Understanding the structural organization of eukaryotic chromatin and its control of gene expression represents one of the most fundamental and open challenges in modern biology. Recent experimental advances have revealed important characteristics of chromatin in response to changes in external conditions and histone composition, such as the conformational complexity of linker DNA and histone tail domains upon compact folding of the fiber. In addition, modeling studies based on highresolution nucleosome models have helped explain the conformational features of chromatin structural elements and their interactions in terms of chromatin fiber models. This minireview discusses recent progress and evidence supporting structural heterogeneity in chromatin fibers, reconciling apparently contradictory fiber models.The 3 billion DNA base pairs of the human genome are densely packed within eukaryotic chromatin, a nucleoprotein complex in which the DNA is wrapped around nucleosomes (see Fig. 1). Nucleosomes and higher order chromatin structures serve essential cellular functions, including condensation of meters-long genomic DNA by several orders of magnitude to enable its packaging into the micrometer-sized cell nucleus and regulation of DNA-directed processes, such as transcription, replication, recombination, and repair through local and dynamic unfolding of chromatin.Whether the higher order structure of nuclear chromatin is organized into a hierarchy of folding states (1) or non-hierarchical fractal geometry (2), previous landmark studies established the nucleosome as the repeating unit of chromatin (Figs.

Bovine enteric caliciviruses (BEC) are associated with diarrhea in young calves. The BEC strains detected in Europe form a third genogroup within the genus "Norwalk-like viruses" (NLV) of the family Caliciviridae. In this report, we present sequence, clinical, and histological data characterizing a novel enteropathogenic BEC strain, NB, detected in fecal specimens from calves in the United States. The complete RNA genome of the NB virus is 7,453 bases long and is organized into two open reading frames (ORFs). ORF-1 is 2,210 amino acids long and encodes a large nonstructural polyprotein contiguous with the major capsid protein (VP1), similar to the lagoviruses and "Sapporo-like viruses" (SLV). The conserved calicivirus motifs were identified in the nonstructural proteins. ORF-2 is located at the 3 end of the genome and encodes a small basic protein (VP2) of 225 amino acids. The 5 and 3 untranslated regions are 74 and 67 bases long, respectively. Among caliciviruses, NB virus shows amino acid identities of 14.1 to 22.6% over the entire ORF-1 nonstructuralprotein sequence with NLV, SLV, vesivirus, and lagovirus strains, while the overall sequence identity of the complete NB VP-1 with other caliciviruses is low, varying between 14.6 and 26.7%. Phylogenetic analysis of the complete VP1 protein, including strains from all four calicivirus genera, showed the closest grouping of NB virus to be with viruses in the genus Lagovirus, which cause liver infections and systemic hemorrhage in rabbits. In gnotobiotic calves, however, NB virus elicited only diarrhea and intestinal lesions that were most severe in the upper small intestine (duodenum and jejunum), similar to the NLV BEC strains. The tissues of major organs, including the lung, liver, kidney, and spleen, had no visible microscopic lesions.

No abstract

First identified in 2012 in a surveillance study in Hong Kong, porcine deltacoronavirus (PDCoV) is a proposed member of the genus Deltacoronavirus of the family Coronaviridae. In February of 2014, PDCoV was detected in pigs with clinical diarrheal symptoms for the first time in the USA. Since then, it has been detected in more than 20 states in the USA and in other countries, including Canada, South Korea, and mainland China. So far, histological lesions in the intestines of pigs naturally infected with PDCoV under field conditions have not been reported. In this report, we describe the characteristic histological lesions in the small intestine that were associated with PDCoV infection, as evidenced by detection of viral nucleic acid by RT-PCR. In addition, we performed genomic analysis to determine the genetic relationship of all PDCoV strains from the four countries. We found that PDCoV mainly caused histological lesions in the small intestines of naturally infected piglets. Sequence analysis demonstrated that the PDCoV strains of different countries are closely related and shared high nucleotide sequence similarity; however, deletion patterns in the spike and 3' untranslated regions are different among the strains from mainland China, Hong Kong, the USA, and South Korea. Our study highlights the fact that continual surveillance is needed to trace the evolution of this virus.

This report describes the use of polymerase chain reaction and DNA in situ hybridization to diagnose Aleutian mink disease parvovirus DNA in various tissue specimens from 2 companion striped skunks. Clinical, laboratory, and microscopic findings also support a clinical diagnosis of Aleutian disease in these mink.

No abstract

Helcococcus ovis is a newly established species in the genus Helcococcus. The clinical significance of this organism in sheep has not been reported. In the current report, isolation of H. ovis from a 6-month-old mixed-breed ewe lamb that died of respiratory disease is described. Pathologic examination revealed severe, focally extensive, chronic necrotizing pleuritis with intralesional coccobacilli and mild, multifocal, subacute mucopurulent bronchopneumonia, indicating a bacterial etiology. A Gram-positive bacterium was isolated in heavy growth from the lung tissue. DNA sequence analysis on the 16S rDNA gene demonstrated that the isolate was H. ovis. To the authors' knowledge, this is the first report of isolation of H. ovis associated with infection in sheep with pleuritis and bronchopneumonia.

Porcine epidemic diarrhea virus (PEDV) was first recognized in pigs in the United States (US) in May 2013. Since then, the virus has spread to over 30 states and caused significant economic losses in the US swine industry due to the high mortality in newborn piglets less than 2 weeks of age. A mild-variant strain OH851 of PEDV in the US was first reported in January 2014. Here, we report histological changes in the small intestines of five piglets infected with the variant strain OH851 of PEDV. The lesions observed were milder, compared to the US classical strain of PEDV. Our study, for the first time, reports the histological lesions caused by the variant PEDV OH851 strain from a field case. In addition, genomic characterization demonstrated that US variant PEDV is more closely related to European-like strains in the first 1170 nt of the 5' spike gene but to US classical PEDV strains in the remaining genome, suggesting that the variant PEDV strain may derive from a recombinant event between the US classical and European-like PEDV strains.