Benabentos Rocio, Hirose Shigenori, Sucgang Richard, Curk Tomaz, Katoh Mariko, Ostrowski Elizabeth A, Strassmann Joan E, Queller David C, Zupan Blaz, Shaulsky Gad, Kuspa Adam
Graduate Program in Cell and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
Curr Biol. 2009 Apr 14;19(7):567-72. doi: 10.1016/j.cub.2009.02.037. Epub 2009 Mar 12.
Self and kin discrimination are observed in most kingdoms of life and are mediated by highly polymorphic plasma membrane proteins. Sequence polymorphism, which is essential for effective recognition, is maintained by balancing selection. Dictyostelium discoideum are social amoebas that propagate as unicellular organisms but aggregate upon starvation and form fruiting bodies with viable spores and dead stalk cells. Aggregative development exposes Dictyostelium to the perils of chimerism, including cheating, which raises questions about how the victims survive in nature and how social cooperation persists. Dictyostelids can minimize the cost of chimerism by preferential cooperation with kin, but the mechanisms of kin discrimination are largely unknown. Dictyostelium lag genes encode transmembrane proteins with multiple immunoglobulin (Ig) repeats that participate in cell adhesion and signaling. Here, we describe their role in kin discrimination. We show that lagB1 and lagC1 are highly polymorphic in natural populations and that their sequence dissimilarity correlates well with wild-strain segregation. Deleting lagB1 and lagC1 results in strain segregation in chimeras with wild-type cells, whereas elimination of the nearly invariant homolog lagD1 has no such consequences. These findings reveal an early evolutionary origin of kin discrimination and provide insight into the mechanism of social recognition and immunity.
在大多数生物界中都观察到了自我与亲属识别现象，并且这种识别是由高度多态性的质膜蛋白介导的。序列多态性对于有效识别至关重要，它通过平衡选择得以维持。盘基网柄菌是社会性变形虫，以单细胞生物形式繁殖，但在饥饿时聚集并形成带有存活孢子和死亡柄细胞的子实体。聚集性发育使盘基网柄菌面临嵌合体的风险，包括欺骗行为，这引发了关于受害者如何在自然环境中生存以及社会合作如何持续存在的问题。盘基网柄菌可以通过优先与亲属合作来最小化嵌合体的成本，但亲属识别的机制在很大程度上尚不清楚。盘基网柄菌的lag基因编码具有多个免疫球蛋白（Ig）重复序列的跨膜蛋白，这些蛋白参与细胞黏附和信号传导。在此，我们描述它们在亲属识别中的作用。我们表明，lagB1和lagC1在自然种群中高度多态，并且它们的序列差异与野生菌株的分离情况密切相关。删除lagB1和lagC1会导致与野生型细胞形成的嵌合体中菌株分离，而消除几乎不变的同源基因lagD1则没有这种结果。这些发现揭示了亲属识别的早期进化起源，并为社会识别和免疫机制提供了见解。
