Abstract
BackgroundWolbachia are endosymbiotic bacteria that are frequently found in arthropods and nematodes. These maternally inherited bacteria manipulate host reproduction by several mechanisms including cytoplasmic incompatibility (CI). CI is the most common phenotype induced by Wolbachia and results in the developmental arrest of embryos derived from crosses between Wolbachia-infected males and uninfected females. Although the molecular mechanisms of CI are currently unknown, several studies suggest that host sperm is modified by Wolbachia during spermatogenesis.ResultsWe compared the gene expression of Drosophila melanogaster larval testes with and without the wMel strain of Wolbachia to identify candidate genes that could be involved in the interaction between Wolbachia and the insect host. Microarray, quantitative RT-PCR and in situ hybridization analyses were carried out on D. melanogaster larval testes to determine the effect of Wolbachia infection on host gene expression. A total of 296 genes were identified by microarray analysis to have at least a 1.5 fold change [q-value < 5%] in expression. When comparing Wolbachia-infected flies to uninfected flies, 167 genes were up-regulated and 129 genes down-regulated. Differential expression of genes related to metabolism, immunity, reproduction and other functions were observed. Quantitative RT-PCR (qRT-PCR) confirmed 12 genes are differentially expressed in the testes of the 3rd instar larvae of Wolbachia-infected and uninfected flies. In situ hybridization demonstrated that Wolbachia infection changes the expression of several genes putatively associated with spermatogenesis including JH induced protein-26 and Mst84Db, or involved in immune (kenny) or metabolism (CG4988-RA).ConclusionsWolbachia change the gene expression of 296 genes in the larval testes of D. melanogaster including genes related to metabolism, immunity and reproduction. Interestingly, most of the genes putatively involved in immunity were up-regulated in the presence of Wolbachia. In contrast, most of the genes putatively associated with reproduction (especially spermatogenesis) were down-regulated in the presence of Wolbachia. These results suggest Wolbachia may activate the immune pathway but inhibit spermatogenesis. Our data provide a significant panel of candidate genes that may be involved in the interaction between Wolbachia and their insect hosts. This forms a basis to help elucidate the underlying mechanisms of Wolbachia-induced CI in Drosophila and the influence of Wolbachia on spermatogenesis.
Highlights
Wolbachia are endosymbiotic bacteria that are frequently found in arthropods and nematodes
Several studies in Drosophila melanogaster and Drosophila simulans have revealed that extensive chromosome bridging appears during early nuclear division in cytoplasmic incompatibility (CI) embryos, which implied that the chromosomes did not replicate completely, resulting in the defects in chromatin condensation and segregation [6,7,8]
Landmann et al showed that a delay of histone H3.3 and H4 deposition occurs on the sperm nuclei during formation of male pronuclei in CI embryos [12], which may have resulted in defects of paternal chromosomal replication
Summary
Wolbachia are endosymbiotic bacteria that are frequently found in arthropods and nematodes. Wolbachia are endosymbiotic bacteria that infect a wide range of invertebrates including up to 66% of insect species, as well as spiders, mites and nematodes [1,2] These intracellular, maternally transmitted bacteria have evolved several strategies such as male killing, Several studies in Drosophila melanogaster and Drosophila simulans have revealed that extensive chromosome bridging appears during early nuclear division in CI embryos, which implied that the chromosomes did not replicate completely, resulting in the defects in chromatin condensation and segregation [6,7,8]. As there were significantly less female offspring from crosses of Hiramutated males with Wolbachia-uninfected females [13], we speculated that it was the sperm-carrying X chromosome with mutated Hira that caused embryonic lethality These results suggest that histone modification in the sperm from Wolbachia-infected males could be involved in embryonic lethality in CI embryos
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
