Table9_Origin and Evolution of the Multifaceted Adherens Junction Component Plekha7.xlsx

Plekha7 is a key adherens junction component involved in numerous functions in mammalian cells. Plekha7 is the most studied member of the PLEKHA protein family, which includes eight members with diverse functions. However, the evolutionary history of Plekha7 remains unexplored. Here, we outline the phylogeny and identify the origins of this gene and its paralogs. We show that Plekha7, together with Plekha4, Plekha5, and Plekha6, belong to a subfamily that we name PLEKHA4/5/6/7. This subfamily is distinct from the other Plekha proteins, which form two additional separate subfamilies, namely PLEKHA1/2 and PLEKHA3/8. Sequence, phylogenetic, exon-intron organization, and syntenic analyses reveal that the PLEKHA4/5/6/7 subfamily is represented by a single gene in invertebrates, which remained single in the last common ancestor of all chordates and underwent gene duplications distinctly in jawless and jawed vertebrates. In the latter species, a first round of gene duplications gave rise to the Plekha4/7 and Plekha5/6 pairs and a second round to the four extant members of the subfamily. These observations are consistent with the 1R/2R hypothesis of vertebrate genome evolution. Plekha7 and Plekha5 also exist in two copies in ray-finned fishes, due to the Teleostei-specific whole genome duplication. Similarities between the vertebrate Plekha4/5/6/7 members and non-chordate sequences are restricted to their N-terminal PH domains, whereas similarities across the remaining protein molecule are only sporadically found among few invertebrate species and are limited to the coiled-coil and extreme C-terminal ends. The vertebrate Plekha4/5/6/7 proteins contain extensive intrinsically disordered domains, which are topologically and structurally conserved in all chordates, but not in non-chordate invertebrates. In summary, our study sheds light on the origins and evolution of Plekha7 and the PLEKHA4/5/6/7 subfamily and unveils new critical information suitable for future functional studies of this still understudied group of proteins.

Plekha7是哺乳动物细胞中参与多种生理功能的关键黏着连接（adherens junction）组分，同时也是研究最为深入的PLEKHA蛋白家族成员，该家族共包含8个功能各异的成员。然而，Plekha7的进化历史至今尚未被探索。本研究对该基因及其旁系同源基因（paralog）的系统发育与起源进行了系统梳理。研究表明，Plekha7与Plekha4、Plekha5、Plekha6同属于一个我们命名为PLEKHA4/5/6/7的亚家族，该亚家族与另外两个独立的Plekha蛋白亚家族（即PLEKHA1/2和PLEKHA3/8）存在显著区别。通过序列比对、系统发育分析、外显子-内含子结构（exon-intron organization）分析以及共线性分析（syntenic analysis），我们发现PLEKHA4/5/6/7亚家族在无脊椎动物中仅以单个基因的形式存在，该单基因在所有脊索动物的最近共同祖先中仍保持单一拷贝，并在无颌类和有颌类脊椎动物中分别发生了独立的基因复制事件。在有颌类脊椎动物中，第一轮基因复制产生了Plekha4/7和Plekha5/6两个基因对，第二轮复制则形成了该亚家族目前已知的4个成员。上述发现与脊椎动物基因组进化的1R/2R假说（1R/2R hypothesis）相一致。由于硬骨鱼纲（Teleostei）特有的全基因组复制事件，Plekha7和Plekha5在辐鳍鱼中存在两个拷贝。脊椎动物PLEKHA4/5/6/7家族成员与非脊索动物序列的相似性仅局限于其N端的PH结构域（PH domain）；而蛋白分子其余区域的相似性仅在少数非脊索动物无脊椎动物物种中零星存在，且仅局限于卷曲螺旋结构域（coiled-coil）和极端C端区域。脊椎动物PLEKHA4/5/6/7蛋白含有大量的内在无序结构域（intrinsically disordered domain），该结构域在所有脊索动物中均具有拓扑和结构保守性，但在非脊索动物无脊椎动物中并不具备。综上，本研究阐明了Plekha7及PLEKHA4/5/6/7亚家族的起源与进化历程，为这一尚未被充分研究的蛋白家族的后续功能研究提供了全新的关键理论依据。