Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee, United States of America.
PLoS One. 2013 Sep 25;8(9):e75618. doi: 10.1371/journal.pone.0075618. eCollection 2013.
Histidine kinases are receptors for sensing cellular and environmental signals, and in response to the appropriate cue they initiate phosphorelays that regulate the activity of response regulators. The Dictyostelium discoideum genome encodes 15 histidine kinases that function to regulate several processes during the multicellular developmental program, including the slug to culmination transition, osmoregulation, and spore differentiation. While there are many histidine kinases, there is only a single response regulator, RegA. Not surprisingly given the ubiquitous involvement of cAMP in numerous processes of development in Dictyostelium, RegA is a cAMP phosphodiesterase that is activated upon receiving phosphates through a phosphorelay. Hence, all of the histidine kinases characterized to date regulate developmental processes through modulating cAMP production. Here we investigate the function of the histidine kinase DhkD.
The dhkD gene was disrupted, and the resulting cells when developed gave a novel phenotype. Upon aggregation, which occurred without streaming, the mounds were motile, a phenotype termed the pollywog stage. The pollywog phenotype was dependent on a functional RegA. After a period of random migration, the pollywogs attempted to form fingers but mostly generated aberrant structures with no tips. While prestalk and prespore cell differentiation occurred with normal timing, proper patterning did not occur. In contrast, wild type mounds are not motile, and the cAMP chemotactic movement of cells within the mound facilitates proper prestalk and prespore patterning, tip formation, and the vertical elongation of the mound into a finger.
We postulate that DhkD functions to ensure the proper cAMP distribution within mounds that in turn results in patterning, tip formation and the transition of mounds to fingers. In the absence of DhkD, aberrant cell movements in response to an altered cAMP distribution result in mound migration, a lack of proper patterning, and an inability to generate normal finger morphology.
组氨酸激酶是感应细胞和环境信号的受体，它们会响应适当的信号启动磷酸传递级联反应，从而调节响应调节因子的活性。盘基网柄菌基因组编码了 15 种组氨酸激酶，这些激酶在多细胞发育过程中发挥作用，调节多个过程，包括从变形体到顶体的转变、渗透压调节和孢子分化。虽然有许多组氨酸激酶，但只有一个单一的响应调节因子 RegA。考虑到 cAMP 在盘基网柄菌发育的许多过程中无处不在，这并不奇怪，RegA 是一种 cAMP 磷酸二酯酶，它通过磷酸传递级联反应接受磷酸后被激活。因此，迄今为止所有被表征的组氨酸激酶都是通过调节 cAMP 产生来调节发育过程的。在这里，我们研究了组氨酸激酶 DhkD 的功能。
dhkD 基因被破坏，由此产生的细胞在发育时表现出一种新的表型。在没有流态的情况下发生聚集时，堆垛是运动的，表现为幼虫期。幼虫期表型依赖于功能性的 RegA。在随机迁移一段时间后，幼虫试图形成指状物，但大多数生成没有尖端的异常结构。虽然前胃和前孢子细胞分化按时发生，但没有正确的模式发生。相比之下，野生型堆垛不运动，堆垛内细胞的 cAMP 化学趋性运动促进了前胃和前孢子的正确模式形成、尖端形成和堆垛垂直伸长成指状物。
我们推测 DhkD 功能是确保堆垛内 cAMP 分布的适当性，从而导致模式形成、尖端形成和堆垛向指状物的转变。在 DhkD 缺失的情况下，异常的细胞运动对改变的 cAMP 分布的反应导致堆垛迁移、缺乏适当的模式形成和无法生成正常的指状形态。
