mir-31 mediated control of bacteriome size in tsetse flies

Tsetse flies are the primary vectors of African trypanosomes, which are transmitted through blood feeding. To supplement this nutritionally limited diet, tsetse evolved an obligate mutualism with the bacterium <i>Wigglesworthia glossinidia</i>, housed within a specialized organ called the bacteriome. While the functional contributions of this symbiosis towards tsetse fitness have been studied, host morphological changes that accommodate this relationship remain less understood. In pregnant flies, variable expression of microRNAs (miRNAs) regulates protein expression, but the specific impacts are unknown. During pregnancy, high expression of fatty acyl-CoA reductase (<i>far</i>) within the bacteriome is indirectly correlated with miR-31 abundance and coincides with bacteriome size increase. We explored the roles of <i>far</i> and miR-31 towards this morphological change. Although RNAi effectively reduced <i>far</i> expression, bacteriome size still increased, suggesting its expansion is independent of <i>far</i>. In contrast, disrupting miR-31 activity resulted in significantly enlarged bacteriomes in virgin flies, resembling those of mated females. These results suggest that gene(s) other than <i>far</i> are regulated by miR-31 and may contribute to bacteriome remodeling during pregnancy, potentially to meet increased symbiosis demands. Ultimately, disrupting this obligate mutualism may present a promising target for future vector control strategies.