For instance, wpgrp1 and tollip genes are good regulator candidates and they could play a crucial role in this inhibition [76, 84]. Recently, Ryu et al. [75] have reported that the Drosophila homeobox gene caudal also regulates the commensal-gut bacteria by repressing the nuclear factor Kappa B-dependent AMP genes. Ongoing RNAi experiments will provide more information about the function and the regulation of these pathways in the Sitophilus system. The high accumulation of transcripts from Rab7, Hrs and SNARE genes could be viewed as being due to intense endosomal trafficking

within the bacteriocyte. These genes are certainly very involved in vesicle synthesis and fusion [62–64]. Moreover, intense vesicle trafficking has already been observed by electronic SB431542 mouse microscopy within Sitophilus bacteriocytes [30]. Vesicle trafficking may aid in metabolic component exchanges between the host and the symbiont, or it may help in endosome fusion, with late endosomes and lysozomes, to favor autophagy. For the latter, we can speculate about the possibility that autophagy could serve as an additional host mechanism to regulate symbiont density. In support of this hypothesis, in silico cDNA comparison between symbiont-full and symbiont-free ovaries has shown

that vesicle trafficking is also highly represented in the presence of Wolbachia in the isopod Armadillidium vulgare [35]. Moreover, receptors of innate immunity have been identified on vertebrate endosome membranes [57, 87] and autophagy has been described as a possible means of eliminating intracellular pathogens [61]. To permanently sequester the GSK2126458 mw endosymbiont within the

bacteriome, and to avoid bacterial invasion into insect tissues, bacteriocyte cells need to maintain homeostasis and to see more survive during insect developmental stages. While apoptosis has been observed as a response to infection by a wide range of animal and plant pathogens [88, 89], very limited data are available on invertebrate symbiotic systems [70]. To tackle filipin this question in the Sitophilus system, we have analyzed genes potentially involved in apoptosis inhibition (iap2 and iap3) and apoptosis execution (caspase-like). We have shown that the high expression of apoptosis inhibitor genes paralleled the low amount of caspase-like gene transcripts in the bacteriome. In addition to the upregulation of genes involved in cell growth, such as Ras and leonardo 14-3-3, these preliminary data suggest that weevil bacteriocytes manage to survive an endosymbiont infection by inhibiting the apoptosis pathway. Inhibition of apoptosis can also be mediated by the expression of the FK506BP gene (or FKBP). In vertebrates, the FKBP38 gene inhibits apoptosis by interacting with Bcl-2 [90]. Moreover, we cannot exclude the possibility that apoptosis inhibition is manipulated by the symbiont for its own survival.