DNA loop extrusion by human cohesin.

Eukaryotic genomes are folded into loops and topologically associating domains, which contribute to chromatin structure, gene regulation, and gene recombination. These structures depend on cohesin, a ring-shaped DNA-entrapping adenosine triphosphatase (ATPase) complex that has been proposed to form loops by extrusion. Such an activity has been observed for condensin, which forms loops in mitosis, but not for cohesin.

Rapid movement and transcriptional re-localization of human cohesin on DNA.

The spatial organization, correct expression, repair, and segregation of eukaryotic genomes depend on cohesin, ring-shaped protein complexes that are thought to function by entrapping DNA It has been proposed that cohesin is recruited to specific genomic locations from distal loading sites by an unknown mechanism, which depends on transcription, and it has been speculated that cohesin movements along DNA could create three-dimensional genomic organization by loop extrusion. However, whether cohesin can translocate along DNA is unknown. Here, we used single-molecule imaging to show that cohesin can diffuse rapidly on DNA in a manner consistent with topological entrapment and can pass over some DNA-bound proteins and nucleosomes but is constrained in its movement by transcription and DNA-bound CCCTC-binding factor (CTCF).

Abdominal ultrasound in the intensive care unit: a 3-year survey on 400 patients.

Objective: This study analyzed 400 ultrasound examinations in the ICU to assess the indications of this imaging modality.

Design And Setting: Retrospective analysis on prospectively collected data on 400 patients in a tertiary care hospital.

Patients And Participants: The observational, prospective, clinical study examined 400 bedside abdominal ultrasound examinations performed in the ICU, of which 2% were performed emergently, 56% urgently, and 42% electively.