Identification and subcellular localization of NbIAP in the microsporidian Nosema bombycis

Many organisms go through a process of programmed cell death called apoptosis while newer cells are created. This has the effect of protecting the organism from cellular parasites and is a major line of defense against invading organisms. Apoptosis inhibitors, then, play an important role in aiding infectious agents by inhibiting caspase protease and thus the apoptopic pathway. In this study, we identified an inhibitor of apoptosis protein (IAP) in the microsporidian Nosema bombycis (NbIAP). NbIAP a composed of 218 amino acids containing two overlapping domains; the BIR domain and a zf-C3HC domain. We show, through indirect immunofluorescence, that NbIAP is present throughout the life cycle of N. bombycis and is localized in the nucleus of the parasite and therefor does not act on caspase protease directly. qRT-PCR analysis shows that the expression of the NbIAP gene was the highest on the first day of infection, then decreased to a relatively stable level. In addition, we show that the downregulation of the NbIAP gene directly inhibits the proliferation of N. bombycis. These findings suggest that NbIAP plays an important role in the N. bombycis life cycle.