β-Catenin localization in the ctenophore Mnemiopsis leidyi suggests an ancestral role in cell adhesion and nuclear function.

BACKGROUND: The emergence of multicellularity in animals marks a pivotal evolutionary event, which was likely enabled by molecular innovations in the way cells adhere and communicate with one another. β-Catenin is significant to this transition due to its dual role as both a structural component in the cadherin-catenin complex and as a transcriptional coactivator involved in the Wnt/β-catenin signaling pathway. However, our knowledge of how this protein functions in ctenophores, one of the earliest diverging metazoans, is limited. RESULTS: To study β-catenin function in the ctenophore Mnemiopsis leidyi, we generated affinity-purified polyclonal antibodies targeting Mlβ-catenin. We then used this tool to observe β-catenin protein localization in developing Mnemiopsis embryos. In this article, we provide evidence of consistent β-catenin protein enrichment at cell-cell interfaces in Mnemiopsis embryos. Additionally, we found β-catenin enrichment in some nuclei, particularly restricted to the oral pole around the time of gastrulation. The Mlβ-catenin affinity-purified antibodies now provide us with a powerful reagent to study the ancestral functions of β-catenin in cell adhesion and transcriptional regulation. CONCLUSIONS: The localization pattern of embryonic Mlβ-catenin suggests that this protein had an ancestral role in cell adhesion and may have a nuclear function as well.