黑果蝇dlts品系的温度敏感时期及dlts基因多效影响的自主性研究

本文采用D.T.Suzuki的方法,研究了黑果蝇Drosophila virilis Sturt dl^ts品系的温度敏感时期和致死时期的相互关系。选择了31℃为限制温度,25℃为许可温度。对于成虫盘缺损的研究用了12个小时为一个脉冲或24个小时为一个脉冲的热处理,用扫描电镜技术辅助对成虫形态缺损的研究。对于成虫盘缺失和重复的关系主要在48小时为一个脉冲的热处理盘中进行,对dlts基因的表达采用了遗传嵌合性的研究,其结果如下：1两个不连续的温度敏感时态对致死的影响是在第1龄幼虫、第2龄幼虫、第3龄幼虫和进入蛹期后的10个小时。温度敏感时态和致死时态并不一致,而是先于致死时态几个小时。2温度敏感时态对成虫形态的影响是：触角的重复和复眼的缺失发生在第2龄和第3龄幼虫期。足关节融合及跗节和腿节的缩短发生在第3龄幼虫期,翅脉硬化主要发生在第3龄幼虫期即将结束进入前蛹期的这段时间。第3龄幼虫期是成虫盘发生缺陷比较集中的时期,可以明显见到足、复眼、翅和刚毛的缺陷,同源异型突变体也在这个时期发生。同源突变体的变化主要是足、触角片段及刚毛和触角片段的相互转移。3每一个成虫盘缺陷部有自己明显的特征,根据它们成虫盘的形态缺陷和热处理的时间性,所有的成虫盘缺陷变化都可以分为这样三类：缺失,重复,缺失和重复并存。4遗传镶嵌测试表明：dl^ts基因是自主表达的,且具有一定的时间、环境和组织的特殊性。     

黑果蝇dlts品系的温度敏感时期及dlts基因多效影响的自主性研究

本文采用D.T.Suzuki的方法,研究了黑果蝇Drosophila virilis Sturt dlts品系的温度敏感时期和致死时期的相互关系.选择了31℃为限制温度,25℃为许可温度.对于成虫盘缺损的研究用了12个小时为一个脉冲或24个小时为一个脉冲的热处理,用扫描电镜技术辅助对成虫形态缺损的研究.对于成虫盘缺失和重复的关系主要在48小时为一个脉冲的热处理盘中进行,对dlts基因的表达采用了遗传嵌合性的研究,其结果如下:1. 两个不连续的温度敏感时态对致死的影响是在第1龄幼虫、第2龄幼虫、第3龄幼虫和进入蛹期后的10个小时.温度敏感时态和致死时态并不一致,而是先于致死时态几个小时.2. 温度敏感时态对成虫形态的影响是:触角的重复和复眼的缺失发生在第2龄和第3龄幼虫期.足关节融合及跗节和腿节的缩短发生在第3龄幼虫期,翅脉硬化主要发生在第3龄幼虫期即将结束进入前蛹期的这段时间.第3龄幼虫期是成虫盘发生缺陷比较集中的时期,可以明显见到足、复眼、翅和刚毛的缺陷,同源异型突变体也在这个时期发生.同源突变体的变化主要是足、触角片段及刚毛和触角片段的相互转移.3. 每一个成虫盘缺陷部有自己明显的特征,根据它们成虫盘的形态缺陷和热处理的时间性,所有的成虫盘缺陷变化都可以分为这样三类:缺失,重复,缺失和重复并存.4. 遗传镶嵌测试表明:dlts基因是自主表达的,且具有一定的时间、环境和组织的特殊性.     

Recovery and Characterization of Temperature-Sensitive Mutations Affecting Adult Viability in DROSOPHILA MELANOGASTER

Temperature-sensitive (ts) autonomous cell-lethal mutations have been used extensively to study important developmental phenomena, such as pattern formation, in Drosophila. Their utility would be enhanced considerably if it were possible to establish which cell type is primarily affected by each lesion. To facilitate such an approach we have isolated and characterized 21 EMS- induced X-linked adult-lethal (adl) mutants, 16 of which are ts. Most of these lesions also elicit ts lethal effects during preimaginal development. They represent 19 different loci distributed randomly along the X chromosome. The general properties of these mutations are described. In addition, results of an in-depth analysis (focus mapping and, in some cases, temperature shift and heat-pulse studies) of four strains, adl-1^ts1, sesE, adl-2^{ts 1} and rex are reported. Two major temperature-sensitive periods (TSPs) of adl-1 lethality were resolved: one during the second half of embryogenesis and the other coinciding with pupariation. Mosaic analysis revealed separate mesodermal foci for leg paralysis. Developmental analysis of adl-1 embryos suggest that the adl-1 product may be required for maintenance of muscle tissue. Two discrete TSPs of sesE lethality exist: one during the second instar and the other extending from late third instar to early pupation. Mosaic analysis of sesE lethality resolved a pair of neural foci, each of which appears to incorporate three separate foci for leg paralysis. Mosaic analysis of adl-2^{ts 1} revealed the existence of paired lethal foci that appear to map to the vicinity of the subesophageal ganglion. Analysis of rex mosaics resolved separate mesodermal foci for leg paralysis.     

Temperature-sensitive mutations in Drosophila melanogaster. 8. Temperature-sensitive periods of the lethal and morphological phenotypes of selected combinations of notch-locus mutations

Temperature-shift experiments were performed on five Notch-locus genotypes with temperature-sensitive phenotypes. The results show that temperature-sensitive periods (TSPs) for lethality may occur at any developmental stage: (1) $\text{N}{}^{\mathrm{g11}}\text{N}{}^{\mathrm{g11}}$;Dp^51b7 having a short embryonic TSP for lethality, (2) $\text{Ax}{}^{16172}\text{N}{}^{\mathrm{?40}}$ having a second-instar TSP for lethality, and (3) $\text{N}{}^{\mathrm{?103}}\text{fa}{}^{\mathrm{no}}$ with a long, possibly polyphasic, TSP, beginning in the embryonic stage and ending in the pupal stage. On the other hand, TSPs for adult morphological phenotypes appear to be restricted to the third larval instar: (1) $\text{Ax}{}^{16172}\text{N}{}^{\mathrm{?40}}$ having third-instar TSPs for wing vein gapping and ocellar bristle loss, and (2) $\text{N}{}^{\mathrm{?103}}\text{spl}$ having third-instar TSPs for eye facet disarray, wing notching, bristle number variation, and fusion of tarsal segments. The significance of these results is discussed in terms of the role of the Notch locus in development.     

Studies of l(3)c43hs1 a polyphasic, temperature-sensitive mutant of Drosophila melanogaster with a variety of imaginal disc defects.

The heat-sensitive, lethal mutation l(3)c43^hs1 (3–49.0) produces wide variety of defects in the imaginal discs of Drosophila melanogaster. At permissive temperatures (20°C or lower), homozygotes are viable, but sterile. At 22°C, lethality occurs during the late pupal stage, and at 25°C or higher, lethality occurs during the third larval instar. The imaginal-disc abnormalities observed after exposure to restrictive temperatures include: deficiencies of head structures, duplications and deficiencies of the antenna, a homeotic transformation of the arista to tarsus, duplications and deficiencies of wing and haltere structures, differentiation of amorphous cuticular material in the wing blade, an increase in the number of sex-comb teeth, and disruption of the normal segmentation of the tarsus. Exposure to 27°C for 24 hr at different times in the life cycle revealed that each of these defects has a characteristic temperature-sensitive period (TSP) during the larval stages. Injection of wing discs before and after their TSP showed that the mutation is expressed autonomously. These results are discussed in relation to the role that the l(3)c43⁺ gene plays in the development of imaginal discs.     

Developmental analysis of two mutations affecting chemotactic behavior in Drosophila melanogaster.

InDrosophila melanogaster, gusA^Q1, a cold-sensitive mutation, affects the behavior of larvae and adults tested with quinine sulfate. The temperature-sensitive period ofgusA^Q1 occurs during embryogenesis. Another cold-sensitive mutation,gusE^N13, alters the response of adults to quinine sulfate without affecting larval behavior. The temperature-sensitive period of this mutation is during the third larval instar.     

Temperature-Sensitive Mutations of the Notch Locus in DROSOPHILA MELANOGASTER

Temperature-conditional mutations of the Notch locus were characterized in an attempt to understand the organization of a "complex locus" and the control of its function in development. Among 21 newly induced Notch alleles, about one-half are temperature-conditional for some effects, and three are temperature-sensitive for viability. One temperature-sensitive lethal, l(1)N^ts1, is functionally non-complementing for all known effects of Notch locus mutations and maps at a single site within the locus. Among the existing alleles involved in complex patterns of interallelic complementation, Ax^59d5 is found to be temperature-sensitive, while fa ^g, spl, and l(1)N are temperature-independent. Whereas temperature-sensitive alleles map predominantly to the right-most fifth of the locus, fa^g, spl, and l(1)N are known to map to the left of this region. Temperature-shift experiments demonstrate that fa^g, spl, and l(1)N cause defects at specific, non-overlapping times in development.—We conclude (1) that the Notch locus is a single cistron (responsible for a single functional molecule, presumably a polypeptide); (2) that the right-most fifth of the locus is, at least in part, the region involved in coding for the Notch product; (3) that the complexity of interallelic complementation is a developmental effect of mutations that cause defects at selected times and spaces, and that complementation occurs because the mutant defects are temporally and spatially non-overlapping; and (4) that mutants express selected defects due to critical temporal and spatial differences in the chemical conditions controlling the synthesis or function of the Notch product. The complexity of the locus appears to reside in controlling the expression (synthesis or function) of the Notch product in development.     

Behavioral mutants of Drosophila melanogaster. IV. Analysis of developmentally temperature-sensitive mutations affecting flight

Mutations in 13 genes with temperature-sensitive (ts), flightless phenotypes have been examined. All hop and fly well when raised at the permissive temperature, but fly poorly, or not at all, when raised at the restrictive temperature. The mutations were divided into three groups on the basis of their temperature-sensitive periods (TSPs) for flightlessness. The TSPs for mutations at five loci, fli-C¹, D¹, E¹, I¹, and shak A¹, in the first group are confined to 24 to 48 hr interval during early pupal development. Mutations in the second group, including eag¹⁰¹, fli B¹, and fu^ts1 have continuous TSPs 3 to 4 days in length, extending from late larval through the early pupal stages. The flight TSPs for mutations in the third class, including fli J¹, fli K², flrd H³, and flrd N¹, are almost continuous, and span most of the larval and pupal periods. Many of the mutations have pleiotropic phenotypes, including semilethality and lethality, and wing posture and cuticle abnormalities, with discernible TSPs. One of the more intriguing pleiotropic phenotypes is the ts optomotor response exhibited by fli J², the TSP for which extends from late larval through late pupal stages.     

Genetic and Developmental Analysis of a Temperature-Sensitive Minute Mutation of DROSOPHILA MELANOGASTER

A temperature-sensitive (ts) third chromosome Minute (M) mutation, designated Q-III, has been recovered and characterized. Q-III heterozygotes raised at 29° exhibit all of the dominant traits of M mutants including small bristles, rough eyes, prolonged development, reduced viability and interactions with several unrelated mutations. Q-III homozygotes raised at 29° are lethal; death occurs primarily during the first larval instar. When raised at 22°, Q-III heterozygotes are phenotypically normal and Q-III homozygotes display moderate M traits. In addition, Q-III elicits ts sterility and maternal-effect lethality. As it true of M lesions, the dominant traits of Q-III are not expressed in triploid females raised at 29°. Complementation tests suggest that Q-III is a ts allele of M(3)LS4, which is located in 3L near the centromere.—Reciprocal temperature-shift experiments revealed that the temperature-sensitive period (TSP) of Q-III lethality is polyphasic, extending from the first instar to the latter half of pupation. Heat-pulse experiments further resolved this into two post-embryonic TSPs: one occurring during the latter half of the second larval instar, and the other extending from the larval/pupal boundary to the second half of pupation. In addition, heat pulses elicited a large number of striking adult phenotypes in Q-III individuals. These included pattern alterations such as deficiencies and duplications and other morphological defects in structures produced by the eye-antennal, leg, wing and genital imaginal discs and the abdominal histoblasts. Each defect or pattern alteration is associated with a specific TSP during development.—We favor the interpretation that most of the major Q-III defects, particularly the structural duplications and deficiencies, result from temperature-induced cell death in mitotically active imaginal anlagen, while the small macrochaete phene probably results from the direct effects of Q-III on bristle synthesis. The hypothesis that the Q-III locus specifices a component required for protein synthesis is discussed, and it is concluded that this hypothesis can account for the pleiotropy of Q-III, and that perhaps it can be extended to M loci in general.     

Temperature sensitivity of muscle and neuron differentiation in embryonic cell cultures from the Drosophila mutant, shibire.

The sex-linked temperature-sensitive mutation, shibire^ts1, which causes, at the restrictive temperature, adult paralysis and pleiotropic morphological defects in embryonic, larval, and pupal development, has been shown to exhibit temperature-sensitive inhibition of differentiation in embryonic cultures in vitro. When shi cultures were incubated at 30°C for 24 hr, both muscle and neuron differentiation were inhibited more than 90% compared to control shi cultures incubated at 20°C. Heat shift experiments showed that the temperature-sensitive periods for neuron and muscle differentiation occurred at 11 to 18 and 14 to 16 hr, respectively, where zero time was the initiation of gastrulation in donor embryos. Short heat pulses (4 and 8 hr) which extended into the temperature-sensitive period resulted in moderate inhibition of differentiation; greater inhibition occurred as the duration of the pulses increased. In contrast, heating wild-type Oregon-R cultures at 30°C for 24 hr did not inhibit muscle cell differentiation and inhibited neuron differentiation relatively little. The temperature-sensitive period in shibire for muscle differentiation occurred well after myoblast division, during the period of myocyte elongation, aggregation, and fusion, whereas that for neuron differentiation took place during a period of enzyme synthesis (acetylcholinesterase and choline acetyltransferase) and axon elongation. Thus, the shi temperature-sensitive gene product affects at least two different cell types, in vitro, at different times during differentiation.     

Genetic Studies of Membrane Excitability in Drosophila: Lethal Interaction between Two Temperature-Sensitive Paralytic Mutations

Two mutants of Drosophila melanogaster, para ^ts1 (1-53.9) and nap^ts (2-56.2) both display similar temperature-sensitive paralysis associated with blockage in the conduction of nerve action potentials, suggesting that the two gene products have a similar function. This idea is supported by the observation that the double mutant is unconditionally lethal. Genetic analysis of this synergistic interaction has revealed the following: 1) it specifically involves the para and nap loci; (2) all para alleles interact with nap^ts, but the strength of the interaction varies in an allele-dependent fashion; (3) lethality of the double mutant occurs during the first larval instar with para^ts1 but differs with other para alleles; (4) hypodosage of para ⁺ causes lethality in a nap^ts background. These results together with previous electrophysiological, behavioral and pharmacological studies of these mutants suggest that both para and nap affect sodium channels and possibly encode different subunits.     

Retrotransposon-induced ectopic expression of the Om(2D) gene causes the eye-specific Om(M) phenotype in Drosophila ananassae

Optic morphology (Om) mutations in Drosophila ananassae map to at least 22 loci, which are scattered throughout the genome. Om mutations are all semidominant, neomorphic, nonpleiotropic, and associated with the insertion of a retrotransposon, tom. We have found that the Om(2D) gene encodes a novel protein containing histidine/proline repeats, and is ubiquitously expressed during embryogenesis. The Om(2D) RNA is not detected in wild-type eye imaginal discs, but is abundantly found in the center of the eye discs of Om(2D) mutants, where excessive cell death occurs. D. melanogaster flies transformed with the Om(2D) cDNA under control of the hsp70 promoter display abnormal eye morphology when heat-shocked at the third larval instar stage. These results suggest that the Om(2D) gene is not normally expressed in the eye imaginal discs, but its ectopic expression, induced by the tom element, in the eye disc of third instar larvae results in defects in adult eye morphology.     

Alterations in the production of hemocytes due to a neoplastic mutation of Drosophila melanogaster

The hemocytes of a genetically induced, temperature-sensitive lethal mutation of Drosophila, Tum¹, were examined both quantitatively and qualitatively during the third larval instar. At the tumor-permissive temperature, 29°C, there was a fourfold increase in the concentration of circulating hemocytes in mutant larvae as compared to control. Additionally, the relative frequency of lamellocytes was 30 times greater in Tum¹ larvae than Basc in the early third instar. However, the severity of this abnormality gradually diminished as Tum¹ approached pupariation; though high frequencies of lamellocytes were always present. At the tumor-restrictive temperature (15°C) the concentration of circulating hemocytes was over twice that found at 29°C for Tum¹ larvae, and did not change during the course of third instar. However, in contrast to 29°C there was no abnormal increase in the frequency of lamellocytes at the tumor-restrictive temperature. Control larvae had equivalent concentrations of hemocytes at both temperatures. In one of two temperature shift experiments, Tum¹ larvae shifted from 15° to 29°C at the beginning of third instar expressed the abnormal hemocyte concentration and differentiation associated with larvae raised continuously at 29°C. In addition, Tum¹ larvae shifted from 29° to 15°C expressed reduced abnormalities of hemocyte differentiation, e.g., with fewer lamellocytes in circulation. The possibility of a temperature-sensitive period for the activation of the Tum¹ gene is discussed.     

Alterations in the cell cycle of Drosophila imaginal disc cells precede metamorphosis

Flow cytometric analyses of imaginal disc and brain nuclei of Drosophila melanogaster have been made throughout the third larval instar. In wing, haltere, and leg discs the proportion of cells in the G₂M phase of the cell cycle (tetraploid cells) increases with larval age. In contrast, in the eye disc and in brain the proportion of tetraploid cells, already low at the outset of the instar, declines further. Measurement of growth rates for disc and brain tissue during the same developmental period was carried out by the cell counting procedure of Martin (1982). Our results are consistent with the conclusion that imaginal discs grow exponentially with an apparent doubling time of 5–10 hr from the resumption of cell division (in the first or second larval instar) until about 95 hr, when the apparent doubling time increases. Cell numbers increase until at least 5 hr after formation of white prepupae (122 hr), but during the preceding 10 hr the rate of increase is low. Thus, for wing and leg discs, but not for the eye disc and brain, the declining growth rate is associated with an increase in the proportions of tetraploid cells. In conjunction with cell counts and flow cytometry, fluorometric determination of disc DNA content at 112 hr indicated that the diploid DNA content of imaginal disc nuclei is 0.45 pg.     

The Pleiotropic Function of Delta during Postembryonic Development of Drosophila Melanogaster

Analysis of the development of Delta (Dl) temperature-sensitive mutants pulsed at restrictive temperature during larval and pupal stages reveals multiple phenocritical periods during which reduction of Dl function affects viability and development of adult structures. Dl function is required during the third larval instar for post-pupal viability and during the first day of pupal development for viability through eclosion. Dl function is required biphasically for the development of sensory bristles. Earlier pulses lead to bristle multiplication and later pulses lead to bristle loss. The exact intervals during which multiplication and loss are induced vary for different bristles. Dl function is also required for development of most, if not all, cell types in the retina. Different pulses result in reduction in eye size, scarring, and glossiness, as well as multiplication and loss of interommatidial bristles. We also define intervals during which Dl function is required for aspects of leg and wing development. Phenocritical periods for Dl function are temporally coincident with those previously reported for Notch (N), consistent with the hypothesis that the proteins encoded by Dl and N interact throughout development to assure correct specification of cell fates in a variety of imaginal tissues.     

Pattern specification in imaginal discs ofDrosophila melanogaster

Summary l(1)su(f)^mad-ts (mad) is a new temperature-sensitive (ts) lethal mutant ofDrosophila melanogaster which produces duplicated legs after temperature pulse treatment during larval development. The ts-lethality was studied in temperature experiments and genetic mosaics. Temperature pulses given during two distinct TSPs of larval development result in two different types of leg pattern duplication. Total differ from partial duplications with respect to the affected leg compartments and the orientation of the planes of symmetry which are perpendicular to the dorso-ventral and the proximo-distal leg axes in total and partial duplications, respectively. Genetic mosaic studies indicate (i) disc autonomy of leg pattern duplication, (ii) clonal separation of the anlagen of the two pattern copies, and (iii) clonal restriction along the antero-posterior compartment border in the two pattern copies of totally duplicated legs.The results suggest thatmad leg pattern duplication is caused by a change in positional information rather than by cell death and subsequent regeneration. Our data are compatible with the assumption that during normal development the leg disc cells acquire information about their position within the disc with respect to the different leg axes independently and at different times.     

Developmental genetics of a temperature-sensitive RNA polymerase II mutation in Drosophila melanogaster

Summary Purified RNA polymerase II (RNA nucleotidyl-transferase; EC 2.7.7.6) extracted from flies possessing lesions in the Ultrabithorax-like (Ubl) locus of Drosophila melanogaster has altered activity in vitro (Greenleaf et al. 1979, 1980; Coulter and Greenleaf 1982). This strongly suggests that the Ubl locus encodes a subunit of RNA polymerase II. Ethyl methanesulfonate was used to induce a temperature-sensitive mutation in this locus. Flies either homozygous or hemizygous for this new X–linked mutation (Ubl ^ts) display viability comparable to that of wild-type flies at 22° C but are lethal at 29° C. The temperature-sensitive period for Ubl ^ts flies is between gastrulation (6 h, 29° C) and pupation (9–10 days, 22° C). Zygotes shifted from 22° C to 29° C die at either the late embryonic or first larval instar stage while temperature shifts of second and third instar larvae result in the lethal phase occurring at the pupal stage. Most pupae shifted from 22° C to 29° C undergo metamorphosis and eclose as adults. Adults are viable if placed at 29° C; however, all females and some males become sterile if maintained at this temperature.Somatic recombination was used to induce clones homozygous for a null allele of Ubl at different stages of development. Clones of this null allele appear to be cell lethal indicating that the Ubl ⁺ gene product is required at all stages of development. The viability of Ubl ^ts pupae and adults at 29° C may result from only a partial reduction in activity caused by the mutation at this nonpermissive temperature.     

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     

The Fission Yeast Minichromosome Maintenance (MCM)-binding Protein (MCM-BP), Mcb1, Regulates MCM Function during Prereplicative Complex Formation in DNA Replication

The minichromosome maintenance (MCM) complex is a replicative helicase, which is essential for chromosome DNA replication. In recent years, the identification of a novel MCM-binding protein (MCM-BP) in most eukaryotes has led to numerous studies investigating its function and its relationship to the MCM complex. However, the mechanisms by which MCM-BP functions and associates with MCM complexes are not well understood; in addition, the functional role of MCM-BP remains controversial and may vary between model organisms. The present study aims to elucidate the nature and biological function of the MCM-BP ortholog, Mcb1, in fission yeast. The Mcb1 protein continuously interacts with MCM proteins during the cell cycle in vivo and can interact with any individual MCM subunit in vitro. To understand the detailed characteristics of mcb1⁺, two temperature-sensitive mcb1 gene mutants (mcb1^ts) were isolated. Extensive genetic analysis showed that the mcb1^ts mutants were suppressed by a mcm5⁺ multicopy plasmid and displayed synthetic defects with many S-phase-related gene mutants. Moreover, cyclin-dependent kinase modulation by Cig2 repression or Rum1 overproduction suppressed the mcb1^ts mutants, suggesting the involvement of Mcb1 in pre-RC formation during DNA replication. These data are consistent with the observation that Mcm7 loading onto replication origins is reduced and S-phase progression is delayed in mcb1^ts mutants. Furthermore, the mcb1^ts mutation led to the redistribution of MCM subunits to the cytoplasm, and this redistribution was dependent on an active nuclear export system. These results strongly suggest that Mcb1 promotes efficient pre-RC formation during DNA replication by regulating the MCM complex.     

Retrotransposon-induced ectopic expression of the Om(2D) gene causes the eye-specific Om(M) phenotype in Drosophila ananassae

Optic morphology (Om) mutations in Drosophila ananassae map to at least 22 loci, which are scattered throughout the genome. Om mutations are all semidominant, neomorphic, nonpleiotropic, and associated with the insertion of a retrotransposon, tom. We have found that the Om(2D) gene encodes a novel protein containing histidine/proline repeats, and is ubiquitously expressed during embryogenesis. The Om(2D) RNA is not detected in wild-type eye imaginal discs, but is abundantly found in the center of the eye discs of Om(2D) mutants, where excessive cell death occurs. D. melanogaster flies transformed with the Om(2D) cDNA under control of the hsp70 promoter display abnormal eye morphology when heat-shocked at the third larval instar stage. These results suggest that the Om(2D) gene is not normally expressed in the eye imaginal discs, but its ectopic expression, induced by the tom element, in the eye disc of third instar larvae results in defects in adult eye morphology.