The obscure parts of the X chromosome inDrosophila melanogaster

Through the use of small atelic fragments derived from T (1; 4) A,B ^S the right arm of the X chromosome ofD. melanogaster has been demonstrated.The proximal portion of XR is a non-chromatic or ghost reversed repeat of the proximal portion of XL.Polytene X chromosomes show no indications of the limits of the heterochromatic blocks which characterize mitotic X chromosomes.The nuclear organizer is a subterminal portion of the polytene XR, whereas it is situated in XL in mitotic neuroblast cells.It is suggested that the non-chromatic XR may contain a ghost allele of the genebobbed, and of perhaps other adjacent genes.This investigation was supported in part by Contract No. AT (30-1)-2113 from the U.S. Atomic Energy Commission, and in part by Public Health Service Research Grant No. C-4362 from the National Institutes of Health.     

Analysis of chromosome 4 inDrosophila melanogaster. I. Spontaneous and X-ray-induced lethals

An analysis of 17 spontaneous and 37 X-ray-induced lethal mutations on the fourth chromosome ofDrosophila melanogaster has revealed a minimum of 22 loci on this microchromosome capable of mutating to lethality. A few of these loci had been identified earlier by their visible alleles but 16 are new discoveries. Seven of the 22 lethal loci are situated within that proximal section of the right arm of chromosome 4 delimited by theMinute-4 deficiency.Genetic tests indicate that two translocations and five deletions are included among the lethals of X-ray origin. No chromosomal aberrations were found among the spontaneous mutants. Allelism was encountered both within and between lethals from the two groups.Three independent estimates of the total number of lethal loci to be expected on this small autosome are presented. These appraisals are based on (1) the size of theMinute-4 deficiency, (2) the number of bands in salivary chromosome 4, and (3) the frequency of recurrence among the lethals. Considering the uncertainties inherent in each determination, the three estimates (34, 35 and 38) show remarkably good agreement.This investigation was supported in part by U.S. Public Health Service Research Grant GM 11627-01, from the Division of General Medical Sciences.     

Correlations between chromosome segments and fitness in Drosophila melanogaster. IV. Fecundity, viability and the third chromosome

Unmarked segments within the third chromosome of three different Drosophila melanogaster lines were assessed for their effects on egg production and egg viability. By making a series of crosses among original and derived recombinant lines, it was possible to estimate parameters representing additive, dominance (for egg production), and interaction effects of the segments. Each segment influences both traits, but to extend which are dependent on the genetic background provided by an adjacent segment. There is no clear pattern, however, with respect to the segments' joint effects on the two characters. Unlike in the previous study involving the X chromosome, the majority of the derived recombinant lines were superior in fitness to their original lines. The agricultural implications of this result with respect to the manipulation of chromosomal segments in order to achieve higher yields are discussed.     

Isolation and characterization ofgrandchildless-like mutants inDrosophila melanogaster

Summary Two temperature-sensitive sex-linkedgrandchildless (gs)-like mutations (gs(1)N26 andgs(1)N441) were induced by ethylmethane sulphonate inDrosophila melanogaster. They complemented each other and mapped at two different loci (1–33.8±0.7 forgs(1)N26 and 1–39.6±1.7 forgs(1)N441), which were not identical to those of any of thegs-like mutants reported in earlier work.Homozygous females of the newly isolated mutants produced eggs that were unable to form pole cells and developed into agametic adults. Competence of the embryos to form pole cells was not restored by wild-type sperm in either mutant; that is, the sterility caused by these mutations is controlled by a maternal effect.Fecundity and fertility ofgs(1)N26 females were low, and their male offspring showed a higher mortality than that of female offspring, causing an abnormal sex ratio. The frequency of agametic progeny was 93.1% and 55.8%, when the female parents were reared at 25° C and 18° C, respectively. In eggs produced by thegs(1)N26 females reared at 25° C, the migration of nuclei to the posterior pole was abnormal, and almost no pole cell formation occurred in these egg. Furthermore, half of these eggs failed to cellularize at the posterior pole. When the females were reared at 18° C, almost all of the eggs underwent complete blastoderm formation, and in half of these blastoderm embryos normal pole cells were formed.In the other mutant,gs(1)N441, the fecundity and fertility of the females were normal. The agametic frequency in the progeny was 70.8% and 18.6% when the female parents were reared at 25° C and 18° C, respectively. In the eggs laid by females reared either at 25° C or at 18° C, the migration of nuclei to the periphery and cellularization proceeded normally; nevertheless, in the majority of the embryos no pole cell formation occured at the stage when nuclei penetrated into the periplasm. When the females were reared at 18° C, some of the embryos from these females formed some round blastoderm cells with cytologically recognizable polar granules and nuclear bodies, which are attributes of pole cells. The temperature sensitive period ofgs(1)N441 was estimated to extend from stage 9 to 13 of King's stages of oogenesis.     

Inbreeding depression and male-mating behavior inDrosophila melanogaster

There have been relatively few studies designed to investigate the effects of inbreeding on behavioral traits. To study this phenomenon, five experimental lines ofDrosophila melanogaster made isogenic for chromosome 2 were evaluated for their male-mating ability and, subsequently, male courtship behavior. All lines showed significant reductions in overall mating ability, and males from all of these lines displayed impaired mating behavior, with two lines displaying particularly aberrant courtship patterns. Line 16 displayed an inability to successfully initiate copulation following successful courtship, while line 17 displayed significant reduction in locomotor activity, resulting in virtually no successful courtship or copulatory activity. The implications of these findings for competitive mating ability in wildDrosophila populations are presented. Further, the importance of mating success as a fitness component in the management of potentially highly inbred populations of endangered species is discussed.     

Parental age and developmental stability inDrosophila melanogaster

Two strains ofDrosophila melanogaster, one outbred, recently derived from nature, and the other created by intensive directional selection on phototactic behavior for 19 years, were used to test the hypothesis that developmental stability is influenced by parental age. Three characters were examined: sternopleural bristle number, wing length, and wing area. The results do not support any relationship between parental age, either young or old, and developmental stability in offspring.     

Isolation and characterization of second chromosome mutagen-sensitive mutations in Drosophila melanogaster

We have undertaken the study of a collection of 32 Drosophila melanogaster mus strains selected on the basis of developmental sensitivity to the DNA-damaging agents, methyl methanesulfonate (MMS), N-acetyl-2-aminofluorene (AAF), nitrogen mustard (HN2), and gamma-radiation. In total, 18 of these strains are sensitive to MMS. In turn, 14 of these exhibit unconditional MMS sensitivity (one of the latter mutants is lethal at 29 degrees C), whereas the other 4 are sensitive to MMS only at higher temperatures. Detailed analysis of the 7 strongest MMS-sensitive strains reveals that they identify 4 new second chromosome mus loci. Two mus loci are each represented by two alleles. One mutant (mus205B1) is allelic to a previously characterized mus locus. Different MMS-sensitive mutants display patterns of mutagen cross-sensitivity (to AAF, HN2, benzo[a]pyrene (BP), and gamma-rays) that parallel the range of responses seen in previously recovered X-linked and autosomal mus loci. In general, mutations that are strongly sensitive to MMS are also sensitive to one or both of the procarcinogens, AAF and BP, as opposed to HN2 and gamma-radiation. In contrast, the moderately MMS-sensitive mutations are sensitive to HN2 and gamma-rays, but not to AAF or BP. Of the 14 mus strains that are not sensitive to MMS, 5 are sensitive to AAF, another 5 are sensitive to HN2, and the remaining 4 are sensitive to gamma-rays.     

Intercellular adhesivity and pupal morphogenesis inDrosophila melanogaster

Summary Leg and wing imaginal discs of mature larvae ofDrosophila melanogaster when treated with 0.1% trypsin for 5–10 min underwent a change in shape that closely resembled normal pupal morphogenesis. Simultaneously, the cells of the disc epithelium changed in shape from tall columnar to cuboidal. Colcemid eliminated microtubules but was without effect on the shape of the imaginal discs or their cells. Tryptic digestion reduced non-junctional intercellular adhesivity but septate desmosomes and gap junctions remained intact.It is proposed that the structure of imaginal discs permits the packaging of the anlagen of the adult integument so that they can change shape and replace the larval structures in a brief period. Apparently most of the definitive form of the pupal leg is built into the disc and becomes visible within a few minutes as intercellular adhesivity is changed.     

Immunocytochemistry of a novel GABA receptor subunitRdl inDrosophila melanogaster

Following our recent cloning of a novel γ-aminobutyric acid (GABA) receptor subunit geneResistance to dieldrin orRdl from the cyclodiene resistance locus inDrosophila melanogaster, we were interested in defining its pattern of expression during development. Here we report the raising of an anti-Rdl polyclonal antibody that recognizes a single protein of the expected 65 kDa size in immunoblots ofDrosophila head homogenates.In situ hybridization usingRdl cDNA probes and the anti-Rdl antibody shows thatRdl message and protein are highly expressed in the developing central nervous system (CNS) of 15–17 h embryos. Interestingly, despite the use of GABA in both the peripheral and CNS of insects,Rdl GABA receptor subunits appear to be confined to the CNS. Detailed immunocytochemistry ofDrosophila brain sections showed particularly strong anti-Rdl antibody staining in the optic lobes, ellipsoid body, fan shaped body, ventrolateral protocerebrum and the glomeruli of the antennal lobes. Results are compared with the distribution of staining observed in the insect CNS with antibodies against GABA itself and synaptotagmin, a synaptic vesicle protein.     

Properties of learning and memory inDrosophila melanogaster

Summary Drosophila melanogaster can be conditioned to avoid an odorant selectively after being shocked in its presence (Quinn et al., 1974). In the following study learning and memory properties of the flies are reported. The major part of the conditioned behavior is acquired after a single training trial (Fig. 2). Similar degrees of learning are obtained by using various odorants in various combinations (Table 1). The flies can learn to avoid selectively several odorants at a time, can learn to discriminate between different concentrations of the same odorant (Fig. 4), and can also learn to distinguish a mixture of odorants from its components. If not extinguished, the selective avoidance decays slowly and can be detected for hours, its magnitude depending upon the intensity of training (Fig. 6). Memory can be disrupted by narcosis during the first 20 min after training, but not afterwards (Fig. 7). A study of learning properties of wild-type strains and various morphological and behavioral mutants reveals differences in performance (Table 2). However, the differences cannot be attributed with certainty to differences in learning and memory, per se, because the mutants differ in other aspects of behavior, e.g., locomotor activity and phototaxis. Of the wild-type strains tested, Canton-S performed the best.I thank Dr. S. Benzer for the hospitality of his laboratory, and S. Benzer, D. Byers, W. Harris, L. Jan, Y.-N. Jan, W. Quinn, D. Ready and M. Shankland for valuable discussions. This work was supported by an EMBO long-term fellowship and by a grant from the National Science Foundation to Dr. S. Benzer.     

Analysis of an SD second chromosome from a natural population of Drosophila melanogaster

The second chromosome Co-122 (Corato-122) extracted from a natural population of Drosophila melanogaster caught in Corato (Apulia) and maintained in the laboratory over the SM5 balancer chromosome, proved to carry: (1) a Segregation distorter factor, named Sd ^Co; (2) a recessive lethal mutation, termed mle-Co (maleless-Corato), which causes the lethality of only males; (3) another recessive lethal mutation, l(2)Co (lethal (2) Corato), probably arisen in the laboratory by mutation. This mutation accounts for the diminished recovery of homozygous females observed in the stock.The genetic features and the cytological analysis of the SD chromosome are reported, as well as the genetic localization of mle-Co and 1(2)Co and their cytogenetic mapping. An allelism test has ascertained that mle-Co is allelic to mle, a male-specific mutation described by Fukunaga et al., 1975. The tight linkage of mle-Co and 1(2)Co with Sd is discussed from the standpoint of population genetics.     

Genetic analysis ofloboid-ophthalmoptera,a homoeotic strain inDrosophila melanogaster

A homoeotic strain in which wing-like outgrowths are produced from the eye region was investigated. The actual wing nature of the malformation was confirmed. Genetically, this homoeotic character depends on the presence of an eye-reducing factor,loboid (ld; 3–102), and of modifier genes. One important sex-linked modifier, probably located at 1–5±, is thought to be the main factor underlying the homoeotic effect. It is designated asopht (ophthalmoptera), and the mutant strain asld-opht Kobel (1968), assuming a specific allele ofld with homoeotic effect, originally described this strain under the nameld ^oph. It is shown that inld-opht, theld factor can be replaced byDfd ^r-L (3–47.5) without irrevokably losing the homoeotic effect.Penetrance and expressivity ofopht are very variable and subject to genetic and environmental changes, and they readily respond to selection. Such properties are common to all homoeotic mutants. The phenomenon of homoeosis is interpreted in terms of allotypic differentiations resulting from a switching of development into other epigenetic pathways. This switching is perhaps due to an altered rate of proliferation.Aided by a grant from the Netherlands Organization for the Advancement of Pure Research (Z.W.O.).     

Sulfite sensitivity and sulfite oxidase actiivty inDrosophila melanogaster

The relationship between sulfite oxidase (SO) and sulfite sensitivity inDrosophila melanogaster is addressed. Significant improvements to the SO assay have provided an investigative tool which can be applied to further studies of this molybdoenzyme. Using the second-instar larval stage ofD. melanogaster, we have shown a direct relationship between measured levels of sulfite oxidase activity and the organism's ability to withstand a sulfite challenge. Implementation of a sulfite-testing procedure confirmed the documented instability of sulfite in solution and may explain some of the conflicting results reported in the SO literature. Results of the tungstate-addition experiments confirm thatDrosophila SO is a molybdoenzyme and its activity was shown to be governed by three of the four loci known to affect more than one molybdoenzyme. The ability ofD. melanogaster to withstand the application of exogenous sulfites is shown to be dependent on sulfite oxidase activity.     

Interaction systems between heterochromatin and euchromatin inDrosophila melanogaster

The constitutive heterochromatin is still one of the major unsolved problems in genetics. InDrosophila melanogaster three genetic systems involving specific interactions between heterochromatic and euchromatic genetic elements are known: the Segregation Distortion, thecrystal-Stellate and theabo-ABO systems. The genetic and molecular analysis of each system will allow the identification of all the components and the elucidation of the mechanisms underlying their interactions. The results of this analysis should provide insights into the biological significance of heterochromatin and into the evolutionary forces that result in the maintainance and stability of this enigmatic genetic material.