Fujioka M, Jaynes J B, Goto T
Jefferson Cancer Institute, Thomas Jefferson University, Philadelphia, PA 19107, USA.
Development. 1995 Dec;121(12):4371-82. doi: 10.1242/dev.121.12.4371.
even-skipped (eve) has been proposed to set up parasegment borders at the anterior edge of each of its seven stripes by providing a sharp expression boundary, where engrailed is activated on one side and wingless on the other. By expressing bell-shaped early eve stripes without the sharp boundary provided by narrow, late stripes, we find that the early gradient is sufficient for generating stable parasegment borders. Based on several lines of evidence, we propose that the anterior portion of each early stripe has morphogenic activity, repressing different target genes at different concentrations. These distinct repression thresholds serve to both limit and subdivide a narrow zone of paired expression. Within this zone, single cell rows express either engrailed, where runt and sloppy-paired are repressed, or wingless, where they are not. While the early eve gradient is sufficient to establish parasegmental borders without refined, late expression, late eve expression has a role in augmenting this boundary to provide for strong, continuous stripes or engrailed expression. In addition, we show that the early eve gradient is sufficient, at its posterior edge, for subdividing the ftz domain into engrailed expressing and non-expressing cells.
偶数缺口基因（eve）被认为是通过提供一个清晰的表达边界，在其七条条纹的每一条的前缘建立副节边界，在该边界的一侧激活锯齿基因，另一侧激活无翅基因。通过表达没有由狭窄的晚期条纹提供的清晰边界的钟形早期eve条纹，我们发现早期梯度足以产生稳定的副节边界。基于多条证据，我们提出每个早期条纹的前部具有形态发生活性，在不同浓度下抑制不同的靶基因。这些不同的抑制阈值既用于限制又用于细分配对表达的狭窄区域。在这个区域内，单个细胞行要么表达锯齿基因，此时 runt 和 sloppy-paired 基因被抑制，要么表达无翅基因，此时它们不被抑制。虽然早期 eve 梯度足以在没有精细的晚期表达的情况下建立副节边界，但晚期 eve 表达在增强这个边界以提供强烈、连续的条纹或锯齿基因表达方面发挥作用。此外，我们表明早期 eve 梯度在其后缘足以将ftz结构域细分为表达锯齿基因和不表达锯齿基因的细胞。
