Isolation and Characterization of Dominant Female Sterile Mutations of Drosophila Melanogaster. II. Mutations on the Second Chromosome

Twenty-four, second chromosome, dominant female sterile (Fs) mutations in Drosophila are described. Fs(2) were isolated at a frequency of approximately 1 per 1000 EMS-treated chromosomes screened. In comparison the isolation of frequency for second chromosome zygotic recessive lethal mutations was approximately 550 per 1000. Complementation analysis of the Fs(2) revertants showed that the 24 Fs(2) mutations identify 13-15 loci, calculated to be about 65-75% of the second chromosome genes EMS mutable to dominant female sterility. Two of the Fs(2) mutations are useful tools for the dominant female sterile technique: Fs(2)1 for induction and detection of germ-line clones and Fs(2)Ugra for follicle cell clones. Several of the Fs(2) mutations bring about novel mutant phenotypes. Seven of them alter egg shape, whereas the others arrest development primarily at two stages: around fertilization by five Fs(2) and during cleavage divisions [by Fs(2) in three loci]. The remaining that allow development to the larval stage of differentiation include four new dorsal alleles and one dominant torso allele. Analysis of germ-line chimeras revealed that with two exceptions all the Fs(2) mutations are germ-line dependent. The Fs(2) mutations were mapped mainly on the basis of mitotic recombination induced in the female germ-line cells of adult females. That most of the Fs(2) may be gain-of-function mutations is indicated by the unusual behavior of the Fs+ germ-line clones and also by the fact that 90% of the could be induced to revert.     

Female Sterile Mutations on the Second Chromosome of Drosophila Melanogaster. I. Maternal Effect Mutations

In mutagenesis screens for recessive female sterile mutations on the second chromosome of Drosophila melanogaster 529 chromosomes were isolated which allow the homozygous females to survive, but cause them to be sterile. In 136 of these lines, mutant females produce morphologically normal eggs which cannot support normal embryonic development. These "maternal-effect" mutations fall into 67 complementation groups which define 23 multiply hit and 44 singly hit loci. In eggs from 14 complementation groups development is blocked before the formation of a syncytial blastoderm. In eggs from 12 complementation groups development is abnormal before cellularization, 17 complementation groups cause abnormal cellularization, 12 complementation groups cause changes in cellular morphology in early gastrulation stages, and 12 complementation groups seem to affect later embryonic development.     

Female Sterile Mutations on the Second Chromosome of Drosophila Melanogaster. II. Mutations Blocking Oogenesis or Altering Egg Morphology

In mutagenesis screens for recessive female sterile mutations on the second chromosome of Drosophila melanogaster 528 lines were isolated which allow the homozygous females to survive but cause sterility. In 62 of these lines early stages of oogenesis are affected, and these females usually do not lay any eggs. In 333 lines oogenesis proceeds apparently normally to stage 8 of oogenesis, but morphological defects become often apparent during later stages of oogenesis, and are visible in the defective eggs produced by these females whereas 133 lay eggs that appear morphologically normal, but do not support normal embryonic development. Of the lines 341 have been genetically characterized and define a total of 140 loci on the second chromosome. Not all the loci are specific for oogenesis. From the numbers obtained we estimate that the second chromosome of Drosophila contains about 13 loci that are relatively specific for early oogenesis, 70 loci that are specifically required in mid to late oogenesis, and around 30 maternal-effect lethals.     

A Female Sterile Screen of the Drosophila Melanogaster X Chromosome Using Hybrid Dysgenesis: Identification and Characterization of Egg Morphology Mutants

We have conducted a hybrid dysgenic screen of the X chromosome for mutations affecting female fertility, with particular attention to those causing abnormal egg and eggshell morphology. In a screen of 4017 dysgenic strains, 398 mutants derived from 168 different germ lines were isolated and assigned to eight classes according to their diverse phenotypes. One interesting class consists of mutants that block oogenesis at specific stages. Our analysis has focused on mutations affecting eggshell formation, including mutants that lay morphologically abnormal sterile eggs as well as those that lay no eggs but exhibit blocks in the late stages of oogenesis. A subset of 48 mutants was assorted into 30 allelic groups by inter se complementation and genetically localized by interval mapping. Two multiallele complementation groups, de1 (7 alleles) and ne1 (8 alleles), were identified as well as five two-allele complementation groups. A search for alleles among mutants generated in other female sterile screens was unsuccessful, pointing to the distinctive nature of the dysgenic mutant collection. The single case of allelism determined in this study was one with a lethal allele of the Broad-Complex, l(1)npr, suggesting a possible involvement of ecdysone in choriogenesis. A subset of 18 dysgenic strains was analyzed for P element hybridization and 16 of these were found to have hybridization signals in the appropriate cytogenetic interval. By examining these signals in two or more alleles of the same complementation group, we have been able to tentatively localize two mutations. Light and electron microscopy of the eggshell in 43 different strains has revealed a variety of effects. The respiratory appendages were defective in 27 of these mutants. Effects on the ultrastructure of the main body of the endochorion were not strongly correlated with the appendage defects, and could be classified as minor (14 mutants) or major (16 mutants). Although 13 mutants showed no ultrastructural chorion defects, six of these had defective respiratory appendages.     

P-Element Insertion Alleles of Essential Genes on the Third Chromosome of Drosophila Melanogaster: Mutations Affecting Embryonic Pns Development

To identify novel genes and to isolate tagged mutations in known genes that are required for the development of the peripheral nervous system (PNS), we have screened a novel collection of 2460 strains carrying lethal or semilethal P-element insertions on the third chromosome. Monoclonal antibody 22C10 was used as a marker to visualize the embryonic PNS. We identified 109 mutant strains that exhibited reproducible phenotypes in the PNS. Cytological and genetic analyses of these strains indicated that 87 mutations affect previously identified genes: tramtrack (n = 18 alleles), string (n = 15), cyclin A (n = 13), single-minded (n = 13), Delta (n = 9), neuralized (n = 4), pointed (n = 4), extra macrochaetae (n = 4), prospero (n = 3), tartan (n = 2), and pebble (n = 2). In addition, 13 mutations affect genes that we identified recently in a chemical mutagenesis screen designed to isolate similar mutants: hearty (n = 3), dorsotonals (n = 2), pavarotti (n = 2), sanpodo (n = 2), dalmatian (n = 1), missensed (n = 1), senseless (n = 1), and sticky ch1 (n = 1). The remaining nine mutations define seven novel complementation groups. The data presented here demonstrate that this collection of P elements will be useful for the identification and cloning of novel genes on the third chromosome, since >70% of mutations identified in the screen are caused by the insertion of a P element. A comparison between this screen and a chemical mutagenesis screen undertaken earlier highlights the complementarity of the two types of genetic screens.     

P Transposon-Induced Dominant Enhancer Mutations of Position-Effect Variegation in Drosophila Melanogaster

P transposon induced modifier mutations of position-effect variegation (PEV) were isolated with the help of hybrid dysgenic crosses (π2 strain) and after transposition of the mutator elements pUChsneory(+) and P[lArB]. Enhancer mutations were found with a ten times higher frequency than suppressors. The 19 pUChsneory(+)- and 15 P[lArB]-induced enhancer mutations can be used for cloning of genomic sequences at the insertion sites of the mutator elements via plasmid rescue. Together with a large sample of X-ray-induced (48) and spontaneous (93) enhancer mutations a basic genetic analysis of this group of modifier genes was performed. On the basis of complementation and mapping data we estimate the number of enhancer genes at about 30 in the third chromosome and between 50 and 60 for the whole autosome complement. Therefore, enhancer of PEV loci are found in the Drosophila genome as frequently as suppressor genes. Many of the enhancer mutations display paternal effects consistent with the hypothesis that some of these mutations can induce genomic imprinting. First studies on the developmentally regulated gene expression of PEV enhancer genes were performed by β-galactosidase staining in P[lArB] induced mutations.     

The Isolation of Polygenic Factors Controlling Bristle Score in Drosophila Melanogaster. II. Distribution of Third Chromosome Bristle Effects within Chromosome Sections

In the present study an attempt has been made to characterize the genetic ``factors' controlling quantitative characters, bristle numbers, in Drosophila melanogaster. A low sternopleural bristle multiple recessive marker third chromosome was used to analyze a high sternopleural third chromosome, in a high sternopleural bristle background. An attempt was made to estimate the minimum number of ``effective factors' involved in the difference in bristle score between the tested and marker chromosomes. Apart from sternopleural, scutellar and ocellar bristles, a new character, subprimal bristles, was also scored. The unselected characters were used to help in the factor locations, and an attempt made to detect epistasis. Concentrations of bristle effects were found, as were a few `factors' of large effect. At least 17 sternopleural bristle factors are required to account for the difference in bristle score between the high tested third chromosome and the low tester third chromosome. There was an ascertainment problem for polygenes with effects of less than about 0.6 phenotypic standard deviation. Only an estimate of the minimum number of factors and approximate locations can be given with any degree of certainty. The results are compatible with the hypothesis (among others) that quantitative characters are under the control of a few major genes supported by numerous genes with smaller effect.     

Age-specific Effects of Novel Mutations in Drosophila Melanogaster I. Mortality

Theories for the evolution of aging rest on the assumption that at least some deleterious mutations have effects that are limited to certain ages. Many mutation accumulation studies have tried to measure the number and magnitude of deleterious mutations, but few studies have tried to determine the extent to which the effects of mutations are limited to particular ages. Here we estimate the age-specific effect of deleterious mutations on mortality rate in an outbred population of the fruit fly, Drosophila melanogaster. We used the ‘middle class neighborhood’ approach to accumulation mutations in populations of flies that had recently been obtained from the wild. There are mutations that increase mortality rates, but whose effects are limited to specific ages. The age-specificity of mutational effects differs between the sexes, between virgin and mated flies, and over time. After 10 and 20 generations of mutation accumulation, there were clear age-specific effects of mutations. After 30 generations, however, the degree of age-specificity decreased. In addition, mutation accumulation led to a steady increase in larval mortality and a small but significant increase in the sex ratio of eclosing flies. We discuss the implications of these results for models of aging, and suggest approaches that future studies should take to obtain accurate information on the age-specificity of novel mutations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dominant Effects of Suppressor of Hairy-Wing Mutations on Gypsy-Induced Alleles of Forked and Cut in Drosophila Melanogaster

Mutations induced by the gypsy retrotransposon in the forked (f) and cut (ct) loci render their expression under the control of the suppressor of Hairy-wing [su(Hw)] gene. This action is usually recessive, but su(Hw) acts as a dominant on the alleles fk, ctk and ctMRpN30. Molecular analysis of the gypsy element present in fk indicates that this allele is caused by the insertion of a modified gypsy in which the region normally containing twelve copies of the octamer-like repeat that interacts with the su(Hw) product is altered. Analysis of the gypsy element responsible for the ctk and ctMRpN30 mutations also reveals a correlation between the dominant action of su(Hw) and disruption of the octamer region. We propose that these disruptions alter the affinity and interaction of su(Hw) protein with gypsy DNA, thereby sensitizing the mutant phenotype to fluctuations in su(Hw) product.     

Zygotic Lethal Mutations with Maternal Effect Phenotypes in Drosophila Melanogaster. II. Loci on the Second and Third Chromosomes Identified by P-Element-Induced Mutations

Screens for zygotic lethal mutations that are associated with specific maternal effect lethal phenotypes have only been conducted for the X chromosome. To identify loci on the autosomes, which represent four-fifths of the Drosophila genome, we have used the autosomal ``FLP-DFS' technique to screen a collection of 496 P element-induced mutations established by the Berkeley Drosophila Genome Project. We have identified 64 new loci whose gene products are required for proper egg formation or normal embryonic development.