Genome-wide in vivo screen of circulating tumor cells identifies SLIT2 as a regulator of metastasis

Circulating tumor cells (CTCs) break free from primary tumors and travel through the circulation system to seed metastatic tumors, which are the major cause of death from cancer. The identification of the major genetic factors that enhance production and persistence of CTCs in the bloodstream at a whole genome level would enable more comprehensive molecular mechanisms of metastasis to be elucidated and the identification of novel therapeutic targets, but this remains a challenging task due to the heterogeneity and extreme rarity of CTCs. Here, we describe an in vivo genome-wide CRISPR knockout screen using CTCs directly isolated from a mouse xenograft. This screen elucidated SLIT2-a gene encoding a secreted protein acting as a cellular migration cue-as the most significantly represented gene knockout in the CTC population. SLIT2 knockout cells are highly metastatic with hypermigratory and mesenchymal phenotype, resulting in enhanced cancer progression in xenograft models.

Rapid On-Cell Selection of High-Performance Human Antibodies

Phage display is a critical tool for developing antibodies. However, existing approaches require many time-consuming rounds of biopanning and screening of potential candidates due to a high rate of failure during validation. Herein, we present a rapid on-cell phage display platform which recapitulates the complex in vivo binding environment to produce high-performance human antibodies in a short amount of time. Selection is performed in a highly stringent heterogeneous mixture of cells to quickly remove nonspecific binders. A microfluidic platform then separates antigen-presenting cells with high throughput and specificity. An unsupervised machine learning algorithm analyzes sequences of phage from all pools to identify the structural trends that contribute to affinity and proposes ideal candidates for validation. In a proof-of-concept screen against human Frizzled-7, a key ligand in the Wnt signaling pathway, antibodies with picomolar affinity were discovered in two rounds of selection that outperformed current gold-standard reagents. This approach, termed μCellect, is low cost, high throughput, and compatible with a wide variety of cell types, enabling widespread adoption for antibody development.

Phage-Based Profiling of Rare Single Cells Using Nanoparticle-Directed Capture

Advances in single-cell level profiling of the proteome require quantitative and versatile platforms, especially for rare cell analyses such as circulating tumor cell (CTC) profiling. Here we demonstrate an integrated microfluidic chip that uses magnetic nanoparticles to capture single tumor cells with high efficiency, permits on-chip incubation, and facilitates in situ cell-surface protein expression analysis. Combined with phage-based barcoding and next-generation sequencing technology, we were able to monitor changes in the expression of multiple surface markers stimulated in response to CTC adherence. Interestingly, we found fluctuations in the expression of Frizzled2 (FZD2) that reflected the microenvironment of the single cells. This platform has a high potential for in-depth screening of multiple surface antigens simultaneously in rare cells with single-cell resolution, which will provide further insights regarding biological heterogeneity and human disease.

A comparison of Personal Dental Service (PDS) and General Dental Service (GDS) patients in terms of reported interventions, oral health and dentists' perceptions

AIMS

The aim of the study was to investigate the reported working patterns, dentist perceptions and patient oral health for dentists in a Personal Dental Services (PDS) pilot and compare this with that of matched dentists working in the General Dental Services (GDS) arrangements in the same part of England.

METHOD

Ten dentists were recruited, five each from PDS and GDS practices in Warwickshire, UK. The number of interventions carried out for adult patients in the year to April 2003 was obtained from the Dental Practice Board (DPB) for the two groups and compared. An Oral Health Index (OHX) (Burke and Wilson, 1995) was used to determine the oral health of a selection of patients from the two groups of dentists in the study. The final stage of the study involved semi-structured interviews with the dentists.

RESULTS

The average age of dentists was similar, in the early to mid 40's (p>0.05). Both groups were, on average, around 20 years post qualification. The GDS dentists made an average of 3,507 activity reports to the Dental Practice Board in the year examined, compared with 3,441 from the PDS dentists. PDS dentists provided fewer simple periodontal treatments than GDS dentists, but otherwise the pattern of reported activity was similar. Both PDS and GDS dentists suggested that GDS dentists carried out more fillings because of a perverse incentive to provide fillings compared with PDS arrangements. PDS dentists believed that their treatment profiles had not changed significantly since changing to PDS, and suggested that their prescribing was based on clinical need only and was not influenced by the remuneration system. A total of 225 OHX scores were obtained for patients attending PDS dentists and a further 214 from patients attending GDS dentists. Overall, the mean OHX score was lower in the GDS patients than for PDS patients.

CONCLUSIONS

PDS dentists provided fewer simple periodontal treatments than their GDS counterparts. There was no difference in the oral health of patients treated under either system. Although there was some evidence of a difference in attitude between GDS and PDS dentists towards charging and claiming for simple periodontal treatment, there was no uniformity of opinion within either group. There would appear to be a number of complex factors impacting upon decisions to treat or monitor dental conditions.

Hypothesis: huntingtin may function in membrane association and vesicular traffickingThis paper is one of a selection of papers published in this Special Issue, entitled CSBMCB — Membrane Proteins in Health and Disease

Huntington’s disease is a progressive neurodegenerative genetic disorder that is caused by a CAG triplet-repeat expansion in the first exon of the IT15 gene. This CAG expansion results in polyglutamine expansion in the 350 kDa huntingtin protein. The exact function of huntingtin is unknown. Understanding the pathological triggers of mutant huntingtin, and distinguishing the cause of disease from downstream effects, is critical to designing therapeutic strategies and defining long- and short-term goals of therapy. Many studies that have sought to determine the functions of huntingtin by determining huntingtin’s protein–protein interactions have been published. Through these studies, huntingtin has been seen to interact with a large number of proteins, and is likely a scaffolding protein for protein–protein interactions. Recently, using imaging, integrative proteomics, and cell biology, huntingtin has been defined as a membrane-associated protein, with activities related to axonal trafficking of vesicles and mitochondria. These functions have also been attributed to some huntingtin-interacting proteins. Additionally, discoveries of a membrane association domain and a palmitoylation site in huntingtin reinforce the fact that huntingtin is membrane associated. In Huntington’s disease mouse and fly models, axonal vesicle trafficking is inhibited, and lack of proper uptake of neurotrophic factors may be an important pathological trigger leading to striatal cell death in Huntington’s disease. Here we discuss recent advances from many independent groups and methodologies that are starting to resolve the elusive function of huntingtin in vesicle transport, and evidence that suggests that huntingtin may be directly involved in membrane interactions.