A conserved role for Snail as a potentiator of active transcription

Abstract

The transcription factors of the Snail family are key regulators of epithelial–mesenchymal transitions, cell morphogenesis, and tumor metastasis. Since its discovery in Drosophila ∼25 years ago, Snail has been extensively studied for its role as a transcriptional repressor. Here we demonstrate that Drosophila Snail can positively modulate transcriptional activation. By combining information on in vivo occupancy with expression profiling of hand-selected, staged snail mutant embryos, we identified 106 genes that are potentially directly regulated by Snail during mesoderm development. In addition to the expected Snail-repressed genes, almost 50% of Snail targets showed an unanticipated activation. The majority of “Snail-activated” genes have enhancer elements cobound by Twist and are expressed in the mesoderm at the stages of Snail occupancy. Snail can potentiate Twist-mediated enhancer activation in vitro and is essential for enhancer activity in vivo. Using a machine learning approach, we show that differentially enriched motifs are sufficient to predict Snail's regulatory response. In silico mutagenesis revealed a likely causative motif, which we demonstrate is essential for enhancer activation. Taken together, these data indicate that Snail can potentiate enhancer activation by collaborating with different activators, providing a new mechanism by which Snail regulates development.

In Vivo Transcriptional Activation Using CRISPR/Cas9 in Drosophila

“…A subset of these terms was also significantly enriched among targets of Twist alone, including muscle organ development (P = 0.003163), but no terms were following Snail activation alone, consistent with the observation that these factors act synergistically (Rembold et al 2014). Furthermore, of the genes upregulated by Snail and Twist together, 38 genes (35.8%) were upregulated only upon co-expression of Snail + Twist.…”

“…Twist is a basic helix-loop-helix activator (Thisse et al 1988;Murre et al 1989), and Snail is a zinc-finger transcription factor, classically considered to be a repressor (Boulay et al 1987;Nieto 2002;Barrallo-Gimeno and Nieto 2005). However, a recent study has suggested that Snail may have additional roles as a transcriptional activator (Rembold et al 2014). Importantly, the genome-wide targets of both genes have been characterized via independent means, allowing for direct comparison with our data (Sandmann et al 2007;Zeitlinger et al 2007;Macarthur et al 2009).…”

Snail mediates medial–lateral patterning of the ascidian neural plate

“…Delta2/Notch refines the initial medial-lateral pattern established by Nodal signals, inducing the specific gene expression states of columns 2 and 4. Snail encodes a C2H2 zinc finger transcription factor that is generally considered to act as a repressor, although it also has an activating function in certain developmental contexts (Hemavathy et al, 2000;Nieto, 2002;Reece-Hoyes et al, 2009;Rembold et al, 2014;Sakai et al, 2006). Snail is implicated in formation of many different tissue types, particularly during mesoderm formation and in cells that undergo the epithelial-mesenchyme transition, such as the premigratory neural crest (Nieto, 2002).…”

Temporal control of bidirectional lipid-droplet motion depends on the ratio of kinesin-1 and its cofactor Halo

“…We developed additional reagents to modulate Halo expression, including the smaller deletion Δhalo AJ (Rembold et al, 2014) and the point allele halo GA . Embryos homozygous for Δhalo AJ (Fig.…”

“…Δhalo AJ has a deletion of ∼19 kb surrounding the halo locus, generated using FLP-FRT-mediated recombination (Rembold et al, 2014 , a missense allele (G at position 544 replaced by S) that we identified using a TILLING approach (Cooper et al, 2008 Halo-coding regions starting with the first or second AUG (encoded proteins referred to as long Halo and short Halo) were subcloned into pET21a, and a 3×HA tag was introduced. Expression was induced in BL21 cells (Stratagene).…”