Empty-spiracles is maternally expressed and essential for neurodevelopment and early embryo determination in Rhodnius prolixus

Abstract

Since empty-spiracles (ems) was identified and characterized in Drosophila melanogaster as a head-gap gene, several studies have been carried out in other insect orders to confirm its evolutionary conserved function. Using the blood-sucking bug Rhodnius prolixus as biological model, we found an ems transcript with three highly conserved regions: Box-A, Box-B, and the homeodomain. R. prolixus embryos silenced by parental RNAi for two of these ems conserved regions showed both maternal and zygotic defects. Rp-emsB fragment results in early lethal embryogenesis, with eggs without any embryonic structure inside. Rp-emsB expression pattern is only maternally expressed and localized in the ovary tropharium, follicular cells, and in the unfertilized female pronucleus. Rp-emsA fragment is zygotically expressed during early blastoderm formation until late developmental stages in two main patterns: anterior in the antennal segment, and in a segmentary in the neuroblast and tracheal pits. R. prolixus knockdown embryos for Rp-emsA showed an incomplete larval hatching, reduced heads, and severe neuromotor defects. Furthermore, in situ hybridization revealed a spatial and temporal expression pattern that highly correlates with Rp-ems observed function. Here,Rp-ems function in R. prolixus development was validated, showing that empty-spiracles does not act as a true head-gap gene, but it is necessary for proper head development and crucial for early embryo determination and neurodevelopment.

Keywords: Empty-spiracles; Head; Maternal expression; Neurodevelopment; Rhodnius prolixus.