Data from: The GPCR repertoire in the demosponge Amphimedon queenslandica: insights into the GPCR system at the early divergence of animals

Background: G protein-coupled receptors (GPCRs) play a central role in eukaryotic signal transduction. However, the GPCR component of this signalling system, at the early origins of metazoans is not fully understood. Here we aim to identify and classify GPCRs in Amphimedon queenslandica (sponge), a member of the Porifera (one of the earliest diverging metazoan lineages). Furthermore, phylogenetic comparisons of sponge GPCRs with eumetazoan and bilaterian GPCRs will be essential to our understanding of the GPCR system at the roots of metazoan evolution. Results: We present a curated list of 220 GPCRs in the sponge genome after excluding incomplete sequences and false positives from our initial dataset of 282 predicted GPCR sequences obtained using Pfam search. Phylogenetic analysis reveals that the sponge contains members belonging to four of the five major GRAFS families including Glutamate (33), Rhodopsin (126), Adhesion (40), and Frizzled (3). Interestingly, the sponge Rhodopsin family sequences lack orthologous relationships with those found in eumetazoan and bilaterian lineages, since they clustered separately to form sponge specific groups in the phylogenetic analysis. This suggests that sponge Rhodopsins diverged considerably from that found in other basal metazoans. A few Adhesion GPCRs clustered basal to Adhesion subfamilies that are commonly found in most of the vertebrates, suggesting some Adhesion subfamilies may have diverged prior to the divergence of Bilateria. Furthermore, at least eight of the sponge Adhesion members have a Hormone binding motif (HRM domain) in their N-termini, although hormones have yet to be identified in sponges. We also phylogenetically clarified that sponge has homologs of metabotropic glutamate (mGluRs) and GABA receptors. Conclusion: Our phylogenetic comparisons of sponge GPCRs with other metazoan genomes suggest that sponge contains a significantly diversified set of GPCRs. This is evident at the family/subfamily level comparisons for most GPCR families, in particular for the Rhodopsin family of GPCRs. In summary, this study provides a framework to perform future experimental and comparative studies to further verify and understand the roles of GPCRs that predates the divergence of bilaterian and eumetazoan lineages.## 背景 G蛋白偶联受体（G protein-coupled receptors, GPCRs）在真核生物信号转导中发挥核心作用。然而，在后生动物起源早期阶段，该信号系统中的GPCR组分尚未被完全阐明。本研究旨在对澳洲大堡礁海绵（Amphimedon queenslandica）——多孔动物门（Porifera，分化最早的后生动物类群之一）——中的GPCR进行鉴定与分类。此外，对海绵GPCR与真后生动物（eumetazoan）、两侧对称动物（bilaterian）GPCR进行系统发育比较，对于理解后生动物演化根源处的GPCR系统至关重要。 ## 结果 本研究从初始通过Pfam搜索获得的282条预测GPCR序列数据集中，剔除不完整序列与假阳性序列后，得到了经过人工整理的海绵基因组220个GPCR列表。系统发育分析显示，海绵中存在5个主要GRAFS家族中的4个家族的成员，分别为谷氨酸受体家族（33个）、视紫红质家族（126个）、黏附类GPCR（40个）以及卷曲蛋白（3个）。值得注意的是，海绵视紫红质家族序列与真后生动物和两侧对称动物类群中的序列不存在直系同源关系：在系统发育分析中，海绵视紫红质序列单独聚类形成海绵特异性类群。这表明海绵视紫红质与其他基底后生动物的视紫红质已发生显著分化。少数黏附类GPCR聚类于大多数脊椎动物中普遍存在的黏附类GPCR亚家族的基部，提示部分黏附类GPCR亚家族可能在两侧对称动物分化之前就已出现。此外，海绵中至少有8个黏附类GPCR成员的N端带有激素结合基序（Hormone binding motif, HRM结构域），尽管目前尚未在海绵中鉴定出相关激素。本研究还通过系统发育分析明确了海绵拥有代谢型谷氨酸受体（metabotropic glutamate receptors, mGluRs）与γ-氨基丁酸（GABA）受体的同源物。 ## 结论 通过将海绵GPCR与其他后生动物基因组进行系统发育比较，本研究发现海绵拥有一套显著多样化的GPCR组。在大多数GPCR家族（尤其是视紫红质家族GPCR）的家族/亚家族层面比较中，这一特征尤为明显。综上，本研究为未来开展实验与比较研究提供了框架，以进一步验证并理解先于两侧对称动物与真后生动物分化的GPCR的功能。