Phenogenetics of triploid intersexes in Drosophila melanogaster

Triploid intersexes homozygous for a mutant (msl-2) known to impede the hyperactivation of the X chromosome in diploid males differentiate into adults, sexually indistinguishable from their heterozygous sibs. A shift toward female sexual differentiation mediated by manipulating the rearing temperature is accompanied by an apparent increase in the level of an X-linked gene product. This unexpected result is rationalized in terms of differential lethality of individuals at the two extremities of the distribution of X-activity levels in intersexes raised at a particular temperature. No evidence of a mosaicism comparable to the sexual mosaicism exhibited could be found with respect to an X-linked gene product in triploid intersexes.     

黑腹果蝇的性别控制

性别的形成包括两个过程,即性别决定和性别分化。果蝇的性别控制研究包括性别决定、性别分化、性别鉴定、性别诱导和性别控制5个方面。性别决定是在两种不同发育途径之间的选择,它提供了一个研究基因调控的模式系统。果蝇的性别决定问题已经研究得相当详细［1］。性别分化是使胚胎向着雌性或雄性发育的过程,决定了性别表型。果蝇的性别分化也取得了不少研究成果。近年来,许多重要的性别调控基因已被克隆和鉴定。随着果蝇基因组全序列测定的完成,果蝇的性别控制研究将会更为深入而完善。本文对与黑腹果蝇性别决定和性别分化相关的一些问题进行综述。     

Development of the genitalia in Drosophila melanogaster

The imaginal discs of Drosophila melanogaster are an excellent material with which to analyze how signaling pathways and Hox genes control growth and pattern formation. The study of one of these discs, the genital disc, offers, in addition, the possibility of integrating the sex determination pathway into this analysis. This disc, whose growth and shape are sexually dimorphic, gives rise to the genitalia and analia, the more posterior structures of the fruit fly. Male genitalia, which develop from the ninth abdominal segment, and female genitalia, which develop mostly from the eighth one, display a characteristic array of structures. We will review here some recent findings about the development of these organs. As in other discs, different signaling pathways establish the positional information in the genital primordia. The Hox and sex determination genes modify these signaling routes at different levels to specify the particular growth and differentiation of male and female genitalia.     

Adaptation of Drosophila to temperature: Heat-shock proteins and survival in Drosophila melanogaster

Two stocks of Drosophila melanogaster, one sensitive (6.5% survival) and one resistant (76.24%) to heat shock (40°C/25 min) were derived through indirect selection [1]. Genetic analysis of heat-sensitive and heat-resistant lines we had selected revealed that the survival rate is chiefly determined by cytoplasmic inheritance but also depends to some extent on the nucleus [1]. The ability of the fly to survive thermal stress was found to have an excellent correlation with the kinetics of protein synthesis in ovaries or glands subjected to heat treatment. The incorporation rate of ³⁵S-methionine into proteins was found to be higher for strains exhibiting higher survival (R₁, R₁S₁) than for strains with a lesser ability (S₁, S₁ R₁) to survive heat shock. Moreover, the intensity of labeling of the proteins synthesized and especially of the hsps (heat-shock proteins) after the heat shock is higher in the R₁ and R₁S₁ stocks than in the S₁ and S₁R₁ stocks. This convergence between survival and the cellular level of hsps (both manipulated by selection) bears on the physiological significance of these proteins which seems to participate in the control of the survival as an additive component.     

The relationship between gene dosage,gene expression,and sex in Drosophila

In Drosophila, the ratio of the number of X chromosomes to sets of other chromosomes initiates a series of events which result in sexual differentiation. In addition, this ratio establishes dosage compensation, a mechanism which equalizes the products of X-linked genes in males and females. The present review discusses possible genetic entities responsible for the interpretation of chromosomal sex and subsequent sex-mediated regulation during development.     

In vivo radiolabeling and turnover of sn-glycerol-3-phosphate dehydrogenase in Drosophila melanogaster: Gene dosage effects

In vivo radiolabeling of Drosophila melanogaster sn-glycerol-3-phosphate dehydrogenase (E.C. 1.1.1.8; GPDH) has been accomplished by microinjection of ³H-leucine into anesthetized flies. Comigration of immunoprecipitated radiolabeled GPDH with purified ¹⁴C-labeled GPDH-1 in SDS polyacrylamide disc gels has established the monospecificity of our immunoprecipitation technique. Short-term uptake experiments have demonstrated that maximum radiolabel incorporation of total TCA precipitable protein and immunoprecipitable GPDH-1 occurs within 4 hours postinjection, with GPDH-1 accounting for approximately 1% of the total radiolabeled TCA precipitable protein. In order to develop the parameters for turnover studies of GPDH in Drosophila, a comparative analysis of the rates of synthesis and degradation of GPDH-1 in flies bearing two and three doses of the structural gene have been conducted by the construction of adult flies aneuploid and euploid for the cytogenetic region 25F-26B on the left arm of chromosome II. Short-term uptake studies have demonstrated that the rate of GPDH-1 synthesis in the three-dose flies is approximately 1.58 times that found in the two-dose euploid flies. This value is in close agreement with data obtained for steady-state levels of CRM by rocket immunoelectrophoresis. In contrast, longterm pulse-chase experiments have revealed that rates of GPDH-1 degradation in these aneumploid and euploid flies appear to be identical. These data suggest that the rate of GPDH-1 synthesis in Drosophila is primarily regulated by a tightly linked cis-acting element which appears to act autonomously with respect to gene copy number as well as steady-state GPDH protein levels.     

Sex-specific paternal age effects on offspring quality in Drosophila melanogaster

Advanced paternal age has been repeatedly shown to modulate offspring quality via male- and/or female-driven processes, and there are theoretical reasons to expect that some of these effects can be sex-specific. For example, sex allocation theory predicts that, when mated with low-condition males, mothers should invest more in their daughters compared to their sons. This is because male fitness is generally more condition-dependent and more variable than female fitness, which makes it less risky to invest in female offspring. Here, we explore whether paternal age can affect the quality and quantity of offspring in a sex-specific way using Drosophila melanogaster as a model organism. In order to understand the contribution of male-driven processes on paternal age effects, we also measured the seminal vesicle size of young and older males and explored its relationship with reproductive success and offspring quality. Older males had lower competitive reproductive success, as expected, but there was no difference between the offspring sex ratio of young and older males. However, we found that paternal age caused an increase in offspring quality (i.e., offspring weight), and that this increase was more marked in daughters than sons. We discuss different male- and female-driven processes that may explain such sex-specific paternal age effects.     

The genetics of position-effect variegation modifying loci in Drosophila melanogaster

Summary The dose dependent effects of position-effect variegation (PEV) modifying genes were studied in chromosome arms2L, 2R and3R. Four groups of PEV modifying genes can be distinguished: haplo-abnormal suppressor and enhancer loci with or without a triplo-effect. using duplications four triplo-abnormal suppressor and four triplo-abnormal enhancer functions were localized. In two cases we proved that these functions correspond to a converse haplo-abnormal one. Altogether 43 modifier loci were identified. Most of these loci proved not to display significant triplo-effects (35). The group of haplo-abnormal loci with a triplo-effect may represent genes which play an important role in heterochromatin packaging.     

Genetic differentiation between American and European Drosophila melanogaster populations could be attributed to admixture of African alleles

A total of 48 polymorphic microsatellite loci were characterized in 13 Drosophila melanogaster populations originating from Europe, America, and Africa. Consistent with previous results, the African D. melanogaster populations were the most differentiated populations and harbored most variation. Despite an overall similarity, American and European populations were significantly differentiated. Interestingly, genetic distances based on the proportion of shared alleles as well as FST values suggested that the American D. melanogaster populations are more closely related to the African populations than European ones are. We also detected a higher proportion of putative African alleles in the American populations, indicating recent admixture of African alleles on the American continent.     

An analysis of genetic differentiation among assortatively mating Drosophila melanogaster in Zimbabwe

African Drosophila melanogaster populations, and those from Zimbabwe in particular, have attracted much interest recently. African flies differ genetically from 'cosmopolitan' populations and were found to exhibit discriminative mating behaviour against individuals from 'cosmopolitan' populations. It has therefore been proposed that Zimbabwean and some other African populations are in an 'incipient stage of speciation'. However, whether the mating behaviour is an effective barrier against gene flow from other populations, and whether intra-population genetic differentiation has already evolved in sympatry is not known. Here, we took a population-based approach to test whether the well-characterized mating type differences have resulted in a genome-wide differentiation at the population level. Using 122 polymorphic microsatellite loci mapping to the third chromosome, we demonstrate a significant genetic differentiation between Zimbabwean flies differing in their mating behaviour. We also provide evidence to suggest that this difference is unlikely to be attributable to population structure within Zimbabwe. However, the analysis of individual microsatellite loci did not indicate more loci differentiating these two groups than expected by chance. Our data suggest that the 'Z'-'M' mating behaviour is strong enough to result in a small but significant genetic differentiation. Thus, future studies based on a larger population sample of flies characterized for their mating behaviour and using more markers are expected to provide more information on the genetic basis of the mating traits in the Zimbabwe flies.     

Mutations in the gene stand still disrupt germ cell differentiation in Drosophila ovaries

During oogenesis in Drosophila, germ cells appear in sequential clusters of 16 interconnected cells. The events surrounding the differentiation of these cells are not fully understood. Here we present genetic and morphological analysis of mutations in the gene stand still (stil). Through complementation analyses we have refined the location of this gene to cyological region 49B-C. Our analyses of ovaries from ethylmethane sulfonate (EMS) - induced mutant alleles of this gene suggest that mutations in the stil gene produce a wide range of phenotypic abnormalities, from the absence of germ cells in the most severe alleles, to egg chambers with cytoskeletal defects in the less severe alleles. Our results suggest a role for this gene in specifying or maintaining a cytoskeletal component, with consequences during oogenesis and possibly during germ line sex determination. © 1996 Wiley-Liss, Inc.     

Sex determination in Drosophila melanogaster: X-linked genes involved in the initial step of Sex-lethal activation

Sex determination is the commitment of an embryo to either the female or the male developmental pathway. The ratio of X chromosomes to sets of autosomes is the primary genetic signal that determines sex in Drosophila, by triggering the functional state of the gene Sex-lethal: in females (2X;2A) Sxl will be ON, whereas in males (X;2A) Sxl will be OFF. Genetic and molecuar studies have defined a set of genes involved in the formation of the X:A signal, as well as other genes, with either maternal or zygotic effects, which are also involved in regulating the initial step of Sex-lethal activation. We review these data and present new data on two more regions of the X chromosome that define other genes needed for Sxl activation. In addition, we report on the interaction between some of the genes regulating Sxl activation. © 1994 Wiley-Liss, Inc.     

Puzzling chromosome behavior in triploid females of Drosophila melanogaster

Based on a particular formation of the chromocenter and trivalents in triploid Drosophila females, as well as on asynapsis in pericentromeric regions (which is a result of trivalent competition), an explanation for the increased frequency of crossing over and nonrandom segregation of the X chromosomes and autosomes in the first meiotic division is suggested. It is proposed that a delay in pairing of the pericentromeric heterochromatic chromosome regions combined into a single chromocenter leads to the following: (1) formation of the heteroduplex structures (X structures) takes more time and, consequently, their number and the frequency of crossing over in the paired chromosome regions increases; (2) in nonhomologous chromosomes, the chromocentral connections, which normally degrade in prometaphase, are retained to fulfill a function of coorientation during the first meiotic division.     

Genetic interaction between homoeotic Sex combs reduced and Regulator of bithorax (or trithorax) genes of Drosophila melanogaster

Summary Regulator of bithorax (Rg-bx)^–, or trithorax (trx)^– lethal larvae occasionally show a homoeotic transformation of the dorsal prothorax to mesothoracic structures. This transformation suggests a reduced activity of the Sex combs reduced (Scr) gene on the basis of gene dosage studies, as well as enhanced expression of the phenotypes of the weak Scr ^– alleles in Rg-bx ^– larvae. Morphological observations of adult flies doubly heterozygous for Rg-bx and Scr mutations also suggest the enhancement of an aspect of Scr adult phenotypes. I conclude that the Rg-bx ⁺ gene function is required for the optimal expression of the Scr gene in larval and imaginai cells.     

Feminization of complex traits in Drosophila melanogaster via female-limited X chromosome evolution*

A handful of studies have investigated sexually antagonistic constraints on achieving sex-specific fitness optima, although exclusively through male-genome-limited evolution experiments. In this article, we established a female-limited X chromosome evolution experiment, where we used an X chromosome balancer to enforce the inheritance of the X through the matriline, thus removing exposure to male selective constraints. This approach eliminates the effects of sexually antagonistic selection on the X chromosome, permitting evolution toward a single sex-specific optimum. After multiple generations of selection, we found strong evidence that body size and development time had moved toward a female-specific optimum, whereas reproductive fitness and locomotion activity remained unchanged. The changes in body size and development time are consistent with previous results, and suggest that the X chromosome is enriched for sexually antagonistic genetic variation controlling these particular traits. The lack of change in reproductive fitness and locomotion activity could be due to a number of mutually nonexclusive explanations, including a lack of sexually antagonistic variance on the X chromosome for those traits or confounding effects of the use of the balancer chromosome. This study is the first to employ female-genome-limited selection and adds to the understanding of the complexity of sexually antagonistic genetic variation.     

Simulation of gene pyramiding in Drosophila melanogaster

Gene pyramiding has been successfully practiced in plant breeding for developing new breeds or lines in which favorable genes from several different lines were integrated.But it has not been used in animal breeding,and some theoretical investigation and simulation analysis with respect to its strategies,feasibility and efficiency are needed before it can be implemented in animals.In this study,we used four different pure fines of Drosophila melanogaster,each of which is homozygous at a specific mutant gene with a visible effect on phenotype,to simulate the gene pyramiding process and analyze the duration and population size required in different pyramiding strategies.We finally got the ideal individuals,which are homozygous at the four target genes simultaneously.This study demonstrates that gene pyramiding is feasible in animal breeding and the interaction between genes may affect the final results.