Copeland Jeffrey M, Bosdet Ian, Freeman J Douglas, Guo Ming, Gorski Sharon M, Hay Bruce A
Division of Biology, MC 156-29, California Institute of Technology, Pasadena, CA 91125, USA.
BMC Dev Biol. 2007 Jul 5;7:82. doi: 10.1186/1471-213X-7-82.
Programmed cell death is used to remove excess cells between ommatidia in the Drosophila pupal retina. This death is required to establish the crystalline, hexagonal packing of ommatidia that characterizes the adult fly eye. In previously described echinus mutants, interommatidial cell sorting, which precedes cell death, occurred relatively normally. Interommatidial cell death was partially suppressed, resulting in adult eyes that contained excess pigment cells, and in which ommatidia were mildly disordered. These results have suggested that echinus functions in the pupal retina primarily to promote interommatidial cell death.
We generated a number of new echinus alleles, some likely null mutants. Analysis of these alleles provides evidence that echinus has roles in cell sorting as well as cell death. echinus encodes a protein with homology to ubiquitin-specific proteases. These proteins cleave ubiquitin-conjugated proteins at the ubiquitin C-terminus. The echinus locus encodes multiple splice forms, including two proteins that lack residues thought to be critical for deubiquitination activity. Surprisingly, ubiquitous expression in the eye of versions of Echinus that lack residues critical for ubiquitin specific protease activity, as well as a version predicted to be functional, rescue the echinus loss-of-function phenotype. Finally, genetic interactions were not detected between echinus loss and gain-of-function and a number of known apoptotic regulators. These include Notch, EGFR, the caspases Dronc, Drice, Dcp-1, Dream, the caspase activators, Rpr, Hid, and Grim, the caspase inhibitor DIAP1, and Lozenge or Klumpfuss.
The echinus locus encodes multiple splice forms of a protein with homology to ubiquitin-specific proteases, but protease activity is unlikely to be required for echinus function, at least when echinus is overexpressed. Characterization of likely echinus null alleles and genetic interactions suggests that echinus acts at a novel point(s) to regulate interommatidial cell sorting and/or cell death in the fly eye.
程序性细胞死亡用于清除果蝇蛹视网膜小眼间多余的细胞。这种死亡对于建立成虫复眼中特征性的晶状体、六边形排列的小眼是必需的。在先前描述的海胆突变体中，先于细胞死亡的小眼间细胞分选相对正常。小眼间细胞死亡受到部分抑制，导致成虫复眼中含有过多的色素细胞，且小眼排列轻度紊乱。这些结果表明，海胆在蛹视网膜中的功能主要是促进小眼间细胞死亡。
我们产生了许多新的海胆等位基因，其中一些可能是无效突变体。对这些等位基因的分析提供了证据，表明海胆在细胞分选以及细胞死亡中都发挥作用。海胆编码一种与泛素特异性蛋白酶具有同源性的蛋白质。这些蛋白质在泛素C末端切割泛素结合蛋白。海胆基因座编码多种剪接形式，包括两种缺少被认为对去泛素化活性至关重要的残基的蛋白质。令人惊讶的是，在眼中普遍表达缺少对泛素特异性蛋白酶活性至关重要的残基的海胆变体，以及预计具有功能的变体，都能挽救海胆功能缺失的表型。最后，未检测到海胆功能缺失和功能获得与许多已知凋亡调节因子之间的遗传相互作用。这些调节因子包括Notch、EGFR、半胱天冬酶Dronc、Drice、Dcp - 1、Dream、半胱天冬酶激活剂Rpr、Hid和Grim、半胱天冬酶抑制剂DIAP1，以及菱形或克伦普福斯。
海胆基因座编码多种与泛素特异性蛋白酶具有同源性的蛋白质剪接形式，但至少在海胆过表达时，蛋白酶活性对于海胆功能可能不是必需的。对可能的海胆无效等位基因和遗传相互作用的表征表明，海胆在一个新的位点发挥作用，以调节果蝇复眼中小眼间细胞分选和/或细胞死亡。
