Amniotes co-opt intrinsic genetic instability to protect germ-line genome integrity.

Unlike PIWI-interacting RNA (piRNA) in other species that mostly target transposable elements (TEs), >80% of piRNAs in adult mammalian testes lack obvious targets. However, mammalian piRNA sequences and piRNA-producing loci evolve more rapidly than the rest of the genome for unknown reasons. Here, through comparative studies of chickens, ducks, mice, and humans, as well as long-read nanopore sequencing on diverse chicken breeds, we find that piRNA loci across amniotes experience: (1) a high local mutation rate of structural variations (SVs, mutations ≥ 50 bp in size); (2) positive selection to suppress young and actively mobilizing TEs commencing at the pachytene stage of meiosis during germ cell development; and (3) negative selection to purge deleterious SV hotspots. Our results indicate that genetic instability at pachytene piRNA loci, while producing certain pathogenic SVs, also protects genome integrity against TE mobilization by driving the formation of rapid-evolving piRNA sequences.

Domestic chickens activate a piRNA defense against avian leukosis virus.

PIWI-interacting RNAs (piRNAs) protect the germ line by targeting transposable elements (TEs) through the base-pair complementarity. We do not know how piRNAs co-evolve with TEs in chickens. Here we reported that all active TEs in the chicken germ line are targeted by piRNAs, and as TEs lose their activity, the corresponding piRNAs erode away. We observed de novo piRNA birth as host responds to a recent retroviral invasion. Avian leukosis virus (ALV) has endogenized prior to chicken domestication, remains infectious, and threatens poultry industry. Domestic fowl produce piRNAs targeting ALV from one ALV provirus that was known to render its host ALV resistant. This proviral locus does not produce piRNAs in undomesticated wild chickens. Our findings uncover rapid piRNA evolution reflecting contemporary TE activity, identify a new piRNA acquisition modality by activating a pre-existing genomic locus, and extend piRNA defense roles to include the period when endogenous retroviruses are still infectious.

Epitope mapping of Campylobacter jejuni flagellar capping protein (FliD) by chicken (Gallus gallus domesticus) sera.

Campylobacter jejuni, a Gram-negative rod, is a zoonotic pathogen associated with human acute bacterial gastroenteritis worldwide. The flagellum, composed of more than 35 proteins, is responsible for colonization of C. jejuni in the host gastrointestinal tract as well as inducing protective antibodies against the homologous serotype. In our previous study, we demonstrated that the flagellar capping protein (FliD) is an immunodominant protein that reacted strongly to sera from field chickens. In this communication, we mapped linear immunoreactive epitopes on FliD using a set of 158 synthetic peptides of 15-mer overlapping with 11 amino acid residues on peptide microarrays with sera from field chickens. The results from peptide microarrays showed (1) no cross-reactivity of the immobilized peptides with the secondary anti-chicken antibody in the control incubation, and (2) heterogeneous patterns of sera reacting to the immobilized peptides. The peptides that reacted to more than three chicken sera and had higher averages of fluorescence units were selected for further validation by the peptide ELISA. The results showed peptides 24, 91 and 92 had relatively high reactivity and less variation among 64 individual serum samples, indicating these peptides represented the shared immunodominant epitopes on the C. jejuni FliD protein. These peptides were also recognized by sera from chickens immunized with the purified recombinant FliD protein. The findings of the specific shared linear immunodominant epitopes on FliD in this study provide a rationale for further evaluation to determine their utility as epitope vaccines covering multiple serotypes for chicken immunization, and subsequently, for providing safer poultry products for human consumption.

DIAGNOSING LYMPHOPROLIFERATIVE DISEASE VIRUS IN LIVE WILD TURKEYS (MELEAGRIS GALLOPAVO) USING WHOLE BLOOD.

Lymphoproliferative disease virus (LPDV) is a retrovirus that infects wild and domestic turkeys ( Meleagris gallopavo ). The first cases of LPDV in the United States were diagnosed in 2009, and subsequent surveillance has revealed the virus to be widespread in wild turkey populations throughout the eastern half of the country. More research is needed to determine whether LPDV is having a negative effect on turkey populations, but progress has been impeded by the lack of a simple method for diagnosing the virus in living birds. Infected animals may appear asymptomatic, and diagnostics currently rely on tissue or bone marrow, which can be difficult to obtain. This study investigated the reliability of polymerase chain reaction (PCR) to detect LPDV in whole blood, compared with previous methods using buffy coat (concentrated white blood cells) and bone marrow. Paired samples of whole blood and buffy coat were collected from 137 live turkeys and paired samples of whole blood and bone marrow were collected from 32 turkeys postmortem. Compared with buffy coat, whole blood had 97% sensitivity and 100% specificity. When compared with bone marrow, whole blood had 100% sensitivity and 89% specificity. Both comparisons had a high degree of agreement using Cohen's kappa statistic. Based on these results, PCR of whole blood provides detection of LPDV in living birds that is on par with both buffy coat and bone marrow.