The enrichment of mobile genetic elements in heterochromatin may be due, in part, to targeted integration. The chromoviruses are Ty3/gypsy retrotransposons with chromodomains at their integrase C termini. Chromodomains are logical determinants for targeting to heterochromatin, because the chromodomain of heterochromatin protein 1 (HP1) typically recognizes histone H3 K9 methylation, an epigenetic mark characteristic of heterochromatin. We describe three groups of chromoviruses based on amino acid sequence relationships of their integrase C termini. Genome sequence analysis indicates that representative chromoviruses from each group are enriched in gene-poor regions of the genome relative to other retrotransposons, and when fused to fluorescent marker proteins, the chromodomains target proteins to specific subnuclear foci coincident with heterochromatin. The chromodomain of the fungal element, MAGGY, interacts with histone H3 dimethyl-and trimethyl-K9, and when the MAGGY chromodomain is fused to integrase of the Schizosaccharomyces pombe Tf1 retrotransposon, new Tf1 insertions are directed to sites of H3 K9 methylation. Repetitive sequences such as transposable elements trigger the RNAi pathway resulting in their epigenetic modification. Our results suggest a dynamic interplay between retrotransposons and heterochromatin, wherein mobile elements recognize heterochromatin at the time of integration and then perpetuate the heterochromatic mark by triggering epigenetic modification.[Supplemental material is available online at www.genome.org.] (Girard et al. 2006;Grivna et al. 2006;Vagin et al. 2006). Mobile element insertions that decorate eukaryotic genomes, therefore, frequently define unique chromatin domains. Whereas the genetic consequences of transposition in terms of mutation and genome rearrangement have long been recognized, the biological consequences of their epigenetic marks, which include effects on gene expression and the formation of heterochromatin, are only beginning to be appreciated (Slotkin and Martienssen 2007).Underlying the genetic and epigenetic impact of mobile elements is integration site choice. Although forces such as selection or recombination contribute to the nonrandom distribution of mobile elements in eukaryotic genomes, an increasing number of studies indicate that many mobile elements target integration to specific chromosomal sites (Bushman 2003). For some elements, target sites are determined by recognizing specific DNA sequences, whereas for others, including several retrotransposons and retroviruses, chromatin impacts target site choice. The Ty1 and Ty3 retrotransposons of Saccharomyces cerevisiae, for example, integrate near sites of RNA polymerase III (pol III) transcription by recognizing pol III transcription complexes or chromatin states associated with pol III transcription (Yieh et al. 2000(Yieh et al. , 2002Bachman et al. 2005;Mou et al. 2006). The Tf1 retrotransposon of Schizosaccharomyces pombe recognizes certain RNA polymerase II (pol II) promoters (Singleton and L...

Although the original US porcine epidemic diarrhea virus (PEDV) was confirmed as highly virulent by multiple studies, the virulence of spike-insertion deletion (S-INDEL) PEDV strains is undefined. In this study, 3–4 day-old conventional suckling piglets were inoculated with S-INDEL PEDV Iowa106 (4 pig litters) to study its virulence. Two litters of age-matched piglets were inoculated with either the original US PEDV PC21A or mock as positive and negative controls, respectively. Subsequently, all pigs were challenged with the original US PEDV PC21A on 21–29 days post-inoculation (dpi) to assess cross-protection. All S-INDEL Iowa106- and the original US PC21A-inoculated piglets developed diarrhea. However, the severity of clinical signs, mortality (0–75%) and fecal PEDV RNA shedding titers varied among the four S-INDEL Iowa106-inoculated litters. Compared with the original PC21A, piglets euthanized/died acutely from S-INDEL Iowa106 infection had relatively milder villous atrophy, lower antigen scores and more limited intestinal infection. Two of four S-INDEL Iowa106-infected sows and the original PC21A-infected sow showed anorexia and watery diarrhea for 1–4 days. After the original PC21A challenge, a subset (13/16) of S-INDEL Iowa106-inoculated piglets developed diarrhea, whereas all (5/5) and no (0/4) pigs in the mock and original PC21A-inoculated pigs had diarrhea, respectively. Our results suggest that the virulence of S-INDEL PEDV Iowa106 was less than the original US PEDV PC21A in suckling pigs, with 100% morbidity and 18% (6/33) overall (0–75%) mortality in suckling pigs depending on factors such as the sow’s health and lactation and the piglets’ birth weight. Prior infection by S-INDEL Iowa106 provided partial cross-protection to piglets against the original PC21A challenge at 21–29 dpi.

Porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV) are economically important swine enteropathogenic coronaviruses. These two viruses belong to two distinct species of the Alphacoronavirus genus within Coronaviridae and induce similar clinical signs and pathological lesions in newborn piglets, but they are presumed to be antigenically distinct. In the present study, two-way antigenic cross-reactivity examinations between the prototype PEDV CV777 strain, three distinct U.S. PEDV strains (the original highly virulent PC22A, S indel Iowa106, and S 197del PC177), and two representative U.S. TGEV strains (Miller and Purdue) were conducted by cell culture immunofluorescent (CCIF) and viral neutralization (VN) assays. None of the pig TGEV antisera neutralized PEDV and vice versa. One-way cross-reactions were observed by CCIF between TGEV Miller hyperimmune pig antisera and all PEDV strains. Enzyme-linked immunosorbent assays, immunoblotting using monoclonal antibodies and Escherichia coli-expressed recombinant PEDV and TGEV nucleocapsid (N) proteins, and sequence analysis suggested at least one epitope on the N-terminal region of PEDV/TGEV N protein that contributed to this crossreactivity. Biologically, PEDV strain CV777 induced greater cell fusion in Vero cells than did U.S. PEDV strains. Consistent with the reported genetic differences, the results of CCIF and VN assays also revealed higher antigenic variation between PEDV CV777 and U.S. strains. IMPORTANCEEvidence of antigenic cross-reactivity between porcine enteric coronaviruses, PEDV and TGEV, in CCIF assays supports the idea that these two species are evolutionarily related, but they are distinct species defined by VN assays. Identification of PEDV-or TGEV-specific antigenic regions allows the development of more specific immunoassays for each virus. Antigenic and biologic variations between the prototype and current PEDV strains could explain, at least partially, the recurrence of PEDV epidemics. Information on the conserved antigenicity among PEDV strains is important for the development of PEDV vaccines to protect swine from current highly virulent PEDV infections. C oronaviruses (CoVs) are spherical, enveloped RNA viruses causing enteric, respiratory, and generalized diseases in humans and animals. Mature CoV virions contain three major structural proteins, spike (S), membrane (M), and envelope (E), in their envelopes, of which the S and M proteins are glycosylated. The nucleocapsid (N) protein is the most abundant viral protein and is associated with the positive-stranded RNA genome (1). Porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV) cause enteritis in pigs of all ages worldwide (2, 3). Both belong to the Coronaviridae family, Coronavirinae subfamily, and Alphacoronavirus genus (4). PEDV and TGEV are mainly transmitted by the fecal-oral route. Airborne transmission of PEDV was recently confirmed experimentally in a single study (5) but not in a prior study (6). The clinical s...

No abstract

Eukaryotic genomes are full of long terminal repeat (LTR) retrotransposons. Although most LTR retrotransposons have common structural features and encode similar genes, there is nonetheless considerable diversity in their genomic organization, reflecting the different strategies they use to proliferate within the genomes of their hosts. The electronic version of this article is the complete one and can be found online at