Sterilizing effect of the mutant allele sbr10 (l(1)ts403) in compound with null alleles in Drosophila melanogaster females

In females of Df(1)v-L4/+(0/+) genotype, the presence of the wild-type allele of small bristles (sbr) gene in a single dose has no significant effect on their fecundity, whereas a reduced dose of the temperature-sensitive allele sbr10(l(1)ts403) causes a strong sterilizing effect in females Df(1)v-L4/sbr10 (0/sbr10) at permissive temperature. We studied the contribution to this effects of the following factors: resorption of egg chambers, decreased oviposition, offspring death at the embryonic and larval stages, and reduced fecundity in females 0/sbr10. Sterilizing effect of the mutant sbr10 allele proved to be primarily caused by offspring lethality at the embryonic and first-instar larval stages. In 0/+ females, the majority of undeveloped eggs contained embryos that perished at the late developmental stages, whereas in females 0/sbr10, at least 50% of undeveloped egg showed no visible signs of development or the embryo development was arrested at early stages of embryogenesis. The results obtained suggest insufficiency of the temperature-sensitive allele sbr10 in haploid state to ensure the reproductive functions of Drosophila melanogaster females.     

Semidominant Effect of the l(1)ts403 (sbr 10) Mutation on Sex Chromosome Nondsjunction in Meiosis in Drosophila melanogaster Females Exposed to Heat

The sbrgene of Drosophila melanogasterbelongs to the NXF(nuclear export factor) family responsible for the mRNA transport from nucleus to cytoplasm. We have shown that in the heat-exposed (37°C, 1 h) females, the l(1)ts403(sbr ¹⁰) mutation leads, in particular, to the high-frequency nondisjunction and loss of sex chromosomes in meiosis. For this trait, the incomplete dominance of the sbr ¹⁰ mutation is observed. At the same time, the sbr ¹⁰ mutation is recessive for many other traits of the heat-exposed flies: reduced viability, low fertility, impaired synthesis of the heat shock proteins, etc. The females heterozygous for the null allele (Df(1)v ^L4, a deletion eliminating gene srb) do not differ from females homozygous for the wild-type allele in frequency of the heat shock-induced nondisjunction and loss of sex chromosomes in meiosis. Because of this, the sbr ¹⁰ mutation can be assigned to the gain-of-function alleles (those gaining the dominance function). Expression of the mutant sbr ¹⁰ allele against the background of the wild-type allele suggests that in the heat shock-exposed females, the heat-modified product of this ts allele has an active effect on sex chromosome disjunction in meiosis.     

Genetic nature of abnormal larval development in the progeny of l(1)ts403(sbr10) females of Drosophila melanogaster

In Drosophila melanogaster the small bristles (sbr) gene is vital and evolutionary conservative and controls nuclear export of mRNA. Sbr mutant alleles had a broad pleiotropic effect. High frequency of abnormal larva dying (up to 18 %) at the first instar stage in progeny of heat shock (37 degrees C, 1 h) treated mutant females is one of the most interesting l(l)ts403(sbr10) allele effects. Abnormal larvae display characteristic phenotype that involves the Malpighian tubules defect. Using interphase FISH method (fluorescence in situ hybridization), we showed that abnormal larvae had monosomy on chromosomes 2 and 3. DNA content in neuroblast interphase nuclei of abnormal larvae is 2.1 times less than in normal larvae. We suggest that abnormal larvae could be full or mosaic haploids that appeared as a result of maternal genome loss during fertilization or the mitotic division. Larvae with the same abnormalities appear in a progeny of females with different genotypes mating with males carrying compound chromosomes 2 or 3. FISH analysis showed that such larvae had monosomy only on a chromosome that is compound in paternal strain. Thus, monosomy on large autosomes may cause aspecial phenotype of abnormal larvae in D. melanogaster.     

Sterilizing Effect of the Mutant Allele sbr 10 (l(1)ts403) in Compound with Null Allele in Drosophila melanogaster Females

In females of Df(1)v-L4/+(0/+) genotype, the presence of the wild-type allele ofsmall bristles (sbr) gene in a single dose has no significant effect on their fecundity, whereas a reduced dose of the temperature-sensitive allele sbr ¹⁰ (l(1)ts403) causes a strong sterilizing effect in females Df(1)v-L4/sbr ¹⁰ (0/sbr ¹⁰) at permissive temperature. We studied the contribution to this effects of the following factors: resorption of egg chambers, decreased oviposition, offspring death at the embryonic and larval stages, and reduced fecundity in females 0/sbr ¹⁰. Sterilizing effect of the mutant sbr ¹⁰ allele proved to be primarily caused by offspring lethality at the embryonic and first-instar larval stages. In 0/+ females, the majority of undeveloped eggs contained embryos that perished at the late developmental stages, whereas in females 0/sbr ¹⁰, at least 50% of undeveloped egg showed no visible signs of development or the embryo development was arrested at early stages of embryogenesis. The results obtained suggest insufficiency of the temperature-sensitive allele sbr ¹⁰ in haploid state to ensure the reproductive functions of Drosophila melanogaster females.     

The effect of high temperature on the frequency of nondisjunction and loss of sex chromosomes in females of Drosophila melanogaster strain I(1)ts403 with a defect in the heat shock protein system

High temperature (37 degrees C) induces sex chromosome non-disjunction and loss in Drosophila melanogaster females l(1)ts403 with the defect in heat-shock protein system. The same temperature has no effect on the females from the T line and other earlier studied lines.     

Maternal and paternal effects on the specific mutation l(1)ts403 of thermosensitivity of early Drosophila melanogaster embryos]

High thermosensitivity of early embryos controlled by mutation l(1)ts403 with disturbed heat-shock response was studied. Thermosensitivity was examined in early (0-1 h) and late (3.5-4.5 h) embryos obtained by reciprocal crosses and backcrosses. It was shown that mutation l(1)ts403 lacks maternal effect. In progeny of reciprocal crosses, early embryonic thermosensitivity was intermediate with regard to that of progeny obtained by interlinear crosses. In early embryos of Drosophila, zygotic genes are not expressed and synthesis heat-shock protein synthesis is not induced. Based on this, it was proposed that the product of gene l(1)ts403, which affects early embryonic thermosensitivity, is transmitted both paternally and maternally and shows dosage effect.     

Heat shock during the development of brain structures of Drosophila: the memory development in the l(1)ts403 mutant of Drosophila melanogaster

The structures and functions of many genes are homologous in Drosophila and humans. Therefore, studying pathological processes in Drosophila, in particular neurogenerative processes accompanied by progressive memory loss, helps to understand the ethiology of corresponding human disorders and to develop therapeutic strategies. It is believed that the development of neurogenerative diseases might result from alterations in the functioning of the heat shock/chaperone machinery. In view of this, we used Drosophila mutant l(1)ts403 with defective synthesis of heat shock proteins for studying learning and memory in a test of conditioned courtship suppression following a heat shock given at different developmental stages. High learning indices were registered immediately and 30 min after training both in the intact controls and in flies subjected to different developmental heat shocks. This indicated normal learning and memory acquisition in the mutant. At the same time, memory retention (3 h after training) suffered to different extent depending on the developmental stage. The remote effects of heat shock given during the formation of the mushroom bodies indicated the important role of this brain structure in the memory formation. The observed memory defects may result from alterations both in mRNA transport and in the functions of molecular chaperones in the l(1)ts403 mutant.     

Heat Shock during the Development of Central Structures of the Drosophila Brain: Memory Formation in the l(1)ts403 Mutant of Drosophila melanogaster

The structures and functions of many genes are homologous in Drosophilaand humans. Therefore, studying pathological processes in Drosophila, in particular neurogenerative processes accompanied by progressive memory loss, helps to understand the ethiology of corresponding human disorders and to develop therapeutic strategies. It is believed that the development of neurogenerative diseases might result from alterations in the functioning of the heat shock/chaperone machinery. In view of this, we used Drosophila mutant l(1)ts403 with defective synthesis of heat shock proteins for studying learning and memory in a test of conditioned courtship suppression following a heat shock given at different developmental stages. High learning indices were registered immediately and 30 min after training both in the intact controls and in flies subjected to different developmental heat shocks. This indicated normal learning and memory acquisition in the mutant. At the same time, memory retention (3 h after training) suffered to different extent depending on the developmental stage. The remote effects of heat shock given during the formation of the mushroom bodies indicated the important role of this brain structure in the memory formation. The observed memory defects may result from alterations both in mRNA transport and in the functions of molecular chaperones in the l(1)ts403 mutant.     

Fertility of Drosophila melanogaster females affected by mutation l(2)M167DTS

We studied the fertility of D. melanogaster females heterozygous for the dominant temperature sensitive mutation l(2)M167DTS, which exerts a recessive lethal effect at 25 degrees C, under the conditions of stable temperature regimes 25, 28, and 29 degrees C and changing regimes 25-->29 degrees C and 29-->25 degrees C. It was shown that inhibition of total activity of oogenesis due to a decreased number of functioning ovarioles is one of the mechanisms underlying the decreased fertility of l(2)M167DTS /+ females. Analysis of individual fertility of each female confirmed also the role of sterility as a component of fertility of the females. Sterilization was realized due both to full depletion of functioning ovarioles and disturbed mechanism of laying the mature eggs onto a substrate as a result of violation of the feedback blocking normal ovulation, which led to the breakdown of ovarioles and filling of the abdominal cavity with mature oocytes. A significant polymorphism of heterozygous females by their fertility was observed. The intensity of sterilization and mortality of l(2)M167DTS/+ females sharply increased at an elevated temperature (29 degrees C), especially at the pupal stage.     

Fertility of Drosophila melanogaster females affected by mutation l(2)M167 DTS

We studied the fertility of D. melanogaster females heterozygous for the dominant temperature sensitive mutation l(2)M167 ^DTS , which exerts a recessive lethal effect at 25°C, under the conditions of stable temperature regimes 25, 28, and 29°C and changing regimes 25 → 29°C and 29 → 25°C. It was shown that inhibition of total activity of oogenesis due to a decreased number of functioning ovarioles is one of the mechanisms underlying the decreased fertility of l(2)M167 ^DTS /+ females. Analysis of individual fertility of each female confirmed also the role of sterility as a component of fertility of the females. Sterilization was realized due both to full depletion of functioning ovarioles and disturbed mechanism of laying the mature eggs onto a substrate as a result of violation of the feedback blocking normal ovulation, which led to the breakdown of ovarioles and filling of the abdominal cavity with mature oocytes. A significant polymorphism of heterozygous females by their fertility was observed. The intensity of sterilization and mortality of l(2)M167 ^DTS /+ females sharply increased at an elevated temperature (29°C), especially at the pupal stage.     

Effect of the l(1)su(f)ts67g mutation ofDrosophila melanogaster on glue protein synthesis

Summary The l(1)su(f)^ts67g mutation has been shown to suppress the developmentally regulated expression of glue protein genes at 30°C. Transferring mutant larvae to the restrictive temperature before the end of the second larval instar results in the absence or extreme reduction of glue protein synthesis while general protein synthesis is unaffected. At the same time, the three glue protein correlated chromosomal regions 3C, 25B, and 68C continue to show prominent puffs. The results suggest that the mutation may be affecting the processing or translatability of specific mRNAs rather than the translational machinery itself.     

Frequency of non-disjunction and loss of sex chromosomes in oogenesis in the Drosophila melanogaster mutant I(1) ts 403 with a defect in the heat-shock protein system in anoxia and at high temperature]

A unique property of Drosophila melanogaster l(1)ts403 strain with the defect in heat shock protein system (HSP) is high frequency of losses and non-disjunction of sex chromosomes induced by heat shock (HS) (37 degrees C, 1 h). This effect was shown in only 6-14-th stages of oocytes. Anoxia was not effective in induction of these mutations. Successive action of anoxia and HS decreased loss frequency and non-disjunction in comparison with the only action of HS. These findings agree with the data in literature indicating that HSP synthesis was increased in the l(1)ts403 mutant when first anoxia and then HS were administered, in contrast to the action of HS only. The role of HSP in the recovery of HS-induced disruptions (chromosomal proteins and meiotic division apparatus) which can lead to chromosome non-disjunction and losses is discussed.     

The nature and time of occurrence of radiation-induced nondisjunction of the acrocentric X and fourth chromosomes in Drosophila melanogaster females

Radiation-induced nondisjunction in Drosophila melanogaster females usually-possibly invariably-involves the participation of chromosomes other than the pair in which the numerical aberration is noted, with one of the two acrocentric pairs frequently being involved in the assortative error of the other. Nearly one-half of all diplo-X eggs produced following the irradiation of immature oocytes of females having free X's are found to be nullo-4, and, in agreement with earlier reports^9,11, about one-fourth of all nullo-X eggs are diplo-4. The incidence of structural alterations is markedly higher in chromosomes involved in nondisjunctions than in those recovered from normal segregations, with the structural changes being those expected from interchange between X and fourth chromosomes where only one of the two interchange products (a “half-translocation”) is recovered. X chromosomes may acquire an arm of chromosome 4, and fourth chromosomes may lose the marker from the left arm, as if the short, heterochromatic right arm of the X had been substituted. Homozygosis of markers near the centromere of the X chromosome shows that nearly all failures of segregation must occur at division I. While the data do not require that there be some division II nondisjunction, neither do they categorically deny the possiblility of its occurring at a very low level. The findings are as expected on the model of heterologous conjunction via chromatid interchange as the major and perhaps exclusive cause of radiation-induced nondisjunction.     

The ecdysoneless (ecd1ts) mutation disrupts ecdysteroid synthesis autonomously in the ring gland of Drosophila melanogaster

Ring glands dissected from homozygous l(3)ecd1ts wandering larvae and upshifted in vitro to the restrictive temperature, 29 degrees C, synthesize abnormally low quantities of ecdysteroid. Nevertheless, ecd1 ring glands retain the ability to respond at 29 degrees C to an extract prepared from wild-type larval neural tissues that presumably contain prothoracicotropic hormone (PTTH), although both basal and stimulated levels of synthesis are lower than those in wild-type ring glands. Extracts prepared from ecd1 neural tissue exhibit an unusually high level of PTTH activity. Mutant ring glands downshifted in vitro to the permissive temperature after removal from larvae maintained at 29 degrees C regain the ability to produce normal basal and stimulated ecdysteroid levels. Collectively, these experiments demonstrate that the ecd1 mutation disrupts the physiology of the ring gland at 29 degrees C autonomously and may also interfere with PTTH release.     

Variations in the radiosensitivity of oocyte chromosomes during meiosis in Drosophila melanogaster

The synaptic stages of meiosis in Drosophila melanogaster females are very resistant to the induction of dominant lethal mutations by ionizing radiation. It is assumed that dominant lethals result from interstitial chromatid deletions, and that almost all potential chromatid breaks are repaired in synaptic cells. The type of dose response curve shown by oocytes at later developmental stages is a function of the degree of chromatid coiling and the presence or absence of an investing nuclear envelope.     

Region-specific defects in l(1)giant embryos of Drosophila melanogaster

Lack of zygotic expression of the l(1)giant locus (l(1)gt;3A1), produces embryos with defects in abdominal A5, 6, and 7 and within the head. Scanning electron microscopy at the time of segment formation reveals two regions of defects in the segmentation pattern: anteriorly the labial lobe and thoracic segments T1 and T2 are fused; posteriorly, abdominal segments A5-7 are disrupted. The mature embryo shows incomplete head involution and defects within A5-7; fusion of T1 and T2 is no longer observed. Localized cell death within neural and mesodermal tissues is observed at 7 hr of development; later ventral ganglia, A5-7, are missing. Double-mutant analyses of l(1)gt with maternal effect lethal mutations and mutations that generate homeotic, segment number, gap, or segment polarity phenotypes indicate that normal activity of l(1)gt is required for differentiation of two embryonic domains: one corresponding to labial, T1 and T2 segments, and the second corresponding to abdominal segments 5, 6, and 7.