Abstract
Gene family encoding small Heat-Shock Proteins (sHSPs containing α-crystallin domain) are found both in prokaryotic and eukaryotic organisms; however, there is limited knowledge of their evolution. In this study, two small HSP genes termed AvHSP28.6 and AvHSP27, both organized in one intron and two exons, were characterised in the Mediterranean snakelocks anemone Anemonia viridis. The release of the genome sequence of Hydra magnipapillata and Nematostella vectensis enabled a comprehensive study of the molecular evolution of α-crystallin gene family among cnidarians. Most of the H. magnipapillata sHSP genes share the same gene organization described for AvHSP28.6 and AvHSP27, differing from the sHSP genes of N. vectensis which mainly show an intronless architecture. The different genomic organization of sHSPs, the phylogenetic analyses based on protein sequences, and the relationships among Cnidarians, suggest that the A.viridis sHSPs represent the common ancestor from which H. magnipapillata genes directly evolved through segmental genome duplication. Additionally retroposition events may be considered responsible for the divergence of sHSP genes of N. vectensis from A. viridis. Analyses of transcriptional expression profile showed that AvHSP28.6 was constitutively expressed among different tissues from both ectodermal and endodermal layers of the adult sea anemones, under normal physiological conditions and also under different stress condition. Specifically, we profiled the transcriptional activation of AvHSP28.6 after challenges with different abiotic/biotic stresses showing induction by extreme temperatures, heavy metals exposure and immune stimulation. Conversely, no AvHSP27 transcript was detected in such dissected tissues, in adult whole body cDNA library or under stress conditions. Hence, the involvement of AvHSP28.6 gene in the sea anemone defensome is strongly suggested.
Highlights
The small heat-shock proteins represent one of the most widespread and poorly conserved family of molecular chaperones [1,2,3]
As first reported by Ingolia and Craig [4], these low-molecular-weight proteins are evolutionarily related to the vertebrate eye lens protein because of the presence of a conserved a-crystallin domain consisting of 80–100 amino acid residues and are defined on the basis of its conserved b-sandwich structure composed of antiparallel b-sheets [5]
A. viridis sHSP cDNA Characterisation Starting from a sequence (FK734577.1) encoding a putative small HSP found in the EST database of the sea anemone A. viridis, a specific primer was designed and used to isolate the 39end of the cDNA
Summary
The small heat-shock proteins (sHSPs) represent one of the most widespread and poorly conserved family of molecular chaperones [1,2,3]. The sHSPs are constitutive and stress-inducible proteins with variable masses between 12 and 43 kDa and usually form large aggregates under normal physiological conditions They are ubiquitously expressed to perform a plethora of housekeeping functions; in response to stress, the oligomeric structure dissociates into suboligomeric species [6,7] and hydrophobic sites are exposed to suppress protein aggregation, promoting the restoration of cellular homeostasis [5,8,9]. The sea anemone Anemonia viridis (Anthozoa: Actinaria) is a widespread and extensively studied Mediterranean species of Cnidaria [21,22,23] This phylum is sister taxa of Bilateria within the Eumetazoan and some studies demonstrated that time of divergence between Cnidarians and Bilaterians dates back to 600 million years ago in the Precambrian era [24,25,26]. QRT-PCR assays indicate that the transcriptional expression of AvHSP28.6 responds to a number of environmental stressors (including extreme temperature, heavy metals and immune system stimulation), suggesting its involvement in the sea anemone defensome [19]
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