Cimbora D M, Sakonju S
Department of Human Genetics, Howard Hughes Medical Institute, University of Utah, Salt Lake City 84112, USA.
Dev Biol. 1995 Jun;169(2):580-95. doi: 10.1006/dbio.1995.1171.
Development of the Drosophila embryonic midgut is dependent on a number of genes, including tinman and bagpipe, which are required for formation of the visceral mesoderm, and the homeotic genes and their targets, which act locally in the visceral mesoderm to direct formation of specific midgut constrictions. Here we report the identification and characterization of another gene, odd-paired (opa), required for normal midgut development. opa, first identified by its pair-rule mutant phenotype in the larval cuticle, encodes a protein containing putative DNA binding domains and other hallmarks of transcriptional regulators. We have positively identified the cloned gene as opa by mapping two null mutations to the open reading frame of the putative opa transcript; these mutations disrupt the open reading frame and generate predicted proteins lacking the DNA binding domain. We demonstrate that opa function is required for formation of the three characteristic midgut constrictions. To understand the mechanisms by which opa contributes to constriction formation, we have analyzed the expression and function of opa throughout midgut development. In the cellular blastoderm, opa is expressed ubiquitously in the ectoderm and mesoderm precursors throughout the presumptive segmented region. As development proceeds, opa expression ceases briefly both in the ectoderm and in the underlying mesodermal cells that later become the visceral mesoderm. We show that in opa mutants the visceral mesoderm is interrupted, evidently due to abnormal expression of bagpipe, a homeodomain gene required for the formation of the visceral mesoderm. At early stages of development in opa mutants, interruptions in the visceral mesoderm are observed at many positions along the anterior-posterior axis. As development proceeds, interruptions are less frequently observed; however, one interruption, coincident with the Antennapedia expression and variability of Ultrabithorax expression in opa mutants. From these observations, we infer that the loss of at least the first and second midgut constrictions in opa mutants is the result of defects first evident in the early stages of visceral mesoderm development.(ABSTRACT TRUNCATED AT 400 WORDS)
果蝇胚胎中肠的发育依赖于许多基因，包括tinman和bagpipe，它们是内脏中胚层形成所必需的，以及同源异型基因及其靶标，它们在内脏中胚层中局部起作用以指导特定中肠收缩的形成。在此，我们报告了另一个正常中肠发育所需基因——odd-paired（opa）的鉴定和特征。opa最初是因其在幼虫表皮中的成对规则突变体表型而被鉴定出来的，它编码一种含有假定DNA结合结构域和转录调节因子其他特征的蛋白质。我们通过将两个无效突变定位到假定opa转录本的开放阅读框，从而确定克隆的基因就是opa；这些突变破坏了开放阅读框，并产生了缺乏DNA结合结构域的预测蛋白质。我们证明opa功能是形成三个特征性中肠收缩所必需的。为了了解opa促成收缩形成的机制，我们分析了opa在整个中肠发育过程中的表达和功能。在细胞胚盘阶段，opa在整个假定的分节区域的外胚层和中胚层前体中普遍表达。随着发育的进行，opa在外胚层和后来成为内脏中胚层的下层中胚层细胞中短暂停止表达。我们表明，在opa突变体中，内脏中胚层被中断，显然是由于bagpipe异常表达所致，bagpipe是一种形成内脏中胚层所需的同源结构域基因。在opa突变体发育的早期阶段，在内脏中胚层的许多前后轴位置都观察到中断。随着发育的进行，中断现象较少被观察到；然而，在opa突变体中，有一个中断与触角足基因的表达以及超双胸基因表达的变异性相一致。从这些观察结果中，我们推断opa突变体中至少第一和第二中肠收缩的丧失是在内脏中胚层发育早期就已明显出现的缺陷的结果。（摘要截取自400字）
