This led to the finding that the nervous system in vertebrates is formed as a default when early embryonic cells do not receive inductive signals to become mesoderm or endoderm.[10] He also pioneered the technique of in vitro transcription with bacterial SP6 RNA polymerase.[11] This RNA transcription system is now widely used to make large amounts of messenger RNAs in vitro and is, for example, the basis for production of the COVID mRNA vaccines.