A dynamic view of domain-motif interactions

Many protein-protein interactions are mediated by domain-motif interaction, where a domain in one protein binds a short linear motif in its interacting partner. Such interactions are often involved in key cellular processes, necessitating their tight regulation. A common strategy of the cell to control protein function and interaction is by post-translational modifications of specific residues, especially phosphorylation. Indeed, there are motifs, such as SH2-binding motifs, in which motif phosphorylation is required for the domain-motif interaction. On the contrary, there are other examples where motif phosphorylation prevents the domain-motif interaction. Here we present a large-scale integrative analysis of experimental human data of domain-motif interactions and phosphorylation events, demonstrating an intriguing coupling between the two. We report such coupling for SH3, PDZ, SH2 and WW domains, where residue phosphorylation within or next to the motif is implied to be associated with switching on or off domain binding. For domains that require motif phosphorylation for binding, such as SH2 domains, we found coupled phosphorylation events other than the ones required for domain binding. Furthermore, we show that phosphorylation might function as a double switch, concurrently enabling interaction of the motif with one domain and disabling interaction with another domain. Evolutionary analysis shows that co-evolution of the motif and the proximal residues capable of phosphorylation predominates over other evolutionary scenarios, in which the motif appeared before the potentially phosphorylated residue, or vice versa. Our findings provide strengthening evidence for coupled interaction-regulation units, defined by a domain-binding motif and a phosphorylated residue.     

Control of ethylene activity in various plant systems by structural analogues of 1-methylcyclopropene

Two structural analogues of 1-methylcyclopropene (1-MCP), 1-ethylcyclopropene (1-ECP) and 1-propylcyclopropene (1-PCP) were found to inhibit ethylene action and thereby the responses to ethylene in various plant systems. When applied prior to exposure to ethylene, the analogues considerably delayed ethylene-induced ripening of avocado and tomato fruits, delayed citrus leaf explants abscission and reversed ethylene-induced swelling and inhibition of elongation in etiolated pea plants. The analogues exerted their effect in a concentration-depended manner, at a range of several parts per million. Of the two analogues, 1-ECP was found in all cases more potent than 1-PCP but less potent then the mother compound 1-MCP. It is proposed that the analogues inhibit ethylene action by competing for the sites of binding on the ethylene receptor, similar to the mode of action suggested for 1-MCP. Findings revealed in this study imply that the competition of ethylene and the analogues for the ethylene site of binding is of a non-competitive nature. The analogues effectively inhibited ethylene action only if applied before the plant material was exposed to ethylene, or in the case of fruits shortly after harvest. Simultaneous application of the analogues and ethylene reduced the inhibitory effect of the analogues. Application of the analogues after exposure to ethylene or after fruit ripening had nullified the inhibitory effect of the analogues. Ripening of fruits, treated with the analogues, was inhibited for a finite period of time after which the fruits ripened normally. This resumption of ripening ability is attributed to presence of free binding sites on the ethylene receptor at the point of recovery from the inhibition. As the analogues are volatile, non-corrosive, non-toxic, odorless compounds and effective at minute concentrations, they can be considered promising candidates for practical use.     

The neurosteroid allopregnanolone impairs object memory and contextual fear memory in male C57BL/6J mice

Allopregnanolone (ALLO, or 3α-hydroxy-5α-pregnan-20-one) is a steroid metabolite of progesterone and a potent endogenous positive allosteric modulator of GABA-A receptors. Systemic ALLO has been reported to impair spatial, but not nonspatial learning in the Morris water maze (MWM) and contextual memory in rodents. These cognitive effects suggest an influence of ALLO on hippocampal-dependent memory, although the specific nature of the neurosteroid's effects on learning, memory or performance is unclear. The present studies aimed to determine: (i) the memory process(es) affected by systemic ALLO using a nonspatial object memory task; and (ii) whether ALLO affects object memory via an influence within the dorsal hippocampus. Male C57BL/6J mice received systemic ALLO either before or immediately after the sample session of a novel object recognition (NOR) task. Results demonstrated that systemic ALLO impaired the encoding and consolidation of object memory. A subsequent study revealed that bilateral microinfusion of ALLO into the CA1 region of dorsal hippocampus immediately following the NOR sample session also impaired object memory consolidation. In light of debate over the hippocampal-dependence of object recognition memory, we also tested systemic ALLO-treated mice on a contextual and cued fear-conditioning task. Systemic ALLO impaired the encoding of contextual memory when administered prior to the context pre-exposure session. Together, these results indicate that ALLO exhibits primary effects on memory encoding and consolidation, and extend previous findings by demonstrating a sensitivity of nonspatial memory to ALLO, likely by disrupting dorsal hippocampal function.     

Staphylococcus epidermidis role in the skin microenvironment

Wound healing is a complex dynamic physiological process in response to cutaneous destructive stimuli that aims to restore the cutaneous’ barrier role. Deciphering the underlying mechanistic details that contribute to wound healing will create novel therapeutic strategies for skin repair. Recently, by using state‐of‐the‐art technologies, it was revealed that the cutaneous microbiota interact with skin immune cells. Strikingly, commensal Staphylococcus epidermidis‐induced CD8+ T cells induce re‐epithelization of the skin after injury, accelerating wound closure. From a drug development perspective, the microbiota may provide new therapeutic candidate molecules to accelerate skin healing. Here, we summarize and evaluate recent advances in the understanding of the microbiota in the skin microenvironment.     

Isolation, characterization, and differentiation of stem cells derived from the rat amniotic membrane

Abstract Stem-cell-based therapies may offer treatments for a variety of intractable diseases. A fundamental goal in stem-cell biology concerns the characterization of diverse populations that exhibit different potentials, growth capabilities, and therapeutic utilities. We report the characterization of a stem-cell population isolated from tissue explants of rat amniotic membrane. Similar to mesenchymal stem cells, these amnion-derived stem cells (ADSCs) express the surface markers CD29 and CD90, but were negative for the lymphohematopoietic markers CD45 and CD11b. ADSCs exist in culture in a multidifferentiated state, expressing neuroectodermal (neurofilament-M), mesodermal (fibronectin), and endodermal (α-1-antitrypsin) genes. To assess plasticity, ADSCs were subjected to a number of culture conditions intended to encourage differentiation into neuroectodermal, mesodermal, and endodermal cell types. ADSCs cultured in a defined neural induction media assumed neuronal morphologies and up-regulated neural-specific genes. Under different conditions, ADSCs were capable of differentiating into presumptive bone and fat cells, indicated by the deposition of mineralized matrix and accumulated lipid droplets, respectively. Moreover, ADSCs cultured in media that promotes liver cell differentiation up-regulated liver-specific genes (albumin) and internalized low-density lipoprotein (LDL), consistent with a hepatocyte phenotype. To determine whether this observed plasticity reflects the presence of true stem cells within the population, we have derived individual clones from single cells. Clonal lines recapitulate the expression pattern of parental ADSC cultures and are multipotent. ADSCs have been cultured for 20 passages without losing their plasticity, suggesting long-term self-renewal. In sum, our data suggest that ADSCs and derived clonal lines are capable of long-term self-renewal and multidifferentiation, fulfilling all the criteria of a stem-cell population.     

Skeletal muscle pericyte subtypes differ in their differentiation potential

Neural progenitor cells have been proposed as a therapy for central nervous system disorders, including neurodegenerative diseases and trauma injuries, however their accessibility is a major limitation. We recently isolated Tuj1 + cells from skeletal muscle culture of Nestin–GFP transgenic mice however whether they form functional neurons in the brain is not yet known. Additionally, their isolation from nontransgenic species and identification of their ancestors is unknown. This gap of knowledge precludes us from studying their role as a valuable alternative to neural progenitors. Here, we identified two pericyte subtypes, type-1 and type-2, using a double transgenic Nestin–GFP/NG2–DsRed mouse and demonstrated that Nestin–GFP +/Tuj1 + cells derive from type-2 Nestin–GFP +/NG2–DsRed +/CD146 + pericytes located in the skeletal muscle interstitium. These cells are bipotential as they generate either Tuj1 + cells when cultured with muscle cells or become “classical” α-SMA + pericytes when cultured alone. In contrast, type-1 Nestin–GFP ?/NG2–DsRed +/CD146 + pericytes generate α-SMA + pericytes but not Tuj1 + cells. Interestingly, type-2 pericyte derived Tuj1 + cells retain some pericytic markers (CD146 +/PDGFRβ +/NG2 +). Given the potential application of Nestin–GFP +/NG2–DsRed +/Tuj1 + cells for cell therapy, we found a surface marker, the nerve growth factor receptor, which is expressed exclusively in these cells and can be used to identify and isolate them from mixed cell populations in nontransgenic species for clinical purposes.     

Control of Relative Timing and Stoichiometry by a Master Regulator

Developmental processes in cells require a series of complex steps. Often only a single master regulator activates genes in these different steps. This poses several challenges: some targets need to be ordered temporally, while co-functional targets may need to be synchronized in both time and expression level. Here we study in single cells the dynamic activation patterns of early meiosis genes in budding yeast, targets of the meiosis master regulator Ime1. We quantify the individual roles of the promoter and protein levels in expression pattern control, as well as the roles of individual promoter elements. We find a consistent expression pattern difference between a non-cofunctional pair of genes, and a highly synchronized activation of a co-functional pair. We show that dynamic control leading to these patterns is distributed between promoter, gene and external regions. Through specific reciprocal changes to the promoters of pairs of genes, we show that different genes can use different promoter elements to reach near identical activation patterns.     

Stretch-grown axons retain the ability to transmit active electrical signals

Little is known about extensive nervous system growth after axons reach their targets. Indeed, postnatal animals continue to grow, suggesting that axons are stretched to accommodate the expanding body. We have previously shown that axons can sustain stretch-growth rates reaching 1 cm/day; however, it remained unknown whether the ability to transmit active signals was maintained. Here, stretch-growth did not alter sodium channel activation, inactivation, and recovery or potassium channel activation. In addition, neurons generated normal action potentials that propagated across stretch-grown axons. Surprisingly, Na and K channel density increased due to stretch-growth, which may represent a natural response to preserve the fidelity of neuronal signaling.