Given the likelihood that the ctenophore lineage is the deepest branch among metazoans, let's have a closer look at the toolkit contained by these creatures to determine if the basic theme of front-loading evolution continues to hold up.
Consider two classes of transcription factors that are known to play crucial roles in metazoan development: the T-box proteins and the SOX proteins. Both factors activate a variety of genes involved in body plan formation, organ formation and cell specification. And as we might expect from a front-loading perspective, PCR analyses have retrieved a rather complex array of both transcription factors from the comb jellies.
Consider the conclusions from two different studies: