Bilateria具有双侧对称性,可细分为Deuterostomia(脊椎动物等动物)和原口(昆虫和软体动物等动物)。神经肽存在于原口和氘口中,并且它们通常在这两个谱系中在结构上相关。例如,属于催产素/加压素家族的肽存在于两个进化枝中。对于这些肽的G蛋白偶联受体(GPCR)也是如此。这些观察结果表明,这些神经肽和它们的GPCRs已经存在于原口和子宫口的共同祖先中,生活在大约7亿年前(MYA)。此外,神经肽和它们的GPCRs发生在两个早期分支的门中,在Bilateria出现之前就已经分化了:Cnidaria(像珊瑚和海葵这样的动物),和胎盘动物(小圆盘状动物,以藻类为食)。这些神经肽的序列和它们的GPCRs,然而,与Bilateria的人没有密切关系。此外,刺胞神经肽及其受体与胎盘动物的神经肽及其受体并不密切相关。我们建议Cnidaria之间的分歧时间,胎盘动物,和Bilateria可能太长了,无法识别序列身份。富含亮氨酸重复序列的GPCRs(LGRs)是一类特殊的GPCRs,其特征在于含有10-20个富含亮氨酸的结构域的长N端,用于配体结合。LGR的配体是二聚体糖蛋白激素,和胰岛素样肽,比如relaxin。LGRs不仅在原口和Deuterostomia中被发现,而且在早期出现的门中,如Cnidaria和Placozoa。人类有8个LGR。在我们目前的审查中,我们已经重新审视了海葵Nematostellavectensis和placozoanTrichoplaxadhaerens的LGR注释。我们从T.adhaerens中鉴定出13个海葵LGR和不少于46个LGR。所有八个人类LGR似乎在海葵和胎盘动物中都具有直系同源物。LGR及其配体,因此,有着悠久的进化历史,回到Cnidaria和Placozoa的共同祖先。
Bilateria have bilateral symmetry and are subdivided into Deuterostomia (animals like vertebrates) and Protostomia (animals like insects and mollusks). Neuropeptides occur in both Proto- and Deuterostomia and they are frequently structurally related across these two lineages. For example, peptides belonging to the oxytocin/vasopressin family exist in both clades. The same is true for the G protein-coupled receptors (GPCRs) of these peptides. These observations suggest that these neuropeptides and their GPCRs were already present in the common ancestor of Proto- and Deuterostomia, which lived about 700 million years ago (MYA). Furthermore, neuropeptides and their GPCRs occur in two early-branching phyla that diverged before the emergence of Bilateria: Cnidaria (animals like corals and sea anemones), and Placozoa (small disk-like animals, feeding on algae). The sequences of these neuropeptides and their GPCRs, however, are not closely related to those from Bilateria. In addition, cnidarian neuropeptides and their receptors are not closely related to those from Placozoa. We propose that the divergence times between Cnidaria, Placozoa, and Bilateria might be too long for recognizing sequence identities. Leucine-rich repeats-containing GPCRs (LGRs) are a special class of GPCRs that are characterized by a long N-terminus containing 10-20 leucine-rich domains, which are used for ligand binding. Among the ligands for LGRs are dimeric glycoprotein hormones, and insulin-like peptides, such as relaxin. LGRs have been found not only in Proto- and Deuterostomia, but also in early emerging phyla, such as Cnidaria and Placozoa. Humans have eight LGRs. In our current
review, we have revisited the annotations of LGRs from the sea anemone Nematostella vectensis and the placozoan Trichoplax adhaerens. We identified 13 sea anemone LGRs and no less than 46 LGRs from T. adhaerens. All eight human LGRs appear to have orthologues in sea anemones and placozoans. LGRs and their ligands, therefore, have a long evolutionary history, going back to the common ancestor of Cnidaria and Placozoa.