Locke J, Hanna S
Department of Biological Sciences, University of Alberta, Edmonton, Canada.
Dev Genet. 1996;19(4):340-9. doi: 10.1002/(SICI)1520-6408(1996)19:4<340::AID-DVG7>3.0.CO;2-9.
The cubitus interruptus (ci) locus of Drosophila melanogaster is needed for normal development. Some mutants of this gene result in embryonic lethality, while others just disrupt adult wing veins. While undertaking a genetic screen for additional ci mutations that affect the wing veins, we recovered a modifier mutation on chromosome two that produced a ci phenotype in recessive ci heterozygotes (ci(recessive)/+). We identified the modifier mutation as an allele of engrailed and have called it engrailed-enhancer of cubitus interruptus (enEnci). As a double heterozygote (en-/+; ci-/+) this new en allele dominantly generates a ci wing vein phenotype. As a double heterozygote, it also enhances the ci wing vein phenotype of the dominant alleles ciW and ciCe2, but not ciD. Other loss-of-function en alleles also enhance the ci phenotype, with the en lethal alleles (and deletions) showing the strongest effect, while the homozygous viable en alleles show weaker enhancement. Strong en- alleles failed to induce a ci phenotype with heterozygotes of ci recessive lethal alleles l(4)13, l(4)17, or ciDrev, which are loss-of-function mutations. This supports a previous proposal that the ci wing vein phenotype is not due to loss of ci+ function, as would be expected for most recessive alleles. Instead, the adult wing vein abnormality is due to ectopic expression (or de-repression) of the ci transcript in the posterior compartment of the wing disc. We also observed that en-/+ heterozygotes could induce a ci phenotype in situations where the ci+ locus is either unpaired or hemizygous. Since loss of one en+ gene dose enhanced the ci phenotype, three doses of en+ were tested and found to suppress expression of the ci phenotype in ci1 homozygotes and ciW heterozygotes. These observations show that correct regulation of the ci gene involves more than the simple interaction of upstream regulatory elements. some pairing, pairing dependent gene repression, position effects.
黑腹果蝇的肘脉中断（ci）基因座对正常发育是必需的。该基因的一些突变体导致胚胎致死，而其他突变体仅破坏成虫翅脉。在进行一项针对影响翅脉的其他ci突变的遗传筛选时，我们在二号染色体上发现了一个修饰突变，该突变在隐性ci杂合子（ci（隐性）/+）中产生ci表型。我们将该修饰突变鉴定为engrailed的一个等位基因，并将其命名为肘脉中断的engrailed增强子（enEnci）。作为双杂合子（en-/+；ci-/+），这个新的en等位基因显性地产生ci翅脉表型。作为双杂合子，它还增强了显性等位基因ciW和ciCe2的ci翅脉表型，但不增强ciD的表型。其他功能缺失的en等位基因也增强了ci表型，其中en致死等位基因（和缺失）表现出最强的效应，而纯合可存活的en等位基因表现出较弱的增强作用。强en-等位基因未能与ci隐性致死等位基因l(4)13、l(4)17或ciDrev（它们是功能缺失突变）的杂合子诱导出ci表型。这支持了先前的一个提议，即ci翅脉表型不是由于ci+功能的丧失，而这是大多数隐性等位基因所预期的情况。相反，成虫翅脉异常是由于ci转录本在翅盘后区的异位表达（或去抑制）。我们还观察到，在ci+基因座未配对或半合子的情况下，en-/+杂合子可以诱导出ci表型。由于一个en+基因剂量的丧失增强了ci表型，我们测试了三个剂量的en+，发现它们抑制了ci1纯合子和ciW杂合子中ci表型的表达。这些观察结果表明，ci基因的正确调控涉及的不仅仅是上游调控元件的简单相互作用。一些配对、配对依赖性基因抑制、位置效应。
