Genetic analysis of chromosomal region 97D2-9 of Drosophila melanogaster

The rough homeobox gene of D. melanogaster is required for the correct patterning of the developing eye. The locus maps to cytological location 97D2-5, a region which has not been extensively characterised. As part of our genetic and molecular characterization of rough we carried out an EMS mutagenesis to generate mutants that map to the surrounding region, 97D2-9 which is deleted in Df(3R)ro-XB3. We have generated 1 visible and 13 lethal mutations which, together with the previously described Toll and ms(3)K10 loci, and other unpublished lethals, define nine complementation groups — four lethal, three semi-lethal, one visible and one male-sterile. In addition to rough, one other locus within this region, 1(3)97De, was shown to be required for formation of the normal pattern of photoreceptor cells in the compound eye.     

Functional genomic analysis of the 61D-61F region of the third chromosome of Drosophila melanogaster.

Assigning functional significance to completed genome sequences is one of the next challenges in biological science. Conventional genetic tools such as deficiency chromosomes help assign essential complementation groups to their corresponding genes. We describe an F2 genetic screen to identify lethal mutations within cytogenetic region 61D-61F of the third chromosome of Drosophila melanogaster. One hundred sixteen mutations were identified by their failure to complement both Df(3L)bab-PG and Df(3L)3C7. These alleles were assigned to 14 complementation groups and 9 deficiency intervals. Complementation groups were ordered using existing deficiencies, as well as new deficiencies generated in this study. With the aid of the genomic sequence, genetic and physical maps in the region were correlated by use of PCR to localize the breakpoints of deficiencies within a 268-kb genomic contig (GenBank accession No. AC005847). Six essential complementation groups were assigned to specific genes, including genes encoding a porphobilinogen deaminase and a Sac1-like protein.     

Genetic analysis of the X-chromosomal region 1E-2A of Drosophila melanogaster

Reversion mutagenesis of three single P elements located in the cytogenetic interval 1E-2A at the tip of the X chromosome of Drosophila melanogaster was used to recover new deletions in this chromosomal region. The deletions obtained include small aberrations within region 2A and larger lesions extending from 2A into 1E and 1B. All three screens also yielded terminal deficiencies. The new deficiencies, together with previously characterized rearrangements, were analyzed for their complementation behaviour with the maternal effect locus fs(1)Nasrat and lethal loci in the region. These analyses provide an overall genetic map of the interval 1E-2A. In addition, the smaller deletions were physically mapped within cloned genomic DNA of the 2A region.     

Cytogenetic analysis of the X-chromosome region 2B1-2-2B9-10 of Drosophila melanogaster

In salivary glands of yellow control stock the puffing pattern in the ecdysone-added artificial C46P medium was on the whole similar to that observed during larval development in vivo. However, underdevelopment of a series of late puffs and a delay in the regression of early puffs were observed. In addition a set of medium puffs not visible in vivo appeared. Late puffs differed from those developing in Grace medium.When salivary glands of homozygotes for the lethal dor ^lt187, a mutation that causes death in the third instar with no signs of ecdysone induction were incubated with ecdysterone, the development of puffs was restored, i.e., the puffing pattern of mutant cells in vitro practically did not differ from that in cells of the control stock. This implies that the dor ^lt187 lethal allele belongs to the class of ecdysone-deficient mutations.     

The kinesin-like protein KLP61F is essential for mitosis in Drosophila

We report here that disruption of a recently discovered kinesin-like protein in Drosophila melanogaster, KLP61F, results in a mitotic mutation lethal to the organism. We show that in the absence of KLP61F function, spindle poles fail to separate, resulting in the formation of monopolar mitotic spindles. The resulting phenotype of metaphase arrest with polyploid cells is reminiscent of that seen in the fungal bimC and cut7 mutations, where it has also been shown that spindle pole bodies are not segregated. KLP61F is specifically expressed in proliferating tissues during embryonic and larval development, consistent with a primary role in cell division. The structural and functional homology of the KLP61F, bimC, cut7, and Eg5 kinesin-like proteins demonstrates the existence of a conserved family of kinesin-like molecules important for spindle pole separation and mitotic spindle dynamics.     

Genetic,cytological, and ultrastructural characterization of a temperature-sensitive lethal in Drosophila melanogaster

Genetic analysis of a strain of Drosophila melanogaster revealed that a recessive mutation [l(1)ER^ts] causing temperature-sensitive embryonic lethality is located in the distal region of the X chromosome approximately at map position 18. At 22–25°C mutant embryos exhibit normal viability, and all eggs arrest prior to gastrulation if they are reared at 29°C. The mutant is biphasic, exhibiting a maternal effect which is expressed throughout the first 8 hr of development as well as a second temperature-sensitive period (TSP) during the first 3 days of larval life. Larvae exposed to the restrictive temperature (RT) during the second TSP must also spend the remainder of larval and pupal life and the time of normal eclosion at RT to die as fully developed pupae which fail to eclose. Light and electron microscopy of arrested embryos reveal disturbances in the distribution of nuclei, cytoplasm, and yolk and abnormal configurations of rough endoplasmic reticulum. The cause of pupal death during the second lethal period is unknown.     

Genetic interactions of modifier genes and modifiable alleles in Drosophila melanogaster

We have examined the effects of mutations in the six allele-specific modifier genes su(Hw), e(we), su(f), su(s), su(wa), and su(pr) on the expression of 18 modifiable alleles, situated at 11 loci. Ten of the modifiable alleles are associated with insertions of the gypsy retrotransposon and the others include alleles associated with insertions of copia and 412. We tested or retested 90 of the 108 possible combinations and examined the expression of modifiable alleles in flies mutant for pairs of modifier genes in various heterozygous and homozygous configurations. Our principal findings are: (1) a screen of 40,000 mutagenized X chromosomes yielded three new mutations in known modifier genes, but revealed no new modifier genes; (2) the modification effects of different mutations in a given modifier gene were qualitatively similar; (3) each of the six modifiers suppressed some modifiable alleles, enhanced others, and had no noticeable effect on still others; (4) the modifier genes could be placed in four classes, according to their effects on the gypsy-insertion alleles; and (5) the effects of mutations in different modifier genes combined additively. Implications of these results for models of modifier gene action are discussed.     

Genetic characterization of the 44D-45B region of the Drosophila melanogaster genome based on an F2 lethal screen

We have performed an F₂ genetic screen to identify lethal mutations that map to the 44D-45B region of the Drosophila melanogaster genome. By screening 8500 mutagenized chromosomes for lethality over Df(2R)Np3, a deficiency which encompasses nearly 1% of the D. melanogaster euchromatic genome, we recovered 125 lines with lethal mutations that represent 38 complementation groups. The lethal mutations have been mapped to deficiencies that span the 44D-45B region, producing an approximate map position for each complementation group. Lethal mutations were analyzed to determine the phase of development at which lethality occurred. In addition, we have linked some of the complementation groups to P element-induced lethals that map to 44D-45B, thus possibly providing new alleles of a previously tagged gene. Some of the complementation groups represent potentially novel alleles of previously identified genes that map to the region. Several genes have been mapped by molecular means to the 44D-45B region, but do not have any reported mutant alleles. This screen may have uncovered mutant alleles of these genes. The results of complementation tests with previously identified genes in 44D-45B suggests that over half of the complementation groups identified in this screen may be novel. Received: 13 July 1999 / Accepted: 4 November 1999     

Genetic analysis of a Y-chromosome region that induces triplosterile phenotypes and is essential for spermatid individualization in Drosophila melanogaster

The heterochromatic Y chromosome of Drosophila melanogaster contains approximately 40 Mb of DNA but has only six loci mutable to male sterility. Region h1-h9 on YL, which carries the kl-3 and kl-5 loci, induces male sterility when present in three copies. We show that three separate segments within the region are responsible for the triplosterility and have an additive effect on male fertility. The triplosterile males displayed pleiotropic defects, beginning at early postmeiotic stages. However, the triplosterility was unaffected by kl-3 or kl-5 alleles. These data suggest that region h1-h9 is complex and may contain novel functions in addition to those of the previously identified kl-3 and kl-5 loci. The kl-3 and kl-5 mutations as well as deficiencies within region h1-h9 result in loss of the spermatid axonemal outer dynein arms. Examination using fluorescent probes showed that males deficient for h1-h3 or h4-h9 displayed a postmeiotic lesion with disrupted individualization complexes scattered along the spermatid bundle. In contrast, the kl-3 and kl-5 mutations had no effect on spermatid individualization despite the defect in the axonemes. These results demonstrate that region h1-h9 carries genetically separable functions: one required for spermatid individualization and the other essential for assembling the axonemal dynein arms.     

Cytogenetic analysis of chromosome segments containing radiosensitivity genes in Drosophila. Radiation mutagenesis in the 44-45 region of chromosome 2 of Drosophila melanogaster

The first step of cytogenetic analysis of Drosophila melanogaster chromosome 2 44F-45D containing the radiosensitivity gene rad(2)201 is described. Using various mutation selection systems as well as lines of different origin and two kinds of ionizing radiation--gamma-rays and neutrons--the mutagenesis in the region of interest is characterized at the cytogenetic level. 85 gamma-induced mutations affecting viability were isolated in the 44F 2-4; 45C6-7 interval, 27% of mutations being chromosomal aberrations. 15 radiation-induced aberrations were obtained by selecting mutations at the white gene inserted into the 45D region by P-mediated transformation. The 44F-45D region is characterized by relatively low frequency of deficiency formation and by significant predomination of heterochromatic aberrations in the spectrum of rearrangements. In these regions, the existence of hot spots for heterochromatic aberrations was discovered. As low deletion frequency is not connected with the presence of haplolethal and haplosterile loci in the region studied, the unusual character of radiation mutagenesis reflects possibly the peculiarities in sequence organization of the chromosomal region mentioned or the packaging in the sperm nuclei.     

Genetic and molecular variation in the RpII215 region of Drosophila melanogaster

Molecular Genetics and Genomics - The RpII215 region of the X chromosome of Drosophila melanogaster was investigated to identify genetic functions and correlate these with the known molecular...     

Genetic aspects of aflatoxin B1 resistance in Drosophila melanogaster

Fifteen wild-type laboratory strains of Drosophila melanogaster were tested for egg-adult viability when exposed to larval development in media containing 0.5 and 1.0 ppm aflatoxin B (AFB1). Significant variation among the strains was demonstrated, especially at the 0.5 ppm AFB1 concentration. Two resistant and two sensitive strains were made isogenic and mated in a 4 X 4 diallel system. Results indicate that differences in AFB1 sensitivity are due to genes with additive effects on viability and that nonsystematic effects due to the interaction of cytoplasms and genes of both paternal and maternal origin are present. A chromosome/cytoplasm substitution analysis was performed using one of the sensitive and one of the resistant strains. Results indicate that genes on chromosomes X and 2 contribute to egg-adult viability differences observed for larval growth on media containing 0.5 and 1.0 ppm AFB1. Also, a significant interaction between chromosome 2 and cytoplasm, both from the resistant strain, was observed, resulting in a twofold increase in viability at 0.5 ppm AFB1 when compared to controls. Possible relationships of these findings with those from vertebrate systems are discussed.     

A cytological and genetic study of oogenesis in Drosophila melanogaster

A newly derived collection of 98 autosomal recessive female-sterile (fs) lines induced by ethyl methanesulfonate (EMS) in Drosophila melanogaster has been studied genetically and cytologically. By the use of phenotype and complementation tests, the 98 fs lines were resolved into 19 fs genes on the 2nd chromosome and 17 fs genes on the 3rd chromosome. Nearly half of the fs lines turned out to be replicates of noninduced fs mutant loci that preexisted in the EMS-treated files.Systematizing these fs genes according to their phenotypic and morphological defects focuses attention on their relevance to five major aspects of oogenesis: (1) the developmental organization of the ovary, (2) the synthesis and deposition of yolk material, (3) the formation of the chorion, (4) the control of egg-laying, and (5) the construction of the internal milieu of the ovarian oocyte for normal embryogenesis.The results of this study demonstrate that a systematic collection and characterization of fs mutants can provide the genetic tools needed to study the complex interactions which proceed undetected during normal oogenesis.