The Evolution of the Krüppel-Like Factor Gene Family and Their Function During Embryonic Development in the Ctenophore Mnemiopsis leidyi

How modifications during development influence large-scale evolutionary changes is a major emphasis in the field of evolutionary developmental biology (evo-devo). Comparing the underlying cellular and molecular basis of development in diverse organisms can provide insight into how alterations of these processes contribute to morphological diversity. Ctenophores, or comb jellies, are a phylum of marine invertebrates and, due to their unique phylogenetic position as one of the earliest branching lineages of extant animals, are an ideal system for investigating the origin and evolution of metazoan character traits. For example, the animal through-gut is thought to have originated in the metazoan stem lineage prior to diversification of Bilateria. However, as part of my dissertation, I showed that ctenophores possess a functional through-gut. These results suggest that the origin of the through-gut may have been much earlier during metazoan diversification than previously thought. Additionally, my studies of gene function in ctenophores provide insight into the molecular mechanisms that, in some part, may be driving early metazoan diversification. Members of the Krüppel-like factor (Klf) gene family are known to play a role in many aspects of development, including maintenance of stem cell renewal and pluripotency, and regulating the balance between cellular proliferation and differentiation. Functional studies of these transcription factors have been restricted to only a handful of bilaterian animals, with little investigation into the evolutionary history of this gene family. To evaluate how the Klf gene family could influence evolutionary changes driving metazoan diversification, I examined the origins and evolutionary history of the Klf gene family, and characterized their function in the ctenophore, Mnemiopsis leidyi. Ultimately, I showed that Klf genes were present in the stem lineage leading to Metazoa, and they regulate cellular proliferation in putative stem cell niches during development in M. leidyi. My findings suggest that regulation of stem cell proliferation was an ancestral function of Klfs in metazoans