小G蛋白BBS3通过BBSome调控纤毛信号蛋白输出纤毛的机制研究

纤毛是真核细胞信号转导器，在发育、分化和器官形成中起重要作用。信号蛋白在纤毛内的稳态失衡可导致遗传性纤毛病巴德-毕德氏症。我们前期的研究表明类ARF6型小G蛋白BBS3与巴德-毕德氏症复合物（BBSome）亚单位BBS1相互作用，在GTP锁定状态时招募BBSome到基体，使其得以和正向鞭毛内运送体偶联进入纤毛。纤毛信号蛋白磷脂酶D（PLD）附着细胞膜以扩散方式进入纤毛。在纤毛顶部，PLD通过BBSome与反向鞭毛内运送体偶联，从而得以输出纤毛。GTP锁定状态的BBS3亦可进入纤毛调控PLD输出纤毛。因此，我们假设BBS3的作用是招募BBSome与PLD进行偶联，从而使得装载PLD的BBSome与反向鞭毛内运送体偶联得以输出纤毛。我们将利用莱茵衣藻为模式生物，利用生化、遗传和单分子活体成像技术来验证BBS3通过BBSome调控PLD输出纤毛分子机理，为更好理解巴德-毕德氏症发病机制奠定基础。

As a signal transducer of eukaryotic cells, cilia play an important role in development, differentiation and organ formation. Defects in maintaining homeostasis of signaling proteins in cilia thus result in hereditary ciliopathy Bardet-Biedl syndrome. Our previous study showed that the ARF-like small GTPase ARL6/BBS3, when in a GTP-bound state, recruits the BBSome from the cell body to the basal body through interacting with the BBSome subunit BBS1. At the basal body, the BBSome loads onto anterograde IFT for entering cilia. It was already known that the ciliary signaling protein phospholipase D (PLD) diffuses into cilia on membrane. At the ciliary tip, PLD couples with retrograde IFT through the BBSome for exiting cilia via IFT. In addition, BBS3 also enters cilia in a GTP-bound configuration and participates in promoting ciliary exit of PLD. Based on those observations, we hypothesize that BBS3 promotes coupling of PLD with IFT through the BBSome for exiting cilia. In this study, we use Chlamydomonas reinhardtii as a model organism. By employing biochemical, genetic and single particle in vivo imaging assays, we try to clarify the molecular mechanism of how BBS3 3 mediates ciliary exit of PLD through the BBSome, so as to better understand the pathogenesis of Bardet-Biedl syndrome.