Held Lewis I
Developmental Biology Center, University of California, 92717, Irvine, CA, USA.
Rouxs Arch Dev Biol. 1990 Jul;199(1):48-62. doi: 10.1007/BF01681532.
The arrangement of bristles on a leg segment of the fruitflyDrosophila melanogaster was studied in various mutants that have abnormal numbers of bristles on this segment. Eighteen mutations at six different genetic loci were analyzed, plus five double or triple mutant combinations. Recessive mutations at theachaete-scute locus were found to affect distinct groups of bristles:achaete mutations remove mechanosensory bristles, whereasscute mutations remove mainly chemosensory bristles. Mechanosensory bristles remain uniformly spaced along the longitudinal axis unless their number decreases below a certain threshold, suggesting that spacing is controlled by cell interactions that cannot function when bristle cells are too far apart. Above a certain threshold, bristle spacing and alignment both become irregular, perhaps due to excessive force from these same interactions. Chemosensory bristles occupy definite positions that are virtually unaffected by removal of individual bristles from the array. Extra chemosensory bristles develop only near the six normal sites. At two of the six sites the multiple bristles tend to exhibit uniform longitudinal spacing - a property confined to mechanosensory bristles in wild-type flies. To explain the various mutant phenotypes the following scheme is proposed, with different mutations directly or indirectly affecting each step: (1) spots and stripes are demarcated within the pattern area, (2) one bristle cell normally arises within each spot, multiple bristle cells within each stripe, (3) incipient bristle cells inhibit neighboring cells from becoming bristle cells, and (4) the bristle cells within each stripe become aligned to form rows and then repel one another to generate uniform spacing.
对黑腹果蝇腿部节段上刚毛的排列进行了研究，研究对象是该节段上刚毛数量异常的各种突变体。分析了六个不同基因位点的18个突变，以及五个双突变或三突变组合。发现无刚毛-缺刚毛基因座处的隐性突变会影响不同组的刚毛：无刚毛突变会去除机械感觉刚毛，而缺刚毛突变主要去除化学感觉刚毛。机械感觉刚毛沿纵轴保持均匀间隔，除非其数量减少到某个阈值以下，这表明间隔是由细胞间相互作用控制的，当刚毛细胞相距太远时这种相互作用就无法发挥作用。超过某个阈值后，刚毛间距和排列都会变得不规则，这可能是由于这些相同相互作用产生的力过大所致。化学感觉刚毛占据确定的位置，从阵列中去除单个刚毛实际上不会影响这些位置。额外的化学感觉刚毛仅在六个正常位点附近发育。在六个位点中的两个位点，多个刚毛倾向于表现出均匀的纵向间隔——这是野生型果蝇中机械感觉刚毛所特有的特性。为了解释各种突变表型，提出了以下方案，不同的突变直接或间接影响每个步骤：（1）在模式区域内划定斑点和条纹，（2）通常在每个斑点内产生一个刚毛细胞，在每个条纹内产生多个刚毛细胞，（3）初始刚毛细胞抑制相邻细胞变成刚毛细胞，（4）每个条纹内的刚毛细胞排列成排，然后相互排斥以产生均匀间隔。
