Abstract
Intersex(ix), a gene involved in the sex-determining cascade of Drosophila melanogaster, works in concert with the female-specific product of doublesex (dsx) at the end of the hierarchy to implement the sex-specific differentiation of sexually dimorphic characters in female individuals. In this study, the ix homolog was identified in the brown planthopper (BPH), Nilaparvata lugens, which contained two splice variants expressed in both female and male insects. We found that Nlix played a vital role in the early nymphal development of BPH, showing an accumulated effect. RNAi-mediated knockdown of Nlix at 4th instar led to the external genital defects in both sexes, consequently resulting in the loss of reproductive ability in female and male individuals. After dsRNA injection, the males were normal on testes, while the females had defective ovarian development. Nlix was also required for early embryogenesis. Notably, when the dsNlix microinjection was performed in newly emerged females, the copulatory bursas were abnormally enlarged while the other tissues of the reproductive system developed normally. Our results demonstrated the pleiotropic roles of Nlix in embryogenesis and development of the reproductive system in a hemimetabolous insect species.
Highlights
With the evolution of organisms, the sex-determining mechanisms presented an astounding diversity in insects, which have affected the sexually dimorphic development at the morphological, behavioral and physiological levels
The intersexual characteristics of the sexual somatic structures in D. melanogaster females resulting from the absence of Dmix could be partially rescued with the expression of ix homologs from B. mori and M. vitrata [3,7,9]
Our results demonstrated that after dsNlix microinjection during the nymph stage (4th instar), the external genitalia of both male and female brown planthopper (BPH) adults displayed a defective phenotype, which led to a reproductive loss in both sexes
Summary
With the evolution of organisms, the sex-determining mechanisms presented an astounding diversity in insects, which have affected the sexually dimorphic development at the morphological, behavioral and physiological levels. Intersex (ix) is a gene involved in the sex-determining cascade of insects. It was first well-characterized in Drosophila melanogaster [1] and showed apparently deep conservation in insect species, as Bombyx mori [2], Maruca vitrata [3], Cyclommatus metallifer [4], Bemisia tabaci [5] and Oncopeltus fasciatus [6]. The ix functioned independently of dsx in B. mori, and the phenotype of Bmix mutants led to irregular development of external genitalia in female insects while leaving the external genitalia of male individuals unaffected. In O. fasciatus and C. metallifer, knockdown of ix gene in females resulted in masculinizing phenotypes as reported in D. melanogaster
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