The yeast two-component SLN1 branch of the HOG pathway and the scaffolding activity of Pbs2 modulate the response to endoplasmic reticulum stress induced by tunicamycin

International Microbiology - In addition to the UPR pathway, yeast cells require components of the HOG pathway to respond to ER stress. In this work, we found that unphosphorylated Sln1 and Ssk1...     

Structural and Molecular Basis for Katanin-Mediated Severing of Glutamylated Microtubules

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High-Resolution Mapping of Two Types of Spontaneous Mitotic Gene Conversion Events in Saccharomyces cerevisiae

Gene conversions and crossovers are related products of the repair of double-stranded DNA breaks by homologous recombination. Most previous studies of mitotic gene conversion events have been restricted to measuring conversion tracts that are <5 kb. Using a genetic assay in which the lengths of very long gene conversion tracts can be measured, we detected two types of conversions: those with a median size of ∼6 kb and those with a median size of >50 kb. The unusually long tracts are initiated at a naturally occurring recombination hotspot formed by two inverted Ty elements. We suggest that these long gene conversion events may be generated by a mechanism (break-induced replication or repair of a double-stranded DNA gap) different from the short conversion tracts that likely reflect heteroduplex formation followed by DNA mismatch repair. Both the short and long mitotic conversion tracts are considerably longer than those observed in meiosis. Since mitotic crossovers in a diploid can result in a heterozygous recessive deleterious mutation becoming homozygous, it has been suggested that the repair of DNA breaks by mitotic recombination involves gene conversion events that are unassociated with crossing over. In contrast to this prediction, we found that ∼40% of the conversion tracts are associated with crossovers. Spontaneous mitotic crossover events in yeast are frequent enough to be an important factor in genome evolution.     

Description of Pintomyia (Pifanomyia) brazilorum sp. nov. a new fossil species from the Dominican Republic (Diptera: Psychodidae: Phlebotominae)

A sand fly fossil was found in amber; a vegetal resin, which allows all the external phlebotomine structures to be seen. The piece that contains the new species is 14 mm long x 8 mm wide x 3 mm high. All the structures from the head, thorax, and abdomen were examined under the microscope and measured with a calibrated micrometric eyepiece. The morphological aspects of the new species suggest its inclusion in the Pintomyia genus, Pifanomyia subgenus though it is not possible to include it in any of the series known for this subgenus. The presence of two atrophied spines on the gonostyles and gonocoxites without tufts of setae permit the exclusion of the new species from the other species of the subgenus Pifanomyia. The new species is named Pintomyia (Pifanomyia) brazilorum sp. nov.     

The effect of season on serum testosterone concentrations in dogs

Photoperiod and environmental temperature are two important factors that may influence the reproductive cycle of various species. The objective of this study was to investigate seasonal influences on serum testosterone concentrations in dogs in a tropical zone, where the variation in day length between winter and summer solstice was approximately 2.5 h. Blood samples were collected every 15 days from seven adult dogs over a 14-month interval and serum testosterone concentrations were determined by radioimmunoassay. The year was divided into four seasons and mean testosterone concentrations for each season were related to the mean environmental temperature and rainfall during that season. Mean testosterone concentrations were 1.81 ng/mL (winter 2002), 1.93 ng/mL (spring 2002), 1.31 ng/mL (summer 2003), 2.02 ng/mL (autumn 2003) and 1.93 ng/mL (winter 2003). The temperature ranged from 10.2 to 32.8 degrees C and the rainfall from 33 to 476 mm. Serum testosterone concentrations were lower in summer 2003 than in both spring 2002 (P = 0.05) and autumn 2003 (P = 0.016). In a tropical zone, a combination of high temperature and substantial rainfall may have reduced serum testosterone concentrations in dogs.     

Search for alpha-helical propensity in the receptor-bound conformation of glucagon-like peptide-1

To elucidate the receptor-bound conformation of glucagon-like peptide-1 (GLP-1), a series of conformationally constrained GLP-1 analogues were synthesized by introducing lactam bridges between Lys(i) and Glu(i)(+4) to form alpha-helices at various positions. The activity and affinity of these analogues to GLP-1 receptors suggested that the receptor-bound conformation comprises two alpha-helical segments between residues 11-21 and 23-34. It is notable that the N-terminal alpha-helix is extended to Thr(11), and that Gly(22) plays a pivotal role in arranging the two alpha-helices. Based on these findings, a highly potent bicyclic GLP-1 analogue was synthesized which is the most conformationally constrained GLP-1 analogue reported to date.     

Decreased connexin43 expression in the mouse heart potentiates pacing-induced remodeling of repolarizing currents

Gap junction redistribution and reduced expression, a phenomenon termed gap junction remodeling (GJR), is often seen in diseased hearts and may predispose toward arrhythmias. We have recently shown that short-term pacing in the mouse is associated with changes in connexin43 (Cx43) expression and localization but not with increased inducibility into sustained arrhythmias. We hypothesized that short-term pacing, if imposed on murine hearts with decreased Cx43 abundance, could serve as a model for evaluating the electrophysiological effects of GJR. We paced wild-type (normal Cx43 abundance) and heterozygous Cx43 knockout (Cx43+/-; 66% mean reduction in Cx43) mice for 6 h at 10-15% above their average sinus rate. We investigated the electrophysiological effects of pacing on the whole animal using programmed electrical stimulation and in isolated ventricular myocytes with patch-clamp studies. Cx43+/- myocytes had significantly shorter action potential durations (APD) and increased steady-state (Iss) and inward rectifier (I(K1)) potassium currents compared with those of wild-type littermate cells. In Cx43+/- hearts, pacing resulted in a significant prolongation of ventricular effective refractory period and APD and significant diminution of Iss compared with unpaced Cx43+/- hearts. However, these changes were not seen in paced wild-type mice. These data suggest that Cx43 abundance plays a critical role in regulating currents involved in myocardial repolarization and their response to pacing. Our study may aid in understanding how dyssynchronous activation of diseased, Cx43-deficient myocardial tissue can lead to electrophysiological changes, which may contribute to the worsened prognosis often associated with pacing in the failing heart.     

The retinoblastoma protein tumor suppressor is important for appropriate osteoblast differentiation and bone development

Mutation of the retinoblastoma (RB) tumor suppressor gene is strongly linked to osteosarcoma formation. This observation and the documented interaction between the retinoblastoma protein (pRb) and Runx2 suggests that pRb is important in bone development. To assess this hypothesis, we used a conditional knockout strategy to generate pRb-deficient embryos that survive to birth. Analysis of these embryos shows that Rb inactivation causes the abnormal development and impaired ossification of several bones, correlating with an impairment in osteoblast differentiation. We further show that Rb inactivation acts to promote osteoblast differentiation in vitro and, through conditional analysis, establish that this occurs in a cell-intrinsic manner. Although these in vivo and in vitro differentiation phenotypes seem paradoxical, we find that Rb-deficient osteoblasts have an impaired ability to exit the cell cycle both in vivo and in vitro that can explain the observed differentiation defects. Consistent with this observation, we show that the cell cycle and the bone defects in Rb-deficient embryos can be suppressed by deletion of E2f1, a known proliferation inducer that acts downstream of Rb. Thus, we conclude that pRb plays a key role in regulating osteoblast differentiation by mediating the inhibition of E2F and consequently promoting cell cycle exit.