Pacific white shrimp (Litopenaeus vannamei) vitelline membrane outer layer protein 1 (VMO1) is produced in the hepatopancreas and transported into ovarian oocytes during vitellogenesis

In birds, vitelline membrane outer layer protein 1 (VMO1) is an exogenous protein that can be absorbed by eggs as a barrier to prevent the mixing of yolk and egg white. However, researches on VMO1 are limited in birds but not other non-avian species until now. In this study, we first identified a novel Vmo1 cDNA (Lv-Vmo1) in Pacific white shrimp (Litopenaeus vannamei), the most important cultured shrimp in the world. We further analyzed its gene organization, phylogenetic relationship and protein structure. The Lv-Vmo1 transcript was specifically expressed in the hepatopancreas without sexual dimorphism. During ovarian development in female, the hepatopancreatic Lv-Vmo1 mRNA levels showed a significant increase. By in situ hybridization, Lv-Vmo1 mRNA was present in three cell types of the hepatopancreas but neither oocytes nor follicle cells of the ovary. In contrast, immunofluorescence revealed that Lv-VMO1 protein was distributed in the cytoplasms of both hepatopancreatic cells and ovarian oocytes. Western blot showed that Lv-VMO1 protein was produced in the hepatopancreas and transported to the ovary via hemolymph circulation. Identification of a species-specific egg-entry guide protein is the key to the receptor-mediated ovarian transduction of cargo, a novel gene editing approach in oviparous animals. This study lays the mechanism for exogenous transport into penaeid shrimp eggs by VMO1, as a foundation for achieving exogenous protein-mediated incorporation into oocytes.