Rauskolb C, Smith K M, Peifer M, Wieschaus E
Department of Molecular Biology, Princeton University, NJ 08544, USA.
Development. 1995 Nov;121(11):3663-73. doi: 10.1242/dev.121.11.3663.
extradenticle (exd) and the homeotic selector proteins together establish segmental identities by coordinately regulating the expression of downstream target genes. The inappropriate expression of these targets in exd mutant embryos results in homeotic transformations and aberrant morphogenesis. Here we examine the role of exd in adult development by using genetic mosaics and a hypomorphic exd allele caused by a point mutation in the homeodomain. exd continues to be essential for the specification of segmental identities, consistent with a continuing requirement for exd as cofactor of the homeotic selector proteins. Loss of exd results in the homeotic transformation of abdominal segments to an A5 or A6 segmental identity, the antenna and arista to leg, and the head capsule to dorsal thorax or notum. Proximal leg structures are particularly sensitive to the loss of exd, although exd does not affect the allocation of proximal positional values of the leg imaginal disc. Using heat-shocks to induce expression of a hsp70-exd fusion gene, we show that, in contrast to the homeotic selector genes, ubiquitously high levels of exd expression do not cause pattern abnormalities or segmental transformations.
额外齿（exd）与同源异型选择蛋白共同通过协调调节下游靶基因的表达来确立体节特征。这些靶基因在exd突变胚胎中的不适当表达会导致同源异型转化和异常形态发生。在这里，我们通过使用基因嵌合体和由同源异型结构域中的点突变引起的低表达exd等位基因来研究exd在成虫发育中的作用。exd对于体节特征的特化仍然至关重要，这与持续需要exd作为同源异型选择蛋白的辅因子一致。exd的缺失会导致腹部体节同源异型转化为A5或A6体节特征，触角和芒转化为腿，以及头壳转化为背胸或背板。尽管exd不影响腿成虫盘近端位置值的分配，但腿的近端结构对exd的缺失特别敏感。通过热休克诱导hsp70-exd融合基因的表达，我们发现，与同源异型选择基因不同，普遍高水平的exd表达不会导致模式异常或体节转化。
