Recombination and Chromosome Segregation during the Single Division Meiosis in SPO12–1 and SPO13–1 Diploids

This paper reports a study of chromosome segregation and recombination during sporulation of spo12–1 and spo13–1 diploid strains of S. cerevisiae. These strains undergo a single division to form asci containing two diploid or near-diploid spores. The segregation of centromere-linked markers in the two-spored (dyad) products indicates that the division is generally equational. However, in a small percentage of the spo12–1 and spo13–1 cells, it appears that a meiosis I-like division occurs. Aberrant segregation of the MAT locus on chromosome III, yielding a monosomic and a trisomic spore pair, occurs in 12% of all dyads. The segregation patterns of markers at various distances from their centromeres and several pairs of markers on the same chromosome indicate that recombination takes place in both strains at nearly standard meiotic levels.     

Esterification of arylhydroxylamines: Evidence for a specific gene product in mutagenesis

Characterization of a $\text{Salmonella}\text{typhmurium}$ mutant strain (TA98/1,8-DNP₆) resistant to the mutagenicity of nitrated polycyclic aromatic hydrocarbons (nitroarenes) revealed that it was also non-responsive to the mutagenic action of nitroso- and N-hydroxylaminoarenes. The mutant strain was fully sensitive to the mutagenic action of the corresponding hydroxamic acid ester. These results suggest that TA98/1,8-DNP₆ is deficient in a specific esterifying enzyme and that esterification of the penultimate mutagenic metabolites of nitro- and aminoarenes ($\text{e.g.}$, arylhydroxylamines) to form potent electrophiles is controlled by a specific gene.     

Probing protein structure by solvent perturbation of nuclear magnetic resonance spectra. Nuclear magnetic resonance spectral editing and topological mapping in proteins by paramagnetic relaxation filtering.

Soluble spin labels, which "bleach" the surface proton resonances of a protein to n.m.r. measurements, can provide useful information about protein conformation and dynamics. The use of the soluble nitroxide, TEMPOL, has been explored to show the correlation of the paramagnetic perturbations of protein two-dimensional n.m.r. data with proton exposure to the free radical in hen egg-white lysozyme. The results demonstrate that the nitroxide approaches the protein randomly, and that the extent of the observed paramagnetic effects reflects the native folding pattern of the protein. A correlation of spectral simplification with the known tertiary structure establishes the feasibility of new strategies for topological mapping of surface and buried protons of the protein. Application to the elucidation of protein structure and to the study of dynamical processes is discussed.     

Right-side dominance for song control in the zebra finch.

Adult male zebra finches underwent unilateral denervation of the syrinx or unilateral lesion of the forebrain nucleus HVC known to be important for song control. Disruptive effects on song were greater after right-side than after left-side operations. After denervation of the right half of the syrinx, the fundamental frequencies of all syllables within a song converged on a value near 500 Hz, and nearly all syllables were altered in type. In contrast, the syllables produced after denervation of the left side of the syrinx largely maintained their preoperative frequencies, and fewer syllables changed in type. Unlike nerve sections, HVC lesions did not result in strikingly lateralized effects on syllable phonology; however, HVC lesions did affect the temporal patterning of a bird's song, whereas nerve sections did not, and changes in temporal patterning were more marked after right than after left HVC lesions. Right-side dominance for zebra finch song control is the reverse of that described in other songbird species with lateral asymmetry for vocal communication. We suggest that the need for a dominant side is more important than the side of dominance.     

Differing Neurochemical and Morphological Sequelae of Global Ischemia: Comparison of Single- and Multiple-Insult Paradigms

The purpose of this investigation was to investigate pathomechanisms responsible for the deleterious effects of repeated episodes of brief forebrain ischemia. Halothane-anesthetized male Wistar rats were subjected to either (a) a single 15-min period or (b) three 5-min periods (separated by 1 h) of global forebrain ischemia by bilateral carotid artery occlusions plus hypotension (50 mm Hg), followed by various periods of recirculation. Brain temperature was normothermic throughout. In one series of rats, extracellular levels of glutamate, glycine, and gamma-aminobutyric acid (GABA) were measured in the dorsolateral striatum (n = 6-8 per group) and lateral thalamus (n = 4-6 per group) by microdialysis and HPLC before and during ischemia and during 3-5 h of recirculation. In a parallel series of rats (n = 6 per group), ischemic cell change was quantified at 2 (dark neurons), 24, or 72 h following either single or multiple ischemic insults. A single 15-min ischemic period led to massive glutamate release (13-fold increase; p = 0.001), which returned to normal by 20-30 min of recirculation and remained normal thereafter. By contrast, in rats with three 5-min periods of ischemia, the glutamate level rise with each repeated insult (four- to 4.5-fold; p < or = 0.02) was smaller than that observed during the single 15-min insult, but a late sustained rise (five- to six-fold; p < 0.05) occurred at 2-3 h of recirculation. Brief ischemia-induced elevations of glycine and GABA levels were detected in both the single- and multiple-insult groups, with normalization during recirculation. In contrast, the excitotoxic index, a composite measure of neurotransmitter release ([glutamate] x [glycine]/[GABA]), differed markedly following single versus multiple insults (p = 0.002 by repeated-measures analysis of variance) and increased by seven- to 12-fold (p < 0.05) at 1-3 h following the third insult. The total amount of glutamate released was 3.3-fold higher in the multiple-insult than in the single-insult group (p < 0.02). At 2 h of recirculation, histopathological analysis of dorsolateral striatum showed a significantly greater frequency of dark neurons in the multiple- than in the single-insult group (p < 0.05 by analysis of variance). In the thalamus, a higher frequency of ischemic neurons was seen in the multiple-than in the single-insult group at all intervals studied. Thus, in rats with multiple ischemic insults, accelerated ischemic damage was found in the striatum, and severe ischemic injury was documented in the thalamus.(ABSTRACT TRUNCATED AT 400 WORDS)     

A repetitive DNA element,associated with telomeric sequences in Drosophila melanogaster,contains open reading frames

He-T sequences are a complex repetitive family of DNA sequences in Drosophila that are associated with telomeric regions, pericentromeric heterochromatin, and the Y chromosome. A component of the He-T family containing open reading frames (ORFs) is described. These ORF-containing elements within the He-T family are designated T-elements, since hybridization in situ with the polytene salivary gland chromosomes results in detectable signal exclusively at the chromosome tips. One T-element that has been sequenced includes ORFs of 1,428 and 1,614 bp. The ORFs are overlapping but one nucleotide out of frame with respect to each other. The longer ORF contains cysteine-histidine motifs strongly resembling nucleic acid binding domains of gag-like proteins, and the overall organization of the T-element ORFs is reminiscent of LINE elements. The T-elements are transcribed and appear to be conserved in Drosophila species related to D. melanogaster. The results suggest that T-elements may play a role in the structure and/or function of telomeres.by W. Hennig     

Morphological changes in human chorionic villi cultivated in conditioned atmospheres of gases.

With the aim to verify the changes that a reduction of the oxygen rate may elicit in the morphological pattern of the human chorionic villi, a new experimental procedure has been suggested. Chorionic villi from human early placentas were incubated in Dulbecco's modified medium of Eagle in the presence of oxygen, air or CO2 at a gas pressure equal to 0.7 atm. The specimens were fixed, dehydrated and embedded in resin, and semithin sections were obtained. Using an image analyser, the thickness of the trophoblastic layer and the mean radius of the villi were evaluated and the results submitted to a statistical analysis. The results show a decrease in the ratio thickness of the trophoblast/mean radius of the villus, directly proportional to the reduction of the oxygen percentage in the employed gases. The interesting conclusions demonstrate that the changes which affect the chorionic villi occur very early and are easily evaluable with quantitative methods; a clinical interest in the use of the proposed quantitative procedure can be emphasized.     

Early macrophage infiltration in mice treated with low-dose streptozocin decreases islet superoxide dismutase levels: prevention by silica pretreatment.

It has been hypothesized that streptozocin (STZ) given in low doses for 5 consecutive days produces diabetes by induction of peroxidation phenomena similar to those induced by free radicals. Moreover, it has been demonstrated that macrophages are among the first to invade the pancreatic parenchyma and destroy islet B cells supposedly by the release of interleukin-1 that induces free radical formation. Superoxide dismutase (SOD) is a free radical scavenger present in cells, and islet B cells are known to have extremely low levels of this enzyme. Therefore, our aim was to observe SOD activity concomitantly with the appearance of intra-islet macrophages, in early diabetes induced by low-dose streptozocin (LDS). Silica-pretreated mice showed SOD values which were comparable to those found in control animals. In LDS-only-treated mice we found that SOD levels were decreased even after only 4 days from the last STZ injection and that it is at this time that the first 'recruited' macrophages appear in the islets. Moreover, the SOD levels found at this early stage (animals were still normoglycaemic and therefore not as yet diabetic) were similar to levels found by us in a previous work, in prediabetic Bio Breeding rats, thereby ascribing a crucial factor to the lowering of SOD levels even in LDS-induced diabetes.     

The in vitro adherence of murine eosinophils, neutrophils and non-induced and induced macrophages to infective larvae of Toxocara canis (Nematoda, Ascarididae)

Infective larvae of the parasite nematode Toxocara canis were incubated in vitro with murine eosinophils, neutrophils and non-induced and induced macrophages. The interactions between the different types of cells and the worms were observed in the presence or absence of immune mouse serum and/or complement. Cells showed considerable differences in the manner, duration and outcome of this interaction. Despite the adhesion of cells to the larvae of T. canis, there was no evidence of damage to the worms. Scanning and transmission electron microscopic observations suggest that the cells adhere to the cuticular surface via an electron-dense material. This material might play a protective role against the helmintotoxic capacity of the inflammatory cells.