The current predominant theapeutic paradigm is based on maximizing drug-receptor occupancy to achieve clinical benefit. This strategy, however, generally requires excessive drug concentrations to ensure sufficient occupancy, often leading to adverse side effects. Here, we describe major improvements to the proteolysis targeting chimeras (PROTACs) method, a chemical knockdown strategy in which a heterobifunctional molecule recruits a specific protein target to an E3 ubiquitin ligase, resulting in the target’s ubiquitination and degradation. These compounds behave catalytically in their ability to induce the ubiquitination of super-stoichiometric quantities of proteins, providing efficacy that is not limited by equilibrium occupancy. We present two PROTACs that are capable of specifically reducing protein levels by >90% at nanomolar concentrations. In addition, mouse studies indicate that they provide broad tissue distribution and knockdown of the targeted protein in tumor xenografts. Together, these data demonstrate a protein knockdown system combining many of the favorable properties of small-molecule agents with the potent protein knockdown of RNAi and CRISPR.

In situ analysis of biomarkers is highly desirable in molecular pathology because it allows the examination of biomarker status within the histopathological context of clinical specimens. Immunohistochemistry and DNA in situ hybridization (ISH) are widely used in clinical settings to assess protein and DNA biomarkers, respectively, but clinical use of in situ RNA analysis is rare. This disparity is especially notable when considering the abundance of RNA biomarkers discovered through whole-genome expression profiling. This is largely due to the high degree of technical complexity and insufficient sensitivity and specificity of current RNA ISH techniques. Here, we describe RNAscope, a novel RNA ISH technology with a unique probe design strategy that allows simultaneous signal amplification and background suppression to achieve single-molecule visualization while preserving tissue morphology. RNAscope is compatible with routine formalin-fixed, paraffin-embedded tissue specimens and can use either conventional chromogenic dyes for bright-field microscopy or fluorescent dyes for multiplex analysis. Unlike grind-and-bind RNA analysis methods such as real-time RT-PCR, RNAscope brings the benefits of in situ analysis to RNA biomarkers and may enable rapid development of RNA ISH-based molecular diagnostic assays.

Dendrites distinguish between sister branches and those of other cells. Self-recognition can often lead to repulsion, a process termed "self-avoidance." Here we demonstrate that dendrite self-avoidance in Drosophila da sensory neurons requires cell-recognition molecules encoded by the Dscam locus. By alternative splicing, Dscam encodes a vast number of cell-surface proteins of the immunoglobulin superfamily. We demonstrate that interactions between identical Dscam isoforms on the cell surface underlie self-recognition, while the cytoplasmic tail converts this recognition to dendrite repulsion. Sister dendrites expressing the same isoforms engage in homophilic repulsion. By contrast, Dscam diversity ensures that inappropriate repulsive interactions between dendrites sharing the same receptive field do not occur. The selectivity of Dscam-mediated cell interactions is likely to be widely important in the developing fly nervous system, where processes of cells must distinguish between self and nonself during the construction of neural circuits.

Dscam is an immunoglobulin (Ig) superfamily member that regulates axon guidance and targeting in Drosophila. Alternative splicing potentially generates 38,016 isoforms differing in their extracellular Ig and transmembrane domains. We demonstrate that Dscam mediates the sorting of axons in the developing mushroom body (MB). This correlates with the precise spatiotemporal pattern of Dscam protein expression. We demonstrate that MB neurons express different arrays of Dscam isoforms and that single MB neurons express multiple isoforms. Two different Dscam isoforms differing in their extracellular domains introduced as transgenes into single mutant cells partially rescued the mutant phenotype. Expression of one isoform of Dscam in a cohort of MB neurons induced dominant phenotypes, while expression of a single isoform in a single cell did not. We propose that different extracellular domains of Dscam share a common function and that differences in isoforms expressed on the surface of neighboring axons influence interactions between them.

Dscam is an immunoglobulin (Ig) superfamily protein required for the formation of neuronal connections in Drosophila. Through alternative splicing, Dscam potentially gives rise to 19,008 different extracellular domains linked to one of two alternative transmembrane segments, resulting in 38,016 isoforms. All isoforms share the same domain structure but contain variable amino acid sequences within three Ig domains in the extracellular region. We demonstrate that different isoforms exhibit different binding specificity. Each isoform binds to itself but does not bind or binds poorly to other isoforms. The amino acid sequences of all three variable Ig domains determine binding specificity. Even closely related isoforms sharing nearly identical amino acid sequences exhibit isoform-specific binding. We propose that this preferential homophilic binding specificity regulates interactions between cells and contributes to the formation of complex patterns of neuronal connections.

Integrating transcriptomic sequencing with conventional cytogenetics, we identified WWTR1 (WW domain-containing transcription regulator 1) (3q25) and CAMTA1 (calmodulin-binding transcription activator 1) (1p36) as the two genes involved in the t(1;3)(p36;q25) chromosomal translocation that is characteristic of epithelioid hemangioendothelioma (EHE), a vascular sarcoma. This WWTR1/CAMTA1 gene fusion is under the transcriptional control of the WWTR1 promoter and encodes a putative chimeric transcription factor that joins the amino terminus of WWTR1, a protein that is highly expressed in endothelial cells, in-frame to the carboxyl terminus of CAMTA1, a protein that is normally expressed only in brain. Thus, CAMTA1 expression is activated inappropriately through a promoter-switch mechanism. The gene fusion is present in virtually all EHEs tested but is absent from all other vascular neoplasms, demonstrating it to be a disease-defining genetic alteration. A sensitive and specific break-apart fluorescence in situ hybridization assay was also developed to detect the translocation and will assist in the evaluation of this diagnostically challenging neoplasm. The chimeric WWTR1/CAMTA1 transcription factor may represent a therapeutic target for EHE and offers the opportunity to shed light on the functions of two poorly characterized proteins.

Human papillomavirus (HPV) is established as causative in oropharyngeal squamous cell carcinomas (OSCCs), being detected in 50% to 80% of tumors by DNA in situ hybridization (ISH) and/or polymerase chain reaction. However, these tests do not assess viral transcription. Many consider E6/E7 messenger ribonucleic acid (mRNA) the best indicator of HPV status, but it has not been detected in situ in OSCC. We constructed tissue microarrays (TMAs) from a cohort of OSCC for which p16 immunohistochemistry and HPV DNA ISH were previously performed on whole sections. We utilized a novel, chromogenic RNA ISH assay called RNAscope to detect E6/E7 mRNA of HPV-16 and other high-risk types on these TMAs. RNA ISH results were obtained for 196 of 211 TMA cases, of which 153 (78.1%) were positive. p16 immunohistochemistry and HPV DNA ISH were positive in 79.0% and 62.4% of cases, respectively. Concordance between RNA and p16, DNA and p16, and RNA and DNA were 96.4%, 78.7%, and 83.5%, respectively. Only 7 cases (3.6%) were discrepant between RNA ISH and p16. In univariate analysis, all 3 tests correlated with better overall survival (OS), disease-specific survival (DSS), and disease-free survival (DFS) (all P<0.001). In multivariate analysis, OS correlated significantly with RNA (hazard ratio=0.39, P=0.001), DNA (0.53, P=0.03), and p16 (0.30, P<0.001), but DSS and DFS correlated significantly only with p16 (DSS: 0.36, P=0.006; DFS: 0.42, P=0.016). RNA ISH is more sensitive than DNA ISH in detecting HPV in OSCC, and it correlates strongly with p16. Although both tests were comparable, p16 more strongly stratified patient outcomes.

Sensory processing centres in both the vertebrate and the invertebrate brain are often organized into reiterated columns, thus facilitating an internal topographic representation of the external world. Cells within each column are arranged in a stereotyped fashion and form precise patterns of synaptic connections within discrete layers. These connections are largely confined to a single column, thereby preserving the spatial information from the periphery. Other neurons integrate this information by connecting to multiple columns. Restricting axons to columns is conceptually similar to tiling. Axons and dendrites of neighbouring neurons of the same class use tiling to form complete, yet non-overlapping, receptive fields1-3. It is thought that, at the molecular level, cellsurface proteins mediate tiling through contact-dependent repulsive interactions1,2,4,5, but proteins serving this function have not yet been identified. Here we show that the immunoglobulin superfamily member Dscam2 restricts the connections formed by L1 lamina neurons to columns in the Drosophila visual system. Our data support a model in which Dscam2 homophilic interactions mediate repulsion between neurites of L1 cells in neighbouring columns. We propose that Dscam2 is a tiling receptor for L1 neurons.The Drosophila visual system is a modular structure6,7. The retina contains 750 simple eyes, each containing eight photoreceptor neurons or R cells (R1-R8). R cells project into the brain, where they make connections within two neuropils, the lamina and medulla. R1-R6 neurons target to the lamina, where they form synapses with lamina neurons (L1-L5). R7, R8 and L1-L5 form connections in single columns within layers in the medulla, and each column contains one axon of each of these cell types. As a consequence of this wiring pattern, each column processes motion (lamina neurons) and colour (R7 and R8) from a single point in space6. Although some progress has been made in understanding how neurons select different layers within each of the 750 columns6, the molecular mechanisms that restrict synaptic connections to a single column are not known.Dscam2 belongs to a conserved family of cell-surface proteins expressed in the nervous systems of many different organisms8-10. Down syndrome cell adhesion molecule (DSCAM) was originally identified as an open reading frame in a region of human chromosome 21 critical for Down's syndrome11. There are four Dscam genes in the fly genome (Dscam,. They encode type I transmembrane proteins that share about 30% sequence identity and have a common extracellular domain comprising ten ©2007 Nature Publishing GroupCorrespondence and requests for materials should be addressed to S.L.Z. (lzipursky@mednet.ucla.edu).. Full Methods and any associated references are available in the online version of the paper at www.nature.com/nature.Supplementary Information is linked to the online version of the paper at www.nature.com/nature.Reprints and permissions information is available at www.nature.com/reprints. The Dscam...