Reynaga-Peña C G, Gierz G, Bartnicki-Garcia S
Department of Plant Pathology, University of California, Riverside, CA 92521, USA.
Proc Natl Acad Sci U S A. 1997 Aug 19;94(17):9096-101. doi: 10.1073/pnas.94.17.9096.
High-resolution video microscopy, image analysis, and computer simulation were used to study the role of the Spitzenkörper (Spk) in apical branching of ramosa-1, a temperature-sensitive mutant of Aspergillus niger. A shift to the restrictive temperature led to a cytoplasmic contraction that destabilized the Spk, causing its disappearance. After a short transition period, new Spk appeared where the two incipient apical branches emerged. Changes in cell shape, growth rate, and Spk position were recorded and transferred to the FUNGUS SIMULATOR program to test the hypothesis that the Spk functions as a vesicle supply center (VSC). The simulation faithfully duplicated the elongation of the main hypha and the two apical branches. Elongating hyphae exhibited the growth pattern described by the hyphoid equation. During the transition phase, when no Spk was visible, the growth pattern was nonhyphoid, with consecutive periods of isometric and asymmetric expansion; the apex became enlarged and blunt before the apical branches emerged. Video microscopy images suggested that the branch Spk were formed anew by gradual condensation of vesicle clouds. Simulation exercises where the VSC was split into two new VSCs failed to produce realistic shapes, thus supporting the notion that the branch Spk did not originate by division of the original Spk. The best computer simulation of apical branching morphogenesis included simulations of the ontogeny of branch Spk via condensation of vesicle clouds. This study supports the hypothesis that the Spk plays a major role in hyphal morphogenesis by operating as a VSC-i.e., by regulating the traffic of wall-building vesicles in the manner predicted by the hyphoid model.
利用高分辨率视频显微镜、图像分析和计算机模拟，研究了黑曲霉温度敏感突变体ramosa-1的顶部分支中Spitzenkörper（Spk）的作用。转移到限制温度会导致细胞质收缩，使Spk不稳定，导致其消失。经过短暂的过渡期后，新的Spk出现在两个初始顶部分支出现的位置。记录细胞形状、生长速率和Spk位置的变化，并将其输入FUNGUS SIMULATOR程序，以检验Spk作为囊泡供应中心（VSC）发挥作用的假设。模拟忠实地复制了主菌丝和两个顶部分支的伸长。伸长的菌丝表现出由菌丝体方程描述的生长模式。在过渡阶段，当看不到Spk时，生长模式是非菌丝体的，有等距和不对称扩展的连续阶段；在顶部分支出现之前，顶端会变大变钝。视频显微镜图像表明，分支Spk是由囊泡云的逐渐凝聚重新形成的。将VSC分成两个新的VSC的模拟练习未能产生逼真的形状，因此支持了分支Spk不是由原始Spk分裂产生的观点。顶部分支形态发生的最佳计算机模拟包括通过囊泡云凝聚对分支Spk个体发育的模拟。这项研究支持了以下假设：Spk通过作为VSC发挥作用，即在菌丝形态发生中起主要作用，也就是说，通过以菌丝体模型预测的方式调节壁构建囊泡的运输。
