Physiological and biochemical responses to dietary protein in the omnivore passerine Zonotrichia capensis (Emberizidae)

We studied the physiological, biochemical and morphological responses of the omnivore sparrow Zonotrichia capensis, a small opportunistic passerine from Central Chile acclimated to high- and low-protein diets. After 4 weeks of acclimation to 30% (high-protein group) or 7% (low-protein group) dietary casein, we collected urine and plasma for nitrogen waste production and osmometry analysis, and measured gross renal morphology. Plasma osmolality and hematocrit were not significantly affected by dietary treatment, but urine osmolality was higher in the high-protein group than in the low-protein group. Kidney and heart masses were higher in animals acclimated to the high-protein diet. Mean total nitrogen waste was significantly higher in the high-protein group, but the proportions of nitrogen excreted as uric acid, urea and ammonia were unaffected by diet. Our data suggest that the response of Z. capensis to an increase in dietary protein content is through greater amounts of total nitrogen excretion and hypertrophy of kidney structures, without any modification of the proportion of excretory compounds.     

Induced ovulation and egg deposition in the direct developing anuran <Emphasis Type="Italic">Eleutherodactylus coqui</Emphasis>

This study investigates ovulation and egg deposition behaviors in the anuran Eleutherodactylus coqui from Puerto Rico in response to stimulation with gonadotropin and gonadotropin releasing hormones. Five hormones were tested by injection over a range of doses, including mammalian LHRH, avian LHRH, fish LHRH, D-Ala6, des-Gly10 ethylamide LHRH and hCG. We report a low level of ovulation and egg deposition in response to all hormones, with the most complete and consistent results from the non-natural D-Ala6, des-Gly10 ethylamide LHRH derivative. To confirm the viability of eggs produced in this manner we performed in vitro fertilization experiments that resulted in the development of normal frogs. Reproductive behaviors in E. coqui are apparently not controlled by a mammalian form of LHRH as reported in other common laboratory anuran species. D-Ala6, des-Gly10 ethylamide LHRH induces ovulation and deposition of mature and fertilizable eggs in E. coqui.     

Neutralization of enteric coronaviruses with Escherichia coli cells expressing single-chain Fv-autotransporter fusions

We report here that fusions of single-chain antibodies (scFvs) to the autotransporter beta domain of the IgA protease of Neisseria gonorrhoeae are instrumental in locating virus-neutralizing activity on the cell surface of Escherichia coli. E. coli cells displaying scFvs against the transmissible gastroenteritis coronavirus on their surface blocked in vivo the access of the infectious agent to cultured epithelial cells. This result raises prospects for antiviral strategies aimed at hindering the entry into target cells by bacteria that naturally colonize the same intestinal niches.     

R-Ras glucosylation and transient RhoA activation determine the cytopathic effect produced by toxin B variants from toxin A-negative strains of Clostridium difficile

Clostridium difficile induces antibiotic-associated diarrhea through the production of toxin A and toxin B; the former toxin has been assumed to be responsible for the symptoms of the disease. Several toxin A-negative strains from C. difficile have recently been isolated from clinical cases and have been reported to produce toxin B variants eliciting an atypical cytopathic effect. Ultrastructural analysis indicated these toxins induce a rounding cytopathic effect and filopodia-like structures. Toxin B variants glucosylated R-Ras, and transfection with a constitutively active mutant of this GTPase protected cells against their cytopathic effect. Treatment of cells with toxin B variants induced detachment from the extracellular matrix and blockade of the epidermal growth factor-mediated phosphorylation of extracellular-regulated protein kinases, demonstrating a deleterious effect on the R-Ras-controlled avidity of integrins. Treatment with toxin B variants also induced a transient activation of RhoA probably because of inactivation of Rac1. Altogether, these data indicate that the cytopathic effect induced by toxin B variants is because of cell rounding and detachment mediated by R-Ras glucosylation, and the induction of filopodia-like structures is mediated by RhoA activation. Implications for the pathophysiology of C. difficile-induced diarrhea are discussed.     

Identification of an unknown promoter,OUTIIp, within the IS10R element

A novel promoter in IS10R (OUTIIp) has been found in one of its ends in an inverted position relative to promoter pOUT. OUTIIp shows characteristics similar to those of rpoS-dependent promoters such as a gearbox expression pattern. It is under catabolite repression and positively regulated by ppGpp or conditioned media. This opens new challenges in IS10R transposition.     

Identification of the Gasa3 and Gasa4 autoimmune gastritis susceptibility genes using congenic mice and partitioned, segregative and interaction analyses

BALB/c mice thymectomized on their third day of life develop a high incidence of experimental autoimmune gastritis (EAG) which closely resembles human chronic atrophic (type A, autoimmune) gastritis. Linkage analysis of (BALB/cCrSlcxC57BL/6)F2 mice previously demonstrated that the Gasa1 and Gasa2 genes on distal Chromosome (Chr) 4 have major effects on the development of EAG in this murine model, while other loci displayed a trend towards linkage. Here, we implemented partitioned chi(2)-analysis in order to develop a better understanding of the genotypes contributing to susceptibility and resistance at each linkage region. This approach revealed that linkage of Gasa1 and Gasa2 to EAG was due to codominant and recessive BALB/cCrSlc alleles, respectively. To identify additional EAG susceptibility genes, separate linkage studies were performed on Gasa1 heterozygotes and Gasa2 C57BL/6 homozygotes plus heterozygotes so as to minimize the effects of these disease genes. The enhanced sensitivity of these analyses confirmed the existence of a third EAG susceptibility gene (designated Gasa3) on Chr 6. Epistatic interactions between the Gasa2 EAG susceptibility gene and the H2 were also identified, and the presence of an H2-linked susceptibility gene (Gasa4) confirmed by analysis of H2 congenic mice.     

Role of 17beta-estradiol administration on insulin sensitivity in the rat: implications for the insulin receptor

The role of 17beta-estradiol in the early steps of insulin action is only partially known, although its effect on glucose homeostasis has been reported. In this paper, we attempt to prove the influence of 17beta-estradiol on the insulin receptor of ovariectomized rats treated with different hormonal doses. Our results show that high doses of estradiol impair insulin sensitivity while low doses improve it. We think that these results are the consequence of changes at a molecular level, because high doses of estradiol produced lower expression of the insulin receptor gene, lower content of this receptor in target tissues, and lower phosphorylation of insulin receptor in these tissues. However, low doses of estradiol seem to produce just the opposite. The possible existence of consensus response elements in the insulin receptor gene promoter to estradiol could be controlling the expression of this gene, this control being dose and timing dependent. Moreover, we cannot discard a possible effect of estradiol on the activity of protein tyrosine phosphatases, and therefore, on the activity of the insulin receptor. These new findings improve knowledge about the possible risk for insulin resistance in women taking oral contraceptives or receiving hormonal replacement therapy around the menopause, but could also open the door towards the possible utilization of 17beta-estradiol in some diabetes cases.