Evolution of the Sry genes

Existing DNA sequence data on the Sry gene, the mammalian sex- determining locus in the Y chromosome, were analyzed for primates, rodents, and bovids. In all three taxonomic groups, the terminal sequences evolved faster than the HMG (high mobility group) boxes, and this applies both to synonymous (Ks) and nonsynonymous (Ka) nucleotide substitutions. Similar intragenic correlation between synonymous and nonsynonymous substitution rates was not found either in other mammalian genes that contain a conservative box (Sox, Msx) or in the MADS-box genes of plants. The rate of nonsynonymous substitutions exceeds significantly that of synonymous substitutions in the terminal Sry sequences of apes. We did not find good support for the hypothesis that the high evolutionary rate of Sry would be associated with a promiscuous mating system.      

A GFP-MAP4 reporter gene for visualizing cortical microtubule rearrangements in living epidermal cells

Microtubules influence morphogenesis by forming distinct geometrical arrays in the cell cortex, which in turn affect the deposition of cellulose microfibrils. Although many chemical and physical factors affect microtubule orientation, it is unclear how cortical microtubules in elongating cells maintain their ordered transverse arrays and how they reorganize into new geometries. To visualize these reorientations in living cells, we constructed a microtubule reporter gene by fusing the microtubule binding domain of the mammalian microtubule-associated protein 4 (MAP4) gene with the green fluorescent protein (GFP) gene, and transient expression of the recombinant protein in epidermal cells of fava bean was induced. The reporter protein decorates microtubules in vivo and binds to microtubules in vitro. Confocal microscopy and time-course analysis of labeled cortical arrays along the outer epidermal wall revealed the lengthening, shortening, and movement of microtubules; localized microtubule reorientations; and global microtubule reorganizations. The global microtubule orientation in some cells fluctuates about the transverse axis and may be a result of a cyclic self-correcting mechanism to maintain a net transverse orientation during cellular elongation.     

Generation cycles

Generation cycles are population cycles with a period of roughly one generation. They have been observed in tropical pest populations and in laboratory populations. Theory suggests that they can arise both from intraspecific competition and from the influence of natural enemies, and ecological studies of populations of insects showing these cycles are starting to shed light on the mechanisms that maintain them.     

Host-parasite population dynamics under combined frequency- and density-dependent transmission

Many host‐parasite models assume that transmission increases linearly with host population density (‘density‐dependent transmission’), but various alternative transmission functions have been proposed in an effort to capture the complexity of real biological systems. The most common alternative (usually applied to sexually transmitted parasites) assumes instead that the rate at which hosts contact one another is independent of population density, leading to ‘frequency‐dependent’ transmission. This straight‐forward distinction generates fundamentally different dynamics (e.g. deterministic, parasite‐driven extinction with frequency‐ but not density‐dependence). Here, we consider the situation where transmission occurs through two different types of contact, one of which is density‐dependent (e.g. social contacts), the other density‐independent (e.g. sexual contacts). Drawing on a range of biological examples, we propose that this type of contact structure may be widespread in natural populations. When our model is characterized mainly by density‐dependent transmission, we find that allowing even small amounts of transmission to occur through density‐independent contacts leads to the possibility of deterministic, parasite‐driven extinction (and lowers the threshold for parasite persistence). Contrastingly, allowing some density‐dependent transmission to occur in a model characterized mainly by density‐independent contacts (i.e. by frequency‐dependent transmission) does not affect the extinction threshold, but does increase the likelihood of parasite persistence. The idea that directly transmitted parasites exploit different types of host contact is not new, but here we show that the impact on dynamics can be fundamental even in the simplest cases. For example, in systems where density‐dependent transmission is normally assumed de facto, we show that parasite‐driven extinction can occur if a small amount of transmission occurs through density‐independent contacts. Many empirical studies are still guided by the traditional density/frequency dichotomy, but our combined transmission function may provide a better model for systems in which both types of transmission occur.     

Ultrastructural analysis of the effect of ethane dimethanesulphonate on the testis of the rat,guinea pig,hamster and mouse

Summary The morphological response of the testis of rats, guinea pigs, Syrian hamsters and mice to treatment with the cytotoxin ethane dimethanesulphonate was examined using light and electron microscopy. One to two days after a single administration of ethane dimethanesulphonate to adult rats, guinea pigs, and hamsters, the Leydig cells showed marked ultrastructural alterations suggestive of degeneration and cell death. The former alterations included karyopyknosis, cytoplasmic vesiculation and accumulation of lipid inclusions and large lipofuscin bodies. Fragments of necrotic Leydig cells were often engulfed by the interstitial tissue macrophages. The morphology of the seminiferous epithelium of these three species was unchanged from the morphology observed in vehicle-injected control animals. In contrast, multiple injections of ethane dimethanesulphonate given to mice produced no ultrastructural alterations to Leydig cells yet the seminiferous epithelium exhibited disruption of spermatogenesis. Although the Leydig cells of the mouse appear resistant to ethane dimethanesulphonate, this agent exerts a selective cytotoxic action upon Leydig cells of the rat, guinea pig and hamster thus identifying ethane dimethanesulphonate as a useful chemical for future endocrine and physiological studies of testicular function in three common laboratory species.     

Influence of nanofibers on growth and gene expression of human tendon derived fibroblast

Background  

Rotator cuff tears are a common and frequent lesion especially in older patients. The mechanisms of tendon repair are not fully understood. Common therapy options for tendon repair include mini-open or arthroscopic surgery. The use of growth factors in experimental studies is mentioned in the literature. Nanofiber scaffolds, which provide several criteria for the healing process, might be a suitable therapy option for operative treatment. The aim of this study was to explore the effects of nanofiber scaffolds on human tendon derived fibroblasts (TDF's), as well as the gene expression and matrix deposition of these fibroblasts.     

The genome of Rhizobium leguminosarum has recognizable core and accessory components

Background

Rhizobium leguminosarum is an α-proteobacterial N₂-fixing symbiont of legumes that has been the subject of more than a thousand publications. Genes for the symbiotic interaction with plants are well studied, but the adaptations that allow survival and growth in the soil environment are poorly understood. We have sequenced the genome of R. leguminosarum biovar viciae strain 3841.

Results

The 7.75 Mb genome comprises a circular chromosome and six circular plasmids, with 61% G+C overall. All three rRNA operons and 52 tRNA genes are on the chromosome; essential protein-encoding genes are largely chromosomal, but most functional classes occur on plasmids as well. Of the 7,263 protein-encoding genes, 2,056 had orthologs in each of three related genomes (Agrobacterium tumefaciens, Sinorhizobium meliloti, and Mesorhizobium loti), and these genes were over-represented in the chromosome and had above average G+C. Most supported the rRNA-based phylogeny, confirming A. tumefaciens to be the closest among these relatives, but 347 genes were incompatible with this phylogeny; these were scattered throughout the genome but were over-represented on the plasmids. An unexpectedly large number of genes were shared by all three rhizobia but were missing from A. tumefaciens.

Conclusion

Overall, the genome can be considered to have two main components: a 'core', which is higher in G+C, is mostly chromosomal, is shared with related organisms, and has a consistent phylogeny; and an 'accessory' component, which is sporadic in distribution, lower in G+C, and located on the plasmids and chromosomal islands. The accessory genome has a different nucleotide composition from the core despite a long history of coexistence.     

Interactions between environmental variables determine immunity in the Indian meal moth Plodia interpunctella

1. Animals raised in good environmental conditions are expected to have more resources to invest in immunity than those raised in poor conditions. Variation in immune activity and parasite resistance in response to changes in environmental temperature, population density and food quality have been shown in many invertebrate species. 2. Almost all studies to date have examined the effects of individual variables in isolation. The aim of this study was to address whether environmental factors interact to produce synergistic effects on phenoloxidase (PO) activity and haemocyte count, both indicators of immune system activity. Temperature, food quality and density were varied in a fully factorial design for a total of eight treatment combinations. 3. Strong interactions between the three environmental variables led to the magnitude and in some cases the direction of the effect of most variables changing as the other environmental factors were altered. Overall, food quality had the most important and consistent influence, larvae raised on a good-quality diet having substantially higher PO activity in every case and substantially higher haemocyte counts in all treatments except unheated/low density. 4. When food quality was good, the larvae showed 'density-dependent prophylaxis': raising their investment in immunity when population density is high. When food quality was poor and the temperature low, however, those larvae raised at high densities invested less in immunity. 5. Increased temperature is often thought to lead to increased immune reactivity in ectotherms, but we found that the effect of temperature was strongly dependent on the values of other environmental variables. PO activity increased with temperature when larvae were raised on good food or when density was high, but when food was poor and density low, a higher temperature led to reduced PO activity. A higher temperature led to higher haemocyte counts when density was high and food quality was poor, but in all other cases, the effect of increased temperature was either close to zero or somewhat negative. 6. Although PO activity and haemocyte count were weakly correlated across the whole data set, there were a number of treatments where the two measures responded in different ways to environmental change. Overall, effect sizes for PO activity were substantially higher than those for haemocyte count, indicating that the different components of the immune system vary in their sensitivity to environmental change. 7. Predictions of the effect of environmental or population change on immunity and disease dynamics based on laboratory experiments that only investigate the effects of single variable are likely to be inaccurate or even entirely wrong.     

Periodontal therapy increases neutrophil extracellular trap degradation

In periodontitis, polymorphonuclear leucocytes (PMNs) are activated. They entrap and eliminate pathogens by releasing neutrophil extracellular traps (NETs). Abnormal NET degradation is part of a pro-inflammatory status, affecting co-morbidities such as cardiovascular disease. We aimed to investigate the ex vivo NET degradation capacity of plasma from periodontitis patients compared to controls (part 1) and to quantify NET degradation before and after periodontal therapy (part 2). Fresh NETs were obtained by stimulating blood-derived PMNs with phorbol 12-myristate 13-acetate. Plasma samples from untreated periodontitis patients and controls were incubated for 3 h onto freshly generated NETs (part 1). Similarly, for part 2, NET degradation was studied for 91 patients before and 3, 6 and 12 mo after non-surgical periodontal therapy with and without adjunctive systemic antibiotics. Finally, NET degradation was fluorospectrometrically quantified. NET degradation levels did not differ between periodontitis patients and controls, irrespective of subject-related background characteristics. NET degradation significantly increased from 65.6 ± 1.7% before periodontal treatment to 75.7 ± 1.2% at 3 mo post periodontal therapy, and this improvement was maintained at 6 and 12 mo, irrespective of systemic usage of antibiotics. Improved NET degradation after periodontitis treatment is another systemic biomarker reflecting a decreased pro-inflammatory status, which also contributes to an improved cardiovascular condition.