Summary The histone H2A-H2B heterodimer is an integral component of the nucleosome. The cellular localization and deposition of H2A-H2B into chromatin is regulated by numerous factors including histone chaperones such as Nucleosome Assembly Protein 1 (Nap1). We use hydrogen-deuterium exchange coupled to mass spectrometry to characterize H2A-H2B and Nap1. Unexpectedly, we find that at low ionic strength the α-helices in H2A-H2B are frequently sampling partially disordered conformations, and that binding to Nap1 reduces this conformational sampling. We identify the interaction surface between H2A-H2B and Nap1, and confirm its relevance both in vitro and in vivo. We show that two copies of H2A-H2B bound to a Nap1 homodimer form a tetramer with contacts between H2B chains similar to those in the four-helix bundle structural motif. The organization of the complex reveals that Nap1 competes with histone-DNA and inter-histone interactions observed in the nucleosome, thereby regulating the availability of histones for chromatin assembly.

BackgroundAccelerometer-based activity monitoring is a promising new tool in veterinary medicine used to objectively assess activity levels in dogs. To date, it is unknown how device orientation, attachment method, and attachment of a leash to the collar holding an accelerometer affect canine activity data. It was our goal to evaluate whether attachment methods of accelerometers affect activity counts. Eight healthy, client-owned dogs were fitted with two identical neck collars to which two identical activity monitors were attached using six different methods of attachment. These methods of attachment evaluated the use of a protective case, positioning of the activity monitor and the tightness of attachment of the accelerometer. Lastly, the effect of leash attachment to the collar was evaluated. For trials where the effect of leash attachment to the collar was not being studied, the leash was attached to a harness. Activity data obtained from separate monitors within a given experiment were compared using Pearson correlation coefficients and across all experiments using the Kruskal-Wallis Test.ResultsThere was excellent correlation and low variability between activity monitors on separate collars when the leash was attached to a harness, regardless of their relative positions. There was good correlation when activity monitors were placed on the same collar regardless of orientation. There were poor correlations between activity monitors in three experiments: when the leash was fastened to the collar that held an activity monitor, when one activity monitor was housed in the protective casing, and when one activity monitor was loosely zip-tied to the collar rather than threaded on using the provided metal loop. Follow-up, pair-wise comparisons identified the correlation associated with these three methods of attachment to be statistically different from the level of correlation when monitors were placed on separate collars.ConclusionsWhile accelerometer-based activity monitors are useful tools to objectively assess physical activity in dogs, care must be taken when choosing a method to attach the device. The attachment of the activity monitor to the collar should utilize a second, dedicated collar that is not used for leash attachment and the attachment method should remain consistent throughout a study period.

Extracapsular stabilization and TPLO are the most commonly employed surgical procedures in the surveyed population; dog size and activity level (but not age) are the major factors influencing treatment decisions.

Veterinary resident training in minimally invasive surgery is currently inconsistent and depends on innate psychomotor skills. Simulation training has been shown to effectively increase basic skills, but demonstration of simulation training effects on advanced skills in the operating room is sparse. We aimed to determine if simulation-trained novice surgeons were able to perform laparoscopic suture ligation in live dogs. Three novice laparoscopic surgeons underwent a 12-session simulation training program with subsequent laparoscopic skills testing to demonstrate competency. The median skills scores of trainees and of one experienced surgeon were 417 and 472, respectively. Eighteen healthy client-owned (shelter) dogs were operated on by four surgeons: one experienced American College of Veterinary Surgeons (ACVS) diplomate, two novice ACVS residents, and one novice ACVS diplomate. Laparoscopic ovariectomy was performed with suture ligation of the ovarian pedicles. Successful surgery was defined as no evidence of ovarian vessel bleeding after transection of the pedicles. Simulation-trained novices performed successful suture-ligated ovariectomies in 11/13 dogs (85%), and the experienced surgeon in 5/5 (100%) dogs. Median total ligation time was 30 minutes (range: 17–57), which was not different among surgeons ( p = .118). Median total surgery time was 105 minutes (range: 69–156) for novices and 89 minutes (range: 65–99) for the experienced surgeon ( p = .038). Extensive simulation training including suturing may contribute toward surgery residents being able to perform complex laparoscopic procedures. These results need to be confirmed in larger numbers of trainees.