. Pc-astakine mRNA levels decrease after both LPS injection and hemolymph withdrawals in the gastropod pest Pomacea canaliculata.

The freshwater gastropod Pomacea canaliculata has recently been included among emerging pests in the EU. Hence, its immune system may be a promising target for pest control strategies. By analyzing a set of P. canaliculata transcriptomes, we have discovered an Astakine-1-like molecule (Pc-Astakine) in this organism. Astakine was first isolated as a hematopoietic cytokine in the crayfish Pacifastacus leniusculus (Pl-Astakine-1), and later found in arthropods and the bivalve Crassostrea gigas. Bioinformatic analyses show that Pc-Astakine is a 121 aa protein with a conserved distribution pattern of cysteines retrievable in both Pl-Astakine-1 and the vertebrate Prokineticin protein family. Pc-astakine is expressed at low levels in circulating hemocytes, but markedly in hemocyte reservoirs (e.g., ampulla) and hematopoietic tissue (pericardial fluid) suggesting a conserved role in hematopoiesis. We tested this potential role of Pc-Astakine in two ways. First, we measured RNA levels of this gene in immune-related tissues 24 h after injection of 50 μg of Escherichia coli-derived lipopolysaccharide (055:B5) (LPS). We observed a sharp decrease of Pc-astakine mRNA in all the analyzed organs, with Pc-astakine mRNA levels almost undetectable in anterior kidney (a hemocyte reservoir) when compared to sham-injected controls. Second, we defined the profile of Pc-astakine expression after a series of 4 hemolymph withdrawals performed within 72 h. As with the LPS-treatment, a general decrease of mRNA levels was observed, with the largest decrease observed in hematopoietic tissue and circulating hemocytes (reduced to 20% of the control). Altogether, we hypothesize that the decrease of Pc-astakine mRNA after both LPS injection and hemolymph withdrawal may be due to an increased rate of translation, rather than a reduction of gene expression. This is in part supported by similar observations in the oyster C. gigas in which massive translation of Cg-astakine is observed as a consequence of environment stress, including immune stimuli, and in P. leniusculus in which increased levels of Astakine in the plasma of LPS-injected animals have been related to an increased translational rate. To our knowledge, this is the first report of an astakine-like molecule in gastropods and our data indicate a potential involvement of Pc-Astakine in both the immune response and hematopoiesis of the molluscan pest P. canaliculata.