A feminizing switch in a hemimetabolous insect

Abstract

The mechanism of sex determination remains poorly understood in hemimetabolous insects. Here, in the brown planthopper (BPH), <i>Nilaparvata lugens</i>, a hemipteran rice pest, we identified a feminizing switch or a <i>female determiner</i> (<i>Nlfmd</i>) that encodes a serine/arginine-rich protein. Knockdown of <i>Nlfmd</i> in female nymphs resulted in masculinization of both the somatic morphology and <i>doublesex</i> splicing. The female-specific isoform of <i>Nlfmd</i>, <i>Nlfmd-F</i>, is maternally deposited and zygotically transcribed. Depletion of <i>Nlfmd</i> by maternal RNAi or CRISPR-Cas9 resulted in female-specific embryonic lethality. Knockdown of an hnRNP40 family gene named <i>female determiner 2</i> (<i>Nlfmd2</i>) also conferred masculinization. In vitro experiments showed that an <i>Nlfmd2</i> isoform, NlFMD2³⁴⁰, bound the RAAGAA repeat motif in the <i>Nldsx</i> pre-mRNA and formed a protein complex with NlFMD-F to modulate <i>Nldsx</i> splicing, suggesting that NlFMD2 may function as an RNA binding partner of the feminizing switch NlFMD. Our results provide novel insights into the diverse mechanisms of insect sex determination.