Characterization of C2H2 superfamily expansions in cephalopods and their contribution to nervous system evolution

Zinc finger proteins comprise a large family of transcription factors involved in diverse processes, from suppression of transposable elements to regulation of neuronal development. In some clades, including vertebrates and coleoid cephalopods, members of the Cys2His2-type (C2H2) class of zinc fingers were shown to be expanded and likely relevant for neuron differentiation. Using genomic data from three octopus and three squid species, we show that C2H2 evolutionary history can be subdivided into duplication steps: (1) the coleoid expansions, (2) octopus-specific expansions, and (3) squid-specific expansions. While the overall expression patterns are consistent among those expansions and are associated with nervous tissues, the coleoid-specific duplicates showed the highest expression levels compared to all other C2H2 genes. We also found that C2H2 duplicates segregated into different co-expression modules, some associated with other duplicated gene families. We propose a scenario of functional divergence of C2H2 duplicates related to regulation within the cephalopod nervous system.