Studies of esterase 6 in Drosophila melanogaster. III. The developmental pattern and tissue distribution

Research gaps and new insights in the evolution of Drosophila seminal fluid proteins

While the striking effects of seminal fluid proteins (SFPs) on females are fairly conserved among Diptera, most SFPs lack detectable homologues among the SFP repertoires of phylogenetically distant species. How such a rapidly changing proteome conserves functions across taxa is a fascinating question. However, this and other pivotal aspects of SFPs' evolution remain elusive because discoveries on these proteins have been mainly restricted to the model Drosophila melanogaster. Here, we provide an overview of the current knowledge on the inter-specific divergence of the SFP repertoire in Drosophila and compile the increasing amount of relevant genomic information from multiple species. Capitalizing on the accumulated knowledge in D. melanogaster, we present novel sets of high-confidence SFP candidates and transcription factors presumptively involved in regulating the expression of SFPs. We also address open questions by performing comparative genomic analyses that failed to support the existence of many conserved SFPs shared by most dipterans and indicated that gene co-option is the most frequent mechanism accounting for the origin of Drosophila SFP-coding genes. We hope our update establishes a starting point to integrate further data and thus widen the understanding of the intricate evolution of these proteins.

Quantitative Proteomics Identification of Seminal Fluid Proteins in Male Drosophila melanogaster

Seminal fluid contains some of the fastest evolving proteins currently known. These seminal fluid proteins (Sfps) play crucial roles in reproduction, such as supporting sperm function, and particularly in insects, modifying female physiology and behavior. Identification of Sfps in small animals is challenging, and often relies on samples taken from the female reproductive tract after mating. A key pitfall of this method is that it might miss Sfps that are of low abundance because of dilution in the female-derived sample or rapid processing in females. Here we present a new and complementary method, which provides added sensitivity to Sfp identification. We applied label-free quantitative proteomics to Drosophila melanogaster, male reproductive tissue - where Sfps are unprocessed, and highly abundant - and quantified Sfps before and immediately after mating, to infer those transferred during copulation. We also analyzed female reproductive tracts immediately before and after copulation to confirm the presence and abundance of known and candidate Sfps, where possible. Results were cross-referenced with transcriptomic and sequence databases to improve confidence in Sfp detection. Our data were consistent with 125 previously reported Sfps. We found nine high-confidence novel candidate Sfps, which were both depleted in mated versus, unmated males and identified within the reproductive tract of mated but not virgin females. We also identified 42 more candidates that are likely Sfps based on their abundance, known expression and predicted characteristics, and revealed that four proteins previously identified as Sfps are at best minor contributors to the ejaculate. The estimated copy numbers for our candidate Sfps were lower than for previously identified Sfps, supporting the idea that our technique provides a deeper analysis of the Sfp proteome than previous studies. Our results demonstrate a novel, high-sensitivity approach to the analysis of seminal fluid proteomes, whose application will further our understanding of reproductive biology.

INHIBITION OF FEMALE DROSOPHILA MELANOGASTER REMATING BY A SEMINAL FLUID PROTEIN (ESTERASE 6)

Recent experiments have indicated that EST 6 transferred to D. melanogaster females during copulation mediates a large decrease in their attractiveness within the first six hours after mating. This decrease in attractiveness could increase the male's fitness if it were associated with less frequent remating by their mates, because a large proportion of the first male's sperm is lost if a female remates within one day. Here, I confirm a strong EST 6 influence on the receptivity of mated females; females with EST 6⁺ first mates remate significantly less frequently between 6 and 18 hours after mating than females that have not received EST 6 in the ejaculate. However, the previously observed effect of EST 6 on the attractiveness of mated females could not be substantiated. Transfer of EST 6 did not lead to a significant difference in attractiveness between EST 6°-and EST 6⁺ -mated females at any time within the first 10 hours after mating for females from either of two strains.

A carboxylesterase, Esterase-6, modulates sensory physiological and behavioral response dynamics to pheromone in Drosophila

Background

Insects respond to the spatial and temporal dynamics of a pheromone plume, which implies not only a strong response to 'odor on', but also to 'odor off'. This requires mechanisms geared toward a fast signal termination. Several mechanisms may contribute to signal termination, among which odorant-degrading enzymes. These enzymes putatively play a role in signal dynamics by a rapid inactivation of odorants in the vicinity of the sensory receptors, although direct in vivo experimental evidences are lacking. Here we verified the role of an extracellular carboxylesterase, esterase-6 (Est-6), in the sensory physiological and behavioral dynamics of Drosophila melanogaster response to its pheromone, cis-vaccenyl acetate (cVA). Est-6 was previously linked to post-mating effects in the reproductive system of females. As Est-6 is also known to hydrolyze cVA in vitro and is expressed in the main olfactory organ, the antenna, we tested here its role in olfaction as a putative odorant-degrading enzyme.

Results

We first confirm that Est-6 is highly expressed in olfactory sensilla, including cVA-sensitive sensilla, and we show that expression is likely associated with non-neuronal cells. Our electrophysiological approaches show that the dynamics of olfactory receptor neuron (ORN) responses is strongly influenced by Est-6, as in Est-6° null mutants (lacking the Est-6 gene) cVA-sensitive ORN showed increased firing rate and prolonged activity in response to cVA. Est-6° mutant males had a lower threshold of behavioral response to cVA, as revealed by the analysis of two cVA-induced behaviors. In particular, mutant males exhibited a strong decrease of male-male courtship, in association with a delay in courtship initiation.

Conclusions

Our study presents evidence that Est-6 plays a role in the physiological and behavioral dynamics of sex pheromone response in Drosophila males and supports a role of Est-6 as an odorant-degrading enzyme (ODE) in male antennae. Our results also expand the role of Est-6 in Drosophila biology, from reproduction to olfaction, and highlight the role of ODEs in insect olfaction.

Male Esterase 6 Catalyzes the Synthesis of a Sex Pheromone in Drosophila melanogaster Females

Esterase 6, a component of the seminal fluid of Drosophila melanogaster males, hydrolyzes cis-vaccenyl acetate, a lipid made only by males, to cis-vaccenyl alcohol. This reaction occurs in the female reproductive tract and is virtually complete within 6 hours after copulation. Both the alcohol and the acetate decrease the number of matings among pairs of virgin flies in which the female is treated topically with these substances. Although females tested 10 minutes after copulation elicit less courtship than virgin females, females tested 6 hours after copulation stimulate even less courtship if they received active esterase 6 in the seminal fluid of their respective mates. Either the alcohol or a derivative appears to be an antiaphrodisiac that decreases courtship elicited by inseminated females and thus reduces the probability of further mating. Thus the activity of the pheromone depends on a final reaction which occurs in the female, using both substrate and enzyme provided by the male.

Studies of esterase 6 inDrosophila melanogaster: XI. Modification of esterase 6 activity by unlinked genes

The often remarkable similarity in structural gene products among related species has led to the hypothesis that species differences may reside largely in changes at regulatory gene loci. This hypothesis assumes that groups capable of speciating have allelic variation at regulatory loci in their natural populations. We have undertaken an analysis of the mode of regulation of theesterase 6(Est 6) locus inDrosophila melanogasterto determine the nature and extent of regulatory gene variation in natural populations. Analyses of esterase 6 (EST 6) activity among strains carrying the same thermostability variants reveal that significant, specific-activity differences are present. Reciprocal crosses between lines having high and low EST 6 activity show that loci other than theEst 6structural gene influence EST 6 activity. Analyses of male hybrids from crosses betweenD. melanogasterandsimulansindicate that theXchromosome of these flies affects the expression of theEst 6locus, resulting in unequal levels of enzyme activity from the two alleles. The effect is sex and tissue specific. Female hybrids carrying theXchromosomes of both species exhibit equal expression of the twoEst 6alleles. We have determined whether natural populations are polymorphic forXchromosomes which affect EST 6 activity by extracting singleXchromosomes from wild-collected males and placing these chromosomes in identical genetic backgrounds. Stocks which are otherwise genetically identical but carry independently derivedXchromosomes show significant differences in the activity of EST 6. These data suggest that regulatory loci may be commonly polymorphic in natural populations.

Latitudinal clines for nucleotide polymorphisms in the Esterase 6 gene of Drosophila melanogaster

Previous studies have found non-neutral patterns of nucleotide polymorphism in the promoter and coding regions of Est6 in D. melanogaster. Coding region polymorphism peaks around two closely linked replacement differences associated with the EST6-F/EST6-S allozyme polymorphism. The promoter contains two common, highly diverged haplotype groups, P1 and P7, that differentially affect Est6 expression. Allozyme studies have also revealed latitudinal clines in EST6-F and EST6-S frequencies that recur across continents. Here we analyse nucleotide polymorphisms across the promoter and the region of peak coding sequence polymorphism in 10 Australian populations along a 25 degrees latitudinal gradient in order to examine the basis for the allozyme clines. As with the earlier studies, we find an excess of intermediate to high frequency variants in both the P1/P7 region and around the two EST6-F/EST6-S replacements in some populations. The two EST6-F/EST6-S replacement polymorphisms show latitudinal clines whereas the P1 and P7 groups of promoter haplotypes do not. However the strongest clines are for three co-segregating silent site polymorphisms in a 4 bp stretch at the 3' end of the sequenced region. Monte Carlo simulations show that the clines for those three sites can explain all others in the data but none of the others can explain those three. Thus the allozyme clines may not reflect selection on either the P1/P7 polymorphism or the two replacements previously associated with the EST6-F/EST-S difference.

Further study on the esterase patterns of sibling species in the Drosophila saltans subgroup (saltans group): intraspecific and interspecific variations in the development

Twenty of the 32 esterase bands previously detected in the adults of D. prosaltans, D. saltans and D. austrosaltans were found in larvae and pupae studied in this work. The results showed that, in addition to expressing the highest number of esterase bands, the adult stage of the three species exhibited the highest degree of expression (amount of synthesis) for most of the bands. Differences between larval and pupal stages were detected in the degree of expression (amount of synthesis) of the bands and in the frequency of samples expressing them. The frequencies of expression of the bands corresponding to genes in loci 1-3 were greater in pupae than in larvae while the frequencies of expression of the bands corresponding to genes in loci 4-9 were predominantly expressed in larvae or were equal in both developmental stages. Like the adults, larvae, pupae and empty pupal cases (which were also studied in this work) showed specific esterases. Taken together, the observations showed that, in the species studied, every developmental stage is characterized by specific bands and by specific frequency and degree of expression of the bands shared with other stages.

Characterization of Esterases in a Brazilian Population of Zaprionus Indianus (Diptera: Drosophilidae)

The aim of this study was to characterize esterases in Zaprionus indianus, a drosophilid recently introduced into Brazil. A further aim was study the variation of activity of esterases in the presence of inhibitors and their expression according to sex, sexual activity and age of individual flies. Polymorphisms were detected in two esterase loci (Est-2 and Est-3) and monomorphisms in four others (Est-1, Est-4, Est-5 and Est-6). Biochemical tests using alpha- and beta-naphthyl acetate and the inhibitors malathion, eserine sulphate and PMSF allowed us to classify EST-2 and EST-5 as beta-esterases, both carboxyl-esterases, and EST-1, EST-3, EST-4 and EST-6 as alpha-esterases. EST-1 and EST-3 were classified as carboxyl-esterases and EST-4 and EST-6 as cholinesterases. EST-5 activity was more pronounced in males and EST-2 was restricted to them or to recently copulated females. EST-4, rarely detected, was not characterized. Based on their biochemical characteristics possible roles for these enzymes are suggested.

Functions and analysis of the seminal fluid proteins of male Drosophila melanogaster fruit flies

The study of insect seminal fluid proteins provides a unique window upon adaptive evolution in action. The seminal fluid of Drosophila melanogaster contains over 80 proteins and peptides, which are transferred together with sperm by mating males. The functions of many of these substances are not yet known. However, those that have been characterized have marked effects on the reproductive success of males and females. For example, seminal fluid proteins and peptides can decrease female receptivity, can increase egg production and can increase sperm storage, and are necessary for sperm transfer and success in sperm competition. In this review we focus on the currently known functions of seminal fluid molecules and on new technologies and approaches that are enabling novel questions about their form and function to be addressed. We discuss how techniques for disrupting the production of seminal fluid proteins, such as homologous recombination and RNA interference, along with the use of microarrays and yeast two hybrid systems, should allow us to address ever more sophisticated questions about seminal fluid protein function. These and similar techniques promise to reveal the function of naturally-occurring variants of these proteins and hence the evolutionary significance of genetic variation for them.

The developments between gametogenesis and fertilization: ovulation and female sperm storage in Drosophila melanogaster

In animals with internal fertilization, ovulation and female sperm storage are essential steps in reproduction. While these events are often required for successful fertilization, they remain poorly understood at the developmental and molecular levels in many species. Ovulation involves the regulated release of oocytes from the ovary. Female sperm storage consists of the movement of sperm into, maintenance within, and release from specific regions of the female reproductive tract. Both ovulation and sperm storage elicit important changes in gametes: in oocytes, ovulation can trigger changes in the egg envelopes and the resumption of meiosis; for sperm, storage is a step in their transition from being "movers" to "fertilizers." Ovulation and sperm storage both consist of timed and directed cell movements within a morphologically and chemically complex environment (the female reproductive tract), culminating with gamete fusion. We review the processes of ovulation and sperm storage for Drosophila melanogaster, whose requirements for gamete maturation and sperm storage as well as powerful molecular genetics make it an excellent model organism for study of these processes. Within the female D. melanogaster, both processes are triggered by male factors during and after mating, including sperm and seminal fluid proteins. Therefore, an interplay of male and female factors coordinates the gametes for fertilization.

Nucleotide polymorphism in the Est6 promoter, which is widespread in derived populations of Drosophila melanogaster, changes the level of Esterase 6 expressed in the male ejaculatory duct

Previous analysis of an Australian population of D. melanogaster revealed two predominant Est6 promoter haplotypes, P1 and P7. These haplotypes, which differ at 14 sites over a 325-bp region, are associated with a 15-20% difference in male EST6 activity. Here we show that the P1/P7 sequence difference causes the male activity variation by recreating the activity difference among >60 independently transformed lines containing representative P1 or P7 promoter alleles fused to an identical Est6 coding region. Furthermore we find that the whole fly difference reflects about a twofold difference in EST6 activity in the anterior sperm ejaculatory duct. EST6 activity variation in this tissue is known to affect reproductive fitness. Using a combination of RFLP analysis and DNA sequencing, we show that P1 and P7 are predominant in six populations from America, Asia, and Australia, albeit less frequent in a population from the presumptively ancestral east African range of the species. The sequence data show significant departures from neutral expectations for the derived American and Australian populations but not the presumptively ancestral Zimbabwean population. Thus the P1/P7 difference could be a major source of adaptively significant EST6 activity variation through much of the now cosmopolitan range of D. melanogaster.

Identification and characterization of the major Drosophila melanogaster mating plug protein

In many insects, semen coagulates into a mating plug at the distal part of the female's genital tract. Mating plugs have been proposed to facilitate sperm movement or to prevent subsequent matings or sperm loss. The molecular constituents of insect mating plugs have not previously been characterized. Here we report that an abundant autofluorescent protein made by the Drosophila melanogaster male's ejaculatory bulb is a major constituent of the posterior region of the mating plug. Identities in size, chromosomal location and expression pattern indicate that the autofluorescent protein is PEB-me, an abundant ejaculatory bulb protein reported by Ludwig et al. [Biochem. Genet. 29 (1991) 215]. We cloned and sequenced the RNA encoding this protein. The transcript, which is male-specific and expressed only in the ejaculatory bulb, encodes a 377 a.a. predicted secreted protein with PGG repeats similar to those in homopolymer-forming proteins found in spider silk.

Genetic dissection of sexual behavior in Drosophila melanogaster

Mating of Drosophila melanogaster is a sterotypically patterned behavior consisting of a fixed sequence of actions that are primarily under genetic control. Mutations that disrupt specific aspects of mating activities offer a starting point for exploring the molecular machineries underlying sexual behavior. Several genes, identified as causing aberrant sexual behavior when mutated, have been isolated and cloned, providing molecular probes for expression and mosaic analyses that can be used in specifying the cells responsible for the behavior. This review presents current understandings of mating behavior obtained by such molecular and cellular approaches and provides an overview of future directions of research in behavioral genetics.

Mutational analysis of N-linked glycosylation of esterase 6 in Drosophila melanogaster

The primary sequence of the esterase 6 (EST6) enzyme of Drosophila melanogaster contains four potential N-linked glycosylation sites, at residues 21, 399, 435, and 485. Here we determine the extent to which EST6 is glycosylated and how the glycosylation affects the biochemistry and physiology of the enzyme. We have abolished each of the four potential glycosylation sites by replacing the required Asn residues with Gln by in vitro mutagenesis. Five mutant genes were made, four containing mutations of each site individually and the fifth site containing all four mutations. Germline transformation was used to introduce the mutant genes into a strain of D. melanogaster null for EST6. Electrophoretic and Western blot comparisons of the mutant strains and wild-type controls showed that each of the four potential N-linked glycosylation sites in the wild-type protein is glycosylated. However, the fourth site is not utilized on all EST6 molecules, resulting in two molecular forms of the enzyme. Digestion with specific endoglycosidases showed that the glycan attached at the second site is of the high-mannose type, while the other three sites carry more complex oligosaccharides. The thermostability of the enzyme is not affected by abolition of the first, third, or fourth glycosylation sites but is reduced by abolition of the second site. Anomalously, abolition of all four sites together does not reduce thermostability. Quantitative comparisons of EST6 activities showed that abolition of glycosylation does not affect the secretion of the enzyme into the male sperm ejaculatory duct, its transfer to the female vagina during mating, or its subsequent translocation into her hemolymph. However, the activity of the mutant enzymes does not persist in the female's hemolymph for as long as wild-type esterase 6. The latter effect may compromise the role of the transferred enzyme in stimulating egg-laying and delaying receptivity to remating.

Biochemical analysis of proteins recognized by anti-HRP antibodies in Drosophila melanogaster: identification and characterization of neuron specific and male specific glycoproteins

Antibodies recognizing horse radish peroxidase (HRP) stain neurons in Drosophila and other insects. We have used Western blots to analyze and characterize some of the anti-HRP reactive components from Drosophila melanogaster. Anti-HRP reactive components can be reproducibly detected during all developmental stages, although the pattern changes at different developmental times. In adults, there are at least 10 reproducibly stained components. Two of the bands, with molecular sizes of 42 and 80 kDa are likely to be the major contributors to neuronal anti-HRP staining in Drosophila. These components are enriched in adult fly heads. In contrast, many of the other anti-HRP reactive components in adults are enriched in abdomen and are present exclusively or at much higher levels in male flies. We have purified and characterized two of the male specific components with molecular sizes of 62 and 48 kDa. Partial N-terminal amino acid sequencing revealed that the 62 kDa protein is identical to a part of D. melanogaster carboxylesterase to EC 3.1.1.1) while he 48 kDa protein does not match any known sequences. Esterase-6 has previously been shown to be enriched in male accessory gland and consistent with this we show staining of this structure with anti-HRP antibodies.

Associations of esterase 6 allozyme and activity variation with reproductive fitness in Drosophila melanogaster

Previous studies have shown that the esterase 6 (EST6) enzyme of D. melanogaster is mainly produced in the sperm ejaculatory duct of the adult male and comparisons of wild-type males with laboratory null mutants have suggested that the enzyme plays a role in reproductive fitness. In this study we have compared 18 field-derived lines each isoallelic for Est6 for differences in five components of male reproductive fitness. No consistent fitness differences were found among lines differing in respect of the two major allozyme classes EST6-F and EST6-S, despite other evidence that these two classes are not selectively equivalent in the field. However, differences in reproductive fitness were found among lines differing in the minor mobility variants that segregate within EST6-F and EST6-S. A failure to distinguish among these minor forms may explain the discrepancies in previous studies on the effects of the major EST6 allozymes on reproductive fitness. The most significant associations we have found between EST6 and reproductive fitness were due to variation in EST6 activity levels. Male EST6 activity levels were found to be positively correlated with their time to first mating, negatively correlated with the numbers of eggs laid and progeny produced by their mates, and negatively correlated with the frequency with which their mates remate. We conclude that some EST6 variants differ in components of male reproductive fitness operative in laboratory cultures. However, the evidence for fitness differences is stronger for variants affecting the amount, rather than the structure of the enzyme, and the direction of the differences varies between some of the fitness components tested.

Regulatory aspects of esterase 6 activity variation in sibling Drosophila species

Esterase 6 in Drosophila melanogaster, Drosophila simulans and Drosophila mauritiana is produced in several life stages and diverse tissues, but the major pulse of expression is in the sperm ejaculatory duct of adult males. Comparison of EST6 activity levels among several lines of D. melanogaster, D. simulans and D. mauritiana reveals two major quantitative differences among the species. First, newly eclosed females of both D. simulans and D. mauritiana show significantly higher EST6 activity than those of D. melanogaster. Secondly, 5-day-old adult D. simulans have significantly higher activities than D. mauritiana in both sexes and significantly higher activity than D. melanogaster in males. The genetic bases of the differences between D. melanogaster and the other species are investigated through germ line transfer of the D. simulans and D. mauritiana Est-6 genes plus 1.2 kb of 5' and 0.2 kb of their 3' flanking sequences into D. melanogaster. The newly eclosed female activities of the transformants resemble those of the two donor species, suggesting that the interspecific differences in this aspect of expression are due to cis-inherited factors contained within the transferred DNA. In contrast, the 5-day adult activity of the D. simulans transgene resembles the recipient species, D. melanogaster, suggesting that the difference between D. simulans and D. melanogaster in this aspect of expression is due to trans-acting factors. We also find that third instar larval activities of the D. simulans transgene and 5-day male activities of the D. mauritiana transgene are lower than those of either parental species, suggesting that not all the promoter elements relevant to these aspects of expression are included in the transferred DNA.

Biochemical and physiological studies of soluble esterases from Drosophila melanogaster

Twenty-two soluble esterases have been identified in D. melanogaster by combining the techniques of native polyacrylamide gel electrophoresis and isoelectric focusing. The sensitivity of each isozyme to three types of inhibitors (organophosphates, eserine sulfate, and sulfydryl reagents) identified 10 as carboxylesterases, 6 as cholinesterases, and 3 as acetylesterases. Three isozymes could not be classified and no arylesterases were identified. The carboxyl- and cholinesterases could each be further divided into two subclasses on the basis of inhibition by organophosphates and sulfhydryl reagents, respectively. Choline- and acetylesterases have characteristic substrate preferences but both subclasses of carboxylesterases are heterogeneous in substrate utilization. Subclass 2 carboxylesterases exhibit diverse temporal expression patterns, with subclass 1 carboxylesterases generally found in larvae and subclass 1 cholinesterases and acetylesterases more characteristic of pupae and adults. Tissues showing the greatest number of isozymes are larval body wall (eight) and digestive tract (six in larvae, six in adults). Carboxylesterases are distributed across a wide range of tissues, but subclass 1 cholinesterases are generally associated with neural or neurosecretory tissues and subclass 2 cholinesterases with digestive tissues.

Physical mapping of the Esterase-6 locus of Drosophila melanogaster

The Esterase-6 gene locus of Drosophila melanogaster although well-characterized, has not been definitely mapped by in situ hybridization. In this paper, a high resolution in situ hybridization protocol using an avidin/biotinylated-horseradish peroxidase/diaminobenzidine system was adopted to refine the physical map position of the Esterase-6 locus. Clarity of signal, detail of banding pattern and absence of background allowed the assignment of a 1.8 kb cDNA encoding Esterase-6 to three bands within subsections 69 A1-A3 on the left arm of polytene chromosome 3. These data refine earlier deletion mapping and low resolution in situ hybridization results, which assigned Esterase-6 to 69A1-A5. The potential use of this high resolution in situ hybridization technique in the analysis of the physical organization of the Esterase-6 gene duplication and surrounding region is discussed.

The number and distribution of esterase 6 alleles in populations of Drosophila melanogaster

High resolution electrophoretic analyses of the polymorphic esterase 6 enzyme have been carried out on 133 isoallelic lines from three Australian populations of Drosophila melanogaster spanning 25 degrees of latitude. These and previous data for 157 lines from another Australian population at an intermediate latitude reveal a total of 14 polymorphic esterase 6 allozymes, falling into five major mobility classes. Two classes, EST6-F and EST6-S, contain eleven of the allozymes but one allozyme, EST6-8 within the EST6-S class, is several times more common than any other. Variation in the frequency of this single allozyme can explain most of the latitudinal clines previously reported for the major EST6-F and EST6-S classes. Thermostability analyses of 52 of the Australian lines and 13 American lines reveal at least seven more EST6 variants within five of the allozymes, bringing the total number of variants to at least 21. Of the six allozymes for which more than one line was subjected to thermostability analyses, only EST6-8 could not be partitioned into additional variants. This corroborates a previous finding that two different isolates of the Est6-8 allele have identical DNA sequences and suggests that this allele, although now the most common, has nevertheless arisen relatively recently.

Variation in the amount and activity of esterase 6 in a natural population of Drosophila melanogaster

Forty-two homozygous lines each isoallelic for the Esterase 6 (Est-6) locus were extracted from a natural population of Drosophila melanogaster. Homogenates of 4-5 day old virgin adults of each sex from several replicate cultures of each line were assayed for EST6 activity. Depending on the line, males had from three to nine times more EST6 activity than females. Both sexes showed highly significant differences in EST6 activity among lines, with 3.2 and 2.7 fold differences between highest and lowest lines for males and females respectively. However, the variation in EST6 activity among lines was only weakly correlated across the two sexes. Female EST6 activity did not differ significantly across the six electrophoretic variants of EST6 found among the 42 lines. On the hand, a significant proportion of the variation among lines in male EST6 activity could be explained by differences among the six electromorphs. However, most of these differences were due to the relatively high activities of males from two relatively rare electromorphs and there were no significant differences in male activity among the four more common EST6 electromorphs. Radial immunodiffusion assays with polyclonal anti-EST6 antibody established that differences among lines in male EST6 activity were largely due to differences in the number of EST6 protein molecules, with negligible differences in their specific activities. It is concluded that the natural population segregates for genetic variance with large effects on the amount of EST6 protein; that there is little overlap in the variance expressed in the two sexes; and that most of the variance is different from the polymorphisms for electrophoretically detectable variants of EST6.

The genetics and expression of an esterase locus in Anopheles gambiae

The main polymorphic system of esterase isoenzymes in adults of the G3 laboratory strain of Anopheles gambiae consists of two to five major bands of activity per individual. The bands are designated 5S, 5F, 13, 14, and 15. In genetic crosses, the genes which coded for the bands assorted as three codominant alleles, Est A, Est B, and Est C, at a single autosomal locus. Homozygotes for the Est C allele were significantly underrepresented among backcross progeny. The developmental pattern of esterase expression was examined. Esterase gene expression in embryos was first detectable between 2 and 12 hr after oviposition. The initiation or termination of expression of some of the bands corresponded to boundaries between developmental stages. Most of the esterase fractions were not specifically localized within the tissues tested, with the exception of a series of bands which were restricted largely to adult male testes.

Trehalase from the bean-shaped accessory glands and the spermatophore of the male mealworm beetle, Tenebrio molitor

In Tenebrio molitor, male adults transfer sperm to the female via a spermatophore or sperm sac. The spermatophore is formed from secretions of the bean-shaped accessory glands (BAGs) and the tubular accessory glands (TAGs) of the male beetle. Trehalase is found in the adult BAGs. During the pupal stage, the activity in the BAGs was very low. After adult ecdysis, the total activity increased 100-fold from 0 days to 6 days and reached maximum levels at 9 days. The specific activity increased 20-fold from the time of ecdysis to 6 days thereafter. In the 10 day adult, trehalase levels in testes, seminal vesicles, vas deferens, TAGs, or ejaculatory ducts, were lower by two orders of magnitude than in the BAGs. However, the specific activity in the spermatophore was similar to that in the BAGs. Trehalases in the BAGs and the spermatophores showed very similar properties (soluble, optimum pH of 5.75 and Km value of 5.4 mM for trehalose). Thus trehalase appears to be secreted from the BAGs and becomes incorporated into the spermatophores.

Biochemical properties, homology, and genetic variation of Drosophila "nonspecific" esterases

The biochemical properties and tissue distribution of two major, soluble "nonspecific" esterases have been studied in Drosophila melanogaster, D. pseudoobscura, and related species. The "alpha-like" activity is due to a monomer enzyme (MW congruent to 60 kd) having a nonspecific tissue distribution, which was inhibited by p-hydroxymercuribenzoate (5 X 10(-4)M) plus eserine (1 X 10(-5)M) and was relatively unstable during polyacrylamide gel electrophoresis. Electrophoretograms of this enzyme could be enhanced by treating gels with beta-mercaptoethanol before staining. This procedure allowed the identification of a new alpha-esterase (Est-4) in D. pseudoobscura. The "beta-like" esterase activity (EC 3.1.1.1) is due to a dimer (MW congruent to 120 kd) in most Drosophila species. D. melanogaster and its siblings (D. simulans and D. mauritiana) were exceptions in which this enzyme had an unusual tissue distribution (increased activity in the male reproductive system) and was a monomer (MW congruent to 60 kd). Differences in the genetic variability of these esterases are discussed and interpreted by a population expansion model rather than by differences in biochemical properties of enzyme forms.

Estimating single gene effects on quantitative traits : 2. Statistical properties of five experimental methods

Experimental designs for measuring the effects of single loci on quantitative traits are compared for statistical properties. The designs tested are single population, combined strains, multiple strains, diallel of strains, and co-isogenic strains. Testing was done by simulating population genotypic and phenotypic arrays. Statistical properties measured are type I error, power, bias and efficiency. The relative ranking of designs is consistent for all properties and over eight conditions examined. The co-isogenic design is superior, followed closely by the single population method. The other three designs are similar in ability, with the diallel design somewhat superior. Based on its good statistical performance and wide feasibility, the single population method is recommended. The diallel method provides the most information on genetic components of variation.

Estimating single gene effects on quantitative traits 1. A diallel method applied to Est 6 in D. melanogaster

A modified diallel cross is used to estimate effects of alleles at the esterase 6 locus, relative to strain and environmental variance, in Drosophila melanogaster. Three strains homozygous for Est 6 (s) and three homozygous for Est 6 (F) were crossed in all 36 combinations. Male progeny were scored for mating speed, copula duration and esterase 6 enzyme activity, and all progeny for developmental time. These alleles show a significant additive effect on mating speed, but not on the other traits. Copula duration, developmental time and enzyme activity show additive strain genetic variance. Enzyme activity and developmental time also have maternal or X-chromosome strain variance, and these two traits are significantly correlated. This modified diallel method is generally useful because it permits the partition of trait variance into additive and dominant locus, background genetic and environmental components.

Studies of esterase 6 in Drosophila melanogaster. XIV. Variation of esterase 6 levels controlled by unlinked genes in natural populations

The esterase 6 (Est-6) locus inDrosophila melanogasteris located on the third chromosome and is the structural gene for a carboxylesterase (E.C.3.1.1.1) and is polymorphic for two major electromorphs (slow and fast). Isogenic lines containingXchromosomes extracted from natural populations and substituted into a common genetic background were used to detect unlinked factors that affect the activity of theEst-6locus. Twofold activity differences of esterase 6 (EST 6) were found among males from these derived lines, which differ only in theirXchromosome. These unlinked activity modifiers identify possible regulatory elements. Immunoelectrophoresis was used to estimate quantitatively the levels of specific cross-reacting material in the derived lines. The results show that the variation in activity is due to differences in the amount of EST 6 present. The data are consistent with the hypothesis that there is at least one locus on the X chromosome that regulates the synthesis of EST 6 and that this regulatory locus may be polymorphic in natural populations.

Studies of esterase 6 in Drosophila melanogaster. XIII. Purification and characterization of the two major isozymes

Esterase-6 (EST 6; carboxylic-ester hydrolase; EC 3.1.1.1) from Drosophila melanogaster was purified to homogenity. Purified enzyme occurs as two closely moving isozymes, slow (EST 6S) and fast (EST 6F), on native polyacrylamide gel electrophoresis. Except for slight differences in their mobility, the two isozymes share similar molecular and catalytic properties. Both isozymes are glycoproteins and have an apparent molecular weight of 62,000 to 65,000 as judged by analytical gel filtration and sodium dodecyl sulfate (SDS) electrophoresis. They have identical mobility on SDS-polyacrylamide gels and an isoelectric point of 4.5. Each isozyme has a single active catalytic site as confirmed by titration with 0,0-diethyl-p-nitrophenyl phosphate (Paraoxon). We conclude that EST 6 is a monomeric enzyme. The amino acid composition of the two isozymes is very similar and both variants lack half-cystine residues. The low pI of the enzyme is due in part to a relatively high proportion of glutamic and aspartic amino acid residues. Characterization of the kinetic parameters of the isozymes using beta-naphthyl and p-nitrophenyl esters revealed no statistically significant differences in catalytic efficiency. There is, however, a suggestion that the two isozymes may differ in their substrate specificity.

Tissue localization of esterase-5 in Drosophila pseudoobscura

Disc gel electrophoresis of dissected adults of Drosophila pseudoobscura showed that most of the esterase-5 activity was in the head (36%) and thorax (51%), with little activity in the abdomen (13%). No activity was found in digestive tissues, reproductive tissues, or nervous tissues. Most of the est-5 activity (61%) was found to be associated with hemolymph. However, the eyes contained 39% of the total est-5 activity. These results were supported by spectrophotometric assays of esterase activity in crude extracts of eyes and whole flies without eyes which showed that 27% of the total est-5 activity was in the eyes.

Esterase-6 allozymes: biochemical studies of two common and one rare variant in Drosophila melanogaster

The biochemical properties of three allozymes coded by the Est-6 locus, two common forms (EST-6S and EST-6F) and one rare form (EST-6VF), were studied. The results show the existence of differences in isoelectric point, activity, activation energy, Km, and temperature coefficient among the three variants, especially between the two common forms and the one rare form. The specific activity of the rare enzymatic variant seems to be less affected by temperature variation. The possible significance of these findings in relation to the mechanism of reproduction is briefly discussed.

Studies of esterase 6 in Drosophila melanogaster. VII. Remating times of females inseminated by males having active or null alleles

Esterase 6 (EST 6) in Drosophila melanogaster is a male reproductive enzyme transferred to females as a component of the seminal fluid [Richmond, R. C., Gilbert, D. G., Sheehan, K. B., Gromko, M. H., and Butterworth, F. W. (1980). Science 207:1483-1485]. Here we report investigation into the relation between EST 6 and remating by females. EST 6 activity in a strain selected for decreased time to remating is increased over control levels. Inseminated females remated to males carrying null or active alleles show no differences in the timing of remating, However, females inseminated by EST 6-active males remate significantly sooner than females inseminated by null males. Interrupted copulation experiments demonstrate that the remating effect is not due to EST 6 alone but requires other components of the ejaculate. Other evidence suggests that sperm stored in the ventral receptacle respond to EST 6 levels and control remating time. As the first mate of a female who will remate, null-EST 6 males have, under laboratory conditions, a significantly higher fitness than males carrying active alleles. Thus the absence of null alleles of EST 6 in natural populations presents a dilemma suggesting that the remating effect of EST 6 may be balanced by other effects on reproduction.

Genetics of male-specific glucose oxidase and the identification of other unusual hexose enzymes in Drosophila melanogaster

A glucose oxidase (GO) has been identified in the ejaculatory duct of male Drosophila melanogaster. Evidence is given that this enzyme was previously misidentified as HEX-1. Genetic analysis indicates that the Go structural gene is located on the third chromosome at 48 + or - 0.5 cm. Go is polymorphic in males in populations of D. melanogaster and D. simulans located in Athens, Georgia. Two other hexose enzymes have also been tentatively identified for the first time in Drosophila. These are NAD(P)-glucose dehydrogenase (GODH) and NAD-gluconate dehydrogenase (GNDH). GODH and GNDH are found in both males and females and may circumvent the initial steps in the pentose shunt.

Esterase 6 and reproduction in Drosophila melanogaster

A nonspecific carboxylesterase (esterase 6) of Drosophila melanogaster shows greater activity in adult males than in females and is highly concentrated in the anterior ejaculatory duct of the reproductive tract of the male. Esterase 6 is depleted in males by copulation and is transferred to females early during copulation as a component of the seminal fluid. That esterase 6 may be involved in a system controlling the timing of remating is suggested by differences in the activity of this enzyme in a strain of Drosophila selected for a decrease in time to remating and by differences in the timing of remating in females initially inseminated by males lacking or having active esterase 6.