Abstract
SNAIL transcriptional factors are key regulators during development and disease. They arose early during evolution, and in cnidarians such as Nematostella vectensis, NvSNAILA/B are detected in invaginating tissues during gastrulation. The function of SNAIL proteins is well established in bilaterians but their roles in cnidarians remain unknown. The structure of NvSNAILA and B is similar to the human SNAIL1 and 2, including SNAG and zinc-finger domains. Here, we performed a molecular analysis on localization and mobility of NvSNAILA/B using mammalian cells and Nematostella embryos. NvSNAILA/B display nuclear localization and mobility similar to HsSNAIL1/2. Strikingly, NvSNAILA is highly enriched in the nucleoli and shuttles between the nucleoli and the nucleoplasm. Truncation of the N-terminal SNAG domain, reported to contain Nuclear Localization Signals, markedly reduces nucleolar levels, without effecting nuclear localization or mobility. Truncation of the C-terminal zinc-fingers, involved in DNA binding in higher organisms, significantly affects subcellular localization and mobility. Specifically, the zinc-finger domains are required for nucleolar enrichment of NvSNAILA. Differently from SNAIL transcriptional factors described before, NvSNAILA is specifically enriched in the nucleoli co-localizing with nucleolar markers even after nucleolar disruption. Our findings implicate additional roles for SNAG and zinc-finger domains, suggesting a role for NvSNAILA in the nucleolus.
Highlights
The Snail gene family, first identified in flies[1], encodes zinc-finger transcription factors probably best known for inducing changes in cell shape and morphology during cell migration[2]
The SNAG domain has been reported to be involved in interactions with cofactors, the arginine in 3rd position and the serine in 4th seem to be involved in transcriptional activity through interaction with cofactors whereas arginine and lysine at the 8th and 9th position have been reported to act as a nuclear localisation signal (NLS)[12,23,22,24]
Together these results indicate that NvSNAILA and B show high conservation of the SNAG, putative NLS and zinc finger domains compared to vertebrates, despite being often characterized as a five zinc-finger domains SNAIL, NvSNAILB might have lost the first finger
Summary
The Snail gene family, first identified in flies[1], encodes zinc-finger transcription factors probably best known for inducing changes in cell shape and morphology during cell migration[2]. They are required for acquisition of cell motility through loss of adhesion in several organisms, including mammals[3]. More than 150 Snail genes, including Scratch and Slug, have been identified in various taxa, such as vertebrates, non-vertebrate chordates, insects, nematodes, cnidarians and placozoans[3,11] These transcription factors all share the same highly conserved C-terminal domain comprising at least four zinc fingers, either C2H2 motifs alone or C2H2 coupled with the C2HC variant. The role of snail during endomesoderm formation in higher metazoans is well established[20], the only study reported to date did not find any obvious role for SNAILA and B during Nematostella vectensis gastrulation
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