Cas9 is mostly orthogonal to human systems of DNA break sensing and repair

CRISPR/Cas9 system is а powerful gene editing tool based on the RNA-guided cleavage of target DNA. The Cas9 activity can be modulated by proteins involved in DNA damage signalling and repair due to their interaction with double- and single-strand breaks (DSB and SSB, respectively) generated by wild-type Cas9 or Cas9 nickases. Here we address the interplay between Streptococcus pyogenes Cas9 and key DNA repair factors, including poly(ADP-ribose) polymerase 1 (SSB/DSB sensor), its closest homolog poly(ADP-ribose) polymerase 2, Ku antigen (DSB sensor), DNA ligase I (SSB sensor), replication protein A (DNA duplex destabilizer), and Y-box binding protein 1 (RNA/DNA binding protein). None of those significantly affected Cas9 activity, while Cas9 efficiently shielded DSBs and SSBs from their sensors. Poly(ADP-ribosyl)ation of Cas9 detected for poly(ADP-ribose) polymerase 2 had no apparent effect on the activity. In cellulo, Cas9-dependent gene editing was independent of poly(ADP-ribose) polymerase 1. Thus, Cas9 can be regarded as an enzyme mostly orthogonal to the natural regulation of human systems of DNA break sensing and repair.

[Mechanisms of the Specificity of the CRISPR/Cas9 System in Genome Editing]

The CRISPR/Cas9 system, which was discovered recently, utilizes nucleases targeted by sequence complementarity and is originally intended to protect bacteria from foreign genetic elements. The system provided a convenient tool for manipulating the genomes of living cells. The CRISPR/Cas9 genomic editing technology moved beyond the laboratory and already found application in biotechnology and agriculture. However, off-target activity of the CRISPR/Cas9 system can cause oncogenic mutations and thus limits its use for genome editing in human cells for medical purposes. Many studies are therefore aimed at developing variants of the CRISPR/Cas9 system with improved accuracy. The review considers the mechanisms of precise and erroneous actions of Cas9 RNA-guided nuclease, natural and artificial variants of RNA-targeted nucleases, possibilities to modulate their specificity through guide RNA modifications, and other approaches to increasing the accuracy of the CRISPR/Cas9 system in genome editing.

[Sudden cardiac death and polymorphism of genes-candidates of cardiovascular diseases]

Aim of the study was to elucidate genetic markers associated with elevated risk of sudden cardiac death (SCD). We collected autopsy material during 1999 - 2001 in a process of forensic medical pathologo-anatomical examination of corpses of 182 men who had died suddenly in Octyabrsky district of Novosibirsk in the age of 25 - 64 years (mean age 53,6 +/- 7,9 years). We studied polymorphisms of the following genes: angiotensin converting enzyme - , glycoprotein IIb/IIIa - GPIIb/IIIa, alpha2b adrenoreceptor - ADRA2B, beta(1)-adrenoreceptor - ADRB1. Control comprised samples of population of men aged 25 - 35 and 55 - 64 years from the same district of Novosibirsk examined within framework of international WHO project MONICA. Comparison of frequencies of genotypes of polymorphism A1/A2 of GPIIb/IIIa gene in combined sample of population and group with SCD revealed in SCD group lowering of portion of A2/A2 homozygotes (5.0 and 1.2%, respectively, =0.029) and elevation of portion of A1/A2 heterozygotes (18.7 and 28.3%, respectively, =0.027). Odds ratio for a heterozygote to enter SCD group was 1.71 (95% confidence interval 1.0 to 2.77). Comparison of frequencies of genotypes and alleles of polymorphism A145G of ADRB1 gene in combined sample of population and group with SCD did not reveal any difference. Comparison of frequencies of polymorphism I/D of ACE gene in combined sample of population and group with SCD revealed significant lowering of frequencies of genotype I/I in SCD group (22.0 and 13.8%, respectively, p=0.033). There were no significant differences between SCD group and control in frequencies of studied polymorphism of alpha2b-adrenoreceptor gene.