Functional role for MAP kinase signaling in cell lineage and dorsoventral axis specification in the basal gastropod Testudinalia testudinalis (Patellogastropoda, Mollusca)

In spiralians, the specification of cell lines in development is provided by maternal factors. However, recent studies demonstrated the importance of inductive processes whose significant element is cellular signaling. Our data argue the conditional specification of a number of cell lines at the early stages of development of the mollusk Testudinalia testudinalis (Testudinalia tessellata, Patellogastropoda), including the period when the determination of the 3D cell takes place, which is accompanied by a change in the shape and establishing of contacts with animal micromeres by one of the macromeres of the third quartet. Exactly at this moment activation of MAPK was registered in the 3D blastomere-organizer. An analysis of the influence of the U0126 inhibitor of the MAP kinase pathway on the development of Testudinalia revealed that the greatest effect of the inhibitor was observed if the treatment of embryos was performed until the sixth cycle of cleavage. Notably, the degree of defects correlates with the concentration increase. Absence of the functioning retractor, disorganization of the muscle system, and abnormal structure of the shell (to the extent of complete absence of the shell), as well as velum, foot, and mantle fold, were observed in a considerable part of larvae after a lengthy bathing of the embryos in the U0126 solution. At the same time, none of the experiments showed a complete disruption of the specification of the dorsoventral axis, which produces a larva with a tetramerous radial symmetry. Our data indicate the existence of various molecular mechanisms of determination of the secondary body axis among the animals from the group Spiralia.