The Molecular Mechanism of Body Axis Induction in Lampreys May Differ from That in Amphibians

Lamprey homologues of the classic embryonic inducer Noggin are similar in expression pattern and functional properties to Noggin homologues of jawed vertebrates. All genes of vertebrates apparently originated from a single ancestral gene as a result of genome duplications. , and of lampreys, like and of gnathostomes, demonstrate the ability to induce complete secondary axes with forebrain and eye structures when overexpressed in embryos. According to current views, this finding indicates the ability of lamprey Noggin proteins to suppress the activity of the BMP, Nodal/Activin and Wnt/beta-catenin signaling pathways, as shown for Noggin proteins of gnathostomes. In this work, by analogy with experiments in embryos, we attempted to induce secondary axes in the European river lamprey by injecting mRNAs into lamprey eggs in vivo. Surprisingly, unlike what occurs in amphibians, secondary axis induction in the lampreys either by mRNAs or by and mRNAs, the inductive properties of which have been described, was not observed. Only mRNA demonstrated the ability to induce secondary axes in the lampreys. Such results may indicate that the mechanism of axial specification in lampreys, which represent jawless vertebrates, may differ in detail from that in the jawed clade.