Embryonic Induction Mechanisms in Vertebrates: Conserved Principles and Flexible Details

Early embryonic differentiation and body axis formation are the most critical events in embryonic development, and serve as a basis for the formation of the body plan of the future organism. The inductive center, the Spemann organizer (the 100th anniversary of its discovery was celebrated by the scientific community in 2024) regulates the early stages of embryogenesis through mechanisms mediated by intercellular interactions. The classical model of neural induction in vertebrates, developed primarily through studies of amphibians, assumes that organizer cells express antagonists of BMP signaling (such as Noggin, Follistatin, and Chordin proteins), thereby determining neural differentiation and inducing body axis formation. Organizer centers have also been identified in representatives of other vertebrate classes, although their full functional equivalence to the classical organizer remains a subject of debate. In the context of studying the fundamental mechanisms of embryonic induction in vertebrates, investigations of extant representatives of evolutionarily ancient groups, such as cyclostomes (lampreys and hagfishes), are of particular interest. Our studies have shown that well-known vertebrate embryonic inducers such as noggin genes do not induce the formation of secondary body axes in lampreys. Moreover, genomic and transcriptomic analyses have revealed the absence of the chordin gene (one of key embryonic inducers) in lampreys, a unique situation among vertebrates. These results suggest that the mechanisms of neural induction in lampreys may differ from the classical model described for amphibians. At the same time, our transcriptomic data analysis has confirmed the activity of key signaling pathways in lampreys (Wnt, Nodal/Activin, and BMP), which are involved in embryonic differentiation in other vertebrates. These findings together show that, while the genetic foundation of embryonic development may be conserved, the details of embryonic induction mechanisms can exhibit plasticity and variability across different evolutionary lineages.