Krüppel-like factor/specificity protein evolution in the Spiralia and the implications for cephalopod visual system novelties.

The cephalopod visual system is an exquisite example of convergence in biological complexity. However, we have little understanding of the genetic and molecular mechanisms underpinning its elaboration. The generation of new genetic material is considered a significant contributor to the evolution of biological novelty. We sought to understand if this mechanism may be contributing to cephalopod-specific visual system novelties. Specifically, we identified duplications in the Krüppel-like factor/specificity protein (KLF/SP) sub-family of C2H2 zinc-finger transcription factors in the squid . We cloned and analysed gene expression of the KLF/SP family, including two paralogs of the gene. These duplicates showed overlapping expression domains but one paralog showed unique expression in the developing squid lens, suggesting a neofunctionalization of . To better understand this neofunctionalization, we performed a thorough phylogenetic analysis of SP6-9 orthologues in the Spiralia. We find multiple duplications and losses of the gene throughout spiralian lineages and at least one cephalopod-specific duplication. This work supports the hypothesis that gene duplication and neofunctionalization contribute to novel traits like the cephalopod image-forming eye and to the diversity found within Spiralia.