Null alleles at two lactate dehydrogenase loci in rainbow trout are associated with decreased developmental stability

Previous studies with rainbow trout (Oncorhynchus mykiss) have shown that allozymic heterozygotes have increased developmental stability, as measured by reduced fluctuating bilateral asymmetry. In this paper, we examine the phenotypic effects of null alleles at two lactate dehydrogenase (LDH) loci. If the association between allozymic heterozygosity and developmental stability is due largely to linked chromosomal segments, then we would expect null allele heterozygotes to have increased developmental stability. In contrast, heterozygotes for LDH null alleles in three populations have reduced developmental stability. This suggests that the reduction in enzyme activity at these loci is having a deleterious effect on development that is strong enough to mask any beneficial effects that may be associated with heterozygosity for these chromosomal segments. The LDH loci examined in this study are members of two different paralogous pairs of duplicate genes produced by the polyploidization of the ancestral salmonid genome. The apparent deleterious effects of these null alleles in heterozygotes could retard the possible loss of duplicate gene expression.     

Sequencing of pools of nucleic acids on oligonucleotide arrays

In sequencing-by-hybridization methods, the nucleotide sequence of a nucleic acid is reconstructed by overlapping oligonucleotides capable of hybridizing with the nucleic acid. In their present form, the methods are hardly suitable for sequencing of long nucleic acid molecules because of the occurrence of non-unique overlaps between the oligonucleotides, and similarly to the conventional sequencing methods, it is necessary to obtain an individual molecule. In the method described here, most ambiguities in reconstruction of a sequence from the constituent oligonucleotides are eliminated by preparing on oligonucleotide arrays and separate surveying of the nucleic acid nested partials. This enables longer nucleic acids to be sequenced, and results in a high redundancy of the input data allowing most hybridization errors to be eliminated by algorithmic means. Furthermore, large pools of nucleic acid strands can be sequenced directly, without isolating individual strands.     

The ontogenetic complexity of developmental constraints

Developmental constraint is a theoretically important construct bridging ontogenetic and evolutionary studies. We propose a new operationalization of this notion that exploits the unusually rich measurement structure of landmark data. We represent landmark configurations by their partial warps, a basis for morphospace that represents a set of localized features of form. A finding of developmental constraint arises from the interplay between age-varying means and age-specific variances in these subspaces of morphospace. Examination of variances and means in 16 ventral skull landmarks in the cotton rat S. fulviventer at ages 1, 10, 20, and 30 days yielded three types of developmental constraint: canalization (constraint to relatively constant form age by age); chreods (reduction of variance orthogonal to the mean trajectory over ages); and opposition (reduction of age-specific variance along the mean trajectory over ages). While canalization and chreodic constraints have been noted previously, the oppositional type of constraint appears novel. Only one of our characters, relative length and orientation of the incisive foramen, appears to be canalized. Although skull growth becomes increasingly integrated through ontogeny, our characters display a remarkable spatiotemporal complexity in patterns of variance reduction. The specific assortment of constraints observed may be related to the precociality of Sigmodon. We suggest that Waddington's diagrammatic presentation of the “epigenetic landscape” may be misleading in quantitative studies of developmental regulation.     

Hydrology shapes microbial communities and microbiome-mediated growth of an Everglades tree island species

Plant-associated microbiomes can improve plant fitness by ameliorating environmental stress, providing a promising avenue for improving outplantings during restoration. However, the effects of water management on these microbial communities and their cascading effects on primary producers are unresolved for many imperiled ecosystems. One such habitat, Everglades tree islands, has declined by 54% in some areas, releasing excess nutrients into surrounding wetlands and exacerbating nutrient pollution. We conducted a factorial experiment, manipulating the soil microbiome and hydrological regime experienced by a tree island native, Ficus aurea, to determine how microbiomes impact growth under two hydrological management plans. All plants were watered to simulate natural precipitation, but plants in the “unconstrained” management treatment were allowed to accumulate water above the soil surface, while the “constrained” treatment had a reduced stage to avoid soil submersion. We found significant effects of the microbiomes on overall plant performance and aboveground versus belowground investment; however, these effects depended on hydrological treatment. For instance, microbiomes increased investment in roots relative to aboveground tissues, but these effects were 142% stronger in the constrained compared to unconstrained water regime. Changes in hydrology also resulted in changes in the prokaryotic community composition, including a >20 log₂fold increase in the relative abundance of Rhizobiaceae, and hydrology-shifted microbial composition was linked to changes in plant performance. Our results suggest that differences in hydrological management can have important effects on microbial communities, including taxa often involved in nitrogen cycling, which can in turn impact plant performance.     

Escherichia coli K12 does not colonize the gastrointestinal tract of Fischer-344 rats

Summary The colonizing potential ofEscherichia coli K12 containing a vector coding for somidobove (bovine somatotropin) was determined. Treated male and female Fischer-344 rats were given a single oral gavage inoculum of sucrose with/without tetracycline (15 g/ml). Untreated control animals received similar drinking water regimes. All animals survived until termination. There were no clinical signs of toxicity observed and no treatment-related effect upon body weight, food consumption, or efficiency of food utilization. Fresh fecal samples were collected from each rat every 24 h following inoculation and the population of the marked strain was quantitated until no bacterial colonies were observed for two consecutive days. While all inoculated rats were positive at 24 h, by 72 and 96 h all had become negative for the test (marked) strain, as were the corresponding control group throughout the test. The frozen stock of the marked strain used as the positive control demonstrated that the agar plates were selective for the test strain. Fourteen days following inoculation, all groups of rats were killed and the gastrointestinal tracts removed and treated to recover the marked strain. There was no evidence of the marked strain in the gastrointestinal tract of any rat from any group. Thus, theE. coli K12 host/vector system used in this experiment does not colonize the gastrointestinal tract of Fischer-344 rats.     

Recombination-deficient mutants of Salmonella typhimurium are avirulent and sensitive to the oxidative burst of macrophages

Mutations in the genes recA and recBC were constructed in the virulent Salmonella typhimurium strain 14028s. Both the recA and recBC mutants were attenuated in mice. The mutants were also sensitive to killing by macrophages in vitro. The recombination mutants were no longer macrophage sensitive in a variant line of J774 macrophage-like cells that fail to generate superoxide. This suggests that repair of DNA damage by Salmonella is necessary for full virulence in vivo and that the oxidative burst of phagocytes is one source of such DNA damage.     

Sensitivity of a two-dimensional biomorphoelastic model for post-burn contraction

We consider a two-dimensional biomorphoelastic model describing post-burn scar contraction. This model describes skin displacement and the development of the effective Eulerian strain in the tissue. Besides these mechanical components, signaling molecules, fibroblasts, myofibroblasts, and collagen also play a significant role in the model. We perform a sensitivity analysis for the independent parameters of the model and focus on the effects on features of the relative surface area and the total strain energy density. We conclude that the most sensitive parameters are the Poisson’s ratio, the equilibrium collagen concentration, the contraction inhibitor constant, and the myofibroblast apoptosis rate. Next to these insights, we perform a sensitivity analysis where the proliferation rates of fibroblasts and myofibroblasts are not the same. The impact of this model adaptation is significant.

     

Die Feinstruktur der Schweineaorta beim experimentellen Lathyrismus

Zusammenfassung Die Veränderungen der Aortenfeinstruktur, welche eine Vergiftung mit-Amino-Propio-Nitril (Lathyrusfaktor) bei jungen Schweinen hervorruft, werden beschrieben.Der Benninghoffsche Spannapparat der Media wird frühzeitig durch eine Lösung der muskulo-elastischen Kontinuität gelockert. Im Vordergrunde der morphologischen Veränderungen stehen dann Zerfallserscheinungen der elastischen Substanz, welche zu einer Desintegration der elastischen Lamellen sowie der elastischen interlamellären Schrägverbinder führen und endlich eine völlige Strukturauflösung der ganzen Mediaorganisation mit herdförmigen Totalnekrosen zur Folge haben. Das mit dem Mediafasersystem strukturell und funktioneil eng verbundene kollagen-elastische Fasergitter der Intima zerfällt; die subendotheliale Intima wird dabei hochgradig aufgetrieben durch eine Einlagerung von Ödemflüssigkeit und wahrscheinlich auch Blutserum. Die feinnetzig-zweiphasige Normaldarstellung der Grundsubstanz geht verloren. Die Feinstruktur der Kollagenfibrillen bleibt unverändert; es wird darauf hingewiesen, daß trotzdem eine schwere Schädigung auch des Kollagens anzunehmen ist. Die Mediamuskelzellen wandeln sich weitgehend in Fibroblasten um; die Langhans-Zellen der Intima werden in gleicher Weise aktiviert. Zellnekrosen treten in der Media nur dann auf, wenn sekundär die subakute Aortenwandverdickung eine Mangelsituation für den Zelleigenstoffwechsel hervorruft.In der Umgebung der Vasa vasorum kommt es zu kleinen Blutungen, die mit Fortschreiten der Mediazerstörung in große, dissezierende Blutungen übergehen können. Der wahrscheinlich durch die Elastizitätsverminderung der Media eingeleitete Mechanismus der Gefäßrupturierung wird beschrieben und mit dem vonGöre und vonDoerr vermuteten Mechanismus der Bildung von Aneurysmata dissecantia der menschlichen Aorta in Parallele gesetzt.Mit Unterstützung durch die Deutsche Forschungsgemeinschaft. — FräuleinElke CarStensen schulden wir Dank für unermüdliche, gewissenhafte und geschickte technische Mitarbeit.