Wessels Deborah, Srikantha Thyagarajan, Yi Song, Kuhl Spencer, Aravind L, Soll David R
W.M. Keck Dynamic Image Analysis Facility, Department of Biological Sciences, The University of Iowa, Iowa City, IA 52242, USA.
J Cell Sci. 2006 Jan 15;119(Pt 2):370-9. doi: 10.1242/jcs.02753.
The Shwachman-Bodian-Diamond syndrome (SBDS) is an autosomal disorder with multisystem defects. The Shwachman-Bodian-Diamond syndrome gene (SBDS), which contains mutations in a majority of SBDS patients, encodes a protein of unknown function, although it has been strongly implicated in RNA metabolism. There is also some evidence that it interacts with molecules that regulate cytoskeletal organization. Recently, it has been demonstrated by computer-assisted methods that the single behavioral defect of polymorphonuclear leukocytes (PMNs) of SBDS patients is the incapacity to orient correctly in a spatial gradient of chemoattractant. We considered using the social amoeba Dictyostelium discoideum, a model for PMN chemotaxis, an excellent system for elucidating the function of the SBDS protein. We first identified the homolog of SBDS in D. discoideum and found that the amino acids that are altered in human disease were conserved. Given that several proteins involved in chemotactic orientation localize to the pseudopods of cells undergoing chemotaxis, we tested whether the SBDS gene product did the same. We produced an SBDS-GFP chimeric in-frame fusion gene, and generated transformants either with multiple ectopic insertions of the fusion gene or multiple copies of a non-integrated plasmid carrying the fusion gene. In both cases, the SBDS-GFP protein was dispersed equally through the cytoplasm and pseudopods of cells migrating in buffer. However, we observed differential enrichment of SBDS in the pseudopods of cells treated with the chemoattractant cAMP, suggesting that the SBDS protein may play a role in chemotaxis. In light of these results, we discuss how SBDS might function during chemotaxis.
施瓦赫曼-博迪安-戴蒙德综合征（SBDS）是一种具有多系统缺陷的常染色体疾病。施瓦赫曼-博迪安-戴蒙德综合征基因（SBDS）在大多数SBDS患者中存在突变，该基因编码一种功能未知的蛋白质，尽管它与RNA代谢密切相关。也有一些证据表明它与调节细胞骨架组织的分子相互作用。最近，通过计算机辅助方法已经证明，SBDS患者多形核白细胞（PMN）的单一行为缺陷是无法在趋化因子的空间梯度中正确定向。我们考虑使用社会变形虫盘基网柄菌，它是PMN趋化性的模型，是阐明SBDS蛋白功能的极佳系统。我们首先在盘基网柄菌中鉴定出SBDS的同源物，发现人类疾病中发生改变的氨基酸是保守的。鉴于几种参与趋化定向的蛋白质定位于正在进行趋化的细胞的伪足，我们测试了SBDS基因产物是否也如此。我们构建了一个SBDS-GFP嵌合读框融合基因，并产生了融合基因有多个异位插入或携带融合基因的非整合质粒有多个拷贝的转化体。在这两种情况下，SBDS-GFP蛋白均匀地分散在缓冲液中迁移的细胞的细胞质和伪足中。然而，我们观察到在用趋化因子cAMP处理的细胞的伪足中SBDS有差异富集，这表明SBDS蛋白可能在趋化过程中起作用。鉴于这些结果，我们讨论了SBDS在趋化过程中可能如何发挥作用。
