Microscopy-Based High-Content Screening.

Image-based screening is used to measure a variety of phenotypes in cells and whole organisms. Combined with perturbations such as RNA interference, small molecules, and mutations, such screens are a powerful method for gaining systematic insights into biological processes. Screens have been applied to study diverse processes, such as protein-localization changes, cancer cell vulnerabilities, and complex organismal phenotypes. Recently, advances in imaging and image-analysis methodologies have accelerated large-scale perturbation screens. Here, we describe the state of the art for image-based screening experiments and delineate experimental approaches and image-analysis approaches as well as discussing challenges and future directions, including leveraging CRISPR/Cas9-mediated genome engineering.

Mapping genetic interactions in human cancer cells with RNAi and multiparametric phenotyping.

Genetic interactions influence many phenotypes and can be used as a powerful experimental tool to discover functional relationships between genes. Here we describe a robust and scalable method to systematically map genetic interactions in human cancer cells using combinatorial RNAi and high-throughput imaging. Through automated, single-cell phenotyping, we measured genetic interactions across a broad spectrum of phenotypes, including cell count, cell eccentricity and nuclear area. We mapped genetic interactions of epigenetic regulators in colon cancer cells, recovering known protein complexes. Our study also revealed the prospects and challenges of studying genetic interactions in human cells using multiparametric phenotyping.

A global genetic interaction network by single-cell imaging and machine learning.

Cellular and organismal phenotypes are controlled by complex gene regulatory networks. However, reference maps of gene function are still scarce across different organisms. Here, we generated synthetic genetic interaction and cell morphology profiles of more than 6,800 genes in cultured Drosophila cells. The resulting map of genetic interactions was used for machine learning-based gene function discovery, assigning functions to genes in 47 modules. Furthermore, we devised Cytoclass as a method to dissect genetic interactions for discrete cell states at the single-cell resolution. This approach identified an interaction of Cdk2 and the Cop9 signalosome complex, triggering senescence-associated secretory phenotypes and immunogenic conversion in hemocytic cells. Together, our data constitute a genome-scale resource of functional gene profiles to uncover the mechanisms underlying genetic interactions and their plasticity at the single-cell level.

A single serine in the carboxyl terminus of cardiac essential myosin light chain-1 controls cardiomyocyte contractility in vivo.

Although it is well known that mutations in the cardiac essential myosin light chain-1 (cmlc-1) gene can cause hypertrophic cardiomyopathy, the precise in vivo structural and functional roles of cMLC-1 in the heart are only poorly understood. We have isolated the zebrafish mutant lazy susan (laz), which displays severely reduced contractility of both heart chambers. By positional cloning, we identified a nonsense mutation within the zebrafish cmlc-1 gene to be responsible for the laz phenotype, leading to expression of a carboxyl-terminally truncated cMLC-1. Whereas complete loss of cMLC-1 leads to cardiac acontractility attributable to impaired cardiac sarcomerogenesis, expression of a carboxyl-terminally truncated cMLC-1 in laz mutant hearts is sufficient for normal cardiac sarcomerogenesis but severely impairs cardiac contractility in a cell-autonomous fashion. Whereas overexpression of wild-type cMLC-1 restores contractility of laz mutant cardiomyocytes, overexpression of phosphorylation site serine 195-deficient cMLC-1 (cMLC-1(S195A)) does not reconstitute cardiac contractility in laz mutant cardiomyocytes. By contrast, introduction of a phosphomimetic amino acid on position 195 (cMLC-1(S195D)) rescues cardiomyocyte contractility, demonstrating for the first time an essential role of the carboxyl terminus and especially of serine 195 of cMLC-1 in the regulation of cardiac contractility.

In-vivo characterization of human dilated cardiomyopathy genes in zebrafish.

Due to lack of families suitable for linkage analysis and positional cloning most of the genetic causes of human dilated cardiomyopathy (DCM) are still unknown. To facilitate rapid identification and validation of novel DCM disease genes appropriate animal models are needed. To assess here for the first time whether the zebrafish is a suitable model organism to validate DCM candidate genes using antisense knock-down strategies, we inactivated in zebrafish known human DCM disease genes and then evaluated the resulting cardiac phenotypes. Consistently, knock-down of the here selected human DCM genes leads to severe heart failure with impairment of systolic cardiac function in zebrafish. Furthermore, gene-specific differences which are also seen in human DCM can be reliably reproduced in the zebrafish model. Our results indicate that the zebrafish is a suitable model organism to rapidly evaluate novel DCM disease genes in-vivo.

Measuring genetic interactions in human cells by RNAi and imaging.

Observation of how genetic interactions modulate phenotypes is a powerful method for dissecting their underlying molecular and functional networks. Whereas in model organisms genetic interaction studies are well established, systematic analysis of genetic interactions in human cells has remained challenging. Here we provide a detailed protocol for large-scale mapping of genetic interactions in human cells using a high-throughput phenotyping approach. Pairwise gene product depletion is induced by siRNA-mediated knockdown, and the resulting phenotypes are quantified by automated imaging and computational analysis to provide the basis for detecting genetic interactions between all pairs of genes tested. The whole workflow, depending on the size of the experiment, takes 3 or more weeks to complete.