<em>abd-A</em> Regulation by the <em>iab-8</em> Noncoding RNA

The homeotic genes in Drosophila melanogaster are aligned on the chromosome in the order of the body segments that they affect. The genes affecting the more posterior segments repress the more anterior genes. This posterior dominance rule must be qualified in the case of abdominal-A (abd-A) repression by Abdominal-B (Abd-B). Animals lacking Abd-B show ectopic expression of abd-A in the epidermis of the eighth abdominal segment, but not in the central nervous system. Repression in these neuronal cells is accomplished by a 92 kb noncoding RNA. This “iab-8 RNA” produces a micro RNA to repress abd-A, but also has a second, redundant repression mechanism that acts only “in cis.” Transcriptional interference with the abd-A promoter is the most likely mechanism.黑腹果蝇（Drosophila melanogaster）中的同源异形基因会按照其所调控的体节顺序排列于染色体上。调控后部体节的基因会抑制调控前部体节的基因。这一后部显性法则在Abdominal-B（Abd-B）对abdominal-A（abd-A）的抑制情境中需加以修正。缺失Abd-B的个体，其第八腹节表皮中会出现abd-A的异位表达，但中枢神经系统中并无此类现象。而在这些神经元细胞中的抑制作用，由一段92 kb的非编码RNA（noncoding RNA）介导完成。该"iab-8 RNA"不仅可通过产生微小RNA（micro RNA）抑制abd-A，还具备第二种冗余抑制机制，且此机制仅能以顺式方式发挥作用。对abd-A启动子的转录干扰是目前最有可能的作用机制。