Perturbation of growth and differentiation of Friend murine erythroleukemia cells by 5-bromodeoxyuridine incorporation in early S phase.

Cultured Friend murine erythroleukemia cells (Friend cells) are induced to undergo erythroid differentiation when grown in the presence of dimethylsulfoxide (DMSO) and other compounds. The effects of unifilar substitution of bromouracil (BU) for thymidine in the DNA (BU-DNA) of Friend cells were examined. Cells were grown in the presence of 5-bromodeoxy-uridine (BrdU) for one generation, then centrifuged and resuspended in medium containing DMSO without BrdU. These cells exhibited a delay in the appearance of heme-producing, benzidine-reative (B+) cells and a decreased rate of cell proliferation in comparison to the control not containing BU-DNA. A transient inhibition of entry into S phase was observed when control cells or cells containing BU-DNA were grown in the presence of DMSO) for 10 to 20 hours. This transient inhibition was increased in the BrdU culture. Thus BU-substitution in Friend cells alters other cellular functions in addition to erythroid differentiation. The rate of increase in the percent of cells committed to differentiate (those forming B+ colonies in plasma clots) was similar in the BrdU and control cultures until 40 to 50 hours. After this time, a delay in the appearance of committed cells was observed in the BrdU culture. The effect of BrdU on the appearance of B+ cells was more pronounced and occurred earlier than its effect on the rate of commitment. Therefore, the delay in the appearance of B+ cells in the BrdU culture was due primarily to perturbation of post-commitment events such as the accumulation of hemoglobin. We also examined the effect on growth and differentiation after BrdU was incorporated during different intervals of S phase in cells synchronized by centrifugal elutriation or by double thymidine block and hydroxyurea treatment. The delay in the appearance of B+ cells and inhibition of cell proliferation were only observed when BrdU was incorporated in the first half of S phase. BrdU (10 muM) had no effect on growth or differentiation when present during late S or G1 and G2. These results, using two very different methods to achieve cell synchrony, indicate that the effects of BrdU on growth and differentiation described above are due to its incorporation into DNA sequences replicating during early S.     

Reassessing Neotropical angiosperm distribution patterns based on monographic data: a geometric interpolation approach

Monographic data rely on specimens deposited in herbaria and museums, which have been thoroughly revised by experts. However, monographic data have been rarely used to map species richness at large scale, mainly because of the difficulties caused by spatially heterogeneous sampling effort. In this paper we estimate patterns of species richness and narrow endemism, based on monographic data of 4,055 Neotropical angiosperm species. We propose a geometric interpolation method to derive species ranges at a 1° grid resolution. To this we apply an inverse distance-weighted summation scheme to derive maps of species richness and endemism. In the latter we also adjust for heterogeneous sampling effort. Finally, we test the robustness of the interpolated species ranges and derived species richness by applying the same method but using a leave-one-out-cross-validation (LOOCV). The derived map shows four distinct regions of elevated species richness: (1) Central America, (2) the Northern Andes, (3) Amazonia and (4) the Brazilian Atlantic coast (‘Mata Atlantica’). The region with the highest estimated species richness is Amazonia, with Central America following closely behind. Centers of narrow endemism are located over the entire Neotropics, several of them coinciding with regions of elevated species richness. Sampling effort has a minor influence on the interpolation of overall species richness, but it substantially influences the estimation of regions of narrow endemism. Thus, in order to improve maps of narrow endemism and resulting conservation efforts, more collection and identification activity is required.     

Solid-phase synthesis of polymyxin B1 and analogues via a safety-catch approach.

As part of a program towards the development of novel antibiotics, a convenient method for solid-phase synthesis of the cyclic cationic peptide polymyxin B1 and analogues thereof is described. The methodology, based on cleavage-by-cyclization using Kenner's safety-catch linker, yields crude products with purities ranging from 37-67%. Antibacterial assays revealed that analogues 23-26, in which the (S)-6-methyloctanoic acid moiety is replaced with shorter acyl chains, exhibit distinct antimicrobial activity. The results suggest that the length of the acyl chain is rather critical for antimicrobial activity. On the other hand, substitution of the hydrophobic ring-segment D-Phe-6/Leu-7 in polymyxin B1 with dipeptide mimics (i.e. analogues 27-33) resulted in almost complete loss of antimicrobial activity.     

Localization of cathepsin D in rat liver. Immunocytochemical study using post-embedding immunoenzyme and protein A-gold techniques

Light and electron microscopic localization of cathepsin D in rat liver was investigated by post-embedding immunoenzyme and protein A-gold techniques. By light microscopy, cytoplasmic granules of parenchymal cells and Kupffer cells were stained for cathepsin D. Weak staining was also noted in sinusoidal endothelial cells. In the parenchymal cells many of positive granules located around bile canaliculi. In the Kupffer cells and the endothelial cells, diffuse staining was noted in the cytoplasm in addition to granular staining. By electron microscopy, gold particles representing the antigenic sites for cathepsin D were seen in typical secondary lysosomes and some multivesicular bodies of the parenchymal cells and Kupffer cells. The lysosomes of the endothelial cells and fat-storing cells were weakly labeled. Quantitative analysis of the labeling density in the lysosomes of these three types of cells demonstrated that the lysosomes of parenchymal cells and Kupffer cells are main containers of cathepsin D in rat liver. The results suggest that cathepsin D functions in the intracellular digestive system of parenchymal cells and Kupffer cells but not so much in that of the endothelial cells.