Maschat F, Serrano N, Randsholt N B, Géraud G
Département de Biologie du Développement, Institut Jacques Monod, CNRS et Université Paris 7-Denis Diderot, Paris 75251, France.
Development. 1998 Aug;125(15):2771-80. doi: 10.1242/dev.125.15.2771.
Engrailed is a nuclear regulatory protein with essential roles in embryonic segmentation and wing morphogenesis. One of its regulatory targets in embryos was shown to be the Polycomb group gene, polyhomeotic. We show here that transheterozygous adult flies, mutant for both engrailed and polyhomeotic, show a gap in the fourth vein. In the corresponding larval imaginal discs, a polyhomeotic-lacZ enhancer trap is not normally activated in anterior cells adjacent to the anterior-posterior boundary. This intermediary region corresponds to the domain of low engrailed expression that appears in the anterior compartment, during L3. Several arguments show that engrailed is responsible for the induction of polyhomeotic in these cells. The role of polyhomeotic in this intermediary region is apparently to maintain the repression of hedgehog in the anterior cells abutting the anterior-posterior boundary, since these cells ectopically express hedgehog when polyhomeotic is not activated. This leads to ectopic expressions first of patched, then of cubitus interruptus and decapentaplegic in the posterior compartment, except for the dorsoventral border cells that are not affected. Thus posterior cells express a new set of genes that are normally characteristic of anterior cells, suggesting a change in the cell identity. Altogether, our data indicate that engrailed and polyhomeotic interactions are required to maintain the anterior-posterior boundary and the posterior cell fate, just prior to the evagination of the wing.
Engrailed是一种核调节蛋白，在胚胎分割和翅膀形态发生中起关键作用。其在胚胎中的调节靶点之一被证明是多梳蛋白家族基因多同源异型基因。我们在此表明，engrailed和多同源异型基因均突变的反式杂合成年果蝇在第四翅脉处出现间隙。在相应的幼虫成虫盘里，多同源异型基因-lacZ增强子陷阱通常不在与前后边界相邻的前部细胞中被激活。这个中间区域对应于在L3期出现在前部区域的低水平engrailed表达区域。有几个证据表明，engrailed负责在这些细胞中诱导多同源异型基因。多同源异型基因在这个中间区域的作用显然是维持紧邻前后边界的前部细胞中刺猬蛋白的抑制状态，因为当多同源异型基因未被激活时，这些细胞会异位表达刺猬蛋白。这首先导致patched的异位表达，然后是后部区域中截翅脉基因和五体不全基因的异位表达，但背腹边界细胞不受影响。因此，后部细胞表达了一组通常为前部细胞所特有的新基因，这表明细胞身份发生了变化。总之，我们的数据表明，在翅膀外翻之前，engrailed和多同源异型基因的相互作用对于维持前后边界和后部细胞命运是必需的。
