The newly characterized Pl‐jun is specifically expressed in skeletogenic cells of the Paracentrotus lividus sea urchin embryo

Abstract

Growing evidence suggests that the transcription factors belonging to the Jun family are involved in many important cellular events, such as the control of bone development in mammalians. We have characterized, for the first time, a member of the Jun family from embryos of the sea urchin Paracentrotus lividus. The Pl‐jun protein sequence includes all the functional domains characteristic of members of the Jun family (i.e. the basic leucine zipper, the basic DNA‐binding and the c‐Jun N‐terminal kinase docking‐like domains), which are evolutionarily conserved. Moreover, all the key serine and threonine residues, which are phosphorylation targets for different kinases necessary for jun activation, appear to be well preserved. A model of the monomeric protein provides a simulation of the three‐dimensional structure and shows the potential sites for dimerization and DNA binding. Pl‐jun mRNA is expressed in the unfertilized egg and throughout sea urchin embryo development. As the development proceeds, Pl‐jun mRNA becomes exclusively expressed in the skeletogenic cells. Intriguingly, these cells contain significant amounts of the phosphorylated active protein entirely localized into their nuclei. These findings strengthen our hypothesis that suggests an active role for Pl‐jun in skeletogenic cells, thus indicating that this transcription factor is a novel component of the gene regulatory networks controlling skeletogenesis. Database Nucleotide sequence data have been deposited in the EMBL databases under the accession number: http://www.ncbi.nlm.nih.gov/protein/HE817756.

Overview of the molecular defense systems used by sea urchin embryos to cope with UV radiation

“…2E, I). As showed by Russo et al (2014b), few ectoderm and endoderm cells were p-jun-positive, as indicated by arrows and arrowhead both in control (Fig. 2B) and in irradiated embryos (Fig.…”

“…The phosphorylated form of jun has been detected in the nuclei of some skeletogenic cells (Russo et al, 2014b), as shown in Fig. 2B, C. Indeed, p-jun co-localized with the skeletogenic cell surface marker WGA (Fig.…”

“…At the same UVB dose, no phosphorylated form of JNK was detectable, while a higher UVB dose (0.8 kJ/m 2 ) activated JNK under the limits of detection in control embryos . In addition, the 0.8 kJ/m 2 UVB dose induced the activation of jun (phospho-jun) at 24hpi, which was detected as a faint band by immunoblot, while no band was detectable in the controls (Russo et al, 2014b). Thus, in sea urchin embryos UV irradiation activates JNK that in turn can activate jun, although a direct relationship between them needs further confirmation.…”

“…Jun is a transcription factor of the AP-1 family that regulates UVB inducible genes in mouse tumorigenic cells, some of which promote cell survival (Cooper and Bowden, 2007). Recently, it has been showed that a Pl-jun transcript is specifically localized in the skeletogenic cells of the sea urchin embryo (Russo et al, 2014b).…”

“…2E). Consequently, UVB irradiation does not affect the p-jun localization, probably in relation to its specialized function related to the embryonic skeletogenesis (Russo et al, 2014b). The signaling pathways potentially affected by UVR in sea urchin embryos need further analysis that should include other kinases, as the PI3K/Akt and ATR/AMT that are known to be involved in the UV response in mammalian cells (Herrlich et al, 2008).…”