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Tissue-specific expression of genes is achieved, at least in part, by the presence of specific sequences termed enhancer elements, usually located upstream of transcription initiation sites (39). Some of these elements represent binding sites for ubiquitous trans-acting factors which increase the expression of genes containing these binding sites in a number of different cell types, whereas other elements are apparently recognized by factors found only in specific cell types. It is these latter factors that contribute, at least in part, to the tissue-specific expression of genes.Negative regulation also has been reported to influence gene expression in specific cell types (24,45). Some, if not all, genes contain both positive enhancer elements and negative regulatory elements (NREs), which may act as binding sites for factors which inhibit gene expression, possibly by interfering with the binding of positively acting factors (1,2,38). In addition, a number of retroviral long terminal repeats (LTRs) have been shown to encode NREs which suppress transcription (5, 14, 37).The endogenous murine retrovirus mouse mammary tumor virus (MMTV) is expressed in several tissues (18). When transgenic mice were made by using reporter genes under the transcriptional control of the MMTV LTR, the transgenes were expressed in the same tissues as was the endogenous virus, namely, the epithelial cells of the mammary and salivary glands, lungs, kidneys, and seminal vesicles and the lymphoid cells of the spleen and thymus (9,26,41,42

A graphene quantum dot (GQD) used as the photosensitizer with high two-photon absorption in the near-infrared region, a large absolute cross section of two-photon excitation (TPE), strong two-photon luminescence, and impressive two-photon stability could be used for dual modality two-photon photodynamic therapy (PDT) and two-photon bioimaging with an ultrashot pulse laser (or defined as TPE). In this study, a GQD efficiently generated reactive oxygen species coupled with TPE, which highly increased the effective PDT ability of both Gram-positive and -negative bacteria, with ultralow energy and an extremely short photoexcitation time generated by TPE. Because of its two-photon properties, a GQD could serve as a promising two-photon contrast agent for observing specimens in depth in three-dimensional biological environments while simultaneously proceeding with PDT action to eliminate bacteria, particularly in multidrug-resistant (MDR) strains. This procedure would provide an efficient alternative approach to easily cope with MDR bacteria.

BackgroundThe results showed that the deciding factor is the culture medium in which the bacteria and the graphene oxide (GO) are incubated at the initial manipulation step. These findings allow better use of GO and GO-based materials more and be able to clearly apply them in the field of biomedical nanotechnology.ResultsTo study the use of GO sheets applied in the field of biomedical nanotechnology, this study determines whether GO-based materials [GO, GO-polyoxyalkyleneamine (POAA), and GO-chitosan] stimulate or inhibit bacterial growth in detail. It is found that it depends on whether the bacteria and GO-based materials are incubated with a nutrient at the initial step. This is a critical factor for the fortune of bacteria. GO stimulates bacterial growth and microbial proliferation for Gram-negative and Gram-positive bacteria and might also provide augmented surface attachment for both types of bacteria. When an external barrier that is composed of GO-based materials forms around the surface of the bacteria, it suppresses nutrients that are essential to microbial growth and simultaneously produces oxidative stress, which causes bacteria to die, regardless of whether they have an outer-membrane-Gram-negative-bacteria or lack an outer-membrane-Gram-positive-bacteria, even for high concentrations of biocompatible GO-POAA. The results also show that these GO-based materials are capable of inducing reactive oxygen species (ROS)-dependent oxidative stress on bacteria. Besides, GO-based materials may act as a biofilm, so it is hypothesized that they suppress the toxicity of low-dose chitosan.ConclusionGraphene oxide is not an antimicrobial material but it is a general growth enhancer that can act as a biofilm to enhance bacterial attachment and proliferation. However, GO-based materials are capable of inducing ROS-dependent oxidative stress on bacteria. The applications of GO-based materials can clearly be used in antimicrobial surface coatings, surface-attached stem cells for orthopedics, antifouling for biocides and microbial fuel cells and microbial electro-synthesis.Electronic supplementary materialThe online version of this article (10.1186/s12951-017-0328-8) contains supplementary material, which is available to authorized users.

The nucleotide sequences of long terminal repeats (LTRs) from several mouse mammary tumor virus (MMTV) proviruses acquired in mouse T-cell lymphomas were determined. All MMTV proviruses cloned from a C57BL/6 lymphoma contained an identical LTR deletion of 491 base pairs (approximately-655 to-165), whereas an MMTV provirus from a BALB/c T-cell lymphoma had a 430-base-pair deletion in the same U3 region. MMTV proviruses with LTR deletions were acquired in these tumors 10 times more frequently than proviruses with intact LTRs. Because the deletions removed a portion of the glucocorticoid response element or "regulated" enhancer, the transcriptional activity of the deleted MMTV LTRs was assessed in both transient expression and stable transfection experiments. Plasmids were constructed in which the deleted or full-length MMTV LTRs were placed upstream of the chloramphenicol acetyltransferase gene. Results from transfection experiments with these constructs showed that the basal expression of the deleted MMTV LTR in the absence of glucocorticoids was higher than that of the full-length Mtv-17 or C3H MMTV LTRs under the same conditions. Moreover, the C3H LTR with a similar deletion (-637 to-255) also promoted high basal