Abstract
Reef building corals precipitate calcium carbonate as an exo-skeleton and provide substratum for prosperous marine life. Biomineralization of the coral’s skeleton is a developmental process that occurs concurrently with other proliferation processes that control the animal extension and growth. The development of the animal body is regulated by large gene regulatory networks, which control the expression of gene sets that progressively generate developmental patterns in the animal body. In this study we have explored the gene expression profile and signaling pathways followed by the calcification process of a basal metazoan, the Red Sea scleractinian (stony) coral, Stylophora pistillata. When treated by seawater with high calcium concentrations (addition of 100 gm/L, added as CaCl2.2H2O), the coral increases its calcification rates and associated genes were up-regulated as a result, which were then identified. Gene expression was compared between corals treated with elevated and normal calcium concentrations. Calcification rate measurements and gene expression analysis by microarray RNA transcriptional profiling at two time-points (midday and night-time) revealed several genes common within mammalian gene regulatory networks. This study indicates that core genes of the Wnt and TGF-β/BMP signaling pathways may also play roles in development, growth, and biomineralization in early-diverging organisms such as corals.
Highlights
Coral calcification is a process of skeletal elements extension and is accompanied by the development of the coral’s tissues
During night-time (23:00), calcification rates were not influenced by the calcium concentration additions (Fig. 2 and File S1)
Significant differences were found during the daytime between calcification in natural seawater and calcification with additional calcium concentration (one-way ANOVA F (2,9) = 5.277, p = 0.03; n = 4), while during night-time no difference was found (one-way ANOVA F (2,9) = 1.052, p = 0.39; n = 4)
Summary
Coral calcification is a process of skeletal elements extension and is accompanied by the development of the coral’s tissues. The biomineralization and development processes are generated by the differential gene expressions with specialized cellular properties, as demonstrated in various organisms (Belcher et al, 1996; Gardner et al, 2011; Kuballa & Elizur, 2008; Reyes-Bermudez et al, 2009). These gene expression characteristics of many cellular processes, among them are biomineralization and tissue growth, which are coordinated by networks of regulatory genes. The mechanism behind the transport of calcium is under debate, and three pathways have been proposed: (i) active transcellular transport of calcium through calicoblastic cells, (ii) passive paracellular diffusion of calcium or seawater between calicoblastic cells, and (iii) a combination of transcellular and paracellular pathways (Reviewed in Allemand et al, 2011 and Allison et al, 2014)
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