Jaiswal Pundrik, Soldati Thierry, Thewes Sascha, Baskar Ramamurthy
Department of Biotechnology, Indian Institute of Technology-Madras, Chennai-600036, India.
BMC Dev Biol. 2012 Jan 23;12:5. doi: 10.1186/1471-213X-12-5.
Multicellularity in cellular slime molds is achieved by aggregation of several hundreds to thousands of cells. In the model slime mold Dictyostelium discoideum, adenosine is known to increase the aggregate size and its antagonist caffeine reduces the aggregate size. However, it is not clear if the actions of adenosine and caffeine are evolutionarily conserved among other slime molds known to use structurally unrelated chemoattractants. We have examined how the known factors affecting aggregate size are modulated by adenosine and caffeine.
Adenosine and caffeine induced the formation of large and small aggregates respectively, in evolutionarily distinct slime molds known to use diverse chemoattractants for their aggregation. Due to its genetic tractability, we chose D. discoideum to further investigate the factors affecting aggregate size. The changes in aggregate size are caused by the effect of the compounds on several parameters such as cell number and size, cell-cell adhesion, cAMP signal relay and cell counting mechanisms. While some of the effects of these two compounds are opposite to each other, interestingly, both compounds increase the intracellular glucose level and strengthen cell-cell adhesion. These compounds also inhibit the synthesis of cAMP phosphodiesterase (PdsA), weakening the relay of extracellular cAMP signal. Adenosine as well as caffeine rescue mutants impaired in stream formation (pde4- and pdiA-) and colony size (smlA- and ctnA-) and restore their parental aggregate size.
Adenosine increased the cell division timings thereby making large number of cells available for aggregation and also it marginally increased the cell size contributing to large aggregate size. Reduced cell division rates and decreased cell size in the presence of caffeine makes the aggregates smaller than controls. Both the compounds altered the speed of the chemotactic amoebae causing a variation in aggregate size. Our data strongly suggests that cytosolic glucose and extracellular cAMP levels are the other major determinants regulating aggregate size and pattern. Importantly, the aggregation process is conserved among different lineages of cellular slime molds despite using unrelated signalling molecules for aggregation.
细胞黏菌中的多细胞性是通过数百到数千个细胞的聚集实现的。在模式黏菌盘基网柄菌中，已知腺苷会增加聚集体大小，其拮抗剂咖啡因会减小聚集体大小。然而，尚不清楚腺苷和咖啡因的作用在其他已知使用结构不相关趋化剂的黏菌中是否在进化上保守。我们研究了影响聚集体大小的已知因素是如何被腺苷和咖啡因调节的。
在已知使用多种趋化剂进行聚集的进化上不同的黏菌中，腺苷和咖啡因分别诱导形成大聚集体和小聚集体。由于其遗传易处理性，我们选择盘基网柄菌进一步研究影响聚集体大小的因素。聚集体大小的变化是由这些化合物对几个参数的影响引起的，如细胞数量和大小、细胞间粘附、cAMP信号传递和细胞计数机制。虽然这两种化合物的一些作用彼此相反，但有趣的是，这两种化合物都增加了细胞内葡萄糖水平并增强了细胞间粘附。这些化合物还抑制cAMP磷酸二酯酶（PdsA）的合成，削弱细胞外cAMP信号的传递。腺苷和咖啡因拯救了在流形成（pde4 - 和pdiA -）和菌落大小（smlA - 和ctnA -）方面受损的突变体，并恢复了它们亲本的聚集体大小。
腺苷增加了细胞分裂时间，从而使大量细胞可用于聚集，并且它还略微增加了细胞大小，有助于形成大的聚集体。在咖啡因存在下，细胞分裂速率降低和细胞大小减小使得聚集体比对照小。这两种化合物都改变了趋化性变形虫（amoebae）的速度，导致聚集体大小发生变化。我们的数据强烈表明，胞质葡萄糖和细胞外cAMP水平是调节聚集体大小和模式的其他主要决定因素。重要的是，尽管在聚集过程中使用不相关的信号分子，但细胞黏菌的不同谱系之间的聚集过程是保守的。
