An ovary-specific mucin is associated with choriogenesis mediated by prostaglandin signaling inSpodoptera exigua

Polytrophic ovarioles ofSpodoptera exigua, a lepidopteran insect, begins with the development of oocytes and differentiation of nurse cells followed by vitellogenesis and choriogenesis. Compared with previtellogenic and vitellogenic developments, choriogenesis has not been clearly understood yet in endocrine control. This study investigated the expression and function of a mucin-like structural protein ofS. exiguacalledSe-Mucin1in choriogenesis. It was highly expressed in ovarioles containing chorionated oocytes. The expression level ofSe-Mucin1was increased during adult stage as early as 18 h after adult emergence, reaching the maximal level at 24 h and later. Interestingly, DNA amount ofSe-Mucin1was increased by almost four folds during early adult stage while other genes (hexokinaseandglyceraldehyde-3-phosphate dehydrogenase) not directly associated with chorion formation did not show genomic DNA increase, suggesting specific gene amplification ofSe-Mucin1. RNA interference (RNAi) suppressedSe-Mucin1expression by injecting 1 mu g of double-strand RNA to teneral females (<5 h after emergence), which exhibited significantly impaired fecundity and egg hatching rate. Eggs laid by RNAi-treated females were malformed in eggshell structures with loss of mesh-like fibers. Treatment with aspirin, a prostaglandin (PG) biosynthesis inhibitor, suppressed the induction ofSe-Mucin1expression during early adult stage and impaired egg development. An addition of PGE(2)significantly rescued such impairment inSe-Mucin1expression and subsequent egg development. These results suggest that PGs mediate choriogenesis ofS. exiguaby activating the expression of chorion-associated genes includingSe-Mucin1.

Automated summary

In the polytrophic ovarioles of Spodoptera exigua, the mucin-like protein Se-Mucin1 plays a crucial role in choriogenesis, with its expression levels increasing during the adult stage. RNA interference of Se-Mucin1 results in reduced fecundity and malformed egg development, while supplementation of PGE(2) rescues these impairments. These results suggest that prostaglandins mediate choriogenesis in S. exigua by activating genes associated with chorion formation, including Se-Mucin1.