SPECIES-SPECIFIC PATTERNS OF SEXUAL DIMORPHISM IN THE EXPRESSION OF FRUITLESS PROTEIN,A NEURAL MUSCULINIZING FACTOR IN DROSOPHILA

In Drosophila melanogaster, male-specific forms of the fruitless (fru) gene product, mFru protein, function as a neural sex-determination factors that directs the development of at least two male characteristics, namely courtship and mating behavior and the formation of the muscle of Lawrence (MOL). In D. melanogaster, the male-specific expression of Fru protein in motoneurons is responsible for the male-limited induction of the MOL by such neurons. Although no Drosophila species whose females have the MOL are known, there are many Drosophila species whose males lack the MOL. We performed immunohistochemical staining of the central nervous system (CNS) from 9 Drosophila species to determine whether the mFru expression profile is different between MOL-present and MOL-absent species. In 8 of the 9 species, Fru protein expression in the CNS is strictly male-specific, regardless of the presence or absence of the MOL. The sole exception is D. suzukii, in which females express the Fru protein though less extensively than males do: Fru expression in the CNS of female D. suzukii is restricted to the lamina and ventral ganglia. Expression of Fru protein in the lamina is observed in males of D. virilis and in both sexes of D. suzukii, but not in males and females of the 7 other species. These results indicate that sexually dimorphic expression of the Fru protein has been subjected to species-specific modulation during evolution.     

X chromosomes and autosomes evolve at similar rates in Drosophila: no evidence for faster-X protein evolution

Recent data from Drosophila suggest that a substantial fraction of amino acid substitutions observed between species are beneficial. If these beneficial mutations are on average partially recessive, then the rate of protein evolution is predicted to be faster for X-linked genes compared to autosomal genes (the "faster-X" hypothesis). We test this prediction by comparing rates of protein substitutions between orthologous genes, taking advantage of variations in chromosome fusions within the genus Drosophila. In members of the Drosophila melanogaster species group, the chromosomal arm 3L segregates as an ordinary autosome (i.e., two homologous copies in both males and females). However, in the Drosophila pseudoobscura species group, this chromosomal arm has become fused to the ancestral X chromosome and is hemizygous in males. The faster-X hypothesis predicts that protein evolution should be faster for genes on this chromosomal arm in the D. pseudoobscura lineage, relative to the D. melanogaster lineage. Here we combine new sequence data for 202 gene fragments in Drosophila miranda (in the pseudoobscura species group) with the completed genomes of D. melanogaster, D. pseudoobscura, and Drosophila yakuba to show that there are no detectable differences in rates of amino acid evolution for orthologous X-linked and autosomal genes. Our results imply that the contribution of the faster-X (if any) to the large-X effect on reproductive isolation in Drosophila is not due to a generally faster rate of protein evolution. The lack of a detectable faster-X effect in these species suggests either that beneficial amino acids are not partially recessive on average, or that adaptive evolution does not often use newly arising amino acid mutations.     

A fruitless upstream region that defines the species specificity in the male-specific muscle patterning in Drosophila

Abstract

The muscle of Lawrence (MOL) is a male-specific muscle present in the abdomen of some adult Drosophila species. Formation of the MOL depends on innervation by motoneurons that express fruitless, a neural male determinant. Drosophila melanogaster males carry a pair of MOLs in the 5th abdominal segment, whereas D. subobscura males carry a pair in both the 5th and 4th segments. We hypothesized that the fru gene of D. subobscura but not that of D. melanogaster contains a cis element that directs the formation of the additional pair of MOLs. Successively extended 5’ DNA fragments to the P1 promoter of D. subobscura or the corresponding fragments that are chimeric (i.e., containing both melanogaster and subobscura elements) were introduced into D. melanogaster and tested for their ability to induce the MOL to locate the hypothetical cis element. We found that a 1.5–2-kb genomic fragment located 4–6-kb upstream of the P1 promoter in D. subobscura but not that of D. melanogaster permits MOL formation in females, provided this fragment is grafted to the distal ～4-kb segment from D. melanogaster, demonstrating that this genomic fragment of D. subobscura contains a cis element for the MOL induction.     

The effect of the homoeotic mutation, Spineless-aristapedia, on female receptivity to male courtship in Drosophila melanogaster.

Drosophila melanogaster females expressing the homoeotic mutation, spineless-aristapedia (SSa), were tested for their ability to hear the song of courting males. Since courtship song increases a females' receptivity to copulation, the frequency of mating within a short observation period was used as a measure of the ability of mutant females to distinguish between singing males and males that were unable to sing. These results show that SSa females, although lacking aristae, could distinguish between the two types of males in that they mated more readily with males that sang. Furthermore, the homoeotic legs of SSa females are not required to be present for the detection of courtship song, since females whose homoeotic legs were removed could still distinguish between singing and non-singing males.     

Dopamine modulates female sexual receptivity in Drosophila melanogaster

Newly eclosed Drosophila melanogaster flies were systemically depleted of dopamine by feeding an inhibitor of the biosynthetic enzyme, tyrosine hydroxylase, and analyzed for abnormalities in courtship behavior. Dopamine-depleted females were significantly less receptive to males than were control females, although males were strongly attracted to treated females. The decrease in receptivity was reversed by the addition of L-DOPA (the product of the tyrosine hydroxylation reaction) to food containing the inhibitor. Male courtship behaviors were unaffected by this treatment. Female receptivity may be regulated via interactions with hormonal pathways, since depletion of dopamine levels via inhibition of tyrosine hydroxylase activity in Drosophila melanogaster adult females has established that dopamine is required for normal ovarian maturation and fecundity.     

Identification and characterization of DAlk: a novel Drosophila melanogaster RTK which drives ERK activation in vivo

BACKGROUND: The mammalian receptor protein tyrosine kinase (RTK), Anaplastic Lymphoma Kinase (ALK), was first described as the product of the t(2;5) chromosomal translocation found in non-Hodgkin's lymphoma. While the mechanism of ALK activation in non-Hodgkin's lymphoma has been examined, to date, no in vivo role for this orphan insulin receptor family RTK has been described. RESULTS: We describe here a novel Drosophila melanogaster RTK, DAlk, which we have mapped to band 53 on the right arm of the second chromosome. Full-length DAlk cDNA encodes a phosphoprotein of 200 kDa, which shares homology not only with mammalian ALK but also with the orphan RTK LTK. Analysis of both mammalian and Drosophila ALK reveals that the ALK family of RTKs contains a newly identified MAM domain within their extracellular domains. Like its mammalian counterpart, DAlk appears to be expressed in the developing CNS by in situ analysis. However, in addition to expression of DAlk in the Drosophila brain, careful analysis reveals an additional early role for DAlk in the developing visceral mesoderm where its expression is coincident with activated ERK. CONCLUSION: In this paper we describe a Drosophila melanogaster Alk RTK which is expressed in the developing embryonic mesoderm and CNS. Our data provide evidence for the existence of a DAlk RTK pathway in Drosophila. We show that ERK participates in this pathway, and that it is activated by DAlk in vivo. Expression patterns of dALK, together with activated ERK, suggest that DAlk fulfils the criteria of the missing RTK pathway, leading to ERK activation in the developing visceral mesoderm.     

<Emphasis Type="Italic">Prospero</Emphasis> Mutants Induce Precocious Sexual Behavior in <Emphasis Type="Italic">Drosophila</Emphasis> Males

Brain maturation, a developmental process influenced by both endogenous and environmental factors, can affect sexual behavior. In vertebrates and invertebrates, sexual maturation is under the influence of hormones and neuromodulators, but the role of developmental genes in this process is still poorly understood. We report that prospero (pros), a gene crucial for nervous system development, can change the age of onset of sexual behavior in Drosophila melanogaster males: adult males carrying a single copy of several pros mutations court females and mate at a younger age than control males. However, these pros mutations had no effect on female sexual receptivity and did not alter other male phenotypes related to mating behavior. The Pros protein was detected in several brain and sensory structures of immature adult males, some of which are normally involved in the regulation of male specific behaviors. Our data suggest that the altered pros expression affects the age of onset of male mating behavior.     

The effects of larval density on adult life-history traits in three species of Drosophila

There is evidence that longevity and starvation resistance are determined by a common genetic mechanism. Starvation resistance in Drosophila strongly correlates with both fat content and longevity, and is affected by density during rearing. In this study, we examine how three species, Drosophila melanogaster, Drosophila ananassae and Drosophila willistoni, respond to three larval density treatments. Starvation resistance after adult eclosion, and after 2 days of feeding, and longevity were examined in each sex. D. willistoni reacted differently to larval density than the other two species. This species showed an effect of density on longevity whilst D. ananassae and D. melanogaster showed no such effects. The results also indicate that starvation resistance is not solely determined by fat content. Resistance to starvation at two time points after eclosion differed among species. This may reflect differences in resource acquisition and allocation, and we discuss our findings in relation to how selection may operate in the different species.     

On the origin of new genes in Drosophila

Several mechanisms have been proposed to account for the origination of new genes. Despite extensive case studies, the general principles governing this fundamental process are still unclear at the whole-genome level. Here, we unveil genome-wide patterns for the mutational mechanisms leading to new genes and their subsequent lineage-specific evolution at different time nodes in the Drosophila melanogaster species subgroup. We find that (1) tandem gene duplication has generated approximately 80% of the nascent duplicates that are limited to single species (D. melanogaster or Drosophila yakuba); (2) the most abundant new genes shared by multiple species (44.1%) are dispersed duplicates, and are more likely to be retained and be functional; (3) de novo gene origination from noncoding sequences plays an unexpectedly important role during the origin of new genes, and is responsible for 11.9% of the new genes; (4) retroposition is also an important mechanism, and had generated approximately 10% of the new genes; (5) approximately 30% of the new genes in the D. melanogaster species complex recruited various genomic sequences and formed chimeric gene structures, suggesting structure innovation as an important way to help fixation of new genes; and (6) the rate of the origin of new functional genes is estimated to be five to 11 genes per million years in the D. melanogaster subgroup. Finally, we survey gene frequencies among 19 globally derived strains for D. melanogaster-specific new genes and reveal that 44.4% of them show copy number polymorphisms within a population. In conclusion, we provide a panoramic picture for the origin of new genes in Drosophila species.     

Drosophila UNR is required for translational repression of male-specific lethal 2 mRNA during regulation of X-chromosome dosage compensation

The inhibition of male-specific lethal 2 (msl-2) mRNA translation by the RNA-binding protein sex-lethal (SXL) is an essential regulatory step for X-chromosome dosage compensation in Drosophila melanogaster. The mammalian upstream of N-ras (UNR) protein has been implicated in the regulation of mRNA stability and internal ribosome entry site (IRES)-dependent mRNA translation. Here we have identified the Drosophila homolog of mammalian UNR as a cofactor required for SXL-mediated repression of msl-2 translation. UNR interacts with SXL, a female-specific protein. Although UNR is present in both male and female flies, binding of SXL to uridine-rich sequences in the 3' untranslated region (UTR) of msl-2 mRNA recruits UNR to adjacent regulatory sequences, thereby conferring a sex-specific function to UNR. These data identify a novel regulator of dosage compensation in Drosophila that acts coordinately with SXL in translational control.     

The baculovirus anti-apoptotic protein Op-IAP does not inhibit Drosophila caspases or apoptosis in Drosophila S2 cells and instead sensitizes S2 cells to virus-induced apoptosis

The Op-IAP protein from the baculovirus Orgyia pseudotsugata M nucleopolyhedrovirus (OpMNPV) is highly effective at inhibiting apoptosis triggered by a variety of different stimuli in lepidopteran cells as well as in several different mammalian cell types, suggesting that it functions at a highly conserved step in the apoptotic pathway. However, the mechanism by which Op-IAP inhibits apoptosis is unclear. Since some IAP proteins can bind and inhibit caspases, we tested whether Op-IAP could inhibit the activity of caspases from Drosophila melanogaster. We found that recombinant Op-IAP protein was not able to bind or directly inhibit the activity of the Drosophila caspases DRONC, DrICE, or DCP-1 in vitro. In addition, expression of Op-IAP was unable to inhibit apoptosis triggered by either actinomycin D or UV light in D. melanogaster S2 cells. Surprisingly, Op-IAP expression in S2 cells enhanced apoptosis caused by baculovirus infection, but did not cause increased sensitivity to either actinomycin D or UV damage-induced apoptosis. The observation that Op-IAP cannot inhibit these insect caspases suggests that it functions by a mechanism that does not involve direct caspase inhibition.     

Dopamine and senescence in Drosophila melanogaster

Five-day-old Drosophila melanogaster males, when exposed to 2-h-old males, will perform courtship rituals; the intensity and duration of this behavior rapidly diminishes with time. The ability of the older males to habituate to the attractive signals given off by the younger males is a dopaminergic-modulated experience-dependent modification of behavior that is abolished with increasing age. Dopamine-depleted females show increased resistance to copulation; 20-day-old females demonstrated an increase in copulation avoidance compared with younger (5-15-day-old) females. These changes in dopaminergic-modulated behaviors observed during aging parallel declines in whole body levels of dopamine. Immunocytochemical analysis of adult brains using an antibody raised against Drosophila tyrosine hydroxylase to visualize catecholaminergic cell bodies revealed increased degeneration of the cell bodies with aging. These results suggest that the deficits seen in dopaminergic-modulated behaviors may arise as a consequence of degenerative changes within the aging brain.     

Mouse staufen genes are expressed in germ cells during oogenesis and spermatogenesis

The Drosophila melanogaster staufen gene encodes an RNA binding protein (Dm Stau) required for the localization and translational repression of mRNAs within the Drosophila oocyte. In mammals translational repression is important for normal spermatogenesis in males and storage of mRNAs in the oocytes of females. In the present study we identified two mouse cDNA expressed sequence tags (ESTs), encoding proteins with significant homology to Dm Stau and used these firstly to screen a mouse kidney cDNA library and secondly to determine whether staufen mRNAs are expressed in the ovaries and testes of mice and rats. Sequence analysis of the cDNAs revealed that they originated from two different genes. Using Northern blots of RNAs from kidneys, ovaries and testes, both cDNAs hybridized to mRNA species of approximately 3 kb in all three tissues. On sections of mouse ovaries, staufen mRNA was localized specifically to oocytes. On sections of mouse testes, staufen mRNA was expressed in spermatocytes found in seminiferous tubules at stages VI-XII of the spermatogenic cycle. In conclusion, we have shown that the mammalian homologues of Dm stau are expressed in germ cells in both male and female mice, consistent with a role for these RNA binding proteins in mammalian gametogenesis.