Forkhead box transcription factor L2 activates <i>Fcp3C</i> to regulate insect chorion formation

Abstract

Most animals are oviparous. However, the genes regulating egg shell formation remain not very clear. In this study, we found that <i>Nilaparvata lugens</i> Forkhead box transcription factor L2 (<i>Nl</i>FoxL2) directly activated follicle cell protein 3C (<i>NlFcp3C</i>) to regulate chorion formation. <i>NlFoxL2</i> and <i>NlFcp3C</i> had a similar expression pattern, both highly expressed in the follicular cells of female adults. Knockdown of <i>NlFoxL2</i> or <i>NlFcp3C</i> also resulted in the same phenotypes: obesity and female infertility. RNA interference (RNAi) results suggested that <i>NlFcp3C</i> is a downstream gene of <i>NlFoxL2</i> Furthermore, transient expression showed that <i>Nl</i>FoxL2 could directly activate the <i>NlFcp3C</i> promoter. These results suggest that <i>NlFcp3C</i> is a direct target gene of <i>Nl</i>FoxL2. Depletion of <i>NlFoxL2</i> or <i>NlFcp3C</i> prevented normal chorion formation. Our results first revealed the functions of Fcp3C and FoxL2 in regulation of oocyte maturation in an oviparous animal.