A scalable CRISPR/Cas9-based fluorescent reporter assay to study DNA double-strand break repair choice

Double-strand breaks (DSBs) are the most toxic type of DNA lesions. Cells repair these lesions using either end protection- or end resection-coupled mechanisms. To study DSB repair choice, we present the Color Assay Tracing-Repair (CAT-R) to simultaneously quantify DSB repair via end protection and end resection pathways. CAT-R introduces DSBs using CRISPR/Cas9 in a tandem fluorescent reporter, whose repair distinguishes small insertions/deletions from large deletions. We demonstrate CAT-R applications in chemical and genetic screens. First, we evaluate 21 compounds currently in clinical trials which target the DNA damage response. Second, we examine how 417 factors involved in DNA damage response influence the choice between end protection and end resection. Finally, we show that impairing nucleotide excision repair favors error-free repair, providing an alternative way for improving CRISPR/Cas9-based knock-ins. CAT-R is a high-throughput, versatile assay to assess DSB repair choice, which facilitates comprehensive studies of DNA repair and drug efficiency testing. Cells employ different repair pathways to repair DNA double strand breaks. Here, the authors develop a CRISPR/Cas9-dependent method to study choices in DNA repair called the Color Assay Tracing-Repair (CAT-R) which simultaneously measure outcomes of DSB repair via end-protection and end-resection pathways

Identification of a Ninein (NIN) mutation in a family with spondyloepimetaphyseal dysplasia with joint laxity (leptodactylic type)-like phenotype

Spondyloepimetaphyseal dysplasia with joint laxity-leptodactylic type (SEMDJL2) is an autosomal dominant skeletal dysplasia which is characterized by midface hypoplasia, short stature, joint laxity with dislocations, genua valga, progressive scoliosis, and slender fingers. Recently, heterozygous missense mutations in KIF22, a gene which encodes a member of the kinesin-like protein family, have been identified in sporadic as well as familial cases of SEMDJL2. In the present study homozygosity mapping and whole-exome sequencing were combined to analyze a consanguineous family with a phenotype resembling SEMDJL2. We identified homozygous missense mutations in the two nearby genes NIN (Ninein) and POLE2 (DNA polymerase epsilon subunit B) which segregate with the disease in the family and were not present in 500 healthy control individuals and in the 1094 control individuals contained within the 1000-genomes database. We present several lines of evidence that mutant Ninein is most likely causative for the SEMDJL2-like phenotype. The centrosomal protein NIN shows a functional relationship with KIF22 and other proteins associated with chromosome congression/movement, centrosomal function, and ciliogenesis, which have been associated with skeletal dysplasias. Moreover, compound heterozygous missense mutations at more N-terminal positions of Ninein have very recently been identified in a family with microcephalic primordial dwarfism. Together with the present report this strongly supports a fundamental role of Ninein in skeletal development. (C) 2013 Elsevier B.V. All rights reserved

Genome-wide Screens Implicate Loss of Cullin Ring Ligase 3 in Persistent Proliferation and Genome Instability in TP53-Deficient Cells

TP53 deficiency is the most common alteration in cancer; however, this alone is typically insufficient to drive tumorigenesis. To identify genes promoting tumorigenesis in combination with TP53 deficiency, we perform genome-wide CRISPR-Cas9 knockout screens coupled with proliferation and transformation assays in isogenic cell lines. Loss of several known tumor suppressors enhances cellular proliferation and transformation. Loss of neddylation pathway genes promotes uncontrolled proliferation exclusively in TP53-deficient cells. Combined loss of CUL3 and TP53 activates an oncogenic transcriptional program governed by the nuclear factor kappa B (NF-kappa B), AP-1, and transforming growth factor beta (TGF-beta) pathways. This program maintains persistent cellular proliferation, induces partial epithelial to mesenchymal transition, and increases DNA damage, genomic instability, and chromosomal rearrangements. Our findings reveal CUL3 loss as a key event stimulating persistent proliferation in TP53-deficient cells. These findings may be clinically relevant, since TP53-CUL3-deficient cells are highly sensitive to ataxia telangiectasia mutated (ATM) inhibition, exposing a vulnerability that could be exploited for cancer treatment

Chromothripsis followed by circular recombination drives oncogene amplification in human cancer

Seismic amplifications arise from several cycles of circular recombination of circular extrachromosomal DNA formed as a result of chromothripsis. The process provides a mechanism for oncogene amplification in a number of different human tumor types. The mechanisms behind the evolution of complex genomic amplifications in cancer have remained largely unclear. Using whole-genome sequencing data of the pediatric tumor neuroblastoma, we here identified a type of amplification, termed 'seismic amplification', that is characterized by multiple rearrangements and discontinuous copy number levels. Overall, seismic amplifications occurred in 9.9% (274 of 2,756) of cases across 38 cancer types, and were associated with massively increased copy numbers and elevated oncogene expression. Reconstruction of the development of seismic amplification showed a stepwise evolution, starting with a chromothripsis event, followed by formation of circular extrachromosomal DNA that subsequently underwent repetitive rounds of circular recombination. The resulting amplicons persisted as extrachromosomal DNA circles or had reintegrated into the genome in overt tumors. Together, our data indicate that the sequential occurrence of chromothripsis and circular recombination drives oncogene amplification and overexpression in a substantial fraction of human malignancies