Effects of the “sexcombless” chromosome (In(1)sx) on males and females ofDrosophila melanogaster

Summary The chromosome which carries the mutationsexcombless (In(1)sx) affects males and females ofD. melanogaster. In the male foreleg basitarsi the number of sexcomb teeth is dramatically reduced from 10 to 0.7 and the number of transverse rows of bristles is increased from 6 to 8. Females homozygous forIn(1)sx show a normal bristle pattern in the foreleg basitarsus. The genital disc derivatives of both male and femaleIn(1)sx flies are strongly affected. While the external genitalia show a duplicated or a reduced bristle pattern, the internal genitalia are mostly absent. However, the sexually dimorphic tergites and sternites of the abdomen remain unaffected. The male-specific effect on the basitarsus and the general effects on the genital disc derivatives are proposed to represent two different phenotypic effects ofIn(1)sx which may derive from mutations at different gene loci in the inverted chromosome.     

Interaction of the mutants sx,tra and dsx in Drosophila melanogaster. Chaetotaxy of the basitarsus of the forelegs in males and females

The basitarsal bristle pattern of the mutants sx (sexcombless), tra (transformer), and dsx (doublesex), and of the combinations sx-dsx and tra-dsx is described. Epistasis of dsx over both sx and tra for many of the chaetotaxal characteristics was found. The various effects of interaction observed, in individuals of male as well as female chromosomal constitution, are discussed in the light of the levels of action of the mutant genes in modifying the development of sex. It is suggested that intersexes induced by dsx are a class by itself, and that the action of dsx might be at a primary level of sex determination.     

New sex-linked mutation of wings fragility with age-depended expression (<Emphasis Type="Italic">fw</Emphasis>) in <Emphasis Type="Italic">Musca domestica</Emphasis> L.

A mutation of wing fragility that was not yet been revealed in adult housefly is described. Criss-cross inheritance of the character of fragility of the wing blade, which indicates localization of gene (fw) for this character in the X chromosome. Phenotypic expression of the mutant allele depends on sex. In male flies, the mutant allele in hemizygous state is expressed at the age of 2–3 weeks and older with penetrance close to 100%. In females, the mutant allele in homozygous state is lethal and in heterozygous state, totally recessive.     

The role of the transformer genes in the development of genitalia and analia of Drosophila melanogaster

The autosomal mutations transformer (tra) and transformer-2 (tra-2) of Drosophila convert chromosomal females (X/X) into phenotypical males. Our analysis aims at an understanding of the role which the transformer genes play in the development of the sexually dimorphic genital disc. In each Drosophila embryo, this disc starts development with a male and a female genital primordium, and an anal primordium. Our experiments involved the production of cell clones that were made homozygous for tra or tra-2 at different times of development. Homozygous clones were obtained by inducing mitotic recombination in three types of females heterozygous for tra or tra-2. The cells of the homozygous tra/tra or tra-2/tra-2 clones responded by changing from the female into the male pathway. Male genital structures developed if the clones were induced not later than 81 hr into development. In the analia, male clones appeared up to 120 hr. Our results show that the action of the wild-type alleles of tra⁺ and tra-2⁺ is required until late in larval development to repress the male genital primordium and to support development of the female primordium, as well as to maintain the anal primordium in the female pathway. Our data also suggest that the embryonic genital disc consists of two compartments, one containing the precursors for penis and analia, the other those of the male and female genitalia.     

Studies of fs(1)1621, a mutation producing ovarian tumors in Drosophila melanogaster

The ethyl methane sulfonate-induced mutation, fs(1)1621, resides at 11.7 on the genetic map and within segment 4F1-5A1 of the cytological map of the X chromosome. When homozygous, fs(1)1621 renders females semisterile but has no effect on their viability; nor does it affect the viability or fertility of hemizygous males. Heterozygous females are fertile and have cytologically normal ovaries. The ovaries of homozygous females first produce normal oocytes, which, if fertilized, can develop into adult males or females. After this period, ovarian chambers containing only pseudonurse cells are formed, and finally mutant germaria produce only tumors. These contain hundreds to thousands of cells that appear to be derived from germarial cystocytes, because they occasionally form clones of interconnected cells and also can differentiate into endopolyploid pseudonurse cells. Raising the temperature speeds the rate at which tumors form; lowering it increases the probability of pseudonurse cell differentiation. Df(1)C159 includes fs(1)1621. The pattern of ovarian chamber production is more temperature sensitive in hemizygous females than in homozygous ones. The morphology of hemizygous tumors and the number of dividing cells within them also differ from homozygotes. These observations support the hypothesis that fs(1)1621 is producing a product, that less is produced by one gene than by two, and that the product plays a role in the mitosis and cytokinesis of ovarian cystocytes.     

POLYGENIC MUTATION IN DROSOPHILA MELANOGASTER: ESTIMATES FROM DIVERGENCE AMONG INBRED STRAINS

A highly inbred line of Drosophila melanogaster was subdivided into 25 replicate sublines, which were independently maintained for 100 generations with 10 pairs of unselected flies per generation. The polygenic mutation rate (V_M) for two quantitative traits, abdominal and sternopleural bristle number, was estimated from divergence among sublines at 10 generation intervals from generations 30-100, and from response of each line to divergent selection after more than 65 generations of mutation accumulation. Estimates of V_M averaged over males and females both from divergence among lines and from response to selection within lines were 3.3 × 10^-3 V_E for abdominal bristles and 1.5 × 10^-3 V_E for sternopleural bristles, where V_E is the environmental variance. The actual rate of production of mutations affecting these traits may be considerably higher if the traits are under stabilizing selection, and if mutations affecting bristle number have deleterious effects on fitness. There was a substantial component of variance for sex × mutant effect interaction and the sublines evolved highly significant mutational variation in sex dimorphism of abdominal bristle number. Pleiotropic effects on sex dimorphism may be a general property of mutations at loci determining bristle number.     

The temperature-sensitive mutation vir ts(virilizer) identifies a new gene involved in sex determination of Drosophila

Summary When XX animals homozygous for the temperature-sensitive mutation vir ^tsof virilizer (2–103.9) are raised at the restrictive temperature of 29° C, they are transformed into sterile intersexes with a morphology comparable to XX flies mutant at the sex-determining gene doublesex (dsx). The gonads of the vir ^tsintersexes are ovaries in which the germ cells undergo abortive oogenesis. At the permissive temperature of 25° C or below, XX vir ^tsanimals develop into marginally fertile females. The temperature-sensitive period of vir ^tsis within the third larval instar. XY males are not affected by the mutation. Animals that are homozygous for vir ^tsand either transformer (tra) or tra2 develop as pseudomales; on the other hand, constitutive expression of a female-specific tra product rescues XX animals from the effect of vir ^ts, but these females are sterile. The data show that tra and tra2 are epistatic to vir. Animals with only one wildtype copy of either tra or tra2 and mutant for vir ^tsare already transformed into intersexes at 25° C. Conversely, the presence of three copies of the tra ⁺ gene largely prevents the effect of vir ^tsat 29° C; such flies are practically female, but sterile. Animals homozygous for vir ^tsand heterozygous for dsx ^D/+, raised at 29° C, are transformed into severely masculinized intersexes or almost pseudomales. The observations suggest that vir acts above and via tra and tra2 to achieve proper female-specific expression of the dsx gene in XX zygotes. Offprint requests to: R. Nöthiger     

Sex and the Single Cell. I. on the Action of Major Loci Affecting Sex Determination in DROSOPHILA MELANOGASTER

Sex determination in Drosophila melanogaster is under the control of the X chromosome:autosome ratio and at least four major regulatory genes: transformer (tra), transformer-2 (tra-2), doublesex (dsx) and intersex (ix). Attention is focused here on the roles of these four loci in sex determination. By examining the sexual phenotype of clones of homozygous mutant cells produced by mitotic recombination in flies heterozygous for a given recessive sex-determination mutant, we have shown that the tra, tra-2 and dsx loci determine sex in a cell-autonomous manner. The effect of removing the wild-type allele of each locus (by mitotic recombination) at a number of times during development has been used to determine when the wild-type alleles of the tra, tra-2 and dsx loci have been transcribed sufficiently to support normal sexual development. The wild-type alleles of all three loci are needed into the early pupal period for normal sex determination in the cells that produce the sexually dimorphic (in pigmentation) cuticle of the fifth and sixth dorsal abdominal segments. tra⁺ and tra-2⁺ cease being needed shortly before the termination of cell division in the abdomen, whereas dsx⁺ is required at least until the end of division. By contrast, in the foreleg, the wild-type alleles of tra⁺ and tra-2⁺ have functioned sufficiently for normal sexual differentiation to occur by about 24 to 48 hours before pupariation, but dsx⁺ is required in the foreleg at least until pupariation.——A comparison of the phenotypes produced in mutant/deficiency and homozygous mutant-bearing flies shows that dsx, tra-2 and tra mutants result in a loss of wild-type function and probably represent null alleles at these genes.—All possible homozygous doublemutant combinations of ix, tra-2 and dsx have been constructed and reveal a clear pattern of epistasis: dsx > tra, tra-2 > ix. We conclude that these genes function in a single pathway that determines sex. The data suggest that these mutants are major regulatory loci that control the batteries of genes necessary for the development of many, and perhaps all, secondary sexual characteristics.—The striking similarities between the properties of these loci and those of the homeotic loci that determine segmental and subsegmental specialization during development suggest that the basic mechanisms of regulation are the same in the two situations. The phenotypes and interactions of these sex-determination mutants provide the basis for the model of how the wild-type alleles of these loci act together to effect normal sex determination. Implications of these observations for the function of other homeotic loci are discussed.     

Genetics of sex determination in the haplodiploid wasp <Emphasis Type="Italic">Nasonia vitripennis</Emphasis> (Hymenoptera: Chalcidoidea)

The parasitoid wasp Nasonia vitripennis reproduces by haplodiploidy; males are haploid and females are diploid. Sex determination in Nasonia is not governed by complementary alleles at one or more sex loci. As in most other insects, the sex-determining pathway consists of the basal switch doublesex that is sex-specifically regulated by transformer. Analysis of a polyploid and a mutant gynandromorphic strain, suggested a parent-specific effect (imprinting) on sex determination in Nasonia. Zygotic activity of transformer is autoregulated and depends on a combination of maternal provision of tra mRNA and a paternal genome set. This constitutes a novel way of transformer control in insect sex determination implying maternal imprinting. The nature of the maternal imprint is not yet known and it remains to be determined how broadly the Nasonia sex-determining mechanism applies to other haplodiploids.     

Identification of hypomorphic and null alleles of<Emphasis Type="Italic"> swallow</Emphasis> via molecular and phenotypic analyses

The swallow gene of Drosophila is required for the localization of two messenger RNAs, bicoid and hu-li tai shao, to the anterior pole of oocytes during the later stages of oogenesis. In addition, swallow appears to play a role in early embryogenesis, as swallow mutant embryos have defects in early nuclear cleavage and migration. In an effort to identify regions of the Swallow protein that are essential for function, we have initiated a molecular characterization of seven existing alleles of swallow. All seven alleles have been sequenced, and comparison to wild-type swallow indicates that the seven alleles include single amino acid substitutions that identify critical residues, as well as lesions that result in truncated proteins. Western blots using affinity-purified antibodies agree well with the DNA sequence data, and identify a probable null protein. In order to determine the extent to which each allele affects swallow function, females homozygous or hemizygous for each allele were tested for the range and abundance of (1) RNA localization defects, and (2) embryonic cuticular defects. Swallow alleles can be grouped into two categories: those that retain partial function, and those indistinguishable from the putative null allele. Some swallow mutant alleles partially rescue the dominant female sterility of mutations in the atypical 67C -tubulin gene, supporting other studies that suggest a link between RNA localization and the microtubule cytoskeleton.Edited by C. Desplan     

New sex-linked mutation of wings fragility with age-depended expression (fw) in Musca domestica L

A mutation of wing fragility that was not yet been revealed in adult housefly is described. Criss-cross inheritance of the character of fragility of the wing blade, which indicates localization of gene (fw) for this character in the X chromosome. Phenotypic expression of the mutant allele depends on sex. In male flies, the mutant allele in hemizygous state is expressed at the age of 2-3 weeks and older with penetrance close to 100%. In females, the mutant allele in homozygous state is lethal and in heterozygous state, totally recessive.     

A Maternal-Effect Sex-Transformation Mutant of the Housefly, MUSCA DOMESTICA L

A maternal-effect sex-transformation mutant, transformer (tra), of the housefly is described. It is located on autosome 4 in close linkage with the Ba locus. Normally, the sex of Musca domestica is determined by the presence or absence of an epistatic factor, M. When produced by tra/tra mothers, a large fraction of the tra/tra genotypic female progeny carrying no M factors are transformed to develop into intersexes or fertile phenotypic males. The tra/+ progeny are also transformed, but less frequently. Aging of the mothers increases the frequency of sex-transformed flies. When produced by tra/+ mothers, tra/tra progeny (but not +/tra) occasionally undergo sex transformation. Thus, tra⁺ is active both maternally and zygotically. Genotypic males carrying the M factor are not affected by the tra mutant. It is concluded that the tra⁺ gene product is required for female determination and/or differentiation. A model is proposed to explain actions of all the known sex-determination genes in M. domestica , and it is discussed in relation to sex-determination mechanisms in several other insect species.     

The genetics of dopa decarboxylase in Drosophila melanogaster. III. Effects of a temperature sensitive dopa decarboxylase deficient mutation on female fertility

The mutation Ddc^ts1 effects female sterility when homozygous, hemizygous, or heterozygous over a series of Ddc null alleles (Ddc^x) indicating that some aspect of Ddc gene function is necessary for female fertility. Ovary transplant experiments demonstrate that the female sterility phenotype is ovary autonomous. Two to 3% of the total DDC activity measurable in newly hatched females is localized in their previtellogenic ovaries. The degree to which females heterozygous for Ddc^ts1 over different Ddc null alleles are fertile at 22°C reflects a continuous spectrum of allelic complementation similar to that observed for the effects of these genotypes on viability at 30°C. Fertility of all the Ddc^ts1/Ddc^x females tested is significantly depressed at 30 vis-a-vis 22°C providing evidence that it is the DDC enzyme activity itself which is required for female fertility. Ddc^ts1/Ddc^ts1 homozygous and Ddc^ts1/Df hemizygous females are nonconditionally, completely sterile at 18, 20, 22, 25, and 30°C. Although all homo- and hemizygous females do lay some eggs, no evidence of embryogenesis or fertilization has ever been detected. The absolute, nonconditional sterility of Ddc^ts1 homo- and hemizygous females stands in stark contrast to the conventional temperature dependent effects of these same genotypes on viability and to the temperature sensitive effects of Ddc^ts1/Ddc^x heterozygous females on both fertility and viability. Reasons for these tissue-specific and genotypic differences are discussed.     

Molecular and genetic analysis of nitrite reductase co-suppression in transgenic tobacco plants

Silencing ofNia host genes and transgenes (encoding nitrate reductase) was previously achieved by introducing into tobacco plants the tobaccoNia2 cDNA cloned downstream of the cauliflower mosaic virus (CaMV) 35S promoter. To check whetherNii host genes and transgenes (encoding nitrite reductase, the second enzyme of the nitrate assimilation pathway) were also susceptible to silencing, a transgene consisting of the tobaccoNii1 gene with two copies of the enhancer of the 35S promoter cloned 1 kb upstream of theNii promoter region was introduced into tobacco plants. Among nine independent transformants analysed, two showed silencing ofNii host genes and transgenes in some descendants after selfing, but never after back-crossing with wild-type plants, suggesting that silencing depends on the number of transgene loci and/or on certain allelic or ectopic combinations of transgene loci. In one transformant carrying a single transgene locus in a homozygous state, silencing was triggered in all progeny plants of each generation, 20 to 50 days after germination. Field trial analysis confirmed that silencing was not triggered when the transgene locus of this latter line was present in a hemizygous state. In addition, it was revealed that silencing can be triggered, albeit at low frequency and later during the development, when this transgene locus is brought into the presence of a non-allelic transgene locus by crossing, suggesting that a homozygous state is not absolutely required.     

The effect of drought stress on the sex ratio variation ofSilene otites

Under dry environmental conditions the sex ratio of many dioecious plants is male-biased, which is usually explained by the higher susceptibility of females to drought stress. We investigated if spatio-temporal variation in the sex ratio ofSilene otites could be explained by the higher sensitivity of female plants to drought stress as compared to males. Long-term field observations, however, did not support this hypothesis. The sex ratio in 34 patches at the study site in Central Germany changed from slightly female biased in 1994 to strongly male-biased in 1997 and 1998. The interannual change in the proportion of plants that were female was positively correlated with the number of days with soil-water deficit in the late summer, suggesting higher mortality in males than in females under drought stress. In two closely studied patches, mortality in males was also higher than in females, although this difference could not be related to drought stress. These field observations were supported by an experiment with potted plants in two climate chambers, in which male mortality was higher during a three-week period without water supply. We conclude that the often reported male bias in patches ofS. otites is not caused by sexual differences in the sensitivity to drought stress. Field data in this study, however, suggest that maleS. otites plants flower earlier than females, which causes a shift in sex ratio to more male bias among flowering plants.     

Pattern formation inDrosophila melanogaster: The effects of mutations on polarity in the developing leg

Summary The effects of the mutations eyeless dominant (ey ^D) and shibire (shi) on bristle pattern in the legs ofDrosophila melanogaster were examined. Both mutations cause gaps in the intersegmental membranes which separate leg segments and often alter the position of these membranes. It was observed that pattern disturbances including reversed bristle polarity and duplication of structures such as sex combs and transverse rows were associated with defects in the intersegmental membranes. The alterations in bristle polarity and most of the duplication of structures could be accounted for by a segmentally reiterated gradient in the legs which controls bristle polarity and which requires the integrity of the intersegmental membrane. A computer simulation of this gradient model was devised which accounted for the observed results. The possible role of cell death as a cause of the gaps in the intersegmental membrane and of some of the pattern disturbances was examined.     

Maternal effects of zygotic mutants affecting early neurogenesis inDrosophila

Summary The size of the neurogenic region ofDrosophila melanogaster is under the control of several genes of zygotic expression. Lack of function from any of those genes produces an increase of the size of the neurogenic region at the expense of the epidermal anlage. However, differences exist in the extent of neuralisation achieved by each of the genetic loci upon mutation. The present results show that in the case ofN andmam phenotype differences are due to different contributions of maternal gene expression. This could be shown by studying the phenotype which appeared in mutant embryos when the oocytes developed from homozygous mutant precursor cells. Clones of mutant cells were induced in the germ line of females heterozygous for the neurogenic mutationin trans over germ line dependent, dominant female sterile mutations. After removing maternal information the phenotype ofN andmam mutants became identical in both cases. Furthermore maternal information fromN ⁺ was found to be necessary for viability of the wildtype.     

Interspecific Relations Between Two Sympatric Species of Hymenoptera, Dinarmus basalis (Rond) and Eupelmus vuilleti (Crw), Ectoparasitoids of the Bruchid Callosobruchus maculatus (F)

Dinarmus basalis (Rond) and Epelmus vuilleti (Crw) are two Hymenopteran species, which are solitary ectoparasitoids of bruchid larvae. In the presence of seeds of Vigna unguiculata (Walp) containing hosts parasitized by E. vuilleti, a high percentage of D. basalis females avoided multiparasitism whatever the age of the eggs or the larvae present on the host. The least avoidance was observed when the hosts were parasitized by E. vuilleti 30 min beforehand. This avoidance behavior is adaptive and is related to the low survival chances of the D. basalis larvae when they are in interspecific competition with E. vuilleti larvae. The analysis of the behavior of D. basalis demonstrated that the avoidance of multiparasitism could be due to the perception of two signals; an external signal deposited on the surface of the seeds during the E. vuilleti oviposition phase and an internal signal due to the presence of the eggs and larvae at the surface of the hosts. E. vuilleti females did not avoid multiparasitism and multiparasitized the hosts bearing D. basalis eggs or larvae. The behavior of E. vuilleti females was not disturbed by the presence of its competitor. Under these conditions of interspecific competition, the survival chances of E. vuilleti larvae were very high whatever the age of its competitor D. basalis. The two species of parasitoids could move in a column containing healthy seeds of V. unguiculata and patches with seeds containing parasitized or unparasitized larvae. The distribution of D. basalis females introduced into these columns depended on the host quality. They avoided the patches containing the hosts parasitized E. vuilleti and were found in the patches with healthy hosts. The behavior of E. vuilleti females was very different; the distribution of the females and the parasitism and multiparasitism rates were not affected by the quality of the hosts present in the patches. The adaptive significance of the behaviors of these two species was analyzed in relation to the survival chances of their offspring.     

Battle of the Xs

Females and males often exhibit conspicuous morphological, physiological and behavioral differences. Similarly, gene expression profiles indicate that a large portion of the genome is sex‐differentially deployed, particularly in the germ line. Because males and females are so fundamentally different, each sex is likely to have a different optimal gene expression profile that is never fully achieved in either sex because of antagonistic selection in females versus males. Males are hemizygous for the X chromosome, which means that recessive male‐favorable de novo mutations on the X chromosome are subject to immediate selection. In females, a recessive female‐favorable mutation on one of two X chromosomes is not available for selection until it becomes frequent enough in the local population to result in homozygous individuals. Given that most mutations are recessive, one would expect that genes or alleles favoring males should accumulate on the X chromosome. Recent microarray work in Drosophila and C. elegans clearly shows the opposite. Why is the X chromosome a highly disfavored location for genes with male‐biased expression in these animals? BioEssays 26:543–548, 2004. Published 2004 Wiley Periodicals, Inc.     

Genetic Control of the Formation and Reorganization of Chromocenter in Drosophila

The chromocenter integrates the entire Drosophilagenome into a unit. The formation and reorganization of chromocenter are genetically determined. Currently, several mutations affecting the structure of chromocenter have been described. In this work, I present evidence on the time of the formation and reorganization of chromocenter in mitotic and meiotic cells of females of the wild type and the ff16mutant line obtained by selection of mosaic clones produced from mitotic recombination of chromosomes in the dividing embryo cells. In females homozygous for this mutation, the second stage of the formation of chromocenter (joining two groups of nonhomologous chromosomes X-4 and 2-3 into a united ring structure =X=2=3=4=) is disturbed. The differences between the mitotic and meiotic reorganization of chromocenter and the role of chromocenter in the control of chromosome segregation are discussed.