Murid gammaherpesvirus 4 establishes latency and reactivates in a strain-dependent manner

Persistent infection with gammaherpesviruses, such as Epstein-Barr virus and Kaposi’s sarcoma-associated herpesvirus may lead to development of various lymphomas and carcinomas in humans. Murid gammaherpesvirus 4 (MuHV-4, also known as MHV-68) is widely used as a model to study all aspects of gammaherpesvirus pathogenesis. Similar to human gammaherpesviruses, MuHV-4 is known for its variability, as evidenced by the existence of multiple strains/variants that differ from each other in primary sequence and some pathogenetic features. Detailed knowledge of the dependence of pathogenic properties on genome structure and sequence would help to better understand the complex host-pathogen interactions. The main aim of this study was to analyze how various strains/variants of MuHV-4, mainly MHV-72 and MHV-4556 induce latency and reactivation. In this study, we characterized the ability of MHV-72 and MHV-4556 to establish latency in spleen, lungs and thymus of immunocompetent mice after intranasal infection. Moreover, we described the potential of these strains to reactivate ex vivo using the method of tissue explantation and stimulation with inhibitor of histone deacetylases, trichostatin A. Our results clearly demonstrate that both MHV-72 and MHV-4556 exhibit a significant deficit in the establishment of deep latency in spleen. Moreover, MHV-72 has a reduced ability to establish latency in lungs as well as thymus. Regarding reactivation, we found that both MHV-72 and MHV-4556 have a significant deficit in ex vivo reactivation from latency in lungs as well as thymus in comparison to MHV-68. Moreover, MHV-72 also possessed a deficit in the ex vivo reactivation from spleen. In contrast, MHV-4556 was able to respond to the trichostatin A-mediated reactivation stimuli by increasing the DNA copy number but had a defect in the release from tissue during the early and deep latency in spleen. Our results contribute to molecular characterization of differences among the MuHV-4 strains in the ability to establish latency and reactivation and could also serve to better understanding of strain-dependent variances among human gammaherpesviruses

Nest Sanitation as the Evolutionary Background for Egg Ejection Behaviour and the Role of Motivation for Object Removal

Higher interclutch colour variation can evolve under the pressure of brood parasitism to increase the detection of parasitic eggs. Nest sanitation could be a prerequisite for the evolution of anti-parasite defence in terms of egg ejection. In this respect, we used nest sanitation behaviour as a tool to identify: i) motivation and its underlying function and, ii) which features provoke ejection behaviour. Therefore, we experimentally tested whether size, colour or shape may influence ejection behaviour using artificial flat objects. We found a high interclutch variation in egg colouration and egg size in our tree sparrow (Passer montanus) population. Using colour and size we were in fact able to predict clutch affiliation for each egg. Our experiments further revealed the existence of direct anti-parasite behaviours and birds are able to recognise conspecific eggs, since only experimentally-deposited eggs have been removed. Moreover, experiments with different objects revealed that the motivation of tree sparrows to remove experimental objects from their nests was highest during egg laying for objects of varying size, most likely because of parasitism risk at this breeding stage. In contrary, motivation to remove white objects and objects with edges was higher during incubation stage as behavioural patterns connected to hatching started to emerge. The fact that rejection rate of our flat objects was higher than real egg ejection, suggests that egg ejection in tree sparrows and probably more general in small passerines, to be limited by elevated costs to eject eggs with their beaks. The presence of anti-parasite behaviour supports our suggestion that brood parasitism causes variation in egg features, as we have found that tree sparrows can recognise and reject conspecific eggs in their clutch. In conclusion, in tree sparrows it seems that nest sanitation plays a key role in the evolution of the removal of parasitic eggs