Defensome against toxic diatom aldehydes in the sea urchin Paracentrotus lividus

Abstract

Many diatom species produce polyunsaturated aldehydes, such as decadienal, which compromise embryonic and larval development in benthic organisms. Here newly fertilized Paracentrotus lividus sea urchins were exposed to low concentration of decadienal and the expression levels of sixteen genes, implicated in a broad range of functional responses, were followed by Real Time qPCR in order to identify potential decadienal targets. We show that at low decadienal concentrations the sea urchin Paracentrotus lividus places in motion different classes of genes to defend itself against this toxic aldehyde, activating hsp60 and two proteases, hat and BP10, at the blastula stage and hsp56 and several other genes (14-3-3ε, p38 MAPK, MTase, and GS) at the prism stage. At this latter stage all genes involved in skeletogenesis (Nec, uni, SM50 and SM30) were also down-expressed, following developmental abnormalities that mainly affected skeleton morphogenesis. Moreover, sea urchin embryos treated with increasing concentrations of decadienal revealed a dose-dependent response of activated target genes. Finally, we suggest that this orchestrated defense system against decadienal represents part of the chemical defensome of P. lividus affording protection from environmental toxicants.

Figure 1. Gene activation in response to a low concentrations of decadienal.

Histogram shows the differences in expression levels of analyzed stress genes, followed by Real Time qPCR. Embryos incubated with decadienal 0.25 µg/ml were collected at 5, 9, 24 and 48 hpf. Data are reported as a fold difference compared to control (mean ± SD), embryos in sea water without decadienal. Fold differences greater than ±2 (see dotted horizontal guidelines at values of 2 and −2) were considered significant. (For more details on genes see also Table 1 and Table S1; see also Materials and Methods for Real Time qPCR).

Figure 2. Dose-dependence effects of decadienal on gene expression.

Histograms show decadienal dose-dependent variations in expression levels. Samples incubated with increasing decadienal concentrations (0.15, 0.20, 0.25, 0.30, 0.35 µg/ml) were collected at different times of development. A) decadienal dose-dependent overexpression for hsp70, hsp60, hat and BP10 genes at 9 hpf; B) overexpression of hsp56 and 14-3-3ε and dow-expression of skeletogenic genes sox9 and SM30 at 24 hpf; C) down-expression of SM50 at 48 hpf. (For more details see Legend to Figure 1).

Figure 3. Dose-dependence effects of decadienal on sea urchin morphogenesis.

(A) Control (embryos in sea water without decadienal), length 364.3 µm. (B) decadienal 0.15 µg/ml, length 317.6 µm, (C) decadienal 0.20 µg/ml, length 288.3 µm, (D) decadienal 0.25 µg/ml, length 261.6 µm, (E) 0.30 µg/ml, length 260.3 µm, (F) decadienal 0.35 µg/ml, length 253.6 µm. The images were taken at 48 hpf.