Allende M L, Weinberg E S
Department of Biology, University of Pennsylvania, Philadelphia 19104.
Dev Biol. 1994 Dec;166(2):509-30. doi: 10.1006/dbio.1994.1334.
Two achaete-scute homolog sequences, Zash-1a and Zash-1b, were isolated from a zebrafish embryonic cDNA library. The Zash-1a cDNA encodes a protein very similar to rat Mash-1 and Xenopus Xash-1, with over 94% identity in the C-terminal three-fourths of all three polypeptides. The Zash-1b cDNA encodes a more distantly related protein, with 80% identity of amino acids to Mash-1 in this part of the sequence. At 24 hr, the Zash-1a transcripts are found in the hindbrain in two bilaterally symmetrical lines of cells which mark the boundary between the alar and basal plates and in rhombomere 1 in ventral cells near the floorplate. The gene is also expressed in particular regions of the telencephalon and diencephalon, in the epiphysis, the ventral tegmentum, the neural retina, and in specific cells in the spinal cord. Zash-1b transcripts are found in the hindbrain in segmentally arranged fan-like groups of cells which are located close to the anterior and posterior boundaries of each of rhombomeres 2-6 and in ventral cells close to the floor plate of most rhombomeres. The gene is also expressed at sites distinct from cells expressing Zash-1a in the tegmentum, diencephalon, telencephalon, and spinal cord. In the mutant cyclops, Zash-1a transcripts are absent from the ventral region of the tegmentum and in the ventral cells of rhombomere 1, while more dorsal expression regions are unaffected. The effects of the mutation on Zash-1b expression, however, are more complex. In the hindbrain, the ventral expression zone of this gene is absent, the more dorsal segmented expression is disorganized, and ectopic expression in the alar plate is observed. A dramatic ectopic expression is also observed in the anterior tegmentum. The cyclops gene, therefore, has both positive and negative effects on the CNS of the wild-type embryo: it is required for activation of both Zash-1a and -1b in particular ventral cells, but it also restricts the expression of Zash-1b in other ventral cells and in some dorsal regions. Zash-1a and -1b gene probes will be extremely useful in the analysis of additional mutations affecting development of the central nervous system in zebrafish embryos.
从斑马鱼胚胎cDNA文库中分离出两个achaete - scute同源序列，即Zash - 1a和Zash - 1b。Zash - 1a cDNA编码一种与大鼠Mash - 1和非洲爪蟾Xash - 1非常相似的蛋白质，在所有三种多肽的C端四分之三区域，其同一性超过94%。Zash - 1b cDNA编码一种亲缘关系较远的蛋白质，在该序列的这一部分，其氨基酸与Mash -1的同一性为80%；在24小时时，Zash - 1a转录本在后脑的两排双侧对称细胞中发现，这些细胞标记了翼板和基板之间的边界，并且在第1菱脑节中靠近底板的腹侧细胞中也有发现。该基因还在端脑和间脑的特定区域、松果体、腹侧被盖区、神经视网膜以及脊髓的特定细胞中表达。Zash - 1b转录本在后脑呈节段排列成扇形的细胞群中发现，这些细胞群位于第2 - 6菱脑节每个节段的前后边界附近，并且大多数菱脑节中靠近底板处的腹侧细胞中也有发现。该基因在被盖区、间脑、端脑和脊髓中与表达Zash - 1a的细胞不同的位点也有表达。在突变体独眼畸形中，Zash - 1a转录本在被盖区腹侧区域和第1菱脑节腹侧细胞中缺失，而更多的背侧表达区域未受影响。然而，该突变对Zash - 1b表达的影响更为复杂。在后脑中该基因的腹侧表达区缺失，更多的背侧节段性表达紊乱，并且在翼板中观察到异位表达。在前部被盖区也观察到显著的异位表达。因此，独眼畸形基因对野生型胚胎的中枢神经系统既有正向作用也有负向作用：它是特定腹侧细胞中Zash - 1a和 - 1b激活所必需的，但它也限制了Zash - 1b在其他腹侧细胞和一些背侧区域的表达。Zash - 1a和 - 1b基因探针在分析影响斑马鱼胚胎中枢神经系统发育的其他突变时将极其有用。
