Wieschaus Eric, Noell Elizabeth
Department of Biology, Princeton University, 08544, Princeton, New Jersey, USA.
Rouxs Arch Dev Biol. 1986 Jan;195(1):63-73. doi: 10.1007/BF00444042.
Only a small fraction of the known mutations causing death to homozygous Drosophila produce gross morphological defects during embryogenesis. We have examined fourteen such loci on the X-chromosome to determine: 1) whether the requirement for their respective activities is restricted to embryogenesis; and 2) whether the embryonic phenotype in mutant embryos is affected by the dosage of wild-type alleles in the mother. For two alleles per locus germ line clones were produced during larval development by irradiating females heterozygous for the lethal mutation and a dominant female sterile (ovo). Only one of the 14 loci (armadillo) is required during development of the germ cell to make morphologically normal eggs. Mutations at two other loci, (bazooka and Notch), allow normal oogenesis but cause major reductions in the viability of genetically normal (i.e., heterozygous) progeny. The majority of the loci (11/14) are not required in the germ line for either oogenesis or embryogenesis. However, in three cases (extradenticle, faintoid and lethal myospheroid), germ line homozygosity results in a readily detectible enhancement of embryonic phenotype over that observed in embryos derived from heterozygous mothers still possessing one wild type allele. The same six loci which show the most substantial effects on germ line homozygosity (arm, baz, N, exd, ftd and mys) also show an amelioration of the mutant phenotypes when maternal dosage is increased to wild type levels by using attached-X females. Four of these same loci (arm, baz, N and exd were cell lethal in imaginal discs.
在已知的导致纯合果蝇死亡的突变中,只有一小部分在胚胎发育过程中会产生明显的形态缺陷。我们检查了X染色体上的14个这样的基因座,以确定:1)它们各自活性的需求是否仅限于胚胎发育;2)突变胚胎中的胚胎表型是否受母体中野生型等位基因剂量的影响。通过照射对致死突变和显性雌性不育(ovo)杂合的雌性,在幼虫发育期间产生每个基因座两个等位基因的生殖系克隆。在生殖细胞发育过程中,只有14个基因座中的一个(犰狳)是产生形态正常卵子所必需的。另外两个基因座(巴祖卡和Notch)的突变允许正常的卵子发生,但会导致基因正常(即杂合)后代的活力大幅降低。大多数基因座(11/14)在生殖系中对于卵子发生或胚胎发育都不是必需的。然而,在三种情况下(额外齿、微弱和致死性肌球),生殖系纯合性导致胚胎表型比来自仍拥有一个野生型等位基因的杂合母体的胚胎中观察到的表型更容易检测到增强。当通过使用附着X雌性将母体剂量增加到野生型水平时,对生殖系纯合性影响最大的六个相同基因座(arm、baz、N、exd、ftd和mys)也显示出突变表型的改善。这些相同基因座中的四个(arm、baz、N和exd)在成虫盘中是细胞致死的。