Cell-based analysis reveals that sex-determining gene signals in <i>Ostrinia</i> are pivotally changed by male-killing <i>Wolbachia</i>

Abstract

<i>Wolbachia</i>, a maternally transmitted bacterium, shows male-killing, an adaptive phenotype for cytoplasmic elements, in various arthropod species during the early developmental stages. In lepidopteran insects, lethality of males is accounted for by improper dosage compensation in sex-linked genes owing to <i>Wolbachia</i>-induced feminization. Herein, we established <i>Ostrinia scapulalis</i> cell lines that retained sex specificity per the splicing pattern of the sex-determining gene <i>doublesex</i> (<i>Osdsx</i>). We found that <i>Wolbachia</i> transinfection in male cell lines enhanced the female-specific splice variant of <i>Osdsx</i> (<i>Osdsx^F</i> ) while suppressing the male-specific variant (<i>Osdsx^M</i> ), indicating that <i>Wolbachia</i> affects sex-determining gene signals even in vitro. Comparative transcriptome analysis isolated only two genes that behave differently upon <i>Wolbachia</i> infection. The two genes were respectively homologous to <i>Masculinizer</i> (<i>BmMasc</i>) and <i>zinc finger-2</i> (<i>Bmznf-2</i>), male-specifically expressed sex-determining genes of the silkworm <i>Bombyx mori</i> that encode CCCH-type zinc finger motif proteins. By using cultured cells and organismal samples, <i>OsMasc</i> and <i>Osznf-2</i> were found to be sex-determining genes of <i>O. scapulalis</i> that are subjected to sex-specific alternative splicing depending upon the chromosomal sex, developmental stage, and infection status. Overall, our findings expound the cellular autonomy in insect sex determination and the mechanism through which sex is manipulated by intracellular selfish microbes.