards the interior of the ER cisternae, the transient lipid membrane and the nonstructural protein NSP4 are lost, while the virus surface proteins VP4 and VP7 rearrange to form the outermost virus protein layer, yielding mature infectious triple-layered particles (TLPs). In this work, we have characterized the role of NSP4 and VP7 in rotavirus morphogenesis by silencing the expression of both glycoproteins through RNA interference. Silencing the expression of either NSP4 or VP7 reduced the yield of viral progeny by 75 to 80%, although the underlying mechanism of this reduction was different in each case. Blocking the synthesis of NSP4 affected the intracellular accumulation and the cellular distribution of several viral proteins, and little or no virus particles (neither DLPs nor TLPs) were assembled. VP7 silencing, in contrast, did not affect the expression or distribution of other viral proteins, but in its absence, enveloped particles accumulated within the lumen of the ER, and no mature infectious virus was produced. Altogether, these results indicate that during a viral infection, NSP4 serves as a receptor for DLPs on the ER membrane and drives the budding of these particles into the ER lumen, while VP7 is required for removing the lipid envelope during the final step of virus morphogenesis.