Dorsoventral patterning beyond the gastrulation stage: Interpretation of early dorsoventral cues and modular development mediated by zic1/zic4.

Dorsoventral (DV) patterning is fundamental to vertebrate development, organizing the entire body across different germ layers. Although early DV axis formation, centered on the Spemann-Mangold organizer through the BMP activity gradient, has been extensively studied, the mechanisms shaping DV traits during later development remain largely unexplored. In this review, we highlight recent findings, especially from studies involving the Double anal fin (Da) spontaneous mutant of the small teleost medaka (Oryzias latipes), focusing on the roles of zic1 and zic4 (zic1/zic4) in regulating late DV patterning. These genes establish the dorsal domain of the trunk by converting the initial BMP gradient into distinct on/off spatial compartments within somites and their derivatives, acting as selector genes that define dorsal-specific traits, including myotome structure, body shape, and dorsal fin development. We also discuss how the zic-mediated dorsal domain is established and maintained from embryogenesis through adulthood. Furthermore, we provide evidence that zic-dependent action on the dorsal characteristics is dosage-dependent. We propose that the zic1/zic4-mediated DV patterning mechanism may represent a conserved regulatory framework that has been adapted to support the diverse body plans observed across vertebrate species.