Cross references: Deuterostomes Deuterostome Nerves
Deuterostome Genomics Transmembrane Transport in General
Transmembrane Signaling in General
Ancestry of neuronal monoamine transporters in the Metazoa (Goog) - 2006
"Selective Na+-dependent re-uptake of biogenic monoamines at mammalian nerve synapses is accomplished by three types of solute-linked carrier family 6 (SLC6) membrane transporter with high affinity for serotonin (SERTs), dopamine (DATs) and norepinephrine (NETs)."
"To clarify the relationships among metazoan monoamine transporters we identified representatives in the major branches of metazoan evolution by polymerase chain reaction (PCR)-amplifying conserved cDNA fragments from isolated nervous tissue and by analyzing available genomic data.
Analysis of conserved motifs in the sequence data suggest that the presumed common ancestor of modern-day Bilateria expressed at least three functionally distinct monoamine transporters in its nervous system:
a SERT currently found throughout bilaterian phyla,
a DAT now restricted in distribution to protostome invertebrates and echinoderms and
a third monoamine transporter (MAT), widely represented in contemporary Bilateria, that is selective for catecholamines and/or phenolamines.
Chordate DATs, NETs, epinephrine transporters (ETs) and arthropod and annelid OATs all belong to the MAT clade."
"Contemporary invertebrate and chordate DATs belong to different SLC6 clades. Furthermore, the genes for dopamine and norepinephrine transporters of vertebrates are paralogous, apparently having arisen through duplication of an invertebrate MAT gene after the loss of an invertebrate-type DAT gene in a basal protochordate."
Since these are transporters, they are probably Ligand-gated Ion Channels , although there are other forms of Transmembrane Transport . Since the synaptic G-Protein Coupled Receptors don't transport anything across the membrane, it is possible that the ionotropic receptors serve only for reuptake of the ligand and that all signal tranduction is via the meabotropic receptors.
Serotonin and its metabolism in basal deuterostomes (Goog) - 2010
"Serotonin (5-HT), an important molecule in metazoans, is involved in a range of biological processes including neurotransmission and neuromodulation. Both its creation and release are tightly regulated, as is its removal. Multiple neurochemical pathways are responsible for the catabolism of 5-HT and are phyla specific; therefore, by elucidating these catabolic pathways we glean greater understanding of the relationships and origins of various transmitter systems. Here, 5-HT catabolic pathways were studied in Strongylocentrotus purpuratus (see below) and Xenoturbellida bocki, two organisms occupying distinct positions in deuterostomes."
Since there's nothing about the identity or location of receptors, this article is of limited utility.
Strongylocentrotus purpuratus (Wiki)
Pacific Ocean extending from Ensenada, Mexico to British Columbia, Canada. "
"The sea urchin genome is estimated to encode about 23,300 genes. Many of these genes were previously thought to be vertebrate innovations or were only known from groups outside the deuterostomes. Thus the sea urchin genome provides a comparison to our own and those of other deuterostomes, the larger group to which both echinoderms and humans belong.
Using the strictest measure, the purple sea urchin and humans share 7,700 genes. Many of these genes are involved in sensing the environment, a fact surprising for an animal lacking a head structure."