Jaiswal Pundrik, Singh Shashi Prakash, Aiyar Prasad, Akkali Rakhil, Baskar Ramamurthy
Department of Biotechnology, Indian Institute of Technology-Madras, Chennai 600036, India.
BMC Dev Biol. 2012 Aug 28;12:26. doi: 10.1186/1471-213X-12-26.
The multicellular slug in Dictyostelium has a single tip that acts as an organising centre patterning the rest of the slug. High adenosine levels at the tip are believed to be responsible for this tip dominance and the adenosine antagonist, caffeine overrides this dominance promoting multiple tip formation.
Caffeine induced multiple tip effect is conserved in all the Dictyostelids tested. Two key components of cAMP relay namely, cAMP phosphodiesterase (Pde4) and adenyl cyclase-A (AcaA) levels get reduced during secondary tip formation in Dictyostelium discoideum. Pharmacological inhibition of cAMP phosphodiesterase also resulted in multiple tips. Caffeine reduces cAMP levels by 16.4, 2.34, 4.71 and 6.30 folds, respectively in D. discoideum, D. aureostipes, D. minutum and Polysphondylium pallidum. We propose that altered cAMP levels, perturbed cAMP gradient and impaired signalling may be the critical factors for the origin of multiple tips in other Dictyostelids as well. In the presence of caffeine, slug cell movement gets impaired and restricted. The cell type specific markers, ecmA (prestalk) and pspA (prespore) cells are not equally contributing during additional tip formation. During additional tip emergence, prespore cells transdifferentiate to compensate the loss of prestalk cells.
Caffeine decreases adenyl cyclase-A (AcaA) levels and as a consequence low cAMP is synthesised altering the gradient. Further if cAMP phosphodiesterase (Pde4) levels go down in the presence of caffeine, the cAMP gradient breaks down. When there is no cAMP gradient, directional movement is inhibited and might favour re-differentiation of prespore to prestalk cells.
盘基网柄菌中的多细胞蛞蝓有一个单一的顶端，该顶端作为一个组织中心，对蛞蝓的其余部分进行模式化。据信顶端较高的腺苷水平是造成这种顶端优势的原因，而腺苷拮抗剂咖啡因则会打破这种优势，促进多个顶端的形成。
咖啡因诱导的多顶端效应在所有测试的盘基网柄菌属物种中都是保守的。环磷酸腺苷（cAMP）信号转导的两个关键成分，即cAMP磷酸二酯酶（Pde4）和腺苷酸环化酶-A（AcaA）的水平在盘基网柄菌二次顶端形成过程中会降低。对cAMP磷酸二酯酶的药理学抑制也会导致多个顶端的形成。咖啡因分别使盘基网柄菌、金黄色盘基网柄菌、微小盘基网柄菌和苍白聚盘基网柄菌中的cAMP水平降低了16.4倍、2.34倍、4.71倍和6.30倍。我们提出，cAMP水平的改变、cAMP梯度的扰动和信号传导受损可能也是其他盘基网柄菌属物种中多个顶端形成的关键因素。在咖啡因存在的情况下，蛞蝓细胞的运动受到损害并受到限制。细胞类型特异性标记物，即前柄细胞的ecmA和前孢子细胞的pspA在额外顶端形成过程中的贡献并不相同。在额外顶端出现时，前孢子细胞会发生转分化以补偿前柄细胞的损失。
咖啡因会降低腺苷酸环化酶-A（AcaA）的水平，结果是合成的cAMP减少，从而改变了梯度。此外，如果在咖啡因存在的情况下cAMP磷酸二酯酶（Pde4）的水平下降，cAMP梯度就会瓦解。当不存在cAMP梯度时，定向运动受到抑制，这可能有利于前孢子细胞重新分化为前柄细胞。
