I have already provided a couple of clues that suggest introns played some important role in the emergence of multicellular life. Let me now add a little depth to those clues.
We saw that the general rule was that complex multicellular genomes tend to be intron-rich, while the genomes of single-celled organisms tend to have very few introns.
But there is a glaring exception. Recall the choanoflagellates – the single-celled organisms thought to be most closely related to metazoans. When their genome was sequenced, it provided a big boost to the hypothesis of front-loading, as it contained a whole toolkit of genes needed for metazoan existence, including the information to make cell adhesion domains, extracellular-matrix-associated protein domains, and an elaborate phosphotyrosine signalling machinery (all of these once believed to be specific to metazoans).
So do the choanoflagellates have introns?