AID-driven deletion causes immunoglobulin heavy chain locus suicide recombination in B cells

Remodeling of immunoglobulin genes by activation-induced deaminase (AID) is required for affinity maturation and class-switch recombination in mature B lymphocytes. In the immunoglobulin heavy chain locus, these processes are predominantly controlled by the 3' cis-regulatory region. We now show that this region is transcribed and undergoes AID-mediated mutation and recombination around phylogenetically conserved switchlike DNA repeats. Such recombination, which we term locus suicide recombination, deletes the whole constant region gene cluster and thus stops expression of the immunoglobulin of the B cell surface, which is critical for B cell survival. The frequency of this event is approaching that of class switching and makes it a potential regulator of B cell homeostasis.     

Detection of bovine leukemia virus in blood and milk by nested and real-time polymerase chain reactions.

Concerns about retroviruses in livestock and products derived from them have necessitated the development of tests to detect the bovine leukemia virus (BLV) in blood and milk from cattle. Dairy cattle (n = 101) from 5 different geographical areas were used for this study. A nested polymerase chain reaction (PCR) identified 98% of BLV seropositive cattle (n = 80) from blood and 65% from milk, whereas real-time PCR detected 94% of BLV seropositive cattle from blood and 59% from milk. Bovine leukemia virus was also detected by PCR in approximately 10% of seronegative cattle (n = 21), most likely because of early detection before seroconversion.     

Comparison of two DNA extractions and nested PCR, real-time PCR, a new commercial PCR assay, and bacterial culture for detection of Mycobacterium avium subsp. paratuberculosis in bovine feces.

In this study, 5 combinations of 2 DNA extractions and 3 polymerase chain reaction (PCR) techniques were compared with culture for the detection of Mycobacterium paratuberculosis directly from bovine feces. These combinations included a new commercial extraction technique combined with a commercial PCR/Southern blot technique, nested PCR (nPCR), or real-time PCR, and a university-developed extraction combined with nPCR or real-time PCR. Four of the 5 combinations had statistically similar sensitivities between 93% and 100% and specificity between 95% and 100%, when compared with culture results from 63 bovine fecal samples. These results indicated that using a commercial extraction with a commercial PCR/Southern blot, nPCR, or real-time PCR, or a university-developed extraction with real-time PCR would result in similar sensitivities to culture for the identification of M. paratuberculosis from bovine feces and are valid alternatives to culture.     

Hematology, plasma chemistry, serology, and Chlamydophila status of the waved albatross (Phoebastria irrorata) on the Galapagos Islands.

Venipuncture was performed on 50 adult, free-ranging waved albatrosses (Phoebastria irrorata) on Espa?ola, Galapagos Islands, Ecuador, to establish hematologic and plasma biochemistry reference ranges and to determine the prevalence of exposure to important domestic avian pathogens. Weights and plasma creatine phosphokinase activities differed significantly between males and females. Serum was tested for evidence of exposure to avian influenza, avian paramyxoviruses 1, 2, and 3, avian cholera, adenovirus groups 1 and 2, avian encephalomyelitis, Marek's disease, infectious bursal disease, and infectious bronchitis virus (Connecticut and Massachusetts strains). Of 44 birds, 29 (66%) seroreacted to adenovirus group 1, and four seroreacted to avian encephalomyelitis. Cloacal swabs were negative for Chlamydophila psittaci DNA.     

A VACUUM-FORMABLE MATTRESS FOR VETERINARY RADIOTHERAPY POSITIONING: COMPARISON WITH CONVENTIONAL METHODS

This prospective study was undertaken to compare the positioning repeatability and setup time of a rigid immobilization device (Vac-Lok mattress) to conventional positioning methods (sandbags, tape, foam wedges) in the clinical veterinary radiotherapy setting. Positioning repeatability was determined by using port films to verify appropriate patient positioning. Setup time was determined by recording the time required to set up each patient using each positioning method. Sixty-seven patients receiving radiotherapy were positioned using both the Vac-Lok mattresses and conventional positioning methods during their treatments. Seventy-eight total sites were treated. Forty-eight were treated daily (Monday through Friday, 2 to 4 weeks) and 30 were treated once weekly (4 weeks). Patients were grouped according to the site treated: head (29), neck/body (24), and limb (25). Vac-Lok mattresses were similar to conventional means in positioning repeatability and setup time. Vac-Lok mattresses are potentially advantageous in specific situations, including use during pre-radiotherapy tumor imaging. These mattresses are not recommended for distal limb positioning.     

Head and facial wounds in dogs and cats.

Injuries to the head and facial area are common in small animal surgery. Although many of the injuries at first may seem formidable, most can be repaired using basic reconstructive surgery procedures. The excel-lent blood supply in this area and the availability of local tissues provide many options for repairing most wounds. This article describes the indications and techniques for reconstructing wounds in this area.     

ANATOMIC REFERENCE FOR COMPUTED TOMOGRAPHY OF THE HEAD OF THE FOAL

The purpose of this study was to produce an anatomic reference for computed tomography (CT) of the head of the foal for use by radiologists, clinicians, and veterinary students. The head from each of 2 foals, euthanized for reasons unrelated to head pathology, was removed and prepared for CT scanning. Using a third-generation CT scanner, 5-mm contiguous transverse images were acquired. The heads were then frozen and sectioned using a band saw, with the cuts matched as closely as possible to the CT slices. The anatomic sections were photographed and radiographed. The radiographs and anatomic photographs were digitized and matched with the corresponding CT image. Each CT image was compared with its corresponding radiographic and anatomic section to assist in the accurate identification of specific structures. Clinically relevant structures were identified and labeled in corresponding images (CT, anatomic slice, and radiograph of slice). Only structures identified in the CT image were labeled in 1 of the other 2 images. Sagittal (reference) images of the horse's head were reconstructed from the transverse CT scans, and were used to indicate the level from which each of the transverse images was obtained. Corresponding labeled images were then formatted together with a legend for identification of specific anatomic structures.     

The successional status of tropical rainforest tree species is associated with differences in leaf carbon isotope discrimination and functional traits

We characterised the among species variability in leaf gas exchange and morphological traits under controlled conditions of seedlings of 22 tropical rainforest canopy species to understand the origin of the variability in leaf carbon isotope discrimination (Δ) among species with different growth and dynamic characteristics (successional gradient). Our results first suggest that these species pursue a consistent strategy in terms of Δ throughout their ontogeny (juveniles grown here versus canopy adult trees from the natural forest). Second, leaf Δ was negatively correlated with WUE and N, and positively correlated with g_s, but among species differences in Δ were mainly explained by differences in WUE. Finally, species belonging to different successional groups display distinct leaf functional and morphological traits. We confirmed that fast growing early successional species maximise carbon assimilation with high stomatal conductance. In contrast, fast and slow growing late successional species are both characterised by low carbon assimilation values, but by distinct stomatal conductance and leaf morphological features. Along the successional gradient, these differences result in much lower Δ for the intermediate species (i.e. fast growing late successional) as compared to the two other groups.     

Genetic parameters for yield in macadamia

Broad-sense heritability, and genetic and phenotypic correlations were estimated for yield (nut-in-shell; kernel yield; and net present value of crop) per tree in macadamia to 10 years after planting from a trial of 40 cultivars replicated over 4locations. In addition, canopy width at 10years of age was measured and used to calculate yield efficiency as yield per square metre of projected canopy area. Stem girth above the graft union was also measured. There was a low broad-sense heritability (0.06 < H <0.22) and correlation of cultivars across locations (r _gloc = 0.14–0.52) for yield per tree. However, the genetic correlation of cumulative yield was high among 3 of the 4locations (g ≥ 0.75), suggesting the higher genetic variance at Rockhampton was the main cause of the genotype by environmental interaction. Heritability was higher for canopy width (H = 0.28) and yield efficiency (H ≈ 0.47) and cultivar performance was highly correlated across locations (r _gloc ≈ 0.70) for these traits. There was a strong genetic correlation (r _g ≥ 0.90) between cumulative yield per tree of cultivars to 7 years and cumulative yield per tree to 10 years. Genetic correlation among all measures of yield per tree were high (r _g ≥ 0.73), but there was no genetic correlation with canopy width. On the other hand, small cultivars tended to have higher yield efficiency (r _g <–0.62). There was also a slight negative correlation between nut-in-shell yield per tree and kernel recovery (r _g = –0.37). These results suggest the use of family information and index selection may improve the efficiency of selection and breeding programs in macadamia. This revised version was published online in July 2006 with corrections to the Cover Date.     

Incremental crop tolerance to weeds: A measure for selecting competitive ability in Australian wheats

Total reliance on herbicides for weed control is unsustainable with the spread of herbicide resistance and the environmental need to reduce pesticide use. Strongly competitive wheat crops that have high tolerance to weed pressure and therefore maintain high yields in the presence of weeds are a low-cost option for reducing dependence on herbicides. We examined the feasibility of selecting for wheat tolerance to weeds by crossing varieties differing for traits associated with competitiveness. Competitive ability and yield potential must be treated as separate traits for selection. Current measures of crop tolerance to weed competition do not separate the two traits so that selection based on these measures is often synonymous with selection for yield potential rather than pure tolerance. We propose a new measure, termed Incremental Crop Tolerance (ICT) that reflects the incremental yield difference between genotypes associated with tolerance, over and above differences in underlying yield potential.