From Follicle Cell Differentiation and Structure to Chorion Biogenesis in Insects: Cellular Mechanisms, Gene Regulation, Biochemical Composition and Structural Diversity

Choriogenesis, the final stage of oogenesis in insects, is a highly coordinated developmental process responsible for the formation of the chorion (eggshell), a specialized multilayered extracellular matrix that protects the embryo and mediates essential physiological functions. Despite its fundamental importance for reproductive success and species survival, the mechanisms underlying chorion biogenesis remain incompletely understood across insect taxa. This review provides an updated synthesis and integrated view of choriogenesis, including cellular, molecular, biochemical, and structural perspectives. We examine the role of follicle cells in chorion formation, the regulatory mechanisms governing chorion gene expression, and the biochemical composition of the eggshell, including proteins, lipids, and carbohydrates. In addition, we compare the structural diversity of the chorion across insect taxa, highlighting both conserved multilayered organization and lineage-specific adaptations in surface morphology and internal architecture.