PAR-CLIP (Photoactivatable Ribonucleoside-Enhanced Crosslinking and Immunoprecipitation): a step-by-step protocol to the transcriptome-wide identification of binding sites of RNA-binding proteins.

We recently developed a protocol for the transcriptome-wide isolation of RNA recognition elements readily applicable to any protein or ribonucleoprotein complex directly contacting RNA (including RNA helicases, polymerases, or nucleases) expressed in cell culture models either naturally or ectopically (Hafner et al., 2010). Briefly, immunoprecipitation of the RNA-binding protein of interest is followed by isolation of the crosslinked and coimmunoprecipitated RNA.

A biophysical miRNA-mRNA interaction model infers canonical and noncanonical targets.

We introduce a biophysical model of miRNA-target interaction and infer its parameters from Argonaute 2 cross-linking and immunoprecipitation data. We show that a substantial fraction of human miRNA target sites are noncanonical and that predicted target-site affinity correlates well with the extent of target destabilization. Our model provides a rigorous biophysical approach to miRNA target identification beyond ad hoc miRNA seed-based methods.

A quantitative analysis of CLIP methods for identifying binding sites of RNA-binding proteins.

Cross-linking and immunoprecipitation (CLIP) is increasingly used to map transcriptome-wide binding sites of RNA-binding proteins. We developed a method for CLIP data analysis, and applied it to compare CLIP with photoactivatable ribonucleoside-enhanced CLIP (PAR-CLIP) and to uncover how differences in cross-linking and ribonuclease digestion affect the identified sites. We found only small differences in accuracies of these methods in identifying binding sites of HuR, which binds low-complexity sequences, and Argonaute 2, which has a complex binding specificity.

Conserved generation of short products at piRNA loci.

Background: The piRNA pathway operates in animal germ lines to ensure genome integrity through retrotransposon silencing. The Piwi protein-associated small RNAs (piRNAs) guide Piwi proteins to retrotransposon transcripts, which are degraded and thereby post-transcriptionally silenced through a ping-pong amplification process. Cleavage of the retrotransposon transcript defines at the same time the 5' end of a secondary piRNA that will in turn guide a Piwi protein to a primary piRNA precursor, thereby amplifying primary piRNAs.

CLIPZ: a database and analysis environment for experimentally determined binding sites of RNA-binding proteins.

The stability, localization and translation rate of mRNAs are regulated by a multitude of RNA-binding proteins (RBPs) that find their targets directly or with the help of guide RNAs. Among the experimental methods for mapping RBP binding sites, cross-linking and immunoprecipitation (CLIP) coupled with deep sequencing provides transcriptome-wide coverage as well as high resolution. However, partly due to their vast volume, the data that were so far generated in CLIP experiments have not been put in a form that enables fast and interactive exploration of binding sites.

PAR-CliP--a method to identify transcriptome-wide the binding sites of RNA binding proteins.

RNA transcripts are subjected to post-transcriptional gene regulation by interacting with hundreds of RNA-binding proteins (RBPs) and microRNA-containing ribonucleoprotein complexes (miRNPs) that are often expressed in a cell-type dependently. To understand how the interplay of these RNA-binding factors affects the regulation of individual transcripts, high resolution maps of in vivo protein-RNA interactions are necessary. A combination of genetic, biochemical and computational approaches are typically applied to identify RNA-RBP or RNA-RNP interactions.

Transcriptome-wide identification of RNA-binding protein and microRNA target sites by PAR-CLIP.

RNA transcripts are subject to posttranscriptional gene regulation involving hundreds of RNA-binding proteins (RBPs) and microRNA-containing ribonucleoprotein complexes (miRNPs) expressed in a cell-type dependent fashion. We developed a cell-based crosslinking approach to determine at high resolution and transcriptome-wide the binding sites of cellular RBPs and miRNPs. The crosslinked sites are revealed by thymidine to cytidine transitions in the cDNAs prepared from immunopurified RNPs of 4-thiouridine-treated cells.

High frequency and diversity of cutaneous appendageal tumors in organ transplant recipients.

Background: Recipients of organ transplant who are immunosuppressed are at greatly increased risk of nonmelanoma skin cancers compared with the general population, but their risk of appendageal tumors is unknown.

Objective: Our aim was to conduct a systematic examination of cutaneous appendageal tumors arising in recipients of organ transplants compared with individuals who were immunocompetent (ICP).

Methods: We conducted a retrospective, clinicopathologic analysis of consecutive appendageal tumors arising in 650 recipients of organ transplants and in the general population of approximately 605,000 people served by our institution.