Hair Cells – Beyond the Transducer

Overview This review considers the “tween twixt and twain” of hair cell physiology, specifically the signaling elements and membrane conductances which underpin forward and reverse transduction at the input stage of hair cell function and neurotransmitter release at the output stage. Other sections of this review series outline the advances which have been made in understanding the molecular physiology of mechanoelectrical transduction and outer hair cell electromotility. Here we outline the contributions of a considerable array of ion channels and receptor signaling pathways that define the biophysical status of the sensory hair cells, contributing to hair cell development and subsequently defining the operational condition of the hair cells across the broad dynamic range of physiological function.     

IL-1β Processing in Host Defense: Beyond the Inflammasomes

Stimulation and release of proinflammatory cytokines is an essential step for the activation of an effective innate host defense, and subsequently for the modulation of adaptive immune responses. Interleukin-1β (IL-1β) and IL-18 are important proinflammatory cytokines that on the one hand activate monocytes, macropages, and neutrophils, and on the other hand induce Th1 and Th17 adaptive cellular responses. They are secreted as inactive precursors, and the processing of pro-IL-1β and pro-IL-18 depends on cleavage by proteases. One of the most important of these enzymes is caspase-1, which in turn is activated by several protein platforms called the inflammasomes. Inflammasome activation differs in various cell types, and knock-out mice defective in either caspase-1 or inflammasome components have an increased susceptibility to several types of infections. However, in other infections and in models of sterile inflammation, caspase-1 seems to be less important, and alternative mechanisms such as neutrophil-derived serine proteases or proteases released from microbial pathogens can process and activate IL-1β. In conclusion, IL-1β/IL-18 processing during infection is a complex process in which the inflammasomes are only one of several activation mechanisms.     

HIV Infection Disrupts the Sympatric Host–Pathogen Relationship in Human Tuberculosis

The phylogeographic population structure of Mycobacterium tuberculosis suggests local adaptation to sympatric human populations. We hypothesized that HIV infection, which induces immunodeficiency, will alter the sympatric relationship between M. tuberculosis and its human host. To test this hypothesis, we performed a nine-year nation-wide molecular-epidemiological study of HIV–infected and HIV–negative patients with tuberculosis (TB) between 2000 and 2008 in Switzerland. We analyzed 518 TB patients of whom 112 (21.6%) were HIV–infected and 233 (45.0%) were born in Europe. We found that among European-born TB patients, recent transmission was more likely to occur in sympatric compared to allopatric host–pathogen combinations (adjusted odds ratio [OR] 7.5, 95% confidence interval [95% CI] 1.21–infinity, p = 0.03). HIV infection was significantly associated with TB caused by an allopatric (as opposed to sympatric) M. tuberculosis lineage (OR 7.0, 95% CI 2.5–19.1, p<0.0001). This association remained when adjusting for frequent travelling, contact with foreigners, age, sex, and country of birth (adjusted OR 5.6, 95% CI 1.5–20.8, p = 0.01). Moreover, it became stronger with greater immunosuppression as defined by CD4 T-cell depletion and was not the result of increased social mixing in HIV–infected patients. Our observation was replicated in a second independent panel of 440 M. tuberculosis strains collected during a population-based study in the Canton of Bern between 1991 and 2011. In summary, these findings support a model for TB in which the stable relationship between the human host and its locally adapted M. tuberculosis is disrupted by HIV infection.     

Human liver AMP-deaminase – oligomeric forms of the enzyme

AMP-deaminase (EC 3.5.4.6) is a key enzyme of nucleotide breakdown involved in regulation of adenine nucleotide pool in the liver. Mechanisms regulating activity of the enzyme are not completely elucidated, till now. In this paper experimental data indicating on the potential regulatory significance of changes in oligomeric structure of the enzyme are presented. SDS-PAG electrophoresis of human liver AMP-deaminase revealed the presence of three enzyme fragments. Only largest of them (the protein fragments weighing 68 kDa) reacted immunologically with monoclonal anti- (human liver) AMP-deaminase antibodies. At physiological pH 7.0, in the absence of regulatory ligands, reaction catalysed by human liver AMP-deaminase was strongly dependent on enzyme concentration used, with half-saturation constant (S_0.5) values increasing significantly with the degree of enzyme dilution. Preincubation with activated long-chain fatty acids – substances promoting dissociation of oligomeric enzymes, inhibited the activity of AMP-deaminase studied nearly completely. Gel filtration on Sepharose CL-6B column demonstrated existence of at least three active oligomeric forms of human liver AMP-deaminase. We postulate that oligomeric structure of the enzyme is a factor determining regulatory profile of AMP-deaminase studied.     

Endocardial Tip Cells in the Human Embryo – Facts and Hypotheses

Experimental studies regarding coronary embryogenesis suggest that the endocardium is a source of endothelial cells for the myocardial networks. As this was not previously documented in human embryos, we aimed to study whether or not endothelial tip cells could be correlated with endocardial-dependent mechanisms of sprouting angiogenesis. Six human embryos (43–56 days) were obtained and processed in accordance with ethical regulations; immunohistochemistry was performed for CD105 (endoglin), CD31, CD34, α-smooth muscle actin, desmin and vimentin antibodies. Primitive main vessels were found deriving from both the sinus venosus and aorta, and were sought to be the primordia of the venous and arterial ends of cardiac microcirculation. Subepicardial vessels were found branching into the outer ventricular myocardium, with a pattern of recruiting α-SMA+/desmin+ vascular smooth muscle cells and pericytes. Endothelial sprouts were guided by CD31+/CD34+/CD105+/vimentin+ endothelial tip cells. Within the inner myocardium, we found endothelial networks rooted from endocardium, guided by filopodia-projecting CD31+/CD34+/CD105+/ vimentin+ endocardial tip cells. The myocardial microcirculatory bed in the atria was mostly originated from endocardium, as well. Nevertheless, endocardial tip cells were also found in cardiac cushions, but they were not related to cushion endothelial networks. A general anatomical pattern of cardiac microvascular embryogenesis was thus hypothesized; the arterial and venous ends being linked, respectively, to the aorta and sinus venosus. Further elongation of the vessels may be related to the epicardium and subepicardial stroma and the intramyocardial network, depending on either endothelial and endocardial filopodia-guided tip cells in ventricles, or mostly on endocardium, in atria.     

Is the Outgrowth of Transplant-Derived Axons Guided by Host Astrocytes and Myelin Loss?

Loss of cortical neurons may lead to sever and sometimes irreversible deficits in motor function in a number of neuropathological conditions. Absence of spontaneous axonal regeneration following trauma in the adult central nervous system (CNS) is attributed to inhibitory factors associated to the CNS white matter and to the non-permissive environment provided by reactive astrocytes that form a physical and biochemical barrier scar. Neural transplantation of embryonic neurons has been widely assessed as a potential approach to overcome the generally limited capacity of the mature CNS to regenerate axons or to generate new neurons in response to cell loss. We have recently shown that embryonic (E14) mouse motor cortical tissue transplanted into the damaged motor cortex of adult mice developed efferent projections to appropriate cortical and subcortical host targets including distant areas such as the spinal cord, with a topographical organization similar to that of intact motor cortex. Several parameters might account for the outgrowth of axonal projections from embryonic neurons within a presumably non-permissive adult brain, among which are astroglial reactions and myelin formation. In the present study, we have examined the role of astrocytes and myelin in the axonal outgrowth of transplanted neurons.     

Is the Outgrowth of Transplant-Derived Axons Guided by Host Astrocytes and Myelin Loss?

Loss of cortical neurons may lead to sever and sometimes irreversible deficits in motor function in a number of neuropathological conditions. Absence of spontaneous axonal regeneration following trauma in the adult central nervous system (CNS) is attributed to inhibitory factors associated to the CNS white matter and to the non-permissive environment provided by reactive astrocytes that form a physical and biochemical barrier scar. Neural transplantation of embryonic neurons has been widely assessed as a potential approach to overcome the generally limited capacity of the mature CNS to regenerate axons or to generate new neurons in response to cell loss. We have recently shown that embryonic (E14) mouse motor cortical tissue transplanted into the damaged motor cortex of adult mice developed efferent projections to appropriate cortical and subcortical host targets including distant areas such as the spinal cord, with a topographical organization similar to that of intact motor cortex. Several parameters might account for the outgrowth of axonal projections from embryonic neurons within a presumably non-permissive adult brain, among which are astroglial reactions and myelin formation. In the present study, we have examined the role of astrocytes and myelin in the axonal outgrowth of transplanted neurons.Key Words: motor cortex, neuronal transplantation, embryonic cells, GFP, GFAP, PLP     

The role of the copper-binding enzyme – laccase – in the biodegradation of polyethylene by the actinomycete Rhodococcus ruber

Polyethylene is considered one of the most durable plastic polymers. Virtually, non-biodegradable polyethylene accumulates in the environment, thus posing an ecological threat to man and wildlife. We have previously isolated a strain of the actinomycete Rhodococcus ruber (designated C208; EC 1.10.3.2.) capable of utilizing and degrading polyethylene. Here, we report the role of the bacterial copper-binding enzyme, laccase, in the oxidation and degradation of polyethylene by this strain. Copper markedly affected the induction and activity of laccase, resulting in polyethylene degradation. mRNA quantification by RT-PCR, revealed a 13-fold increase in laccase mRNA levels, in copper-treated cultures compared with the untreated control. Addition of copper to C208 cultures containing polyethylene enhanced the biodegradation of polyethylene by 75%, as compared with the non-amended control. Furthermore, when an extracellular isoform of laccase collected from the media of copper-induced cells was incubated with polyethylene, reductions of 20% and 15% were obtained in the Average Molecular Weight (Mw) and Average Molecular Number (Mn) with the polymer, respectively. FTIR analysis of similar polyethylene films incubated with the extracellular laccase exhibited an increase in the carbonyl peak, indicating that enzymatic oxidation by laccase plays a major role in the biodegradation of polyethylene.     

Beyond the beaten path: improving natural products bioprospecting using an eco-evolutionary framework – the case of the octocorals

Marine natural products (NPs) represent an impressive source of novel bioactive molecules with major biotechnological applications. Nevertheless, the usual chemical and applied perspective leading most of bioprospecting projects come along with various limitations blurring our understanding of the extensive marine chemical diversity. Here, we propose several guidelines: (i) to optimize bioprospecting and (ii) to refine our knowledge on marine chemical ecology focusing on octocorals, one of the most promising sources of marine NPs. We identified a significant phylogenetic bias in the octocoral bioprospecting, which calls for the development of a concerted discovery strategy. Given the gap existing between the number of isolated NPs and the knowledge regarding their functions, we provide an ecologically centered workflow prioritizing biological function ahead of chemical identification. Furthermore, we illustrate how -omic technologies should rapidly increase our knowledge on solving different aspects of the ecology and evolution of marine NPs.     

Conventional and novel modes of exine patterning in members of the Araceae – the consequence of ecological paradigm shifts?

Summary. In the family Araceae, the members of all subfamilies except Aroideae follow the conventional mode of exine formation pattern, which conforms with the textbook view of sporoderm stratification and chemistry (sporopollenin ektexine formed before the endexine). Only members of the subfamily Aroideae show a quite uncommon mode of exine formation pattern, with an endexine formed prior to the nonsporopollenin, polysaccharidic outer exine layer. The intine is formed simultaneously with this non-sporopollenin layer. From the differing timetable and especially from the different origin it is concluded that this outer exine layer is not homologous to the angiosperm ektexine. The fundamental question, why members of the Aroideae lack an elaborated sporopollenin ektexine, is discussed in terms of functionality of the nonsporopollenin outer exine layer. It seems that a major change in aroid evolution took place at the point when the family phylogenetically and ecologically shifted from bisexual (most subfamilies) to unisexual flowers (Aroideae only). The hypothesis is that ephemeral spathes and the absence of sporopollenin are the consequence of an adaptive syndrome for a short pollination time window in many members of the Aroideae, with short-lived pollen, an energetically not costly pollen wall, rapid germination of pollen tube, and brief receptivity of stigma. Correspondence and reprints: Institute of Botany, University of Vienna, Rennweg 14, 1030 Vienna, Austria.     

Host–parasite coevolution beyond the nestling stage? Mimicry of host fledglings by the specialist screaming cowbird

Egg mimicry by obligate avian brood parasites and host rejection of non-mimetic eggs are well-known textbook examples of host-parasite coevolution. By contrast, reciprocal adaptations and counteradaptations beyond the egg stage in brood parasites and their hosts have received less attention. The screaming cowbird (Molothrus rufoaxillaris) is a specialist obligate brood parasite whose fledglings look identical to those of its primary host, the baywing (Agelaioides badius). Such a resemblance has been proposed as an adaptation in response to host discrimination against odd-looking young, but evidence supporting this idea is scarce. Here, we examined this hypothesis by comparing the survival rates of young screaming cowbirds and non-mimetic shiny cowbirds (Molothrus bonariensis) cross-fostered to baywing nests and quantifying the similarity in plumage colour and begging calls between host and cowbird fledglings. Shiny cowbirds suffered higher post-fledging mortality rates (83%) than screaming cowbirds (0%) owing to host rejection. Visual modelling revealed that screaming cowbirds, but not shiny cowbirds, were indistinguishable from host young in plumage colour. Similarly, screaming cowbirds matched baywings' begging calls more closely than shiny cowbirds. Our results strongly support the occurrence of host fledgling mimicry in screaming cowbirds and suggest a role of visual and vocal cues in fledgling discrimination by baywings.