Target regulated the formation of G

Target-regulated the formation of G-quadruplex was used here to “kill two FTY720 Phosphate with one stone” for the detection of melamine and I− with one probe DNA. G-quadruplexes are higher-order structures formed from G-rich oligonucleotides through the stacking of planar G-tetrads [43,44]. They have been extensively used in proteins, nucleic acids and enzymes detection due to their label-free properties [[45], [46], [47], [48], [49], [50]]. The N-methyl mesoporphyrin IX (NMM), as a fluorophore, which can produce strong fluorescence emission once binding with G-quadruplex [51,52]. What need to be pointed out is that when the G-rich DNA probe is locked, such as formed hairpin structure or aggregated with nanomaterials, the non-G-quadruplexes structure probe DNA can't associate with NMM to produce fluorescence [[53], [54], [55], [56]]. Inspired by these concepts, a label free, multiplex and parallel analysis method for two targets based on G-quadruplexes was developed in this work. A schematic of the assay is shown in Scheme 1. A novel DNA junction including specific G-quadruplex DNA sequences of melamine and I− was firstly constructed. The designed G-rich DNA probe can associate with NMM and K+ to form G-quadruplex-NMM-K+, which can produce a strong fluorescence signal. As shown in Scheme 1A, in the presence of melamine, melamine can induce T-rich probe DNA to form a T-M-T hairpin structure through hydrogen bond for preventing the formation of G-quadruplex [57], which results a great fluorescence reducing. Similar with the T-M-T structure, the designed probe DNA can coordinate with Hg2+ to form a T-Hg2+-T hairpin structure, which can also inhibit the probe DNA to form of the G-quadruplex structure [23,58,59]. I− can completely capture the Hg2+ from T-Hg2+-T and then G-quadruplex structure was formed. These G-quadruplex-forming sequences associated with NMM to exhibit significantly enhanced fluorescent signal for sensitive monitoring of I−, the schematic diagram was shown in Scheme 1B. With this strategy, this system not only presented sensitive and selective fluorescence quenching detection of melamine, but also successfully achieved fluorescence enhanced detection of I−.
Experimental
Results and discussion
Conclusions A target-regulated the formation of G-quadruplex strategy was successfully constructed in this work for melamine and iodide sensing. With G-quadruplex/NMM as fluorescence indicator, fluorescence reduces for melamine and fluorescence enhancing for I− were achieved, respectively. This method is simple, cost-effective, label-free, highly sensitive and selective for both melamine and iodide analysis. Besides, such methods can also be realized with other spectrometers or coupled with various nucleic acid-based amplification technologies to greatly further broaden their applications and improve their analytical performance. And this strategy may combine some nanomaterials like QDs, NCs to realize multiple substances analysis. Miniaturization of the sensing system is possible, e.g. combined with microfluidic technology and used portable fluorometer. In addition, visual detection can be achieved by introducing a luminescent substrate such as TMB or ABTS into the system.
Acknowledgements The authors thank the National Natural Science Foundation of China (No. 21605108) and the Foundation of Sichuan Normal University No. ZZYQ2018-04 and SYJS2018-05 for financial support.
Introduction The Xp11.2 (TFE3) translocation is reported in many type of cancers viz. Alveolar Soft Part Sarcoma(ASPS) [1], [2], Perivascular Epitheloid Cell neoplasms(PECOMAs) [3], Epithelioid Hemangio-Endothelioma(EHE) [4] and Renal Cell Carcinoma(RCC). ASPL-TFE3, SFPQ-TFE3, YAP-TFE3 are the translocations which are present in ASPS, PECOMAS and EHE respectively. RCC is more heterogeneous in terms of Xp11.2 translocation partners e.g. PRCC, ASPL, PSF, NONO, CLTC, RCC17, RBM10 etc. [5], [6], [7], [8], [9], [10], [11], [12], [13]. TFE3 gene present on Xp11.2 locus is a basic helix-loop-helix leucine zipper (bHLH-Zip) transcription factor involved in TGF-Smad signaling pathway [14]. This bHLH-LZ transcription factors comprise a family of closely related proteins MiTF, TFE3, TFEB and TFEC and acts as a transactivator of genes that are regulated by an E-box (CANNTG) in their promoters [15]. TFE3 expressed as two alternatively spliced isoforms TFE3L & TFE3S with different activating properties [16]. Chromosomal rearrangements a hallmark of cancer often leading to oncogenic fusion genes. DNA sequences eg. triplexes, quadruplexes, hairpin/cruciforms etc. with the potential to fold into secondary structures may predispose DNA to break [17]. Bioinformatics study has shown that the different types of altered DNA structures are present near translocation breakpoint regions. 70% of genes involved in rearrangements in lymphoid cancers are associated with presence of G-quadruplex forming motifs in the fragile regions [18]. G-quadruplexes are higher-order non-B form of nucleic acid secondary structures and formed by the plannar G-quartet building blocks through a cyclic Hoogsten hydrogen-bonding arrangement of four guanines [19]. G-quadruplex structures responsible for genomic fragility was studied in HOX11 gene in t(10;14) translocation in T-cell leukemia [20]. In follicular lymphoma t(14;18) translocation BCL2 major breakpoint region has G-rich sequence capable of forming a stable G-quadruplex which can be cleaved by the RAG complex [21], [22]. In B-cell lymphomas G-loops are present in the c-MYC regions which are associated with the Translocation and aberrant hypermutation [23]. Tumor suppressor gene TP53 has G-quadruplex in Intron 3 which modulates the splicing of intron 2 leading to the change in different isoform size and level [24]. A G-quadruplex is present in PAX9 intron 1 near the exon-intron boundary, have a key role on splicing efficiency of intron 1 [25]. Telomerase down regulation in A549 cells by a G-quadruplex ligand 12459 causes aberrant hTERT alternative splicing leading to the almost complete disappearance of the active form and an over-expression of the inactive transcript (26). A G-rich sequence controls splice site selection within exon 3 of BACE1 and mutation of the G-rich sequence decreased use of the normal 5′ splice site leading to full-length and proteolytically active BACE1. Increased use of an alternative splice site leads to a shorter, essentially inactive isoform of BACE1 [27].