The origin of nervous systems is a main theme in biology and its mechanisms are largely underlied by synaptic neurotransmission. One problem to explain synapse establishment is that synaptic orthologs are present in multiple aneural organisms. We questioned how the interactions among these elements evolved and to what extent it relates to our understanding of the nervous systems complexity. We identified the human neurotransmission gene network based on genes present in GABAergic, glutamatergic, serotonergic, dopaminergic, and cholinergic systems. The network comprises 321 human genes, 83 of which act exclusively in the nervous system. We reconstructed the evolutionary scenario of synapse emergence by looking for synaptic orthologs in 476 eukaryotes. The Human-Cnidaria common ancestor displayed a massive emergence of neuroexclusive genes, mainly ionotropic receptors, which might have been crucial to the evolution of synapses. Very few synaptic genes had their origin after the Human-Cnidaria common ancestor. We also identified a higher abundance of synaptic proteins in vertebrates, which suggests an increase in the synaptic network complexity of those organisms.

中文翻译：

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离子型受体是人类突触建立背后的驱动力

神经系统的起源是生物学的一个主要主题，其机制在很大程度上受到突触神经传递的支持。解释突触建立的一个问题是突触直向同源物存在于多种非生物中。我们质疑这些元素之间的相互作用如何演变，以及在多大程度上与我们对神经系统复杂性的理解有关。我们基于存在于GABA能，谷氨酸能，血清素能，多巴胺能和胆碱能系统中的基因确定了人类神经传递基因网络。该网络包含321个人类基因，其中83个仅在神经系统中起作用。我们通过寻找476个真核生物中的突触直向同源物，重建了突触出现的进化场景。人类-人参共同祖先显示出大量神经排他性基因，主要是离子型受体，这可能对突触的进化至关重要。很少有突触基因起源于人类-唇ni目的共同祖先。我们还发现了脊椎动物中突触蛋白的丰度更高，这表明这些生物的突触网络复杂性增加。