An Elk transcription factor is required for Runx-dependent survival signaling in the sea urchin embryo

Abstract

Elk proteins are Ets family transcription factors that regulate cell proliferation, survival, and differentiation in response to ERK (extracellular-signal regulated kinase)-mediated phosphorylation. Here we report the embryonic expression and function of Sp-Elk, the single Elk gene of the sea urchin Strongylocentrotus purpuratus. Sp-Elk is zygotically expressed throughout the embryo beginning at late cleavage stage, with peak expression occurring at blastula stage. Morpholino antisense-mediated knockdown of Sp-Elk causes blastula-stage developmental arrest and embryo disintegration due to apoptosis, a phenotype that is rescued by wild-type Elk mRNA. Development is also rescued by Elk mRNA encoding a serine to aspartic acid substitution (S402D) that mimics ERK-mediated phosphorylation of a conserved site that enhances DNA binding, but not by Elk mRNA encoding an alanine substitution at the same site (S402A). This demonstrates both that the apoptotic phenotype of the morphants is specifically caused by Elk depletion, and that phosphorylation of serine 402 of Sp-Elk is critical for its anti-apoptotic function. Knockdown of Sp-Elk results in under-expression of several regulatory genes involved in cell fate specification, cell cycle control, and survival signaling, including the transcriptional regulator Sp-Runt-1 and its target Sp-PKC1, both of which were shown previously to be required for cell survival during embryogenesis. Both Sp-Runt-1 and Sp-PKC1 have sequences upstream of their transcription start sites that specifically bind Sp-Elk. These results indicate that Sp-Elk is the signal-dependent activator of a feed-forward gene regulatory circuit, consisting also of Sp-Runt-1 and Sp-PKC1, which actively suppresses apoptosis in the early embryo.

Spatial and temporal patterns of gene expression during neurogenesis in the sea urchin Lytechinus variegatus

“…Knockdown studies have shown that Elk-1 effects transcription of several genes in the mouse brain and is considered a pro-differentiation factor there [25]. In the sea urchin S. purpuratus , elk has been shown to suppress apoptosis and promote cell proliferation in the early embryo [26]. Lv - elk is expressed at 10–18 hpf in the skeletogenic mesoderm (Fig.…”

A bipolar role of the transcription factor ERG for cnidarian germ layer formation and apical domain patterning

“…The ETS family of genes is evolutionarily conserved [42,43,46,47] and formed by transcriptional regulators involved in various aspects of development, differentiation, hormone responses and tumorgenesis [4,48–55]. Our genome wide survey of ETS transcription factors present in Nematostella revealed the presence of 12 members of this gene family (Fig S1).…”

Transcriptional and post‐transcriptional regulation of histone variant H2A.Z during sea urchin development

“…; Rizzo et al . ). Quenching of translation‐blocking MASO was accomplished by annealing the quenching sense photomorpholino AAATGGCTGGAPGAAAAGCTG (P stands for photosensitive moiety) at a 1.1:1 concentration ratio to the antisense morpholino, following a previously established approach (Tallafuss et al .…”

“…The possibility of unintended splicing disruption by the translation-blocking MASO is also very low, because the highest contiguous similarity after scanning the genome is 18 bp and intergenic. Standard 3 0 -fluorescein-labeled morpholino CCTCTTACCT-CAGTTACAATTTATA was used as a negative control; this standard control morpholino has been previously tested by multiple researchers to determine the generic morpholino dose causing non-specific effects (Arenas-Mena et al 2006;Ooka et al 2010;Rizzo et al 2016). Quenching of translation-blocking MASO was accomplished by annealing the quenching sense photomorpholino AAATGGCTGGAPGAAAAGCTG (P stands for photosensitive moiety) at a 1.1:1 concentration ratio to the antisense morpholino, following a previously established approach (Tallafuss et al 2012).…”