Early evolutionary history (from bacteria to hemichordata) of the omnipresent purinergic signalling: A tribute to Geoff Burnstock inquisitive mind

Purines and pyrimidines are indispensable molecules of life; they fundamental for genetic code bioenergetics. From the very early evolution life purines have acquired meaning damage-associated extracellular signaller purinergic receptors emerged in unicellular organisms. Ancestral purinoceptors P2X-like ionotropic ligand-gated cationic channels showing 20–40% homology with vertebrate P2X receptors; genes encoding ancestral been detected Protozoa, Algae, Fungi Sponges; also present some invertebrates, but absent from genome insects, nematodes, higher plants. Plants nevertheless evolved a sophisticated widespread signalling system relying on idiosyncratic purinoceptor P2K1/DORN1 linked to intracellular Ca2+ signalling. The advance metabotropic starts later adenosine preceding emergence P2Y nucleotide P0 adenine receptors. In vertebrates mammals reaches summit operates throughout all tissues systems without anatomical or functional segregation.