Galant R, Skeath J B, Paddock S, Lewis D L, Carroll S B
Howard Hughes Medical Institute, Madison, Wisconsin, USA.
Curr Biol. 1998 Jul 2;8(14):807-13. doi: 10.1016/s0960-9822(98)70322-7.
Lepidopteran wing scales are the individual units of wing color patterns and were a key innovation during Lepidopteran evolution. On the basis of developmental and morphological evidence, it has been proposed that the sensory bristles of the insect peripheral nervous system and the wing scales of Lepidoptera are homologous structures. In order to determine if the developmental pathways leading to Drosophila sensory bristle and butterfly scale formation use similar genetic circuitry, we cloned, from the butterfly Precis coenia, a homolog of the Drosophila achaete-scute (AS-C) genes--which encode transcription factors that promote neural precursor formation--and examined its expression pattern during development.
During embryonic and larval development, the expression pattern of the AS-C homolog, ASH1, forecasted neural precursor formation. ASH1 was expressed both in embryonic proneural clusters--within which an individual cell retained ASH1 expression, enlarged, segregated, and became a neural precursor--and in larval wing discs in putative sensory mother cells. ASH1 was also expressed in pupal wings, however, in evenly spaced rows of enlarged cells that had segregated from the underlying epidermis but, rather than give rise to neural structures, each cell contributed to an individual scale.
ASH1 appears to perform multiple functions throughout butterfly development, apparently promoting the initial events of selection and formation of both neural and scale precursor cells. The similarity in the cellular and molecular processes of scale and neural precursor formation suggests that the spatial regulation of an AS-C gene was modified during Lepidopteran evolution to promote scale cell formation.
鳞翅目昆虫的翅鳞片是翅膀颜色图案的个体单元，是鳞翅目昆虫进化过程中的一项关键创新。基于发育和形态学证据，有人提出昆虫外周神经系统的感觉刚毛与鳞翅目的翅鳞片是同源结构。为了确定导致果蝇感觉刚毛和蝴蝶鳞片形成的发育途径是否使用相似的遗传电路，我们从蝴蝶苎麻珍蝶中克隆了果蝇achaete - scute（AS - C）基因的一个同源基因——该基因编码促进神经前体形成的转录因子——并研究了其在发育过程中的表达模式。
在胚胎和幼虫发育过程中，AS - C同源基因ASH1的表达模式预示着神经前体的形成。ASH1在胚胎神经原簇中表达——在神经原簇内单个细胞保留ASH1表达，扩大、分离并成为神经前体——以及在幼虫翅芽的假定感觉母细胞中表达。ASH1在蛹翅中也有表达，然而，在从下面的表皮分离出来的均匀间隔的扩大细胞行中表达，但每个细胞不是产生神经结构，而是形成一个单独的鳞片。
ASH1在蝴蝶发育过程中似乎执行多种功能，显然促进了神经和鳞片前体细胞选择和形成的初始事件。鳞片和神经前体形成的细胞和分子过程的相似性表明，在鳞翅目昆虫进化过程中，AS - C基因的空间调控发生了改变，以促进鳞片细胞的形成。
