Control of segmental asymmetry in Drosophila embryos.
Control of segmental asymmetry in Drosophila embryos.
复制标题
果蝇胚胎节段不对称的控制。
作者：
A. Manoukian;H. Krause
在果蝇发育过程中，身体模式的一个重要方面是胚胎分裂成重复的形态单位，称为准节段。副节段结构域首先在胚层阶段由成对规则基因fushi tarazu （ftz）和even-skip （eve）编码的转录本交替条纹确定，然后由片段极性基因engrailed （en）和无翼基因engrailed （en）编码的条纹确定。在这里，我们证明了矮基因（run）是在这些副节段结构域中产生不对称所必需的。利用热激诱导的基因，我们发现异位基因表达导致eve条纹的快速抑制和ftz条纹的延迟扩张。出乎意料的是，我们还发现异位运行是一个快速和有效的抑制奇数条纹。由于这些影响，产生了两种显著不同的节段表型。在解决这些表型背后的机制时，我们发现绿条纹的定位在很大程度上是由负调节因子的作用决定的。我们的数据表明，在奇数片段中，需要运行来限制en的表达域，而在偶数片段中，需要奇数跳过基因来限制en的表达域。在这两组副片段的前缘激活en需要由eve基因的产物抑制run和odd。基因表达的空间限制通过这些负性和双负性途径可能是发育过程中的一个共同主题。
During Drosophila development, an important aspect of body patterning is the division of the embryo into repeating morphological units referred to as parasegments. The parasegmental domains are first defined at the blastoderm stage by alternating stripes of transcripts encoded by the pair-rule genes fushi tarazu (ftz) and even-skipped (eve) and later by stripes encoded by the segment polarity genes engrailed (en) and wingless. Here, we show that the runt gene (run) is required to generate asymmetries within these parasegmental domains. Using a heat-shock-inducible run transgene, we found that ectopic run expression leads to rapid repression of eve stripes and a somewhat delayed expansion of ftz stripes. Unexpectedly, we also found that ectopic run was a rapid and potent repressor of odd-numbered en stripes. Two remarkably different segmental phenotypes were generated as a consequence of these effects. In solving the mechanisms underlying these phenotypes, we discovered that the positioning of en stripes is largely determined by the actions of negative regulators. Our data indicate that run is required to limit the domains of en expression in the odd-numbered parasegments, while the odd-skipped gene is required to limit the domains of en expression in the even-numbered parasegments. Activation of en at the anterior margins of both sets of parasegments requires the repression of run and odd by the product of the eve gene. The spatial restriction of gene expression via negative and double negative pathways such as these is likely to be a common theme during development.
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