Distribution of microtubules in prolactin cells of lactating rats

The intracellular distribution of microtubules was studied using serial sections of prolactin cells in anterior pituitary glands from lactating rats. Numerous microtubules were present in these cells following fixation with glutaraldehyde and osmium tetroxide. The greatest number of microtubules were present in the Golgi complex, situated around the perimeter and in association with the cisternae, vesicles and developing secretory granules. Microtubules were found in channels between groups of parallel cisternae of rough surfaced endoplasmic reticulum and in close proximity to small vesicles. They were also located adjacent to mitochondria, the plasmalemma, the nuclear envelope, and among mature secretory granules. Due to their orientation within the cell, it is suggested that the microtubules may act to direct the movement of organelles from one region of the cell to another and to give internal support to the cell.     

Spatial patterns of trees in natural forests of East-Central Europe

The analysis of spatial patterns is one of the ways to estimate the role of competition among trees in forest dynamics. Three hypotheses concerning distribution patterns in old-growth stands were tested: (1) fine-scale spatial patterns of trees are regular; (2) patterns do not differ significantly from a random distribution, and (3) spatial patterns at larger scales are clumped because of site heterogeneity. Old-growth forest stands in Poland and the Czech Republic were analysed with a modified Ripley K function, using distribution maps of tree stems. Fine-scale spatial patterns (with distances among trees not exceeding 15 m) were usually intermediate between random and regular. Trends towards a regular distribution occurred more often among dead than among live individuals. No significant relationships between tree species were found at smaller scales; however, at larger scales (distances from 15–25 m) negative associations between some species were found. This reflects site heterogeneity rather than any direct influence of one tree species upon another.     

Macrophyte and macroinvertebrate patterns in unimpacted mountain rivers of two European ecoregions

Hydrobiologia - The aim of the study was to compare the patterns of development of macrophytes and macroinvertebrates in different types of reference mountain rivers. The study is based on...     

Theoretical Investigation of the Molecular Structure of the πκ DNA Base Pair

Abstract

The structure of the nonclassical πκ base pair (7–methyl-oxoformycin … 2,4-diaminopyrimidine) was studied at the ab initio Hartree-Fock (HF) and MP2 levels using the 6–31G* and 6–31G** basis sets. The πκ base pair is bound by three parallel hydrogen bonds with the donor-acceptor-donor recognition pattern. Recently, these bases were proposed as an extension of the genetic alphabet from four to six letters (Piccirilli et al. Nature 343, 33(1990)). By the HF/6- 31G* method with full geometry optimization we calculated the 12 degree propeller twist for the minimum energy structure of this complex. The linearity of hydrogen bonds is preserved in the twisted structure by virtue of the pyramidal arrangement of the κ-base amino groups. The rings of both the π and κ molecules remain nearly planar. This nonplanar structure of the πκ base pair is only 0.1 kcal/mol more stable than the planar (Cs) conformation. The HF/6- 31G* level gas-phase interaction energy of πκ (—13.5 kcal/mol) calculated by us turned out to be nearly the same as the interaction energy obtained previously for the adenine-thymine base pair (—13.4 kcal/mol) at the same computational level. The inclusion of p-polarization functions on hydrogens, electron correlation effects (MP2/6–31G** level), and the correction for the basis set superposition error (BSSE) increase this energy to -14.0 kcal/mol.     

Repetitive DNA in and around translocation breakpoints of the Philadelphia chromosome

This paper describes systematic sequence studies of repetitive DNA in and around translocation breakpoints on chromosomes 9 and 22, which are involved in the formation of the Philadelphia chromosome in acute leukemias. In addition to Alu repeats described in previous studies, the breakpoint regions appear to contain many other repetitive elements, including a member of a new repetitive family (MER34) reported in this paper. Identification of these repeats broadens current studies on the possible involvement of repetitive DNA in this intensely studied chromosomal translocation.     

Localization of immunoglobulins G, A and M in glial cells of reactive and neoplastic origin

The localization of immunoglobulins G, A and M in glial cells of neoplastic and reactive origin have been investigated by the use of the PAP (peroxidase-antiperoxidase) method on paraffin embedded tissue previously fixed in calcium formol. It has been found, that some glial cells of astrocyte type showed a very intense staining when oligoclonal antibodies to human immunoglobulins G, A and M specific for gamma, alpha, and mu chains were used. The localization of immunoglobulins was disclosed in astrocytes of various morphology; astrocytes with well developed processes, gemistocyte type cells without or only with short and thick cell processes and in small cells with scanty cytoplasm. The number of cells with immunoglobulins localized is very small. No positive results have been noted if the normal brain tissue is concerned. The specificity of the method is discussed.     

The Genetic Basis of Escherichia coli Pathoadaptation to Macrophages

Antagonistic interactions are likely important driving forces of the evolutionary process underlying bacterial genome complexity and diversity. We hypothesized that the ability of evolved bacteria to escape specific components of host innate immunity, such as phagocytosis and killing by macrophages (MΦ), is a critical trait relevant in the acquisition of bacterial virulence. Here, we used a combination of experimental evolution, phenotypic characterization, genome sequencing and mathematical modeling to address how fast, and through how many adaptive steps, a commensal Escherichia coli (E. coli) acquire this virulence trait. We show that when maintained in vitro under the selective pressure of host MΦ commensal E. coli can evolve, in less than 500 generations, virulent clones that escape phagocytosis and MΦ killing in vitro, while increasing their pathogenicity in vivo, as assessed in mice. This pathoadaptive process is driven by a mechanism involving the insertion of a single transposable element into the promoter region of the E. coli yrfF gene. Moreover, transposition of the IS186 element into the promoter of Lon gene, encoding an ATP-dependent serine protease, is likely to accelerate this pathoadaptive process. Competition between clones carrying distinct beneficial mutations dominates the dynamics of the pathoadaptive process, as suggested from a mathematical model, which reproduces the observed experimental dynamics of E. coli evolution towards virulence. In conclusion, we reveal a molecular mechanism explaining how a specific component of host innate immunity can modulate microbial evolution towards pathogenicity.     

Telocytes: new insight into the pathogenesis of gallstone disease

The major mechanisms of gallstone formation include biliary cholesterol hypersecretion, supersaturation and crystallization, mucus hypersecretion, gel formation and bile stasis. Gallbladder hypomotility seems to be a key event that triggers the precipitation of cholesterol microcrystals from supersaturated lithogenic bile. Telocytes, a new type of interstitial cells, have been recently identified in many organs, including gallbladder. Considering telocyte functions, it is presumed that these cells might be involved in the signalling processes. The purpose of this study was to correlate the quantity of telocytes in the gallbladder with the lithogenicity of bile. Gallbladder specimens were collected from 24 patients who underwent elective laparoscopic cholecystectomy for symptomatic gallstone disease. The control group consisted of 25 consecutive patients who received elective treatment for pancreatic head tumours. Telocytes were visualized in paraffin sections of gallbladders with double immunofluorescence using primary antibodies against c‐Kit (anti‐CD117) and anti‐mast cell tryptase. Cholesterol, phospholipid and bile acid levels were measured in gallbladder bile. The number of telocytes in the gallbladder wall was significantly lower in the study group than that in the control group (3.03 ± 1.43 versus 6.34 ± 1.66 cell/field of view in the muscularis propria, P < 0.001) and correlated with a significant increase in the cholesterol saturation index. The glycocholic and taurocholic acid levels were significantly elevated in the control subjects compared with the study group. The results suggest that bile composition may play an important role in the reduction in telocytes density in the gallbladder.