Severe Fertility Effects of sheepish Sperm Caused by Failure To Enter Female Sperm Storage Organs in Drosophila melanogaster.

In Drosophila, mature sperm are transferred from males to females during copulation, stored in the sperm storage organs of females, and then utilized for fertilization. Here, we report a gene named sheepish (shps) of Drosophila melanogaster that is essential for sperm storage in females. shps mutant males, although producing morphologically normal and motile sperm that are effectively transferred to females, produce very few offspring. Direct counts of sperm indicated that the primary defect was correlated to failure of shps sperm to migrate into the female sperm storage organs. Increased sperm motion parameters were seen in the control after transfer to females, whereas sperm from shps males have characteristics of the motion parameters different from the control. The few sperm that occasionally entered the female sperm storage organs showed no obvious defects in fertilization and early embryo development. The female postmating responses after copulation with shps males appeared normal, at least with respect to conformational changes of uterus, mating plug formation, and female remating rates. The shps gene encodes a protein with homology to amine oxidases, including as observed in mammals, with a transmembrane region at the C-terminal end. The shps mutation was characterized by a nonsense replacement in the third exon of CG13611, and shps was rescued by transformants of the wild-type copy of CG13611 Thus, shps may define a new class of gene responsible for sperm storage.

Electron microscopic observation of the sagittal structure of Drosophila mature sperm.

Observation of sperm development and determination of their morphological characteristics are very important to the understanding of phylogenetic relationships and the study of sperm function during fertilization. Although ultrastructural studies of sperm development in the testes of the fruit fly Drosophila have been performed, there are few reports describing electron microscopic morphology of mature sperm, that is, those released from the testes to the seminal vesicles. Here, we present the first report of the sagittal organization of Drosophila sperm head and neck regions by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The head and tail structures of a mature sperm, for example, the acrosome, nucleus, and flagellum, were easy to distinguish by the morphological characteristics of the sperm surface by SEM. The morphological relationships between the surface and internal structures of mature sperm were confirmed by observing longitudinal sections with TEM. Our approach overcame the technical difficulties involved in sample preparation for electron microscopic observation of the Drosophila mature sperm head, and therefore, this study serves as an important foundation for future genetic dissection of sperm ultrastructure and function in male sterile mutants.

Elimination of Y chromosome-bearing spermatids during spermiogenesis in an autosomal sex-ratio mutant of Drosophila simulans.

Sex ratio distortion, which is commonly abbreviated as sex-ratio, has been studied in many Drosophila species, but the mechanism remains largely unknown. Here, we report on the sex-ratio mutant of D. simulans named excess of females (exf). The third chromosomal recessive mutation results in a sex ratio of approximately 0.2 or less (males/total). Cytological observation demonstrated that meiosis appeared to be completed normally, but that most Y chromosome-bearing nuclei failed to elongate during spermiogenesis, as revealed by fluorescence in situ hybridization using sex chromosome-specific probes. These aberrant nuclei contained membranous inclusions as revealed by electron microscopic analysis. Most of the aberrant exf spermatids failed to individualize and mature, suggesting that a later stage of spermiogenesis is involved in prevention of production of sperm with abnormal morphology. On the one hand, in exf seminal vesicles, sperm nuclei with a length of 5-8.5 µm were occasionally observed, in addition to those with wild-type sperm dimensions, that is, a length of approximately 10 µm. Thus, spermatids with less severe nuclear defects can escape elimination and be released into the seminal vesicles as mature sperm. Furthermore, we constructed His2AvD-GFP and ProtamineB-eGFP transgenic lines in D. simulans, and examined the processes involved in replacement of chromatin proteins over a time course, according to nuclear morphology. We found that both normal and abnormal sperm heads demonstrated equal chromatin replacement during late spermiogenesis. Our results suggest that exf belongs to a unique class of meiotic drive systems in that (1) intranuclear membranous inclusions cause failure of nuclear shaping of Y-bearing spermatids without affecting the histone-protamine transition, and (2) a portion of the aberrant spermatids differentiate into mature sperm; these are transferred to and stored by females.

Distribution and morphological changes of the Golgi apparatus during Drosophila spermatogenesis.

In spermatogenesis, the Golgi apparatus is important for the formation of the acrosome, which is a sperm-specific organelle essential for fertilization. Comprehensive examinations of the spatiotemporal distribution and morphological characterizations of the Golgi in various cells during spermatogenesis are necessary for functional analyses and mutant screenings in the model eukaryote Drosophila. Here, we examined the distribution and morphology of the Golgi during Drosophila spermatogenesis with immunofluorescence and electron microscopy. In pre-meiotic germ cells, the Golgi apparatuses were distributed evenly in the cytoplasm. In contrast, they were located exclusively in two regions near the poles during the meiotic metaphase, where they were segregated prior to the chromosomes. In cells in anaphase to telophase, the Golgi were predominantly left behind in the equatorial region between the separating daughter nuclei. After completion of meiosis, the dispersed Golgi were assembled at the apical side of the spermatid nucleus to form the acrosome. Further investigation of the Golgi distribution in ß2-tubulin mutants showed aberrant and uneven distributions of the Golgi among sister cells in the meiotic spermatocytes and in the post-meiotic spermatids. At the ultrastructural level, the Golgi apparatus in pre-meiotic spermatocytes comprised a pair of stacks. The two stacks were situated adjacent to each other, as if they had duplicated before entering into meiotic division. These results highlight the dynamic nature of the Golgi during spermatogenesis and provide a framework for analyzing the correlations between the dynamics of the Golgi and its function in sperm development.

Crossing over does occur in males of Drosophila ananassae from natural populations.

Spontaneous crossing over in males of Drosophila ananassae has been well demonstrated using F(1) individuals from crosses between marker stocks and wild type strains. However, the question of its occurrence in males from natural populations remained open. Here we present the cytological evidence that crossing over does occur in males of D. ananassae from two Brazilian populations, sampled nearly 21 years apart, and in two recently sampled populations, one from Indonesia and one from Okinawa, Japan. Cytological analysis of meiosis in males collected from nature and in sons of females from the same population inseminated in nature revealed the presence of chiasmata, inversion chiasmata, and isosite chromosome breakages in the diplotene cells in all sampled populations. These data demonstrate that reciprocal and nonreciprocal exchanges and chromosome breakages, previously reported as related events of male crossing over, do occur at variable frequencies among males from natural populations.

Homologous recombination via synthesis-dependent strand annealing in yeast requires the Irc20 and Srs2 DNA helicases.

Synthesis-dependent strand-annealing (SDSA)-mediated homologous recombination replaces the sequence around a DNA double-strand break (DSB) with a copy of a homologous DNA template, while maintaining the original configuration of the flanking regions. In somatic cells at the 4n stage, Holliday-junction-mediated homologous recombination and nonhomologous end joining (NHEJ) cause crossovers (CO) between homologous chromosomes and deletions, respectively, resulting in loss of heterozygosity (LOH) upon cell division. However, the SDSA pathway prevents DSB-induced LOH. We developed a novel yeast DSB-repair assay with two discontinuous templates, set on different chromosomes, to determine the genetic requirements for somatic SDSA and precise end joining. At first we used our in vivo assay to verify that the Srs2 helicase promotes SDSA and prevents imprecise end joining. Genetic analyses indicated that a new DNA/RNA helicase gene, IRC20, is in the SDSA pathway involving SRS2. An irc20 knockout inhibited both SDSA and CO and suppressed the srs2 knockout-induced crossover enhancement, the mre11 knockout-induced inhibition of SDSA, CO, and NHEJ, and the mre11-induced hypersensitivities to DNA scissions. We propose that Irc20 and Mre11 functionally interact in the early steps of DSB repair and that Srs2 acts on the D-loops to lead to SDSA and to prevent crossoverv.

The double-stranded break-forming activity of plant SPO11s and a novel rice SPO11 revealed by a Drosophila bioassay.

BACKGROUND: SPO11 is a key protein for promoting meiotic recombination, by generating chromatin locus- and timing-specific DNA double-strand breaks (DSBs). The DSB activity of SPO11 was shown by genetic analyses, but whether SPO11 exerts DSB-forming activity by itself is still an unanswered question. DSB formation by SPO11 has not been detected by biochemical means, probably because of a lack of proper protein-folding, posttranslational modifications, and/or specific SPO11-interacting proteins required for this activity. In addition, plants have multiple SPO11-homologues. RESULTS: To determine whether SPO11 can cleave DNA by itself, and to identify which plant SPO11 homologue cleaves DNA, we developed a Drosophila bioassay system that detects the DSB signals generated by a plant SPO11 homologue expressed ectopically. We cytologically and genetically demonstrated the DSB activities of Arabidopsis AtSPO11-1 and AtSPO11-2, which are required for meiosis, in the absence of other plant proteins. Using this bioassay, we further found that a novel SPO11-homologue, OsSPO11D, which has no counterpart in Arabidopsis, displays prominent DSB-forming activity. Quantitative analyses of the rice SPO11 transcripts revealed the specific increase in OsSPO11D mRNA in the anthers containing meiotic pollen mother cells. CONCLUSIONS: The Drosophila bioassay system successfully demonstrated that some plant SPO11 orthologues have intrinsic DSB activities. Furthermore, we identified a novel SPO11 homologue, OsSPO11D, with robust DSB activity and a possible meiotic function.

Association between circadian clock genes and diapause incidence in Drosophila triauraria.

Diapause is an adaptive response triggered by seasonal photoperiodicity to overcome unfavorable seasons. The photoperiodic clock is a system that controls seasonal physiological processes, but our knowledge about its physiological mechanisms and genetic architecture remains incomplete. The circadian clock is another system that controls daily rhythmic physiological phenomena. It has been argued that there is a connection between the two clocks. To examine the genetic connection between them, we analyzed the associations of five circadian clock genes (period, timeless, Clock, cycle and cryptochrome) with the occurrence of diapause in Drosophila triauraria, which shows a robust reproductive diapause with clear photoperiodicity. Non-diapause strains found in low latitudes were compared in genetic crosses with the diapause strain, in which the diapause trait is clearly dominant. Single nucleotide polymorphism and deletion analyses of the five circadian clock genes in backcross progeny revealed that allelic differences in timeless and cryptochrome between the strains were additively associated with the differences in the incidence of diapause. This suggests that there is a molecular link between certain circadian clock genes and the occurrence of diapause.

Sperm of the wasted mutant are wasted when females utilize the stored sperm in Drosophila melanogaster.

Females of many animal species store sperm after copulation for use in fertilization, but the mechanisms controlling sperm storage and utilization are largely unknown. Here we describe a novel male sterile mutation of Drosophila melanogaster, wasted (wst), which shows defects in various processes of sperm utilization. The sperm of wst mutant males are stored like those of wild-type males in the female sperm storage organs, the spermathecae and seminal receptacles, after copulation and are released at each ovulation. However, an average of thirteen times more wst sperm than wild type sperm are released at each ovulation, resulting in rapid loss of sperm stored in seminal receptacles within a few days after copulation. wst sperm can enter eggs efficiently at 5 hr after copulation, but the efficiency of sperm entry decreases significantly by 24 hr after copulation, suggesting that wst sperm lose their ability to enter eggs during storage. Furthermore, wst sperm fail to undergo nuclear decondensation, which prevents the process of fertilization even when sperm enter eggs. Our results indicate that the wst gene is essential for independent processes in the utilization of stored sperm; namely, regulation of sperm release from female storage organs, maintenance of sperm efficiency for entry into eggs, and formation of the male pronucleus in the egg at fertilization.

Drosophila Genetic Resource and Stock Center; The National BioResource Project.

The fruit fly, Drosophila melanogaster, is not categorized as a laboratory animal, but it is recognised as one of the most important model organisms for basic biology, life science, and biomedical research. This tiny fly continues to occupy a core place in genetics and genomic approaches to studies of biology and medicine. The basic principles of genetics, including the variations of phenotypes, mutations, genetic linkage, meiotic chromosome segregation, chromosome aberrations, recombination, and precise mapping of genes by genetic as well as cytological means, were all derived from studies of Drosophila. Recombinant DNA technology was developed in the 1970s and Drosophila DNA was the first among multicellular organisms to be cloned. It provided a detailed characterization of genes in combination of classical cytogenetic data. Drosophila thus became the pioneering model organism for various fields of life science research into multicellular organisms. Here, I briefly describe the history of Drosophila research and provide a few examples of the application of the abundant genetic resources of Drosophila to basic biology and medical investigations. A Japanese national project, the National BioResource Project (NBRP) for collection, maintainance, and provision of Drosophila resources, that is well known and admired by researchers in other countries as an important project, is also briefly described.

Proteome profiling reveals tissue-specific protein expression in the male reproductive system of Drosophila melanogaster.

The reproductive systems of male and female Drosophila have been well studied genetically and cytologically because of the importance of meiotic mechanisms in understanding inheritance and speciation. Recently, there has been increasing interest in proteomics of Drosophila melanogaster, because detailed and comprehensive gene annotations have made it straightforward to identify proteins analyzed by mass spectrometry. We have applied proteomic analysis to the male reproductive system with the aim of understanding sperm maturation not only during the process of spermatogenesis, but also during the movement of sperm from the seminal vesicle through the male reproductive system and into the uterus following copulation. In this article, we will provide an overview of the principles of recent proteomic technologies and describe a few proteomic profiles of the male reproductive organs.

Proteome mapping of the Drosophila melanogaster male reproductive system.

The fruit fly Drosophila melanogaster is an excellent model organism for studying insect reproductive biology. Although the gene expression profiles of both male and female reproductive organs have been studied in detail, their proteomic profiles and functional characteristics largely remained to be clarified. In this study, we conducted proteome mapping of the male internal reproductive organs using 2-DE. We identified a total of 440 protein components from gels of the male reproductive organs (testis, seminal vesicle, accessory gland, ejaculatory duct, and ejaculatory bulb). A number of proteins associated with odorant/pheromone-binding, lipid metabolism, proteolysis, and antioxidation were expressed tissue specifically in the male reproductive system. Based on our proteomic data set, we constructed reference proteome maps of the reproductive organs, which will provide valuable information toward a comprehensive understanding of Drosophila reproduction.

Transgenic Drosophila simulans strains prove the identity of the speciation gene Lethal hybrid rescue.

Speciation genes are responsible for genetic incompatibilities in hybrids of incipient species and therefore participate in reproductive isolation leading to complete speciation. Hybrid males between Drosophila melanogaster females and D. simulans males die at late larval or prepupal stages due to a failure in chromosome condensation during mitosis. However a mutant male of D. simulans, named Lethal hybrid rescue (Lhr), produces viable hybrid males when crossed to females of D. melanogaster. Recently the Lhr gene has been proposed as corresponding to the CG18468 gene in D. melanogaster. However this identification relied on sequence characteristics more than on a precise mapping and the use of the GAL4/UAS system to drive the transgene in D. melanogaster might have increased the complexity of interaction. Thus here we propose an independent identification of the Lhr gene based on a more precise mapping and transgenic experiments in D. simulans. We have mapped the Lhr gene by using Single Nucleotide Polymorphisms (SNPs) and identified within the candidate region the gene homologous to CG18468 as the Lhr gene as it was previously reported. Transgenic experiments in D. simulans with the native promoter of CG18468 prove that it is the Lhr gene of D. simulans by inducing the lethality of the hybrid males.

BAC library construction and BAC end sequencing of five Drosophila species: the comparative map with the D. melanogaster genome.

We constructed and characterized arrayed bacterial artificial chromosome (BAC) libraries of five Drosophila species (D. melanogaster, D. simulans, D. sechellia, D. auraria, and D. ananassae), which are genetically well characterized in the studies of meiosis, evolution, population genetics, and developmental biology. The BAC libraries comprise 8,000 to 12,500 clones for each species, estimated to cover the most of the genomes. We sequenced both ends of most of these BAC clones with a success rate of 91%. Of these, 53,701 clones consisting of non-repetitive BAC end sequences (BESs) were mapped with reference of the public D. melanogaster genome sequences. The BES mapping estimated that the BAC libraries of D. auraria and D. ananassae covered 47% and 57% of the D. melanogaster genome, respectively, and those of D. melanogaster, D. sechellia, and D. simulans covered 94-97%. The low coverage by BESs of D. auraria and D. ananassae may be due to the high sequence divergence with D. melanogaster. From the comparative BES mapping, 111 possible breakpoints of chromosomal rearrangements were identified in these four species. The breakpoints of the major chromosome rearrangement between D. simulans and D. melanogaster on the third chromosome were determined within 20 kb in 84E and 30 kb in 93E/F. Corresponding breakpoints were also identified in D. sechellia. The BAC clones described here will be an important addition to the Drosophila genomic resources.

Novel eye-specific calmodulin methylation characterized by protein mapping in Drosophila melanogaster.

Post-translational methylation of the epsilon-amino group of lysine residues regulates a number of protein functions. Calmodulin, a key modulator of intracellular calcium signaling, is methylated on lysine 115 in many species. Although the amino acid sequence of calmodulin is highly conserved in eukaryotes, it has been shown that lysine 115 is not methylated in Drosophila calmodulin and no other methylation site has been reported. In this study, we characterized in vivo modification states of Drosophila calmodulin using proteomic methodology involving the protein mapping of microdissected Drosophila tissues on 2-D gels. We found that Drosophila calmodulin was highly expressed in methylated forms in the compound eye, whereas its methylation was hardly detected in other tissues. We identified that lysine 94 located in an EF-hand III is the methylation site in Drosophila calmodulin. The predominance of methylated calmodulin in the compound eye may imply the involvement of calmodulin in photoreceptor-specific functions through methylation.

Prevalence of full-size P and KP elements in North American populations of Drosophila melanogaster.

The P transposable element invaded the Drosophila melanogaster genome in the middle of the twentieth century, probably from D. willistoni in the Caribbean or southeastern North America. P elements then spread rapidly and became ubiquitous worldwide in wild populations of D. melanogaster by 1980. To study the dynamics and long-term fate of transposable genetic elements, we examined the molecular profile of genomic P elements and the phenotype in the P-M system of the current North American natural populations collected in 2001-2003. We found that full-size P and KP elements were the two major size classes of P elements present in the genomes of all populations ("FP + KP predominance") and that the P-related phenotypes had largely not changed since the 1980s. Both FP + KP predominance and phenotypic stability were also seen in other populations from other continents. As North American populations did not show many KP elements in earlier samples, we hypothesize that KP elements have spread and multiplied in the last 20 years in North America. We suggest that this may be due to a transpositional advantage of KP elements, rather than to a role in P-element regulation.

A rapid decrease in number of the complete ninja element and concomitant increase of the defective element in a strain of Drosophila simulans.

The ninja element, originally isolated from an unstable white mutant strain white-milky (w(mky)) of Drosophila simulans, is a member of the retrotransposon family with long terminal repeats (LTRs). We show that ninja is present in high copy numbers in the w(mky)-derivative sublines white-chocolate (w(cho)) and white-persimmonl (w(psm1)), in a low copy number in another derivative subline white-milky 3 (w(mky3)), and in only a few copies in a wild type strain. We have cloned the ninja elements from these sublines and examined their structures. Most of the elements cloned (38 out of 41 independent clones) from w(cho) were full length. In contrast, only 9 of 23 independent clones from w(mky3) were full length. We hypothesize that ninja elements were integrated and lost frequently in the w(mky) strain and its derivative genomes, and that a rapid decrease in numbers of the ninja element was caused not by an increased rate of loss but by a reduction of integration of full length ninja elements in w(mky3). Each defective element had a unique deletion and/or an insertion except for the three from w(mky3), which had exactly the same 81-bp deletion in each of the 5' and 3' LTRs. The 5' and 3' ends of the deletion appeared to represent sequences similar to those of Drosophila consensussplicing sites. Ectopic splicing may have produced these defective ninja elements.

Targeted expression of Ip3 sponge and Ip3 dsRNA impaires sugar taste sensation in Drosophila.

We evaluated the role of IP(3) in sugar taste reception in Drosophila melanogaster by inactivating the IP(3) signaling using genetic tools. We used the "IP(3) sponge," composed of the modified ligand-binding domain from the mouse IP(3) receptor, which was designed to absorb IP(3) in competition with native IP(3) receptors. Another tool was a transgene that generates double-stranded RNA against IP(3) receptor mRNA. Both inhibitors diminished the sensitivity of flies to trehalose and sucrose, as estimated by behavioral assays and electrophysiological recordings from the sugar receptor cells. The result indicates that IP(3) signaling is indispensable for sugar reception in Drosophila.

Mutations in orbit/mast reveal that the central spindle is comprised of two microtubule populations, those that initiate cleavage and those that propagate furrow ingression.

We address the relative roles of astral and central spindle microtubules (MTs) in cytokinesis of Drosophila melanogaster primary spermatocytes. Time-lapse imaging studies reveal that the central spindle is comprised of two MT populations, "interior" central spindle MTs found within the spindle envelope and "peripheral" astral MTs that probe the cytoplasm and initiate cleavage furrows where they contact the cortex and form overlapping bundles. The MT-associated protein Orbit/Mast/CLASP concentrates on interior rather than peripheral central spindle MTs. Interior MTs are preferentially affected in hypomorphic orbit mutants, and consequently the interior central spindle fails to form or is unstable. In contrast, peripheral MTs still probe the cortex and form regions of overlap that recruit the Pav-KLP motor and Aurora B kinase. orbit mutants have disorganized or incomplete anillin and actin rings, and although cleavage furrows initiate, they ultimately regress. Our work identifies a new function for Orbit/Mast/CLASP and identifies a novel MT population involved in cleavage furrow initiation.