Sustained oscillations in extended genetic oscillatory systems

Various dynamic cellular behaviors have been successfully modeled in terms of elementary circuitries showing particular characteristics such as negative feedback loops for sustained oscillations. Given, however, the increasing evidences indicating that cellular components do not function in isolation but form a complex interwoven network, it is still unclear to what extent the conclusions drawn from the elementary circuit analogy hold for systems that are highly interacting with surrounding environments. In this article, we consider a specific example of genetic oscillator systems, the so-called repressilator, as a starting point toward a systematic investigation into the dynamic consequences of the extension through interlocking of elementary biological circuits. From in silico analyses with both continuous and Boolean dynamics approaches to the four-node extension of the repressilator, we found that 1), the capability of sustained oscillation depends on the topology of extended systems; and 2), the stability of oscillation under the extension also depends on the coupling topology. We then deduce two empirical rules favoring the sustained oscillations, termed the coherent coupling and the homogeneous regulation. These simple rules will help us prioritize candidate patterns of network wiring, guiding both the experimental investigations for further physiological verification and the synthetic designs for bioengineering.     

Transfer of exogenous cholesterol to microsomes of hepatocytes investigated with [3H]desmosterol tracer.

The molybdenum centre of spinach (Spinacia oleracea) nitrate reductase has been investigated by e.p.r. spectroscopy of molybdenum(V) in reduced forms of the enzyme. The resting enzyme gives no signals attributable to Mo(V). However, on reduction with NADH, Mo(V) signals appeared at relatively short reaction times but decreased again on prolonged exposure to excess of the substrate as the enzyme was further reduced. On brief treatment of such samples with nitrate, Mo(V) signals reappeared but disappeared again on longer exposure to excess nitrate as the enzyme became fully reoxidized. Detailed investigation of the signals carried out in both 1H2O and 2H2O revealed the presence of two signal-giving species, referred to as 'signal A' and 'signal B', analogous to corresponding signals from nitrate reductase from Escherichia coli and from liver sulphite oxidase. Signal A has gav. 1.9767 and shows coupling to a single proton, exchangeable with the solvent, with A(1H)av. 1.3mT, whereas signal B shows no more than weak coupling to protons. Investigation of interconversion between the two species indicated that decreasing the pH from 8.0 to 6.7 had little effect, but that signal A was favoured by the presence of Cl-. This suggests, by analogy with recent work on sulphite oxidase by Bray, Gutteridge, Lamy & Wilkinson [Biochem. J. (1983) 211, 227-236] that Cl- is a ligand of molybdenum in the species giving signal A.     

Synthetic RNA Silencing of Actinorhodin Biosynthesis in Streptomyces coelicolor A3(2)

We demonstrate the first application of synthetic RNA gene silencers in Streptomyces coelicolor A3(2). Peptide nucleic acid and expressed antisense RNA silencers successfully inhibited actinorhodin production. Synthetic RNA silencing was target-specific and is a new tool for gene regulation and metabolic engineering studies in Streptomyces.     

Therapy model for advanced intracerebral B16 mouse melanoma using radiation therapy combined with immunotherapy

A reproducible therapy model for advanced intracerebral B16 melanoma is reported. Implanted tumors (D0), suppressed by a single 15 Gy radiosurgical dose of 100 kVp X-rays (D8), were further suppressed by a single ip injection of a Treg-depleting mAb given 2 days prior to the initiation (D9) of four weekly then eight bi-monthly sc injections of GMCSF-transfected, mitotically disabled B16 cells. The trends of seven independent experiments were similar to the combined result: The median (days) [SD/total N] of survival went from 15[1.09/62] (no treatment control) to 35.8[8.8/58] (radiation therapy only) to 52.5[13.5/57] (radiation therapy plus immunotherapy). Within 2 weeks after immunization, tumors in mice receiving radiation therapy plus immunotherapy were significantly smaller than tumors in mice treated only with radiosurgery. Splenocytes and lymph node cells from immunized mice showed increased interferon γ production when cultured with syngeneic tumor cells. We suggest that our model will be useful for the development and testing of novel combination therapies for brain tumors.     

The potential role of cofilin-1 in promoting triple negative breast cancer (TNBC) metastasis via the extracellular vesicles (EVs)

Triple negative breast cancer (TNBC) is an aggressive cancer, particularly prone to metastasis and is associated with poor survival outcomes. The key to unravelling the aggressiveness of TNBC lies in decoding the mechanism by which it metastasises. Cofilin-1 is a well-studied member of the cofilin family, involved in actin depolymerisation. Studies have described the diverse roles of cofilin-1 including cell motility, apoptosis and lipid metabolism. Levels of cofilin-1 have been shown to be increased in many different types of malignant cells, with increased cofilin-1 protein levels associated with poor prognosis in patients with TNBC. Extracellular vesicles (EVs) are microvesicles typically around 100 nm in size, found in all biological fluids examined to date (Lötvall et al., 2014). Proteomic studies on extracellular vesicles (EVs) have shown that cofilin-1 is amongst the most frequently detected. Moreover, decreased levels of cofilin-1 potentially inhibit the release of EVs from cells. Additionally, Cofilin-1 is essential for the maturation of EVs and may also play a key role in the establishment of the pre-metastatic niche, thus promoting tumour cell migration. Further work into the exact mechanism by which cofilin-1 advances TNBC metastasis, may potentially prevent disease progression and improve outcomes for patients with TNBC.     

Avian predation on a parasitic fly of cervids during winter: can host‐related cues increase the predation risk?

The deer ked (Lipoptena cervi) is an ectoparasitic fly on cervids that has expanded its distribution rapidly in Northern Europe. However, the regulating biotic factors such as predation remain unknown. The host‐independent pupal stage of the fly lasts for several months. Blackish pupae are visible against snow, especially on the bedding sites of hosts, and are thus exposed to predators. To evaluate the role of predation on the invasion dynamics and evolution of L. cervi, we monitored pupal predation on artificial bedding sites in three geographical areas in Finland during winter. We explored: (1) possible predators; (2) magnitude of predation; and (3) whether predation risk is affected by host‐derived cues. We demonstrate that pupae are predated by a number of tit species. Any reddish brown snow discoloration on bedding sites, indicating heavy infestation of the host, serves as an exploitable cue for avian predators, thereby increasing the risk of pupal predation. The ability of tits to use this host‐derived cue seems to be dependent on the prevalence of L. cervi and the period of invasion history, which suggests that it may be a learned behavioural response. Predation by tits may potentially affect the L. cervi population dynamics locally. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 275–286.     

Involvement of intracellular Ca2+ in blue light-dependent proton pumping in guard cell protoplasts from Vicia faba

Recent studies have suggested that Ca²⁺/calmodulin (CaM) or CaM-like proteins may be involved in blue light (BL)-dependent proton pumping in guard cells. As the increase in cytosolic concentration of Ca²⁺ is required for the activation of CaM and CaM-like proteins, the origin of the Ca²⁺ was investigated by measuring BL-dependent proton pumping with various treatments using guard cell protoplasts (GCPs) from Vicia faba . BL-dependent proton pumping was affected neither by Ca²⁺ channel blockers nor by changes of Ca²⁺ concentration in the medium used for the GCPs. Addition of Ca²⁺ ionophores and an agonist to GCPs did not induce proton pumping. However, BL-dependent proton pumping was inhibited by 10 m M caffeine, which releases Ca²⁺ from the intracellular stores, and by 10 μ M 2,5-di-( tert -butyl)-1,4-benzohydroquinone (BHQ) and 10 μ M cyclopiazonic acid (CPA), inhibitors of Ca²⁺-ATPase in the sarcoplasmic and endoplasmic reticulum (ER). By contrast, the inhibitions were not observed by 10 μ M thapsigargin, an inhibitor of animal ER-type Ca²⁺-ATPase. The inhibitions by caffeine and BHQ were reversible. Light-dependent stomatal opening in the epidermis of Vicia was inhibited by caffeine, BHQ, and CPA. From these results, we conclude that the Ca²⁺ thought to be required for BL-dependent proton pumping may originate from intracellular Ca²⁺ stores, most likely from ER in guard cells, and that this origin of Ca²⁺ may generate a stimulus-specific Ca²⁺ signal for stomatal opening.     

Protein replenishment in pitcher fluids of Nepenthes × ventrata revealed by quantitative proteomics (SWATH-MS) informed by transcriptomics

Journal of Plant Research - Carnivorous plants capture and digest insects for nutrients, allowing them to survive in soil deprived of nitrogenous nutrients. Plants from the genus Nepenthes produce...