Project description:Endogenous single-stranded DNA (essDNA) can form in a mammalian genome as the result of a variety of molecular processes and can both play important roles inside the cell as well as have detrimental consequences to genome integrity — much of which remains to be fully understood. Here we established SSiNGLe-P1 approach based on limited digestion by P1 endonuclease for high-throughput genome-wide identification of essDNA regions in human cells. We applied this method to profile essDNA in both the mitochondrial and nuclear genomes. In the mitochondrial genome, the profiles of essDNA provide new evidence to support the strand-displacement model of mitochondrial DNA replication. In the nuclear genome, essDNAs were found to be enriched in certain types of functional genomic elements, particularly, origins of DNA replication, R-loops, and to a lesser degree, in promoters. Furthermore, many of the essDNA regions identified by SSiNGLe-P1 have not been annotated and thus represent yet unknown functional elements.
Project description:Endogenous single-stranded DNA (essDNA) can form in a mammalian genome as the result of a variety of molecular processes and can both play important roles inside the cell as well as have detrimental consequences to genome integrity, much of which remains to be fully understood. Here, we established the SSiNGLe-P1 approach based on limited digestion by P1 endonuclease for high-throughput genome-wide identification of essDNA regions. We applied this method to profile essDNA in both human mitochondrial and nuclear genomes. In the mitochondrial genome, the profiles of essDNA provide new evidence to support the strand-displacement model of mitochondrial DNA replication. In the nuclear genome, essDNA regions were found to be enriched in certain types of functional genomic elements, particularly, the origins of DNA replication, R-loops, and to a lesser degree, in promoters. Furthermore, interestingly, many of the essDNA regions identified by SSiNGLe-P1 have not been annotated and thus could represent yet unknown functional elements.
Project description:DNA microarrays are two-dimensional arrangements of specific probes deposited on a substrate that have been widely used in gene expression analysis by measuring mRNA accumulation. The use of this type of microarrays involves the synthesis of cDNA, which has to be double stranded (ds) if the microarray probes are of the positive strand. We have used a custom-synthesized non-commercial NimbleGen microarray from melon to evaluate an alternative method of ds cDNA synthesis, which differs substantially in its economical cost relative to a widely recommended method. The results suggested that both methods produce cDNA representative of the melon transcriptome to a similar extent, indicating that the alternative technique provides a cheaper method of ds cDNA synthesis for microarray gene expression assays. Recently, we have analyzed the transcriptome of melon in response to WMV infection. Cotyledons of two genotypes of melon were virus inoculated and transcriptomic responses to the infection were analyzed by comparing infected and mock inoculated samples at 1, 3, and 7 days post-inoculation (dpi). Three biological replicates were performed for each sample. Double stranded cDNA was obtained with the Double stranded cDNA synthesis kit (Invitrogen, Carlsbad, CA, USA), based on the nick translation approach (Mol. Cell. Biol (1982) 2:161-170; Gene (1983) 25:263-269). Raw and processed microarray data are freely available from GEO database under the accession number GSE30111. By using this set of microarray hybridizations as a reference, RNA corresponding to infected cotyledons replicate 3 at 1 dpi (A1) and replicate 1 at 3 dpi (A2) (GEO accession numbers GSM745566 and GSM745567) were used to perform cDNA synthesis by the alternative method (samples B1 and B2, respectively), based on the SMART approach (BioTechniques (2001) 30:892-897), and microarray data were compared.
Project description:To accelerate previous RNA structure probing approaches, which focus on analyzing one RNA sequence at a time, we have developed FragSeq, a high-throughput RNA structure probing method that uses high-throughput RNA sequencing to identify single-stranded RNA (ssRNA) regions from fragments generated by nuclease P1, which is specific for single-stranded nucleic acids. In the accompanying study, we show that we can accurately and simultaneously map ssRNA regions in multiple non-coding RNAs with known structure in experiments probing the entire mouse nuclear transcriptome. We carried out probing in two cell types to assess reproducibility. We also identified and experimentally validated structured regions in ncRNAs never previously probed.
Project description:To accelerate previous RNA structure probing approaches, which focus on analyzing one RNA sequence at a time, we have developed FragSeq, a high-throughput RNA structure probing method that uses high-throughput RNA sequencing to identify single-stranded RNA (ssRNA) regions from fragments generated by nuclease P1, which is specific for single-stranded nucleic acids. In the accompanying study, we show that we can accurately and simultaneously map ssRNA regions in multiple non-coding RNAs with known structure in experiments probing the entire mouse nuclear transcriptome. We carried out probing in two cell types to assess reproducibility. We also identified and experimentally validated structured regions in ncRNAs never previously probed. We examined mouse nuclear RNA from two cell types: undifferentiated embryonic stem cells (UNDIFF) and cells differentiated into neural precursors (D5NP). For each cell type, nuclear RNA was purified and deproteinized, denatured, and refolded in vitro, from which we prepared three barcoded samples: "nuclease" (RNA partially digested with P1 ssRNA-specific nuclease, yielding 5'-PO4/3'-OH end chemistry at each cleavage site), "control" (control for "nuclease" sample to idenfity endogenous 5'-PO4/3'-OH), and "PNK" (same as "control" but followed by a polynucleotide kinase treatment to convert 5'-OH/3'-cyclic-phosphate ends to clonable 5'-PO4/3'-OH ends). Resulting RNA fragments were cloned using the SOLiD Small RNA Expression Kit (SREK) protocol, which ligates linkers only to 5'-PO4/3'-OH containing RNA, enriching for clones of products resulting from P1 cleavage in "nuclease" sample and selecting against random degradation. Two cell types, three treatments each, thus resulted in six barcoded samples total (barcodes 01, 02, 04, 05, 07, 08). Four other barcoded samples were prepared for separate experiments not used in our study (barcodes 03, 06, 09, 10), so their preparation is not described here. The total run of ten barcodes was done on the ABI SOLiD3 platform and a custom algorithm (FragSeq v0.0.1) was used to compute "cutting scores" (as described in our paper) that show ssRNA regions in hundreds of ncRNAs.
Project description:DNA microarrays are two-dimensional arrangements of specific probes deposited on a substrate that have been widely used in gene expression analysis by measuring mRNA accumulation. The use of this type of microarrays involves the synthesis of cDNA, which has to be double stranded (ds) if the microarray probes are of the positive strand. We have used a custom-synthesized non-commercial NimbleGen microarray from melon to evaluate an alternative method of ds cDNA synthesis, which differs substantially in its economical cost relative to a widely recommended method. The results suggested that both methods produce cDNA representative of the melon transcriptome to a similar extent, indicating that the alternative technique provides a cheaper method of ds cDNA synthesis for microarray gene expression assays.