Alkaline phosphatase in cholestatic and cirrhotic rats. A biochemical and histochemical study

Alkaline phosphatase (ALP) was studied by enzyme histochemical methods and by biochemical quantitations in rat livers with chronic bile duct obstruction and experimental cirrhosis. The most evident ALP increase was histochemically found in portal tracts of rats with bile duct obstruction and localized to the walls of proliferating blood vessels. Furthermore, a slight canalicular membrane enzyme increase was histochemically found in both groups, most evident in cirrhosis, whereas the biochemical assay of ALP in serum and liver from both pathological groups showed 3 times higher values compared to controls. The portal tracts did not seem to contribute to the serum increase, since the rise of serum ALP was similar in chronic bile duct obstruction and in experimental cirrhosis without changes of the portal tracts. It is concluded that the increase ALP activity in serum from rats with bile duct obstruction and cirrhosis mainly has a hepatocytic origin.     

Antagonistic effects of mutant elongation factor Tu and ribosomal protein S12 on control of translational accuracy, suppression and cellular growth

Kirromycin-resistant mutant forms of elongation factor Tu, which are coded by tufA (Ar) or tufB (Bo) and are associated with an increased rate of translational error formation, have been analysed. In vivo, Ar was found to increase misreading as well as suppression of non-sense codons irrespective of Bo in a strain with wild type ribosomes. It is therefore not necessary to evoke both tufA (Ar) and tufB (Bo) mutations together in order to increase translational error as suggested earlier [1]. When combined with a hyperaccurate ribosomal rpsL (S12) mutation, Ar counteracts the restrictive effects on translational error formation caused by the altered protein S12, thus restoring the levels of missense error in vitro and non-sense error and suppression in vivo to near wild type values. As judged from in vitro experiments this results principally from a lowered selectivity of the Ar ternary complex at the initial discrimination step on the ribosome during translation. In vivo, this compensatory effect on the rpsL mutation on non-sense error formation and suppression is seen irrespective of the nature of tRNA or codon context. Furthermore, the tufA mutation enhances the cellular growth rate of the rpsL mutant, whereas it decreases growth of strains with normal ribosomes. Inactivation of one of the two genes coding for EF-Tu (tufB), while leaving the other gene (tufA) intact, can by itself, increase non-sense error formation and suppression.     

Immunohistochemical localization of insulin-like growth factor I in the adult rat

Rabbit antisera against native human insulin-like growth factor I (IGF-I; somatomedin C) or a synthetic tetradecapeptide, representing the carboxyterminal amino acids 57-70 of human IGF-I, were used to map immunohistochemically the distribution of IGF-I immunoreactive material in adult rats. Both antisera were specific for IGF-I, as characterized by immunoabsorption, immunoblotting and radioimmunoassay. There was no cross-reactivity to IGF-II, relaxin or pro-insulin; substances having a high degree of structural homology with IGF-I. High IGF-I immunoreactivity was observed in spermatocytes of the testis; in oocytes, granulosa and theca interna cells of the ovary during early stages of follicle development; in some lymphocytes and in reticular cells of lymphoid and hematopoietic organs; in salivary gland duct cells; in the adrenal medulla, the parathyroid gland and the Langerhans' islets. Chondrocytes in the epiphyseal and rib growth plates and at articular surfaces showed strong IGF-I immunoreactivity. Brown but not white fat cells were stained. Nerve cells in the peripheral and autonomic nervous system showed faint to intense IGF-I immunoreactivity. In contrast, neurons and neuroglial cells in the central nervous system were generally negative; motor neurons being an exception. Erythropoietic, thrombocytopoietic and myeloic cells in the bone marrow showed IGF-I immunoreactivity, but only at defined developmental stages. Hepatocytes showed faint IGF-I immunoreactivity, but became more intensely stained after pretreatment with colchicine. The present results suggest that IGF-I is synthetized by cells in several tissues and organs in the adult rat. There was an apparent association between the localization of IGF-I and cell differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lysosomal enzymes in pregnant and steroid treated rats

The contents of three lysosomal enzymes (beta-hexosaminidase, beta-glucuronidase and alpha-fucosidase) were studied in plasma and different tissues of pregnant and steroid treated rats. All these enzymes were found to be increased in plasma from pregnant rats in analogy with the findings in pregnant women. In liver tissue only beta-hexosaminidase and alpha-fucosidase were significantly increased. In rats with diethylstilbestrol (DES) and a combination of DES and progesterone, there was an increase of alpha-fucosidase in plasma and liver. No significant changes were observed for the other two enzymes. Thus, steroid treatment did not fully reproduce the enzyme changes seen in pregnancy, which may indicate that these are not solely due to a hormone effect.     

Functional interactions in vivo between suppressor tRNA and mutationally altered ribosomal protein S4

Summary Ribosomal mutants (rpsD) which are associated with a generally increased translational ambiguity were investigated for their effects in vivo on individual tRNA species using suppressor tRNAs as models. It was found that nonsense suppression is either increased, unaffected or decreased depending on the codon context and the rpsD allele involved as well as the nature of the suppressor tRNA. Missense suppression of AGA and AGG by glyT(SuAGA/G) tRNA as well as UGG by glyT(SuUGG-8) tRNA is unaffected whereas suppression of UGG by glyT(SuUGA/G) or glyV(SuUGA/G) tRNA is decreased in the presence of an rpsD mutation. The effects on suppressor tRNA are thus not correlated with the ribosomal ambiguity (Ram) phenotype of the rpsD mutants used in this study. It is suggested that the mutationally altered ribosomes are changed in functional interactions with the suppressor tRNA itself rather than with the competing translational release factor(s) or cognate aminoacyl tRNA. The structure of suppressor tRNA, particularly the anticodon loop, and the suppressed codon as well as the codon context determine the allele specific functional interactions with these ribosomal mutations.     

A temperature-sensitive mutant of Escherichia coli that shows enhanced misreading of UAG/A and increased efficiency for some tRNA nonsense suppressors

Summary A spontaneous mutant was isolated that harbors a weak suppressing activity towards a UAG mutation, together with an inability to grow at 43° C in rich medium. The mutation is shown to be associated with an increased misreading of UAG at certain codon contexts and UAA. UGA, missense or frameshift mutations do not appear to be misread to a similar extent. The mutation gives an increased efficiency to several amber tRNA suppressors with-out increasing their ambiguity towards UAA. The ochre suppressors SuB and Su5 are stimulated in their reading of both UAG and UAA with preference for UAG. An opal suppressor is not affected. The effect of the mutation on the efficiency of amber and ochre suppressors is dependent on the codon context of the nonsense codon.The mutated gene (uar) has been mapped and found to be recessive both with respect to suppressor-enhancing ability as well as for temperature sensitivity. The phenotype is partly suppressed by the ochre suppressor SuC. It is suggested that uar codes for a protein, which is involved in translational termination at UAG and UAA stop codons.     

The Electrical Conductivity of Bovine Milk in Mastitis Diagnosis

The electrical conductivity (EC) of milk is mainly a function of the electrolyte concentration in the milk and therefore raised in mastitis. The present investigation was aimed at elaborating, if possible, a diagnostic model for screening purposes based on EC determinations and consistent with the diagnostic procedures and interpretations commonly used in laboratory milk diagnosis in the Nordic countries (Klastrup 1975). According to this diagnosis (here called reference diagnosis) cell numbers above 300,000/ml (cell count or the corresponding CMT-score) in foremilk quarter samples during the main part of the lactation period and significantly above the lowest value on within-udder comparison during late lactation are considered indicative of mastitis and bacteriological examinations are made when called for.     

Mechanisms of Injury-Induced Calcium Entry into Peripheral Nerve Myelinated Axons: Role of Reverse Sodium-Calcium Exchange

Abstract: To investigate the route of axonal Ca²⁺ entry during anoxia, electron probe x-ray microanalysis was used to measure elemental composition of anoxic tibial nerve myelinated axons after in vitro experimental procedures that modify transaxolemmal Na⁺ and Ca²⁺ movements. Perfusion of nerve segments with zero-Na⁺/Li⁺-substituted medium and Na⁺ channel blockade by tetrodotoxin (1 µM) prevented anoxia-induced increases in Na and Ca concentrations of axoplasm and mitochondria. Incubation with a zero-Ca²⁺/EGTA perfusate impeded axonal and mitochondrial Ca accumulation during anoxia but did not affect characteristic Na and K responses. Inhibition of Na⁺-Ca²⁺ exchange with bepridil (50 µM) reduced significantly the Ca content of anoxic axons although mitochondrial Ca remained at anoxic levels. Nifedipine (10 µM), an L-type Ca²⁺ channel blocker, did not alter anoxia-induced changes in axonal Na, Ca, and K. Exposure of normoxic control nerves to tetrodotoxin, bepridil, or nifedipine did not affect axonal elemental composition, whereas both zero-Ca²⁺ and zero-Na⁺ solutions altered normal elemental content characteristically and significantly. The findings of this study suggest that during anoxia, Na⁺ enters axons via voltage-gated Na⁺ channels and that subsequent increases in axoplasmic Na⁺ are coupled functionally to extraaxonal Ca²⁺ import. Intracellular Na⁺-dependent, extraaxonal Ca²⁺ entry is consistent with reverse operation of the axolemmal Na⁺-Ca²⁺ exchanger, and we suggest that this mode of Ca²⁺ influx plays a general role in peripheral nerve axon injury.     

Phosphorylation of Drosophila Jun by the MAP kinase rolled regulates photoreceptor differentiation.

Drosophila Jun (D-Jun) is a nuclear component of the receptor tyrosine kinase/Ras signal transduction pathway which triggers photoreceptor differentiation during eye development. Here we show that D-Jun is a substrate for the ERK-related Drosophila MAP kinase Rolled, which has previously been shown to be a part of this pathway. A D-Jun mutant that carries alanines in place of the Rolled phosphorylation sites acts as a dominant suppressor of photoreceptor cell fate if expressed in the eye imaginal disc. In contrast, a mutant in which the phosphorylation sites are replaced by phosphate-mimetic Asp residues, as well as a VP16-D-Jun fusion protein, can promote photoreceptor differentiation. These data implicate Jun phosphorylation in the choice between neuronal and non-neuronal fate during Drosophila eye development.     

Interactive effects of rising temperatures and urbanisation on birds across different climate zones: A mechanistic perspective

Climate change and urbanisation are among the most pervasive and rapidly growing threats to biodiversity worldwide. However, their impacts are usually considered in isolation, and interactions are rarely examined. Predicting species' responses to the combined effects of climate change and urbanisation, therefore, represents a pressing challenge in global change biology. Birds are important model taxa for exploring the impacts of both climate change and urbanisation, and their behaviour and physiology have been well studied in urban and non-urban systems. This understanding should allow interactive effects of rising temperatures and urbanisation to be inferred, yet considerations of these interactions are almost entirely lacking from empirical research. Here, we synthesise our current understanding of the potential mechanisms that could affect how species respond to the combined effects of rising temperatures and urbanisation, with a focus on avian taxa. We discuss potential interactive effects to motivate future in-depth research on this critically important, yet overlooked, aspect of global change biology. Increased temperatures are a pronounced consequence of both urbanisation (through the urban heat island effect) and climate change. The biological impact of this warming in urban and non-urban systems will likely differ in magnitude and direction when interacting with other factors that typically vary between these habitats, such as resource availability (e.g. water, food and microsites) and pollution levels. Furthermore, the nature of such interactions may differ for cities situated in different climate types, for example, tropical, arid, temperate, continental and polar. Within this article, we highlight the potential for interactive effects of climate and urban drivers on the mechanistic responses of birds, identify knowledge gaps and propose promising future research avenues. A deeper understanding of the behavioural and physiological mechanisms mediating species' responses to urbanisation and rising temperatures will provide novel insights into ecology and evolution under global change and may help better predict future population responses.