Phylogeny of Salmonine Fishes Based on Growth Hormone Introns: Atlantic (Salmo) and Pacific (Oncorhynchus) Salmon Are Not Sister Taxa

Though salmonid fishes are a well-studied group, phylogenetic questions remain, especially with respect to genus-level relationships. These questions were addressed with duplicate growth hormone (GH) introns. Intron sequences from each duplicate gene yielded phylogenetic trees that were not significantly different from each other in topology. Statistical tests supported validity of the controversial monotypic genusParahucho,monophyly ofOncorhynchus,and inclusion ofAcantholingua ohridanawithinSalmo.Suprisingly, GH1 intron C (GH1C) did not support the widely accepted hypothesis thatOncorhynchus(Pacific salmon and trout) andSalmo(Atlantic salmon and trout) are sibling genera; GH2C was ambiguous at this node. Previously published data were also examined for support ofSalmoandOncorhynchusas sister taxa and only morphology showed significant support. If not sister taxa, the independent evolution of anadromy—the migration to sea and return to freshwater for spawning—is most parsimonious. While there was incongruence with and among published data sets, the GH1C intron phylogeny was the best hypothesis, based on currently available molecular data.     

Structure and function of the bacterial mechanosensitive channel of large conductance.

Mechanosensation in bacteria involves transducing membrane stress into an electrochemical response. In Escherichia coli and other bacteria, this function is carried out by a number of proteins including MscL, the mechanosensitive channel of large conductance. MscL is the best characterized of all mechanosensitive channels. It has been the subject of numerous structural and functional investigations. The explosion in experimental data on MscL recently culminated in the solution of the three-dimensional structure of the MscL homologue from Mycobacterium tuberculosis. In this review, much of these data are united and interpreted in terms of the newly published M. tuberculosis MscL crystal structure.     

Association of beta-arrestin with G protein-coupled receptors during clathrin-mediated endocytosis dictates the profile of receptor resensitization.

Resensitization of G protein-coupled receptors (GPCRs) following agonist-mediated desensitization is a necessary step for maintaining physiological responsiveness. However, the molecular mechanisms governing the nature of GPCR resensitization are poorly understood. Here, we examine the role of beta-arrestin in the resensitization of the beta(2) adrenergic receptor (beta(2)AR), known to recycle and resensitize rapidly, and the vasopressin V2 receptor (V2R), known to recycle and resensitize slowly. Upon agonist activation, both receptors recruit beta-arrestin to the plasma membrane and internalize in a beta-arrestin- and clathrin-dependent manner. However, whereas beta-arrestin dissociates from the beta(2)AR at the plasma membrane, it internalizes with the V2R into endosomes. The differential trafficking of beta-arrestin and the ability of these two receptors to dephosphorylate, recycle, and resensitize is completely reversed when the carboxyl-terminal tails of these two receptors are switched. Moreover, the ability of beta-arrestin to remain associated with desensitized GPCRs during clathrin-mediated endocytosis is mediated by a specific cluster of phosphorylated serine residues in the receptor carboxyl-terminal tail. These results demonstrate that the interaction of beta-arrestin with a specific motif in the GPCR carboxyl-terminal tail dictates the rate of receptor dephosphorylation, recycling, and resensitization, and thus provide direct evidence for a novel mechanism by which beta-arrestins regulate the reestablishment of GPCR responsiveness.     

Elevated Levels of Petite Formation in Strains of SACCHAROMYCES CEREVISIAE Restored to Respiratory Competence. I. Association of Both High and Moderate Frequencies of Petite Mutant Formation with the Presence of Aberrant Mitochondrial DNA

When recently arisen spontaneous petite mutants of Saccharomyces cerevisiae are crossed, respiratory competent diploids can be recovered. Such restored strains can be divided into two groups having sectored or unsectored colony morphology, the former being due to an elevated level of spontaneous petite mutation. On the basis of petite frequency, the sectored strains can be subdivided into those with a moderate frequency (5–16%) and those with a high frequency (>60%) of petite formation. Each of the three categories of restored strains can be found on crossing two petites, suggesting either that the parental mutants contain a heterogeneous population of deleted mtDNAs at the time of mating or that different interactions can occur between the defective molecules. Restriction endonuclease analysis of mtDNA from restored strains that have a wild-type petite frequency showed that they had recovered a wild-type mtDNA fragmentation pattern. Conversely, all examined cultures from both categories of sectored strains contained aberrant mitochondrial genomes that were perpetuated without change over at least 200 generations. In addition, sectored colony siblings can have different aberrant mtDNAs. The finding that two sectored, restored strains from different crosses have identical but aberrant mtDNAs provides evidence for preferred deletion sites from the mitochondrial genome. Although it appears that mtDNAs from sectored strains invariably contain duplications, there is no apparent correlation between the size of the duplication and spontaneous petite frequency.     

Trypsin-susceptible cell surface characteristics of Streptococcus sanguis

The adherence of Streptococcus sanguis to saliva-coated hydroxylapatite was markedly reduced by treatment of the cells with trypsin. In Scatchard plots of adherence data, protease-treated S. sanguis did not exhibit the characteristic positive slopes, suggesting that trypsin prevented cooperative interactions between the cells and artificial pellicle. Trypsin also reduced the tendency of S. sanguis to bind to hexadecane and to octyl-Sepharose. When sodium dodecyl sulfate was used to elute S. sanguis from columns of octyl-Sepharose, it was observed that the elution profiles of trypsin-treated cells were more complex than those of control cells. Water and salts were incapable of removing the cells from octyl-Sepharose. The results suggest that adherence to saliva-coated hydroxylapatite, binding to hexadecane and to octyl-Sepharose depend on trypsin-susceptible cell surface molecules.     

Mitotic gene conversion, reciprocal recombination and gene replacement at the benA, beta-tubulin, locus of Aspergillus nidulans

Summary We have developed a procedure for determining the rates of mitotic recombination of an interrupted duplication created by integration of transforming plasmid sequences at the benA, beta-tubulin, locus of Aspergillus nidulans. Transformation of a strain carrying a benomyl-resistant benA allele with plasmid AIpGM4, which carries the wild-type benA allele and the pyr4 (orotidine-5-phosphate decarboxylase) gene of Neurospora crassa, creates an interrupted duplication with plasmid sequences flanked by two benA alleles, one wild type and one benomyl resdistant. Such transformants will not grow in the presence of high levels of benomyl. Mitotic recombination causes the loss of the wild-type benA allele or conversion of the wild-type to the mutant allele resulting in nuclei carrying only the benomylresistant allele. Conidia containing such nuclei can be selected on media with high benomyl allowing easy quantitation of mitotic recombination. We found that the rate of recombination giving rise to benomyl-resistant conidia was 4.6×10^-4. Reciprocal recombination leading to benomyl-resistant conidia lacking plasmid sequences occurred at a rate of 2.0×10^-4 and gene conversion leading to benomylresistant conidia occurred at a rate of 2.6×10^-4. We selected for reciprocal recombination leading to loss of pyr4 sequences on 5-fluoro-orotic acid and used this selection for two-step gene replacement of a mutant benA allele with the wild-type allele.     

Altruistic surrogacy and informed consent

A crucial premise in many recent arguments against the moral permissibility of surrogate motherhood arrangements is the claim that a woman cannot autonomously consent to gestating and relinquishing a child to another couple, because she cannot be fully informed about what her future emotional responses will be to the foetus developing within her, and to the giving up of the newborn infant to its social parents. When conjoined with some moral principle about the justifiable limits on the ways others can be expected to exercise their autonomy on our behalf, this claim is often taken to establish that various forms of surrogate motherhood arrangements are morally wrong. In this paper I want to show that there is a serious non sequitur in this kind of argument. That is, I want to show that even if women cannot in fact have this kind of information about what their future emotional responses to pregnancy and relinquishment will be, nothing follows about the wrongness or otherwise of surrogacy. For, when we consider what counts as informed consent in the context of other important ventures with uncertain consequences, it becomes clear that informed consent does not require having this kind of information about one's future emotional states. In putting these arguments, I also hope to clarify some of the connections which might be thought to hold between informed consent and autonomous decision-making generally.     

Conversion of rat muscle fiber types

Summary Rats were used in this study to determine the time course of conversion of muscle fiber types. The right or left gastrocnemius muscle was removed thereby causing an overload on the ipsilateral soleus and plantaris muscles. The contralateral limb served as a control. The type II to type I fiber conversion was followed histochemically in the soleus and plantaris muscles for one to six weeks following surgery. Muscle sections were stained for myofibrillar actomyosin ATPase and NADH tetrazolium reductase. The type I population in the soleus muscle was 99.3% six weeks after synergist removal. The plantaris muscle underwent a two fold increase in the percentage of type I fibers after six weeks. Transitional fibers were prominent in the plantaris muscle and reached their peak at 4% (P<0.05) of the total population, four weeks after surgery.This research was funded in part by grants from The Graduate School at Washington State University, and The Society of the Sigma Xi     

Evidence supporting the paraphyly of Hucho (Salmonidae) based on ribosomal DNA restriction maps

Relationships among the less derived genera in the subfamily Salmoninae were investigated by phylogenetic analysis of data from restriction maps of the ribosomal DNA using Osmerus mordax (rainbow smelt), Coregonus hoyi (bloater), and Thymattus arcticus (Arctic grayling) as outgroups. Analysis of the results suggests that Hucho h. taimen is more closely related to Brachymystax lenok (lenok) than to Hucho perryi (Sakhalin taimen) and that B. lenok and Hucho h. taimen (Eurasian taimen) form the most ancestral clade of the Salmoninae.