P2X receptors in Aplysia californica: Chemosensory systems, bio-energetic and development

Abstract

ATP and its ionotropic P2X receptors are components of one of the most ancient signaling systems. However, little is known about the distribution and function of purinergic transmission in invertebrates. Here, we cloned, expressed, and pharmacologically characterized P2X receptors in the sea slug Aplysia californica - a prominent model in cellular and system neuroscience. We showed that ATP and P2X receptors are essential signaling components within the unique bioenergetic center located in the CNS of Aplysia, also known as the cerebral F-cluster of insulin-containing neurons. Functional P2X receptors were successfully expressed in Xenopus oocytes to characterize their ATP-dependence (EC50=306M), two-phased kinetics, ion selectivity (Na+-dependence), sensitivity to the ATP analog Bz-ATP (~20% compare to ATP) and antagonists (with PPADS as a more potent inhibitor compared to suramin). Next, using RNA-seq, we characterized the expression of P2X receptors across more than a dozen Aplysia peripheral tissues and developmental stages. We showed that P2X receptors are predominantly expressed in chemosensory structures and during early cleavage stages. The localization and pharmacology of P2X receptors in Aplysia highlight the evolutionary conservation of bioenergetic sensors and chemosensory purinergic transmission across animals. This study also provides a foundation to decipher homeostatic mechanisms in development and neuroendocrine systems. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=124 SRC="FIGDIR/small/243196v1_ufig1.gif" ALT="Figure 1"> View larger version (47K): org.highwire.dtl.DTLVardef@d5c2faorg.highwire.dtl.DTLVardef@1f3dab3org.highwire.dtl.DTLVardef@9b49daorg.highwire.dtl.DTLVardef@10dc71f_HPS_FORMAT_FIGEXP M_FIG C_FIG We show that ATP and its ligand-gated P2X receptors are essential signaling components within both the chemosensory systems and the unique bioenergetic center, present in the CNS of the sea slug Aplysia californica - a prominent model in neuroscience. Expression and pharmacology of P2X receptors in Aplysia confirms the preservation of evolutionary conserved bioenergetic sensors across animals and provide new tools to decipher homeostatic mechanisms in neuro-endocrine systems in general.