Résumé
Wolbachia are required for filarial nematode survival and
fertility and contribute to the immune responses associated with human filarial
diseases. Here we developed whole-mount immunofluorescence techniques to
characterize Wolbachia somatic and germline transmission
patterns and tissue distribution in Brugia malayi, a nematode
responsible for lymphatic filariasis. In the initial embryonic divisions,
Wolbachia segregate asymmetrically such that they occupy
only a small subset of cells in the developing embryo, facilitating their
concentration in the adult hypodermal chords and female germline.
Wolbachia are not found in male reproductive tissues and
the absence of Wolbachia from embryonic germline precursors in
half of the embryos indicates Wolbachia loss from the male
germline may occur in early embryogenesis. Wolbachia rely on
fusion of hypodermal cells to populate adult chords. Finally, we detect
Wolbachia in the secretory canal lumen suggesting living
worms may release bacteria and/or their products into their host. Filarial diseases affect over 150 million people in tropical countries. They are
caused by parasitic nematodes like Brugia malayi that rely on
their endosymbiont Wolbachia for their survival and fertility.
These bacteria are a recognized drug target in the search for treatments killing
adult worms. To understand the transmission of Wolbachia from
the embryonic to adult stages, we developed new techniques to track these
bacteria at the cellular and tissue levels. These techniques include
immunofluorescence in whole mount adult tissues and embryos. We found that
Wolbachia segregate asymetrically in specific cells, in a
lineage-specific manner during early Brugia embryogenesis, and
rely on cell fusion to subsequently populate the adult hypodermal chords. From
the chords, the Wolbachia can be secreted in the
secretory-excretory canal, suggesting that in addition to dead worms releasing
the bacteria in the human body, living worms may also secrete
Wolbachia, whose role in stimulating the immune system in
filarial pathologies is now well established.