Central Exendin‐4 Infusion Reduces Body Weight without Altering Plasma Leptin in (fa/fa) Zucker Rats

Objective: To investigate whether chronic administration of the long‐acting glucagon‐like peptide‐1 receptor agonist exendin‐4 can elicit sustained reductions in food intake and body weight and whether its actions require an intact leptin system. Research Methods and Procedures: Male lean and obese Zucker (fa/fa) rats were infused intracerebroventricularly with exendin‐4 using osmotic minipumps for 8 days. Results: Exendin‐4 reduced body weight in both lean and obese Zucker rats, maximum suppression being reached on Day 5 in obese (8%) and Day 7 in lean (16%) rats. However, epididymal white adipose tissue weight was not reduced, and only in lean rats was there a reduction in plasma leptin concentration. Food intake was maximally suppressed (by 81%) on Day 3 in obese rats but was reduced by only 18% on Day 8. Similarly, in lean rats food intake was maximally reduced (by 93%) on Day 4 of treatment and by 45% on Day 8. Brown adipose tissue temperature was reduced from Days 2 to 4. Plasma corticosterone was elevated by 76% in lean but by only 28% in obese rats. Discussion: Chronic exendin‐4 treatment reduced body weight in both obese and lean Zucker rats by reducing food intake: metabolic rate was apparently suppressed. These effects did not require an intact leptin system. Neither does the absence of an intact leptin system sensitize animals to exendin‐4. Partial tolerance to the anorectic effect of exendin‐4 in lean rats may have been due to elevated plasma corticosterone and depressed plasma leptin levels, but other counter‐regulatory mechanisms seem to play a role in obese Zucker rats.     

Mutants of pheV in Escherichia coli affecting control by attenuation of the pheS, T and pheA operons. Two distinct mechanisms for de-attenuation

Two mutants of pheV, a gene coding for tRNA(Phe) in Escherichia coli, were previously isolated because they affect attenuator control of the pheS, T operon when the mutant pheV genes are carried by the plasmid pBR322. We show that the two mutants (A44 and A46) affect attenuator control by different mechanisms. The effect of mutant A44 on pheS, T expression can be progressively decreased by overproduction of Phe-tRNA synthetase, consistent with the mutant tRNA acting as a competitive inhibitor of the enzyme. By contrast, the effect on attenuation of mutant A46 increases with overproduction of Phe-tRNA synthetase, indicating that the mutant must be charged to affect attenuation; we propose that this mutant affects translation directly and causes derepression by competing with wild-type tRNA in translation of the attenuator region leader peptide. Mutant A46 but not mutant A44 leads to further de-attenuation in a miaA background. The presence of two different mechanisms for de-attenuation is further indicated by the finding that a second attenuator controlled by Phe codon translation, from the pheA operon, is affected quite differently by the mutant tRNAs. Finally, experiments involving the introduction of the mutations A44 and A46 into an amber suppressor derived from tRNA(Phe) suggest that both species can function in protein synthesis but with reduced efficiency; mutant A46 is less efficient than mutant A44, consistent with a defect in elongation.     

Functional mutants of phenylalanine transfer RNA from Escherichia coli.

The gene pheV from Escherichia coli, coding for tRNAPhe and carried on a plasmid, has been mutagenised with hydroxylamine. Mutants in the structural gene have been identified using two criteria: (i) de-attenuation of beta-galactosidase expression, while under the control of the attenuator region of the pheS,T operon by means of an operon fusion; (ii) loss of ability to complement thermosensitivity of a mutant Phe-tRNA synthetase. Mutants showing de-attenuation were sequenced and two nucleotide changes identified: G44----A44 (found five times) and m7G46----A46 (found once). Sequencing of mutants that lost complementation identified two further tRNA mutants, C2---U2 and G15----A15; the mutant m7G46----A46 was also re-isolated by this criterion. Three of the mutants involve bases implicated in tertiary rather than secondary structure hydrogen bonding. One hypothesis for the mechanism of de-attenuation is that mutant tRNAPhe molecules compete with the wild-type tRNAPhe on the ribosome but are inefficient at some step in the elongation process.     

A developmental study of the abnormal expression of alpha-cardiac and alpha-skeletal actins in the striated muscle of a mutant mouse

BALB/c mice possess a 5' duplication of the alpha-cardiac actin gene which is associated with abnormal levels of alpha-cardiac and alpha-skeletal actin mRNAs in adult cardiac tissue. This mutation therefore provides a potential tool for the study of the inter-relationship between the striated muscle actins. We have examined the expression of this actin gene pair throughout the development of skeletal and cardiac muscle in BALB/c mice. During embryonic and fetal development, the expression of these two genes is indistinguishable from that in normal mice, as determined by in situ hybridization. A quantitative postnatal study demonstrates that in the hearts of normal mice the level of alpha-cardiac actin mRNA declines, whereas that of alpha-skeletal actin increases. In mutant mice, these trends are exaggerated so that whereas normal mice have 95.8% alpha-cardiac mRNA and 4.2% alpha-skeletal mRNA in the adult heart, BALB/c mice have 52.4 and 47.6% of these mRNAs, respectively. This difference is also reflected at the protein level. In developing skeletal muscle, the expression of these genes follows kinetics similar to that observed in the heart with a decrease in the relative level of alpha-cardiac mRNA as the muscle matures. Cardiac actin mRNA levels are again lower in the mutant mouse, but here the effect is less striking because skeletal actin is the predominant isoform. These results are discussed in the context of the interaction between this actin gene pair in developing and adult striated muscle.     

The human homeobox gene HOX7 maps to chromosome 4p16.1 and may be implicated in Wolf-Hirschhorn syndrome

Summary The gene encoding human 17beta-hydroxy-steroid dehydrogenase (17-HSD; EC 1.1.1.62) is assigned to chromosome 17 by Southern blotting analyses of panels of human x rodent somatic cell hybrids and independently to 17q12–q21 using chromosomal in situ hybridization. A search for physical linkage between 17-HSD and the proto-oncogenes, THRA1 and ERBB2 (both reported to be located in this region of chromosome 17) was performed by pulsed-field gel electrophoresis (PFGE) using several rare-cutting restriction endonucleases. Because all three genes hybridized to DNA fragments of different lengths it seems unlikely that the gene for 17-HSD is located very close to THRA1 and ERBB2. Further evidence for this assumption was obtained from the absence of any coamplification of the 17-HSD gene in 9 breast tumors with amplification of the ERBB2 gene. Analyses of Southern blots of ScaI-digested DNAs from unrelated individuals from Northern Finland revealed a relatively infrequent diallelic restriction fragment length polymorphism, the allele frequencies of which were 0.04 (A1) and 0.96 (A2).     

Evaluating the effectiveness of a process medical audit in a teaching general hospital.

Medical auditing has moved beyond the traditional chart review to the process audit, which identifies deficiencies in care and suggests remedies. In 1981 the audit committee of the Department of Psychiatry at Toronto General Hospital audited the use of hypnotic drugs in the inpatient unit. The audit produced two recommendations: that nursing staff record sleep graphs for inpatients more often, and that an educational program be instituted to change the physicians'' patterns of prescribing hypnotics. In 1983 the audit was repeated to test the effectiveness of the 1981 auditing process. The 1981 recommendation produced the desired improvement in recording of sleep graphs. However, the medical staff failed to change their patterns of prescribing hypnotics: oxazepam remained the preferred hypnotic. For the process audit to be effective in improving patient care those using it must ensure that the methods reflect the nature and structure of the professional group they are trying to influence.     

Mutant ribosomes can generate dominant kirromycin resistance.

Mutations in the two genes for EF-Tu in Salmonella typhimurium and Escherichia coli, tufA and tufB, can confer resistance to the antibiotic kirromycin. Kirromycin resistance is a recessive phenotype expressed when both tuf genes are mutant. We describe a new kirromycin-resistant phenotype dominant to the effect of wild-type EF-Tu. Strains carrying a single kirromycin-resistant tuf mutation and an error-restrictive, streptomycin-resistant rpsL mutation are resistant to high levels of kirromycin, even when the other tuf gene is wild type. This phenotype is dependent on error-restrictive mutations and is not expressed with nonrestrictive streptomycin-resistant mutations. Kirromycin resistance is also expressed at a low level in the absence of any mutant EF-Tu. These novel phenotypes exist as a result of differences in the interactions of mutant and wild-type EF-Tu with the mutant ribosomes. The restrictive ribosomes have a relatively poor interaction with wild-type EF-Tu and are thus more easily saturated with mutant kirromycin-resistant EF-Tu. In addition, the mutant ribosomes are inherently kirromycin resistant and support a significantly faster EF-Tu cycle time in the presence of the antibiotic than do wild-type ribosomes. A second phenotype associated with combinations of rpsL and error-prone tuf mutations is a reduction in the level of resistance to streptomycin.