Control of mating plug expelling and sperm storage in Drosophila: A gynandromorph- and mutation-based dissection

INTRODUCTION

In this study, we analyzed gynandromorphs with female terminalia, to dissect mating-related female behaviors in Drosophila.

MATERIALS AND METHODS

We used gynandromorphs, experimentally modified wild-type (Oregon-R) females, and mutant females that lacked different components of the female reproductive apparatus.

RESULTS

Many of the gynandromorphs mated but did not expel the mating plug (MP). Some of these - with thousands of sperm in the uterus - failed to take up sperm into the storage organs. There were gynandromorphs that stored plenty of sperm but failed to release them to fertilize eggs. Expelling the MP, sperm uptake into the storage organs, and the release of stored sperm along egg production are separate steps occurring during Drosophila female fertility. Cuticle landmarks of the gynandromorphs revealed that while the nerve foci that control MP expelling and also those that control sperm uptake reside in the abdominal, the sperm release foci derive from the thoracic region of the blastoderm.

DISCUSSION AND CONCLUSION

The gynandromorph study is confirmed by analyses of (a) mutations that cause female sterility: Fs(3)Avar (preventing egg deposition), Tm2^gs (removing germline cells), and iab-4^DB (eliminating gonad formation) and (b) by experimentally manipulated wild-type females: decapitated or cut through ventral nerve cord.

Sexual behavior: how Sex Peptide flips the postmating switch of female flies

Drosophila male Sex Peptide elicits an amazing variety of postmating responses in mated females, some of which are transmitted via a receptor on specific neurons of the female genital tract. New work shows that neurons expressing the sex-determination gene doublesex (dsx) play a pivotal role in the female postmating switch.

Sexual behavior: dietary food switch induced by sex

Pregnancy in humans induces cravings for special food: the same occurs in Drosophila females. New work now shows that mating throws a nutritional switch in favor of a high-protein diet and that modulation of nutritional balance depends on the sex peptide receptor and involves neuronal TOR-S6 kinase signaling.

Sexual behaviour: a receptor for sex control in Drosophila females

Male Drosophila manipulate the sexual behaviour of their female mating partners by release of a Sex-peptide, but how does this work? A G-protein-coupled receptor has now been identified which acts in the female flies to detect male Sex-peptide and trigger increased egg laying and reduced sexual receptivity.

The effect of mating on immunity can be masked by experimental piercing in female Drosophila melanogaster

Mating and immunity are two major components of fitness and links between them have been demonstrated in a number of recent investigations. In Drosophila melanogaster, a seminal fluid protein, sex-peptide (SP), up-regulates a number of antimicrobial peptide (AMP) genes in females after mating but the resulting effect on pathogen resistance is unclear. In this study, we tested (1) whether SP-induced changes in gene expression affect the ability of females to kill injected non-pathogenic bacteria and (2) how the injection process per se affects the expression of AMP genes relative to SP. The ability of virgin females and females mated to SP lacking or control males to clear bacteria was assayed using an established technique in which Escherichia coli are injected directly into the fly body and the rate of clearance of the injected bacteria is determined. We found no repeatable differences in clearance rates between virgin females and females mated to SP producing or SP lacking males. However, we found that the piercing of the integument, as occurs during injection, up-regulates AMP gene expression much more strongly than SP. Thus, assays that involve piercing, which are commonly used in immunity studies, can mask more subtle and biologically relevant changes in immunity, such as those induced by mating.

The hydroxyproline motif of male sex peptide elicits the innate immune response in Drosophila females

Seminal fluid elicits a variety of physiological and behavioral changes in insect females. In Drosophila melanogaster females, sex peptide (SP) is the major seminal agent eliciting oviposition and reduction of receptivity. But SP also has many other effects; for example, it stimulates food intake, egg production, ovulation, juvenile hormone production and antimicrobial peptide synthesis. Thus, SP very probably has several receptors. To identify putative targets and signaling cascades, we studied the genome-wide regulation of genes by microarray analysis of RNA isolated from females after mating with wild-type males or males lacking SP, respectively. In addition, we studied the effects of SP on the proteome of females. Sex peptide regulates gene activity differentially in the head and in the abdomen. Genes coding for unspecific antimicrobial peptides are specifically transcribed in the abdomen, e.g. the antimicrobial peptide drosocin in epithelial tissues of the female genital tract (oviduct and calyx). Hence, SP elicits a systemic [Peng J, Zipperlen P & Kubli E (2005) Curr Biol15, 1690-1694] and an epithelial immune response. Ectopic expression of SP in the fat body of transgenic virgin females (with subsequent secretion into the hemolymph) does not elicit drosocin synthesis in the genital tract. Thus, the receptors for the stimulation of the systemic and the epithelial responses by SP are compartmentalized. The hydroxyproline (P*) motif of SP, P*TKFP*IP*SP*NP*, is identified as a novel elicitor of the innate immune response. We suggest that SP acts by chemical mimicry of sugar components of the bacterial cell wall. Thus, SP may induce the immune system via pattern recognition receptors.

Sex-peptide-regulated female sexual behavior requires a subset of ascending ventral nerve cord neurons

BACKGROUND

Male-derived Sex-peptide (SP) elicits egg laying and rejection of courting males in mated Drosophila females. Little is known about the genes that specify the underlying neuronal circuits and mediate this switch in female sexual behavior.

RESULTS

Here we show that the egghead gene involved in glycosphingolipid biosynthesis provides an essential component to the SP response. We have isolated viable alleles of the vital egghead gene that abolish egghead expression from a distal promoter resulting in the absence of the largest transcript of this complex transcription unit. Temporally and spatially restricted expression of egghead revealed a requirement for egghead early in the development of apterous-expressing ventral nerve cord neurons to rescue the SP response. In viable egghead alleles, these ascending interneurons, three per abdominal and seven per thoracic hemisegment, fail to innervate the central brain. egghead expression in apterous neurons rescues neuronal targeting and the response to SP. Furthermore, neurotransmission in apterous neurons is required to elicit the SP response.

CONCLUSION

Together with the former finding of SP binding to afferent nerves , these results suggest that SP-mediated modification of sensory input switches female sexual behavior from the virgin to the mated state.

The Drosophila calcipressin sarah is required for several aspects of egg activation

Activation of mature oocytes initiates development by releasing the prior arrest of female meiosis, degrading certain maternal mRNAs while initiating the translation of others, and modifying egg coverings. In vertebrates and marine invertebrates, the fertilizing sperm triggers activation events through a rise in free calcium within the egg. In insects, egg activation occurs independently of sperm and is instead triggered by passage of the egg through the female reproductive tract ; it is unknown whether calcium signaling is involved. We report here that mutations in sarah, which encodes an inhibitor of the calcium-dependent phosphatase calcineurin, disrupt several aspects of egg activation in Drosophila. Eggs laid by sarah mutant females arrest in anaphase of meiosis I and fail to fully polyadenylate and translate bicoid mRNA. Furthermore, sarah mutant eggs show elevated cyclin B levels, indicating a failure to inactivate M-phase promoting factor (MPF). Taken together, these results demonstrate that calcium signaling is involved in Drosophila egg activation and suggest a molecular mechanism for the sarah phenotype. We also find the conversion of the sperm nucleus into a functional male pronucleus is compromised in sarah mutant eggs, indicating that the Drosophila egg's competence to support male pronuclear maturation is acquired during activation.

Drosophila sex-peptide stimulates female innate immune system after mating via the Toll and Imd pathways

Insect immune defense is mainly based on humoral factors like antimicrobial peptides (AMPs) that kill the pathogens directly or on cellular processes involving phagocytosis and encapsulation by hemocytes. In Drosophila, the Toll pathway (activated by fungi and gram-positive bacteria) and the Imd pathway (activated by gram-negative bacteria) lead to the synthesis of AMPs. But AMP genes are also regulated without pathogenic challenge, e.g., by aging, circadian rhythms, and mating. Here, we show that AMP genes are differentially expressed in mated females. Metchnikowin (Mtk) expression is strongly stimulated in the first 6 hr after mating. Sex-peptide (SP), a male seminal peptide transferred during copulation, is the major agent eliciting transcription of Mtk and of other AMP genes. Both pathways are needed for Mtk induction by SP. Furthermore, SP induces additional AMP genes via the Toll (Drosomycin) and the Imd (Diptericin) pathways. SP affects the Toll pathway at or upstream of the gene spätzle, the Imd pathway at or upstream of the gene imd. Mating may physically damage females and pathogens may be transferred. Thus, endogenous stimulation of AMP transcription by SP at mating might be considered as a preventive step to encounter putative immunogenic attacks.

Gradual release of sperm bound sex-peptide controls female postmating behavior in Drosophila

BACKGROUND

In many female insects, peptides transferred in the seminal fluid induce postmating responses (PMR), such as a drastic increase of egg laying and reduction of receptivity (readiness to mate). In Drosophila melanogaster, sex-peptide (SP) elicits short- and long-term PMR, but only the latter in the presence of stored sperm (sperm effect).

RESULTS

Here, we elucidate the interaction between SP and sperm by immunofluorescence microscopy. Transgenic males were used to study the effects of SP modification on the PMR of females in vivo. We report that SP binds to sperm with its N-terminal end. In females, the C-terminal part of SP known to be essential to induce the PMR is gradually released from stored sperm by cleavage at a trypsin cleavage site, thus prolonging the PMR. These findings are confirmed by analyzing the PMR elicited by males containing transgenes encoding modified SPs. SP lacking the N-terminal end cannot bind, and SP without the trypsin cleavage site binds permanently to sperm.

CONCLUSION

By binding to sperm tails, SP prolongs the PMR. Thus, besides a carrier for genetic information, sperm is also the carrier for SP. Binding to sperm may protect the peptide from degradation by proteases in the hemolymph and, thus, prolong its half-life. Longer sperm tails may transfer more SP and thus increase the reproductive fitness of the male. We suggest that this could explain the excessive length of sperm tails in some Drosophila species.

Evolutionary ecology of the prezygotic stage

The life cycles of sexually reproducing animals and flowering plants begin with male and female gametes and their fusion to form a zygote. Selection at this earliest stage is crucial for offspring quality and raises similar evolutionary issues, yet zoology and botany use dissimilar approaches. There are striking parallels in the role of prezygotic competition for sexual selection on males, cryptic female choice, sexual conflict, and against selfish genetic elements and genetic incompatibility. In both groups, understanding the evolution of sex-specific and reproductive traits will require an appreciation of the effects of prezygotic competition on fitness.

The presence of Drosophila melanogaster sex peptide-like immunoreactivity in the accessory glands of male Helicoverpa armigera

In this study a highly specific polyclonal antibody to DrmSP was produced and used to develop and standardize a sensitive direct ELISA. Structure-activity studies revealed that the antiserum is specific to the N-terminal of DrmSP. This ELISA was used for the detection of DrmSP-like immunoreactivity in the reproductive tissues of male Helicoverpa armigera moths at femtomole levels. Two positive immunoreactive peaks were found in HPLC purified extracts of male accessory glands. The immunoreactive peak, which contained a higher amount of immunoreactivity, was also found to be pheromonostatic in PBAN-injected decapitated females as well as in intact female moths during their peak pheromone production. Lower levels of DrmSP-like immunoreactivity were found in younger males (1-2 day-old) when compared to older males (3-7 day-old).

The sex-peptide DUP99B is expressed in the male ejaculatory duct and in the cardia of both sexes

Mating elicits two postmating responses in many insect females: the egg laying rate increases and sexual receptivity is reduced. In Drosophila melanogaster, two peptides of the male genital tract, sex-peptide and DUP99B, elicit these postmating responses when injected into virgin females. Here we show that the gene encoding DUP99B is expressed in the male ejaculatory duct and in the cardia of both sexes. The DUP99B that is synthesized in the ejaculatory duct is transferred, during mating, into the female genital tract. Expression of the gene is first seen in a late pupal stage. Males containing an intact ejaculatory duct, but lacking accessory glands, initiate the two postmating responses in their female partners [Xue, L. & Noll, M. (2000) Proc. Natl Acad. Sci. USA97, 3272-3275]. Although such males synthesize DUP99B in wild-type quantities, they elicit only weak postmating responses in their mating partners. Males lacking the Dup99B gene elicit the two postmating responses to the same extent as wild-type males. These results suggest that both sex-peptide and DUP99B can elicit both responses in vivo. However, sex-peptide seems to play the major role in eliciting the postmating responses, while DUP99B may have specialized for other, as yet unknown, functions.

Sex-peptides: seminal peptides of the Drosophila male

Mating affects the reproductive behaviour of insect females: the egg-laying rate increases and courting males are rejected. These post-mating responses are induced mainly by seminal fluid. In Drosophila melanogaster, males transfer two peptides (sex-peptides, = Sps) that reduce receptivity and elicit increased egg laying in their mating partners. Similarities in the open reading frames of the genes suggest that they have arisen by gene duplication. In females, Sps bind to specific sites in the central and peripheral nervous system, and to the genital tract. The binding proteins of the nervous system and genital tract are membrane proteins, but they differ molecularly. The former protein is proposed to be a receptor located at the top of a signalling cascade leading to the two post-mating responses, whereas the latter is a carrier protein moving Sps from the genital tract into the haemolymph. Sps bind to sperm. Together with sperm they are responsible for the persistence of the two post-mating responses. But Sps are the molecular basis of the sperm effect; sperm is merely the carrier.

Sex-peptide is the molecular basis of the sperm effect in Drosophila melanogaster

Mating elicits two major changes in the reproductive behavior of many insect females. The egg-laying rate increases and the readiness to accept males (receptivity) is reduced. These postmating responses last approximately 1 week in Drosophila melanogaster. Males that do not transfer sperm but transfer seminal fluid during mating induce a short-term response of 1 day. The long-term response of 1 week requires the presence of sperm (sperm effect). Hence, sperm is essential for the long-term persistence of the postmating responses. Three seminal fluid peptides elicit postmating responses: ovulin, sex-peptide (SP), and DUP99B. Using the technique of targeted mutagenesis by homologous recombination, we have produced males with mutant SP genes. Here, we report that males lacking functional SP elicit only a weak short-term response. However, these males do transfer sperm. Thus, (i) SP is the major agent eliciting the short-term and the long-term postmating responses and (ii) sperm is merely the carrier for SP. The second conclusion is supported by the finding that SP binds to sperm. The 36-aa-encoding SP gene is the first small Drosophila gene knocked out with the method of homologous recombination.

Sex-peptides bind to two molecularly different targets in Drosophila melanogaster females

Sex-Peptide (SP) and the peptide DUP99B elicit two postmating responses in Drosophila melanogaster females: receptivity is reduced and oviposition is increased. Both are synthesized in the male genital tract and transferred into the female during copulation. To elucidate their function, we characterized the binding properties of SP and DUP99B in females. Cryostat sections of adult females were incubated with alkaline phosphatase (AP)-tagged peptides. In virgin females, both peptides have specific target sites in the nervous system and in the genital tract. The binding pattern is almost identical for both peptides. Incubation of sections of mated females confirm that some of these target sites correspond to the in vivo targets of the two peptides. Neuronal binding is dependent on an intact C-terminal sequence of SP, binding in the genital tract is less demanding in terms of amino acid sequence requirement. On affinity blots the AP-SP probe binds to membrane proteins extracted from abdomen and head plus thorax, respectively. The binding proteins in the nervous system and the genital tract differ in their molecular properties. Calculation of dissociation constants (K(d)), and also determination of the minimal peptide concentrations necessary for binding, indicate that SP is the more important peptide inducing the postmating responses. Our results suggest that binding of SP in the nervous system is responsible for eliciting the postmating responses, whereas binding in the genital tract reflects the presence of a peptide transporter.

Inhibition of pheromone biosynthesis in Helicoverpa armigera by pheromonostatic peptides

Male insect accessory glands contain factors that are transferred during mating to the female, some inducing post-mating behavior, including the cessation of pheromone production, non-receptivity and the initiation of oviposition. One such factor is the Drosophila melanogaster sex-peptide (DrmSP). A pheromone suppression peptide, termed HezPSP, was identified in the moth Helicoverpa zea, isolated by HPLC and the active peak sequenced, but the activity of the synthesized peptide has not been reported to date. HezPSP bears no sequence homology to DrmSP. However, both peptides contain a disulfide bridge separated by an equal number, but dissimilar, amino acids. We herein report on the pheromonostatic activity of HezPSP partial peptides in the moth Helicoverpa armigera.

Mushroom bodies and post-mating behaviors of Drosophila melanogaster females

After mating, Drosophila melanogaster females lay substantially more eggs and mate rarely. Central to these changes is Sex peptide (SP), a male peptide transferred into the female during copulation. Injected into virgins, SP induces the same post mating response as observed after mating. In this study we investigated the role of the mushroom body (MB) in the SP response system. The SP response of females with either chemically ablated or mutant MBs was analyzed. After injection of SP, females with chemically ablated MBs reduce their receptivity and increase their ovulation and oviposition to the level of females with intact MBs. Virgin females with ablated MBs, however, show a constitutively elevated oviposition rate. Hence in untreated females, MBs are not implicated in the SP-induced reduction of receptivity and increase of ovulation. However, they depress the oviposition rate of virgins. Thus, SP has two functions for oviposition: it de-represses the MB-dependent block on the egg laying activity of virgins and additionally stimulates oviposition. SP-injected mushroom body miniature (mbm) females lay fewer eggs, ovulate less frequently, and mate more often than wild-type females. A model of the putative role of MBs and the gene product of mbm in SP-induced oviposition is presented.

Ductus ejaculatorius peptide 99B (DUP99B), a novel Drosophila melanogaster sex-peptide pheromone

We have characterized a glycosylated, 31 amino-acid peptide of 4932 Da isolated from Drosophila melanogaster males. The mature peptide contains a sugar moiety of 1184 Da at a NDT consensus glycosylation site and a disulfide bond. It is synthesized in the male ejaculatory duct via a 54 amino-acid precursor containing an N-terminal signal peptide and Arg-Lys at the C-terminus which is cleaved off during maturation. The gene contains an intron of 53 bp and is localized in the cytological region 99B of the D. melanogaster genome. The peptide is therefore named DUP99B (for ductus ejaculatorius peptide, cytological localization 99B). The C-terminal parts of mature DUP99B and D. melanogaster sex-peptide (ACP70A) are highly homologous. Injected into virgin females, DUP99B elicits the same postmating responses as sex-peptide (increased oviposition, reduced receptivity). These effects are also induced by de-glycosylated native peptide or synthetic DUP99B lacking the sugar moiety. Presence of the glycosyl group, however, decreases the amount needed to elicit the postmating responses. Homologies in the coding regions of the two exons of DUP99B and sex-peptide, respectively, suggest that the two genes have evolved by gene duplication. Thus, we consider these two genes to be members of the new sex-peptide gene family.

Common functional elements of Drosophila melanogaster seminal peptides involved in reproduction of Drosophila melanogaster and Helicoverpa armigera females

Sex peptide (SP) and Ductus ejaculatorius peptide (Dup) 99B are synthesized in the retrogonadal complex of adult male Drosophila melanogaster, and are transferred in the male seminal fluid to the female genital tract during mating. They have been sequenced and shown to exhibit a high degree of homology in the C-terminal region. Both affect subsequent mating and oviposition by female D. melanogaster. SP also increases in vitro juvenile hormone (JH) biosynthesis in excised corpora allata (CA) of D. melanogaster and Helicoverpa armigera. We herein report that the partial C-terminal peptides SP(8-36) and SP(21-36) of D. melanogaster, and the truncated N-terminal SP(6-20) do not stimulate JH biosynthesis in vitro in CA of both species. Both of these C-terminal peptides reduce JH-III biosynthesis significantly. Dup99B, with no appreciable homology to SP in the N-terminal region, similarly lacks an effect on JH production by H. armigera CA. In contrast, the N-terminal peptides - SP(1-11) and SP(1-22) - do significantly activate JH biosynthesis of both species in vitro. We conclude that the first five N-terminal amino acid residues at the least, are essential for allatal stimulation in these disparate insect species. We have previously shown that the full-length SP(1-36) depresses pheromone biosynthesis in H. armigera in vivo and in vitro. We now show that full-length Dup99B and the C-terminal partial sequence SP(8-36) at low concentrations strongly depress (in the range of 90% inhibition) PBAN-stimulated pheromone biosynthesis of H. armigera. In addition, the N-terminal peptide SP(1-22), the shorter N-terminal peptide SP(1-11) and the truncated N-terminal SP(6-20) strongly inhibit pheromone biosynthesis at higher concentrations.

Binding sites of Drosophila melanogaster sex peptide pheromones

Drosophila melanogaster sex peptide (SP) and Ductus ejaculatorius peptide (DUP99B) are male pheromones transferred in the seminal fluid to the female during copulation. Both reduce sexual receptivity and stimulate oviposition in females. The presence of high-affinity SP and DUP99B binding sites in the female were investigated by incubation of cryostat tissue sections with (125)I-iodinated peptides and subsequent autoradiography. We found that in adult females radiolabeled SP and DUP99B bind to peripheral nerves, the subesophageal ganglion, the cervical connective, to discrete parts of the thoracic ganglion, and to the genital tract. Weak and uniform labeling was detected in the neuropil of the brain and the thoracic ganglion. The labeling pattern in the nervous system suggests binding of the peptides to sensory afferents or glial cells. Scatchard analysis of the binding of (125)I-DUP99B to antennal nerves yielded a dissociation constant K(d) of 6.4 nM. Competition experiments with peptide fragments show that the peptides bind with their homologous C-terminal regions. Binding sites in the nervous system of females are established throughout sexual maturation. Prominent binding of the peptides to afferent nerves suggests modification of sensory input.

Control of oocyte maturation in sexually mature Drosophila females

In many sexually mature insects egg production and oviposition are tightly coupled to copulation. Sex-Peptide is a 36-amino-acid peptide synthesized in the accessory glands of Drosophila melanogaster males and transferred to the female during copulation. Sex-Peptide stimulates vitellogenic oocyte progression through a putative control point at about stage 9 of oogenesis. Here we show that application of the juvenile hormone analogue methoprene mimics the Sex-Peptide-mediated stimulation of vitellogenic oocyte progression in sexually mature virgin females. Apoptosis is induced by 20-hydroxyecdysone in nurse cells of stage 9 egg chambers at physiological concentrations (10(-7) M). 20-Hydroxyecdysone thus acts as an antagonist of early vitellogenic oocyte development. Simultaneous application of juvenile hormone analogue, however, protects early vitellogenic oocytes from 20-hydroxyecdysone-induced resorption. These results suggest that the balance of these hormones in the hemolymph regulates whether oocytes will progress through the control point at stage 9 or undergo apoptosis. These data are further supported by a molecular analysis of the regulation of yolk protein synthesis and uptake into the ovary by the two hormones. We conclude that juvenile hormone is a downstream component in the Sex-Peptide response cascade and acts by stimulating vitellogenic oocyte progression and inhibiting apoptosis. Since juvenile hormone analogue does not elicit increased oviposition and reduced receptivity, Sex-Peptide must have an additional, separate effect on these two postmating responses.

Drosophila melanogaster sex peptide stimulates juvenile hormone synthesis and depresses sex pheromone production in Helicoverpa armigera

Previous studies demonstrate that virgin female adult Helicoverpa armigera (Lepidoptera: Noctuidae) moths exhibit calling behaviour and produce sex pheromone in scotophase from the day after emergence, and that mating turns off both of these pre-mating activities. In the fruit fly Drosophila melanogaster, a product of the male accessory glands, termed sex peptide (SP), has been identified as being responsible for suppressing female receptivity after transfer to the female genital tract during mating. Juvenile hormone (JH) production is activated in the D. melanogaster corpus allatum (CA) by SP in vitro. We herein demonstrate cross-reactivity of D. melanogaster SP in the H. armigera moth: JH production in photophase virgin female moth CA in vitro is directly activated in a dose-dependent manner by synthetic D. melanogaster SP, and concurrently inhibits pheromone biosynthesis activating neuropeptide (PBAN)-activated pheromone production by isolated pheromone glands of virgin females. Control peptides (locust adipokinetic hormone, AKH-I, and human corticotropin, ACTH) do not inhibit in vitro pheromone biosynthesis. Moreover, SP injected into virgin H. armigera females, decapitated 24 h after eclosion, or into scotophase virgin females, suppresses pheromone production. In the light of these results, we hypothesize the presumptive existence of a SP-like factor among the peptides transmitted to female H. armigera during copulation, inducing an increased level of JH production and depressing the levels of pheromone produced thereafter.

Mating and sex peptide stimulate the accumulation of yolk in oocytes of Drosophila melanogaster

Mating elicits two reactions in many insect females: egg deposition is increased and receptivity to males is reduced. Central to the control of receptivity and oviposition in Drosophila melanogaster is the sex peptide (SP), a 36-amino-acid peptide sex pheromone synthesized in the male accessory glands and transferred to the female during copulation. To identify regulatory mechanisms involved in the maintenance of the oviposition response, we have compared the effects of mating and SP application with respect to oogenesis. The distribution of the various stages of oogenesis in the ovary, yolk protein (YP) synthesis by the fat body, as well as YP content, uptake and synthesis by the ovary were investigated. Transcripts of the yolk protein genes (yp) were quantified by Northern blotting. Based on our results, we conclude that mating and SP injection into virgin females stimulate yp gene transcription in the fat body only moderately above the background level. However, uptake into the ovary and transcription of the yp genes in the ovary is strongly enhanced after either mating or SP injection. These data are supported by the finding that the abundance of the vitellogenic stage 10 oocytes is also increased. In contrast, early vitellogenic stages 8 and 9 of oogenesis are present in the same numbers in virgin, mated, and SP-injected females, which suggests a control point at about stage 9 determining vitellogenic oocyte progression. The finding that SP can elicit equally all changes observed after copulation suggests that in the sexually mature female it is the major component controlling and stimulating oogenesis after mating.

Sex-peptide activates juvenile hormone biosynthesis in the Drosophila melanogaster corpus allatum

Mating elicits two well-defined reactions in sexually matured females of many insects: reduction of receptivity and increased oviposition. These post-mating responses have been shown to be induced by factors synthesized in the reproductive tract of the adult male and transferred in the seminal fluid to the female during copulation. One of these factors, named sex-peptide (SP), has been identified in Drosophila melanogaster. Using an in vitro radiochemical assay, we show that synthetic sex-peptide considerably activates juvenile hormone III-bisepoxide (JHB3) synthesis in corpus allatum (CA) excised from Days 3 and 4 post-eclosion virgin females. Base levels are significantly lower at emergence (Day 0) than on subsequent days, and only weak stimulation is obtained on Day 1, while none is obtained on Day 2, where maximal basal synthesis occurs. The CA of mated females cannot be stimulated further for at least 7 days, but regain responsiveness by Day 10 after mating. Synthesis of JHB3 stimulated by SP in vitro persists for at least 4 h after removal of the peptide. Development of responsiveness of the CA to SP in vitro is compared with development of the post-mating reactions of sex-peptide injected virgin females. Our results suggest that the CA is a direct target for SP in vivo and that sexual maturity is established separately for the two post-mating reactions.

The sex-peptide

Injection of a peptide of 36 amino acids into virgin Drosophila females changes their reproductive properties drastically: males are rejected and egg laying is increased. The neuronal and physiological properties of the virgin state are replaced by a new pattern of behavior and stimulation of egg production and deposition. Under natural conditions, the peptide is synthesized by the male and transferred into the female during copulation. The sex-peptide, therefore, can be considered as a pheromone. In this review, I shall limit my discussion to Drosophila melanogaster.

Drosophila suzukii contains a peptide homologous to the Drosophila melanogaster sex-peptide and functional in both species

A peptide homologous to the Drosophila melanogaster sex-peptide (SP) was isolated from Drosophila suzukii accessory glands and its amino acid sequence determined. The D. suzukii peptide contains 41 amino acids and has a calculated molecular weight of 5100 Da. Comparison of the sequences reveals strong homologies in the N-terminal and C-terminal parts of the peptides. In the D. suzukii sex-peptide, however, five additional amino acids are inserted after amino acid 7. Based on the sequence of the peptide, a cDNA coding for the D. suzukii peptide was isolated by PCR. Sequence analysis of the cDNA confirmed the SP amino acid sequence determined by peptide sequencing. Furthermore, based on the cDNA sequence, we isolated the D. suzukii sex-peptide gene by inverse PCR. The D. suzukii sex-peptide gene contains an intron and codes for a 60 amino acid precursor. The D. melanogaster and the D. suzuki sex-peptides elicit rejection behaviour in the presence of males and an increased egg laying in virgin females of both species.

Ectopic expression of sex peptide alters reproductive behavior of female D. melanogaster

Sex peptide, a secreted component of the male accessory glands, has been shown to induce behavioral and physiological changes in mated Drosophila. We transformed flies with a hybrid gene containing an hsp70 promoter fused to a cDNA encoding sex peptide. Heat-induced ectopic expression of the peptide in transgenic virgin females altered their reproductive behavior, in the presence of courting males, to that observed in mated females. This demonstrates that the peptide is functional as expected. Time course studies revealed that the behavioral change appeared earlier than the stimulated ovulation. We have also introduced a modified sex peptide gene that is driven by the yp1 enhancer, conferring expression in adult females, and shown that these flies refuse mating constitutively in the presence of courting males and lay unfertilized eggs at the rate of mated females.

The primary structure of six leucine isoacceptor tRNAs of yellow lupin seeds. The structural requirements for amber tRNA suppressor activity

Six tRNA(Leu) isoacceptors from yellow lupin seeds were purified, sequenced, and their readthrough properties over the UAG stop codon were tested using TMV RNA as a messenger. The tested tRNAs(Leu) did not show amber suppressor activity. The partial structure of tRNA(Gln), a minor species in yellow lupin, was also determined. Comparison of the nucleotide sequence of all known isoacceptors of tRNA(Tyr), tRNA(Gln) and tRNA(Leu) from plants, mammals and ciliates enabled us to find general structural requirements for tRNA to be a UAG suppressor. From the partial sequence of lupin tRNA(Gln) we suggest that it will have readthrough properties.

tRNA(Tyr) genes of Drosophila melanogaster: expression of single-copy genes studied by S1 mapping

Six Drosophila melanogaster tRNA(Tyr) genes have been isolated and sequenced. They contained introns of different sequences and two size classes: 20 or 21 base pairs (bp) (five genes) and 113 bp (one gene). However, the sequences coding for the mature tRNA(Tyr) were identical in all six genes. The 113-bp intron-containing gene was a single-copy gene. Hence, its primary transcript could be traced by S1 mapping. The gene was turned on during embryogenesis and continually expressed to various degrees during the following developmental stages. Thus, S1 mapping is a feasible method to follow the transcriptional activity of individual genes with identical mature products, provided that their primary transcripts are unique. The six genes were organized in two clusters of three and two genes, respectively (each containing a 20- or a 21-bp intron; cytological localization, 85A), and a single-copy gene (113-bp intron; cytological localization, 28C). We show that four of the six tRNA(Tyr) genes characterized were localized in putative 5' control regions of developmentally controlled genes transcribed by polymerase II.

Pseudouridine modification in the tRNA(Tyr) anticodon is dependent on the presence, but independent of the size and sequence, of the intron in eucaryotic tRNA(Tyr) genes

In Saccharomyces cerevisiae, pseudouridine formation in the middle position of the tRNA(Tyr) anticodon (psi 35) is dependent on the presence of the intron in the tRNA(Tyr) gene (Johnson and Abelson, Nature 302:681-687, 1983). Drosophila melanogaster tRNA(Tyr) genes contain introns of three size classes: 20 or 21 base pairs (bp) (six genes), 48 bp (one gene), and 113 bp (one gene). As in yeast, removal of the intron led to loss of psi 35 in the anticodon when transcription was assayed in Xenopus laevis oocytes. All Drosophila intron sizes supported psi 35 formation. The same results were obtained with the homologous X. laevis tRNA(Tyr) genes containing introns of 12 or 13 bp or with a deleted intron. The introns of yeast (Nishikura and DeRobertis, J. Mol. Biol. 145:405-420, 1981), D. melanogaster, and X. laevis tRNA(Tyr) wild-type genes, while they all supported psi 35 synthesis, did not share any consensus sequences. As discussed, these results, taken together, suggest that for appropriate function the psi 35 enzyme in the X. laevis oocyte needs the presence of an unqualified intron in the tRNA gene and a tRNA(Tyr)-like structure in the unprocessed tRNA precursor.

Identification of an amber nonsense mutation in the rosy516 gene by germline transformation of an amber suppressor tRNA gene

Seven xanthine dehydrogenase and cross-reacting material negative Drosophila melanogaster rosy stocks were screened for amber and ochre nonsense mutations. Amber and ochre nonsense suppressors were created by site-directed mutagenesis starting from a wild-type tRNA(Tyr) gene. The suppressor tRNA genes were subcloned into a pUChsneo transformation vector providing heat-shock controlled neomycin resistance. The seven rosy stocks were germline transformed with amber and ochre tDNA(Tyr), and the G1 generation was screened for Geneticin resistance. Surviving rosy516 flies transformed with the amber suppressor showed an eye colour intermediate between the original ry516 stock and the wild-type, suggesting that ry516 is an amber nonsense mutant. This was confirmed by sequencing the relevant part of the ry516 gene; the analysis revealed a C-to-T transition in a CAG glutamine codon at nucleotide 1522 of the wild-type rosy gene.

The nucleotide sequence of two homogeneic Drosophila melanogaster tRNATyr isoacceptors: application of a rapid tRNA anticodon sequencing method using S-1 nuclease

The nucleotide sequence of the two major Drosophila melanogaster tRNATyr isoacceptors was determined to be pC-C-U-U-C-G-A-U-A-m2G-C-U-C-A-G-D-D-G-G-acp3 U-A-G-A-G-C-m2(2)G-G-psi-G-G-A-C-U-G/Q-psi-A-m1G-A-Um-C-C-A-U-A-G-m7 G-D-C-G-C-U-G-G-U(T)-psi-C-A-m1A-A-U-C-C-G-G-C-U-C-G-A-A-G-G-A-A-C-C-AOH . The two isoacceptors differ by the presence of a G or a Q in the wobble position. Both contain a partial modification in position 54 (U/T). Thus, these tRNAs are transcribed from a single gene (or many genes with identical sequences). A fast and sensitive postlabeling method for sequencing tRNA anticodons is described. Nuclease S-1-treated tRNA is labeled with 5[32P]-pCp using T-4 RNA ligase. The tRNA fragments are then separated on 7 M urea/20% PAA gels. After autoradiography the RNA is eluted and digested with T-2 RNase. The nature of the labeled nucleotides is determined by two-dimensional thin-layer chromatography. The same method can be used to determine the 5' sequence of a tRNA by 3' labeling 5' tRNA halves with 5[32P]-pCp and subsequent chemical sequencing.

The primary structure of wheat germ tRNAArg--the substrate for arginyl-tRNAArg:protein transferase

Besides its major role in protein synthesis, wheat germ arginyl-tRNAArg can serve as an amino acid donor in an enzymatic reaction to bovine serum albumin catalysed by the enzyme arginyl-tRNAArg: protein transferase. The nucleotide sequence of the tRNAArg involved in this reaction was determined to be: pG-A-C-U-C-C-G-U-m1G-m2G-C-C-C-A-A-D-Gm-G-A-X-A-A-G-G-C-m2(2) G-C-U-G-G-U-Cm-U-I-C-G-m2A-A-A-C-C-A-G-A-G-A-D-U-m5C-U-G-G-G-T-psi -C-G-m1 A-U-C-C-C-C-A-G-C-G-G-A-G-U-C-G-C-C-AOH. We suggest that the decapentanucleotide 5'-G-U-Pu-m2G-C-N-C-A-A-D-Gm-G-A-X-A-3', localized in the D-region, interacts specifically with the protein transferase.

Queuosine modification of the wobble base in tRNAHis influences 'in vivo' decoding properties

The 'in vivo' decoding properties of four tRNAHis isoacceptors, two from Drosophila melanogaster and two from brewer's yeast, were studied after their microinjection, along with turnip yellow mosaic virus (TYMV) coat protein mRNA, into Xenopus laevis oocytes. The two Drosophila isoacceptors are identical besides containing either a guanosine (G) or the hypermodified nucleoside queuosine (Q) in the wobble position. The brewer's yeast isoacceptors differ by four bases in the anticodon stem, and by one base in the amino acceptor stem. Our results show that, under competing 'in vivo' conditions, the Drosophila tRNAHis with the anticodon GUG clearly prefers the histidine codon CAC to the codon CAU, whereas little preference is observed for the tRNAHis with the anticodon QUG for the codon CAU, and no preference for either codon by the two yeast isoacceptors. Hence, it can be concluded that the presence of the Q-base clearly affects the choice of the codon. This is the first demonstration of an 'in vivo' codon preference by tRNA isoacceptors differing in the modification of the wobble base during the elongation step of protein synthesis. These results imply that one function of the Q-base is at the translational level.

The genes coding for 4 snRNAs of Drosophila melanogaster: localization and determination of gene numbers

Four small nuclear RNAs (snRNAs) have been isolated from Drosophila melanogaster flies. They have been characterized by base analysis, fingerprinting, and injection into Axolotl oocytes. The size of the molecules and the modified base composition suggest that the following correlations can be made: snRNA1 approximately U2-snRNA; snRNA2 approximately U3-snRNA; snRNA3 approximately U4-snRNA; snRNA4 approximately U6-snRNA. The snRNAs injected into Axolotl oocytes move into the nuclei, where they are protected from degradation. The genes coding for these snRNAs have been localized by "in situ" hybridization of 125-I-snRNAs to salivary gland chromosomes. Most of the snRNAs hybridize to different regions of the genome: snRNA1 to the cytological regions 39B and 40AB; snRNA2 to 22A, 82E, and 95C; snRNA3 to 14B, 23D, 34A, 35EF, 39B, and 63A; snRNA4 to 96A. The estimated gene numbers (Southern-blot analysis) are: snRNA1:3; snRNA2:7; snRNA3:7; snRNA4:1-3. The gene numbers correspond to the number of sites labeled on the polytene salivary gland chromosomes.

In vitro suppression of a nonsense mutant of Drosophila melanogaster

When RNA isolated from the Drosophila melanogaster alcohol dehydrogenase (ADH) negative mutant CyOnB was translated "in vitro" in the presence of yeast opal suppressor tRNA, a wild type size ADH protein was obtained in addition to the mutant gene product. This identifies the CyOnB mutant as an opal (UGA) nonsense mutant. From the molecular weight of the mutant protein, and from the known sequence of the ADH gene (Benyajati et al., Proc.Natl.Acad.Sci. USA 78, 2717-2721, 1981), we conclude that the tryptophan codon UGG in position 234 has been changed into a UGA nonsense codon in the CyOnB mutant. Furthermore, we show that the UAA stop codon of the wild type ADH gene is resistant to suppression by a yeast ochre suppressor tRNA. This is in contrast to the high efficiency of suppression of the CyOnB UGA nonsense codon, despite an almost identical codon context.

The initiator tRNA genes of Drosophila melanogaster: evidence for a tRNA pseudogene

We have isolated four segments of Drosophila melanogaster DNA that hybridize to homologous initiator tRNAMet. Three of the cloned fragments contain initiator tRNA genes, each of which can be transcribed in vitro. The fourth clone, pPW568, contains an initiator tRNA pseudogene which is not transcribed in vitro by RNA polymerase III. The pseudogene is contained in a 1.15 kb DNA fragment. This fragment has the characteristics of dispersed repetitive DNA and hybridizes in situ to at least 30 sites in the Drosophila genome. The arrangement of the initiator tRNA genes we have isolated, is different to that of other Drosophila tRNA gene families. The initiator tRNA genes are not clustered nor intermingled with other tRNA genes. They occur as single copies within an approximately 415-bp repeat segment, which is separated from other initiator tRNA genes by a mean distance of 17 kb. In situ hybridization to polytene chromosomes localizes these genes to the 61D region of the Drosophila genome. Hybridization analysis of genomic DNA indicates the presence of 8-9 non-allelic initiator tRNA genes in Drosophila melanogaster.

Rapid and high resolution detection of in situ hybridisation to polytene chromosomes using fluorochrome-labeled RNA

Fluorochrome-labeled RNA allows the rapid detection of in situ hybrids without the need for long exposure times as in the autoradiographical hybridisation methods. Resolution is high because of the high resolving power of fluorescence microscopy. The application of a previously reported method for the hybrido-cytochemical detection of DNA sequences to polytene chromosomes of Drosophilia is described. The specificity and sensitivity of the method are demonstrated by the hybridisation with polytene chromosomes of 1) rhodamine-labeled 5S RNA, to the 5S rRNA sites of D. melanogaster (56F) and D. hydei (23B), 2) rhodamine-labeled RNA complementary to a plasmid containing histone genes, to the 39DE region of D. melanogaster, 3) rhodamine-labeled D. melanogaster tRNA species (Gly-3 and Arg-2), to their respective loci in D. melanogaster, 4) rhodamine-labeled RNA complementary to the insert of plasmid 232.1 containing part of a D. melanogaster heat shock gene from locus 87C, to D. hydei heat shock locus 2-32A. In the latter instance it was possible to demonstrate the labeling of a double band which escaped unambiguous detection by autoradiography in the radioactive cytochemical hybridisation procedure because of the low topological resolution of autoradiograms. The sensitivity of the fluorochrome-labeled RNA method is compared with the radioactive methods which use 3H- or 125 I-labeled RNAs. The factors governing the sensitivity and the number of bound fluorochrome molecules to be expected are discussed.

The genes coding for tRNA Tyr of Drosophila melanogaster: localization of determination of the gene numbers

Transfer RNA(Tyr) (anticodon G psi A) was isolated from Drosophila melanogaster by means of Sepharose 4B, RPC-5, and polyacrylamide gel electrophoresis. The rRNA was iodinated in vitro with Na125 I and hybridized in situ to salivary gland chromosomes from Drosophila. The genes of rRNA(Tyr) were localized in eight regions of the genome by autoradiography. Restriction enzyme analysis of genomic DNA indicated that the haploid Drosophila genome codes for about 23 tRNA(Tyr) genes. The regions 22F and 85A each contain four to five tRNA(Tyr) genes, whereas the regions 28C, 41AB, 42A, 42E, and 56D each contain two to three tRNA(Tyr) genes.

Usage of the three termination codons in a single eukaryotic cell, the Xenopus laevis oocyte

Oocytes from Xenopus laevis were injected with purified amber (UAG), ochre (UAA), and opal (UGA) suppressor tRNAs from yeasts. The radioactively labeled proteins translated from the endogenous mRNAs were then separated on two-dimensional gels. All three termination codons are used in a single cell, the Xenopus laevis oocyte. But a surprisingly low number of readthrough polypeptides were observed from the 600 mRNAs studied in comparison to uninjected oocytes. The experimental data are compared with the conclusions obtained from the compilation of all available termination sequences on eukaryotic and prokaryotic mRNAs. This comparison indicates that the apparent resistance of natural termination codons against readthrough, as observed by the microinjection experiments, cannot be explained by tandem or very close second stop codons. Instead it suggests that specific context sequences around the termination codons may play a role in the efficiency of translation termination.

The structure and function of tRNA genes of higher eukaryotes

The most recent findings concerning the structure and function of tRNA genes of higher eukaryotes are discussed in an exemplary way. The tRNA genes of higher organisms are either dispersed or clustered at different sites of the genome. Clusters contain tRNA genes oriented in both directions and on both strands of the DNA with spacers of various length inbetween. Some genes contain intervening sequences close to the 3' side of the anticodon. The primary transcription product possesses a 5' leader and a 3' trailer sequence which are removed by several maturation steps in a strict temporal and spacial order. Internal transcription control regions (promotors) are located at the 5' and 3' ends of the mature tRNA coding section of the tRNA gene. External sequences modulating the efficiency of the expression are present at the immediate 5' ends of the genes. Transfer RNA genes are located nonrandomly in the nucleosomes.

Nonsense suppression in eukaryotes: the use of the Xenopus oocyte as an in vivo assay system

Amber, ochre, and opal nonsense suppressor tRNAs isolated from yeast were injected into Xenopus laevis oocytes together with purified mRNAs (globin mRNA from rabbit, tobacco mosaic virus-RNA). Yeast opal suppressor tRNA is able to read the UGA stop codon of the rabbit beta-globin mRNA, thus producing a readthrough protein. A large readthrough product is also obtained upon coinjection of yeast amber or ochre suppressor tRNA with TMV-RNA. The amount of readthrough product is dependent on the amount of injected suppressor tRNA. The suppression of the terminator codon of TMV-RNA is not susceptible to Mg++ concentration or polyamine addition. Therefore, the Xenopus laevis oocyte provides a simple, sensitive, and well buffered in vivo screening system for all three types of eukaryotic nonsense suppressor tRNAs.