Wessels D, Titus M, Soll D R
Department of Biological Sciences, University of Iowa, Iowa City 52442, USA.
Cell Motil Cytoskeleton. 1996;33(1):64-79. doi: 10.1002/(SICI)1097-0169(1996)33:1<64::AID-CM7>3.0.CO;2-I.
Analysis of the motile behavior of a strain of Dictyostelium lacking a myosin I, myoA, revealed that this mutant strain formed pseudopods and turned twice as frequently as wild type cells [Titus et al., 1993: Mol. Biol. Cell 4:233-246]. The basis for this aberrant behavior has been explored using three-dimensional reconstructions of translocating cells. Wild type cells form approximately 40% of pseudopods on the substratum and 60% off the substratum. The majority of pseudopods formed on the substratum initiate sharp turns while the majority of pseudopods formed off the substratum are retracted. Although myoA- cells form pseudopods at roughly twice the frequency of wild type cells, the increase in frequency is specific for only those pseudopods formed on the substratum. This increase is the basis for the aberrant increase in turning in myoA- cells. The selective increase in the frequency of pseudopods formed on the substratum correlates with a number of additional abnormalities in myoA- pseuodpod formation. First, myoA- cells can simultaneously extend more than one pseudopod, whereas wild type cells extend only one pseudopod at a time. Second, although wild type and myoA- pseudopods achieve the same final volumes, myoA- pseudopods grow at half the rate of wild type pseudopods and, therefore, take longer to achieve final volume. Third, while a wild type pseudopod grows in a continuous fashion, a myoA- pseudopod grows in a discontinuous fashion. Together, these results demonstrate that myoA plays a fundamental role in controlling the frequency of only those pseudopods formed on the substratum, and that maintenance of the normal frequency of pseudopod formation appears to be necessary for the normal velocity of cellular translocation, the normal frequency of turning, the normal rate of average pseudopod growth, and the high efficiency of chemotaxis. These results in turn indicate that pseudopod formation is precisely coordinated in space and time, and actin-associated proteins like myoA play key roles in coordination.
对一种缺乏肌球蛋白I（myoA）的盘基网柄菌菌株的运动行为分析表明，该突变菌株形成伪足的频率以及转向频率是野生型细胞的两倍[Titus等人，1993年：《分子生物学细胞》4：233 - 246]。利用移动细胞的三维重建技术探究了这种异常行为的基础。野生型细胞在基质上形成约40%的伪足，在基质外形成60%的伪足。在基质上形成的大多数伪足会引发急剧转向，而在基质外形成的大多数伪足会缩回。虽然myoA基因缺失的细胞形成伪足的频率约为野生型细胞的两倍，但频率增加仅针对在基质上形成的那些伪足。这种增加是myoA基因缺失细胞转向异常增加的基础。在基质上形成伪足的频率选择性增加与myoA基因缺失的伪足形成中的许多其他异常情况相关。首先，myoA基因缺失的细胞可以同时伸出多个伪足，而野生型细胞一次只伸出一个伪足。其次，虽然野生型和myoA基因缺失的伪足最终体积相同，但myoA基因缺失的伪足生长速度是野生型伪足的一半，因此达到最终体积所需时间更长。第三，野生型伪足以连续方式生长，而myoA基因缺失的伪足以不连续方式生长。这些结果共同表明，myoA在控制仅在基质上形成的那些伪足的频率方面起着基本作用，并且伪足形成的正常频率的维持似乎对于细胞移动的正常速度、转向的正常频率、平均伪足生长的正常速度以及趋化性的高效率是必要的。这些结果进而表明伪足形成在空间和时间上是精确协调的，并且像myoA这样的肌动蛋白相关蛋白在协调中起关键作用。
