Septin homologs cooperating in the Proliferative Stage of Microsporidia Nosema bombycis

Abstract

The single-celled pathogen Nosema bombycis, that can infect silkworm Bombyx mori and other lepidoptera including Spodoptera, is the first identified Microsporidia which has diplokaryotic nuclei throughout the life cycle. Septin proteins can form highly ordered filaments, bundles or ring structures related to the cytokinesis in fungi. Here, three septin proteins (NbSeptin1, NbSeptin2 and NbSeptin3) from Nosema bombycis CQ I are described. These proteins, appear to be conserved within the phylum Microsporidia. NbSeptins transcripts were detected throughout the pathogen developmental cycle and were significantly enhanced from second days of infection, which lead to our hypothesis that NbSeptins play a role in merogony. Immunofluorescence assay (IFA) revealed a broad distribution of NbSeptins in meronts and partly co-localization of NbSeptins. Interestingly, in some of meronts, NbSeptin2 and NbSeptin3 showed localization between the nuclei of the diplokaryon. Yeast two-hybrid and co-immunoprecipitation analysis verified that NbSeptins can interact with each other. Our findings suggest that NbSeptins can cooperate in the proliferation stage of Nosema bombycis and contribute towards the understanding of the rols of septins in microsporidia development.