Understanding the Role of Dicer in Astrocyte Development

The Dicer1 allele is used to show that microRNAs (miRNAs) play important roles in astrocyte development and functions. While it is known that astrocytes that lack miRNAs are dysregulated, the in vivo phenotypes of these astrocytes are not well understood. In this study, we use Aldh1l1-EGFP transgene, a marker of astrocytes, to characterize mouse models with conditional Dicer1 ablation (via either human or mouse GFAP-Cre). This transgene revealed novel features of the defective astrocytes from the absence of miRNA. Although astrocyte miRNAs were depleted in both lines, we found histological and molecular differences in the Aldh1l1-EGFP cells between the two Cre lines. Aldh1l1-EGFP cells from hGFAP-Cre mutant lines displayed up-regulation of Aldh1l1-EGFP with increased proliferation and a genomic profile that acquired many features of wildtype primary astrocyte cultures. In the young mGFAP-Cre mutant lines we found that Aldh1l1-EGFP cells were disorganized and hyperproliferative in the developing cerebellum. Using the Aldh1l1-EGFP transgene, our work provides new insights into the roles of miRNAs in astrocyte development and the features of astrocytes in these two mouse models.     

Conjugation of phosphonoacetic acid to nucleobase promotes a mechanism-based inhibition

Small molecule inhibitors have a powerful blocking action on viral polymerases. The bioavailability of the inhibitor, nevertheless, often raise a significant selectivity constraint and may substantially limit the efficacy of therapy. Phosphonoacetic acid has long been known to possess a restricted potential to block DNA biosynthesis. In order to achieve a better affinity, this compound has been linked with natural nucleotide at different positions. The structural context of the resulted conjugates has been found to be crucial for the acquisition by DNA polymerases. We show that nucleobase-conjugated phosphonoacetic acid is being accepted, but this alters the processivity of DNA polymerases. The data presented here not only provide a mechanistic rationale for a switch in the mode of DNA synthesis, but also highlight the nucleobase-targeted nucleotide functionalization as a route for enhancing the specificity of small molecule inhibitors.     

Bioelectrorheological model of the cell. 5. Electrodestruction of cellular membrane in alternating electric field.

Recently proposed analysis of the extensil stress developed in a cellular membrane subjected to an alternating electric field (Pawłowski, P., and M. Fikus, 1993. Bioelectrorheological model of the cell. 4. Analysis of the extensil deformation of the membrane in an alternating field. Biophys. J. 65:535-540) was applied in calculations of extensil stress threshold values, sigma eo[d], producing experimentally observed electrodestruction of cells within the frequency range of 7 x 10(1) - 3 x 10(5) Hz. It was shown that the susceptibility (s[d] = 1/sigma eo[d]), of the membrane to this process varies with field frequency and depends on the type of cells. Electrodestruction is facilitated in the 10(5)-Hz field. A rheological hypothesis explaining the experimentally observed dependence of membrane stability on electric field frequency was proposed and successfully tested for two other phenomena: electroporation and electrofusion.     

Occurrence ofEnterococcus spp. in waters

We studied 630 bacterial strains isolated from surface waters and determined as enterococci on the basis of their growth on Slanetz-Bartley agar in typical colonies. The strains were tested and characterized by several key conventional tests for basic differentiation of enterococci and by commercial test kits. We identified 135 strains ofE. fœcium (21%), 115E. fœcalis (18%), 30E. mundtii (5%), 27E. hirae (4%), 22E. casseliflavus (3%), 21E. gallinarum (3%), 17E. durans-E. hirae complex (3%), 5E. durans (1%), and 1 strain ofE. avium. 150 strains were classified only asEnterococcus sp. (25%) and 107 strains (17%) isolated from Slanetz-Bartley agar were not enterococci. We found that the non-enterococcal group consisted of other Gram-positive cocci and Gram-positive and Gram-negative rods. Based on the identification we tried to find a relation between taxonomic position of isolated strains and their colony morphology on Slanetz-Bartley agar. Out of the total of 523 identified enterococci, 345 strains (66%) formed purple colonies, 136 red colonies (26%), 37 pink colonies (7%) and 5 cream colored colonies (1%). There was no correlation among the color, size or colony morphology and the taxonomic characterization of enterococcal strains.     

Convenient Assay for Staphylococcal Nuclease by the Metachromatic Well-Agar-Diffusion Technique

The metachromatic agar-diffusion (MAD) microslide technique was adapted for quantitative assay for staphylococcal thermonuclease in heterogeneous systems, such as milk and broth. When an enzyme-containing solution was placed in a well cut in the agar, a bright pink halo was obtained. The diameter of the pink zone of hydrolysis was related to time and temperature of incubation and to nuclease concentration. Concentrations of nuclease as low as 0.005 mug/ml and as high as 2.0 mug/ml were conveniently determined after 3 hr at 37 C.