Yañez-Guerra Luis Alfonso, Elphick Maurice R
School of Biological and Chemical Sciences, Faculty of Science and Engineering, Queen Mary University of London, London, United Kingdom.
Front Neurosci. 2020 Feb 18;14:130. doi: 10.3389/fnins.2020.00130. eCollection 2020.
Luqin is a neuropeptide that was discovered and named on account of its expression in left upper quadrant cells of the abdominal ganglion in the mollusc . Subsequently, luqin-type peptides were identified as cardio-excitatory neuropeptides in other molluscs and a cognate receptor was discovered in the pond snail Phylogenetic analyses have revealed that orthologs of molluscan luqin-type neuropeptides occur in other phyla; these include neuropeptides in ecdysozoans (arthropods, nematodes) that have a C-terminal RYamide motif (RYamides) and neuropeptides in ambulacrarians (echinoderms, hemichordates) that have a C-terminal RWamide motif (RWamides). Furthermore, precursors of luqin-type neuropeptides typically have a conserved C-terminal motif containing two cysteine residues, although the functional significance of this is unknown. Consistent with the orthology of the neuropeptides and their precursors, phylogenetic and pharmacological studies have revealed that orthologous G-protein coupled receptors (GPCRs) mediate effects of luqin-type neuropeptides in spiralians, ecdysozoans, and ambulacrarians. Luqin-type signaling originated in a common ancestor of the Bilateria as a paralog of tachykinin-type signaling but, unlike tachykinin-type signaling, luqin-type signaling was lost in chordates. This may largely explain why luqin-type signaling has received less attention than many other neuropeptide signaling systems. However, insights into the physiological actions of luqin-type neuropeptides (RYamides) in ecdysozoans have been reported recently, with roles in regulation of feeding and diuresis revealed in insects and roles in regulation of feeding, egg laying, locomotion, and lifespan revealed in the nematode Furthermore, characterization of a luqin-type neuropeptide in the starfish (phylum Echinodermata) has provided the first insights into the physiological roles of luqin-type signaling in a deuterostome. In conclusion, although luqin was discovered in over 30 years ago, there is still much to be learnt about luqin-type neuropeptide signaling. This will be facilitated in the post-genomic era by the emerging opportunities for experimental studies on a variety of invertebrate taxa.
鲁金是一种神经肽，因其在软体动物腹神经节左上象限细胞中的表达而被发现并命名。随后，鲁金型肽在其他软体动物中被鉴定为心脏兴奋神经肽，并在池塘螺中发现了同源受体。系统发育分析表明，软体动物鲁金型神经肽的直系同源物存在于其他门中；这些包括蜕皮动物（节肢动物、线虫）中具有C端RY酰胺基序（RY酰胺）的神经肽，以及步带动物（棘皮动物、半索动物）中具有C端RW酰胺基序（RW酰胺）的神经肽。此外，鲁金型神经肽的前体通常具有一个包含两个半胱氨酸残基的保守C端基序，尽管其功能意义尚不清楚。与神经肽及其前体的直系同源性一致，系统发育和药理学研究表明，直系同源的G蛋白偶联受体（GPCR）介导鲁金型神经肽在螺旋动物、蜕皮动物和步带动物中的作用。鲁金型信号传导起源于两侧对称动物的共同祖先，是速激肽型信号传导的旁系同源物，但与速激肽型信号传导不同，鲁金型信号传导在脊索动物中消失了。这可能在很大程度上解释了为什么鲁金型信号传导比许多其他神经肽信号系统受到的关注较少。然而，最近有报道称对蜕皮动物中鲁金型神经肽（RY酰胺）的生理作用有了深入了解，在昆虫中发现其在摄食和利尿调节中起作用，在秀丽隐杆线虫中发现其在摄食、产卵、运动和寿命调节中起作用。此外，对海星（棘皮动物门）中一种鲁金型神经肽的表征首次揭示了鲁金型信号传导在后口动物中的生理作用。总之，尽管鲁金是在30多年前被发现的，但关于鲁金型神经肽信号传导仍有许多有待了解的地方。在基因组时代之后，对各种无脊椎动物类群进行实验研究的新机会将有助于这方面的研究。
