Abstract
P2X receptors are ATP-gated cations channels formed by the homo or hetero-trimeric association from the seven cloned subunits (P2X1-7). P2X receptors are widely distributed in different organs and cell types throughout the body including the nervous system and are involved in a large variety of physiological but also pathological processes in adult mammals. However, their expression and function during embryogenesis remain poorly understood. Here, we report the cloning and the comparative expression map establishment of the entire P2X subunit family in the clawed frog Xenopus. Orthologous sequences for 6 mammalian P2X subunits were identified in both X. laevis and X. tropicalis, but not for P2X3 subunit, suggesting a potential loss of this subunit in the Pipidae family. Three of these genes (p2rx1, p2rx2, and p2rx5) exist as homeologs in the pseudoallotetraploid X. laevis, making a total of 9 subunits in this species. Phylogenetic analyses demonstrate the high level of conservation of these receptors between amphibian and other vertebrate species. RT-PCR revealed that all subunits are expressed during the development although zygotic p2rx6 and p2rx7 transcripts are mainly detected at late organogenesis stages. Whole mount in situ hybridization shows that each subunit displays a specific spatio-temporal expression profile and that these subunits can therefore be grouped into two groups, based on their expression or not in the developing nervous system. Overlapping expression in the central and peripheral nervous system and in the sensory organs suggests potential heteromerization and/or redundant functions of P2X subunits in Xenopus embryos. The developmental expression of the p2rx subunit family during early phases of embryogenesis indicates that these subunits may have distinct roles during vertebrate development, especially embryonic neurogenesis.
Highlights
The nucleotide ATP, as the universal source of energy, is an essential intracellular molecule to the survival of cells and whole organisms
The p2rx subunit sequences were identified by bioinformatics analysis, this work having benefited from the recent X. tropicalis and X. laevis genome sequencing (Hellsten et al, 2010; Session et al, 2016)
Our study reveals that all members of the p2rx family, except p2rx3, are present in Xenopus laevis and tropicalis
Summary
The nucleotide ATP, as the universal source of energy, is an essential intracellular molecule to the survival of cells and whole organisms. The discovery of the first P2 purinergic receptor at the beginning of the 1990s confirmed Geoffrey Burnstock’s hypothesis that ATP acts as an extracellular signaling molecule (Burnstock, 2014). The metabolic breakdown of extracellular ATP by ectonucleotidases is a source of ADP and adenosine. Both ATP derivatives act as extracellular signaling molecule through the activation of P2Y and adenosine G-protein coupled receptors (Adora) respectively (Yegutkin, 2014). It is nowadays recognized that the purinergic signaling in various organs play important physiological roles and in diseases, placing purinergic receptors and ectonucleotidases as theurapeutic targets (Burnstock, 2018). The description of the ectonucleotidases and purinoreceptors embryonic expression profile in vivo provides indication of their implication during nervous system development (Massé and Dale, 2012)
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