Hormones and Sex-Specific Transcription Factors Jointly Control Yolk Protein Synthesis in Musca domestica

In the housefly Musca domestica, synthesis of yolk proteins (YPs) depends on the level of circulating ecdysteroid hormones. In female houseflies, the ecdysterone concentration in the hemolymph oscillates and, at high levels, is followed by expression of YP. In male houseflies, the ecdysterone titre is constantly low and no YP is produced. In some strains, which are mutant in key components of the sex-determining pathway, males express YP even though their ecdysterone titre is not significantly elevated. However, we find that these males express a substantial amount of the female variant of the Musca doublesex homologue, Md-dsx. The dsx gene is known to sex-specifically control transcription of yp genes in the fat body of Drosophila melanogaster. Our data suggest that Md-dsx also contributes to the regulation of YP expression in the housefly by modulating the responsiveness of YP-producing cells to hormonal stimuli

The transformer2 gene in Musca domestica is required for selecting and maintaining the female pathway of development

We present the isolation and functional analysis of a transformer2 homologue Mdtra2 in the housefly Musca domestica. Compromising the activity of this gene by injecting dsRNA into embryos causes complete sex reversal of genotypically female individuals into fertile males, revealing an essential function of Mdtra2 in female development of the housefly. Mdtra2 is required for female-specific splicing of Musca doublesex (Mddsx) which structurally and functionally corresponds to Drosophila dsx, the bottom-most regulator in the sex-determining pathway. Since Mdtra2 is expressed in males and females, we propose that Mdtra2 serves as an essential co-factor of F, the key sex-determining switch upstream of Mddsx. We also provide evidence that Mdtra2 acts upstream as a positive regulator of F supporting genetic data which suggest that F relies on an autocatalytic activity to select and maintain the female path of development. We further show that repression of male courtship behavior by F requires Mdtra2. This function of F and Mdtra2 appears not to be mediated by Mddsx, suggesting that bifurcation of the pathway at this level is a conserved feature in the genetic architecture of Musca and Drosophil

Sex determination in Drosophila melanogaster and Musca domestica converges at the level of the terminal regulator doublesex

Sex-determining cascades are supposed to have evolved in a retrograde manner from bottom to top. Wilkins' 1995 hypothesis finds support from our comparative studies in Drosophila melanogaster and Musca domestica, two dipteran species that separated some 120million years ago. The sex-determining cascades in these flies differ at the level of the primary sex-determining signal and their targets, Sxl in Drosophila and F in Musca. Here we present evidence that they converge at the level of the terminal regulator, doublesex (dsx), which conveys the selected sexual fate to the differentiation genes. The dsx homologue in Musca, Md-dsx, encodes male-specific (MdDSXM) and female-specific (MdDSXF) protein variants which correspond in structure to those in Drosophila. Sex-specific regulation of Md-dsx is controlled by the switch gene F via a splicing mechanism that is similar but in some relevant aspects different from that in Drosophila. MdDSXF expression can activate the vitellogenin genes in Drosophila and Musca males, and MdDSXM expression in Drosophila females can cause male-like pigmentation of posterior tergites, suggesting that these Musca dsx variants are conserved not only in structure but also in function. Furthermore, downregulation of Md-dsx activity in Musca by injecting dsRNA into embryos leads to intersexual differentiation of the gonads. These results strongly support a role of Md-dsx as the final regulatory gene in the sex-determining hierarchy of the housefl

Genome of the house fly, <i>Musca domestica</i> L., a global vector of diseases with adaptations to a septic environment

Background: Adult house flies, Musca domestica L., are mechanical vectors of more than 100 devastating diseases that have severe consequences for human and animal health. House fly larvae play a vital role as decomposers of animal wastes, and thus live in intimate association with many animal pathogens. Results: We have sequenced and analyzed the genome of the house fly using DNA from female flies. The sequenced genome is 691 Mb. Compared with Drosophila melanogaster, the genome contains a rich resource of shared and novel protein coding genes, a significantly higher amount of repetitive elements, and substantial increases in copy number and diversity of both the recognition and effector components of the immune system, consistent with life in a pathogen-rich environment. There are 146 P450 genes, plus 11 pseudogenes, in M. domestica, representing a significant increase relative to D. melanogaster and suggesting the presence of enhanced detoxification in house flies. Relative to D. melanogaster, M. domestica has also evolved an expanded repertoire of chemoreceptors and odorant binding proteins, many associated with gustation. Conclusions: This represents the first genome sequence of an insect that lives in intimate association with abundant animal pathogens. The house fly genome provides a rich resource for enabling work on innovative methods of insect control, for understanding the mechanisms of insecticide resistance, genetic adaptation to high pathogen loads, and for exploring the basic biology of this important pest. The genome of this species will also serve as a close out-group to Drosophila in comparative genomic studies

Molecular Characterization of the Key Switch F Provides a Basis for Understanding the Rapid Divergence of the Sex-Determining Pathway in the Housefly

The housefly, Musca domestica, is an excellent model system to study the diversification of the pathway that specifies the sexual fate. A number of different mechanisms have been described in the housefly, which reflects in part the broad diversity of sex-determining strategies used in insects. In this study we present the molecular identification and characterization of F, which acts as the master switch in the housefly pathway. We provide evidence that F corresponds to the transformer ortholog in Musca (Mdtra), which, as a result of alternative processing, expresses functional products only in individuals committed to the female fate. We demonstrate that, once activated, a self-sustaining feedback loop will maintain the female-promoting functions of Mdtra. Absence of Mdtra transcripts in eggs of Arrhenogenic (Ag) mutant females suggests that maternally deployed Mdtra activity initiates this self-sustaining loop in the zygote. When an M factor is paternally transmitted to the zygote, the establishment of the loop is prevented at an early stage before cellularization and splicing of Mdtra shifts irreversibly to the male nonproductive mode. On the basis of the analysis of two mutant alleles we can explain the different sex-determining systems in the housefly largely as deviations at the level of Mdtra regulation. This plasticity in the housefly pathway may provide a suitable framework to understand the evolution of sex-determining mechanisms in other insect species. For instance, while sex determination in a close relative, the tsetse fly Glossina morsitans, differs at the level of the instructive signal, we find that its tra ortholog, Gmtra, is regulated in a mode similar to that of Mdtra

Bifurcation of the sex-determination pathway: a general principle in holometabolous insects?

<p>The phylogenetic relationship and the sex-determining pathways of several dipteran species and the hymenopteran species Nasonia are depicted in this scheme. Despite considerable differences regarding the nature of the instructive sex-determining signal (X-counting in Drosophila, male [M] dominant determiners in Musca and Ceratitis, haplo-maternal [mat] versus diplo-maternal-paternal [pat+mat] in Nasonia) many insects use <i>tra</i> as the binary on/off switch downstream of the signal <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062476#pone.0062476-Verhulst1" target="_blank">[54]</a>, though the molecular basis of this switch in <i>A. gambiae</i> remains still elusive <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062476#pone.0062476-Gailey2" target="_blank">[24]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062476#pone.0062476-Suzuki1" target="_blank">[55]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062476#pone.0062476-Salvemini3" target="_blank">[56]</a>. The <i>dsx</i> gene, expressing sex-specific variants DSX^F and DSX^M, appears to be a conserved target of the binary switch and its use as a bifunctional executor of the instructive signal was validated by gene function studies in the depicted insect species <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062476#pone.0062476-Salvemini2" target="_blank">[26]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062476#pone.0062476-Hediger2" target="_blank">[30]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062476#pone.0062476-Salvemini3" target="_blank">[56]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062476#pone.0062476-Oliveira1" target="_blank">[57]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062476#pone.0062476-Saccone1" target="_blank">[58]</a> Also, homologs of <i>fru</i> were identified in these species that express sex-specific variants FRU^F and FRU^M<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062476#pone.0062476-Gailey2" target="_blank">[24]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062476#pone.0062476-Salvemini2" target="_blank">[26]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062476#pone.0062476-Bertossa1" target="_blank">[27]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062476#pone.0062476-Salvemini4" target="_blank">[59]</a>. For Musca we here present evidence that <i>fru</i> is a downstream target of the <i>tra</i> branch which is involved in controlling proper display of courtship. Though no functional <i>fru</i> data from other holometabolous insects are available as yet, we propose that <i>fru</i> independently from <i>dsx</i> represents another conserved effector of the instructive signal. Hence, bifurcation of the pathway downstream of <i>tra</i> may have already existed before the divergence of holometabolous insect orders.</p

<i>Md-fru</i> P1 transcripts are expressed in the CNS and in peripheral sensory organs.

<p>(A) Frontal section of a male head hybridised with <i>Md-fru</i> P1-specific antisense RNA probe. Strong ubiquitous staining is observed in the layers below the retina and around the optic lobes (Re: Retina, La: Lamina, Me: Medulla, Lo; Lobula), as wells as around the central complex (CC) and the subesophageal ganglion (S). (B) Frontal section of a male head hybridised with the <i>Md-fru</i> P1 sense RNA probe. (C) Higher magnification of the stained areas in the optic lobes. (D) Close-up of basal neurons (arrowhead) connected to a sensory bristle (black star) located in the labellum and expressing <i>Md-fru</i> P1 transcripts. (E) Overview of the sectioned labellum shown in D (boxed). (F) SEM imaging of the fly’s mouthpart (labellum) and surrounding sensory bristles. (G). Primers used to prepare templates for P1-specific sense and antisense RNA probes are indicated as black triangles (Md-fru-27 and Md-fru-29).</p