Purification and physical properties of the male and female double sex proteins of Drosophila

DMRT Transcription Factors in the Control of Nervous System Sexual Differentiation

Sexual phenotypic differences in the nervous system are one of the most prevalent features across the animal kingdom. The molecular mechanisms responsible for sexual dimorphism throughout metazoan nervous systems are extremely diverse, ranging from intrinsic cell autonomous mechanisms to gonad-dependent endocrine control of sexual traits, or even extrinsic environmental cues. In recent years, the DMRT ancient family of transcription factors has emerged as being central in the development of sex-specific differentiation in all animals in which they have been studied. In this review, we provide an overview of the function of Dmrt genes in nervous system sexual regulation from an evolutionary perspective.

Doublesex Evolution Is Correlated with Social Complexity in Ants

The Dmrt (doublesex and mab-3-related transcription factor) genes are transcription factors crucial for sex determination and sexual differentiation. In some social insects, doublesex (dsx) exhibits widespread caste-specific expression across different tissues and developmental stages and has been suggested as a candidate gene for regulating division of labor in social insects. We therefore conducted a molecular evolution analysis of the Dmrt gene family in 20 ants. We found that the insect-specific oligomerization domain of DSX, oligomerization domain 2, was absent in all ants, except for the two phylogenetically basal ant species (Ponerinae), whose social structure and organization resemble the presumed ancestral condition in ants. Phylogenetic reconstruction and selection analysis revealed that dsx evolved faster than the other three members of the Dmrt family. We found evidence for positive selection for dsx in the ant subfamilies with more advanced social organization (Myrmicinae and Formicinae), but not in the Ponerinae. Furthermore, we detected expression of two Dmrt genes, dsx and DMRT11E, in adult ants, and found a clear male-biased expression pattern of dsx in most species for which data are available. Interestingly, we did not detect male-biased expression of dsx in the two ant species that possess a genetic caste determination system. These results possibly suggest an association between the evolution of dsx and social organization as well as reproductive division of labor in ants.

Double nexus--Doublesex is the connecting element in sex determination

In recent years, our knowledge of the conserved master-switch gene doublesex (dsx) and its function in regulating the development of dimorphic traits in insects has deepened considerably. Here, a comprehensive overview is given on the properties of the male- and female-specific dsx transcripts yielding DSX^F and DSX^M proteins in Drosophila melanogaster, and the many downstream targets that they regulate. As insects have cell-autonomous sex determination, it was assumed that dsx would be expressed in every somatic cell, but recent research showed that dsx is expressed only when a cell is required to show its sexual identity through function or morphology. This spatiotemporal regulation of dsx expression has not only been established in D. melanogaster but in all insect species studied. Gradually, it has been appreciated that dsx could no longer be viewed as the master-switch gene orchestrating sexual development and behaviour in each cell, but instead should be viewed as the interpreter for the sexual identity of the cell, expressing this identity only on request, making dsx the central nexus of insect sex determination.

Molecular cloning of Pcc-dmrt1s and their specific expression patterns in Pengze crucian carp (Carassius auratus var. Pengze) affected by 17α-methyltestosterone

Dmrt1, an important transcription factor associated with testicular differentiation, is conserved among teleost, which could also be detected in ovaries. In the present study, three isoforms of Pcc-dmrt1s (Pcc-dmrt1a, Pcc-dmrt1b and Pcc-dmrt1c) resulting from alternative splicing of the dmrt1 gene were cloned and characterized in the triploid gynogenetic fish, the Pengze crucian carp. Their mRNA expression profiling was investigated in juvenile developmental stages, tissues of the adult fish, and the juveniles under 84.2 ng/L 17α-methyltestosterone (MT) treatments. Results showed that their putative proteins shared high identities to Dmrt1 in cyprinid fish species. Gene expression profiling in the developmental stages showed that all the three target genes had a highest/lowest expression at 56/40 days post-hatching (dph), respectively. The period of 40 dph appeared to be a key time during the process of the ovary development of Pengze crucian carp. The tissue distribution results indicated that Pcc-dmrt1s were predominantly expressed in hepatopancreas, brain, spleen and ovary of the female fish. MT significantly increased the mRNA expression of Pcc-dmrt1a (all 4-week exposures) and Pcc-dmrt1b (except for week 2), while repressed Pcc-dmrt1c transcripts at all exposure period except for week 2. MT extremely significant repressed cyp19a1a transcripts for 1 week. The present study indicated that MT could influence the ovary development of Pengze crucian carp by disturbing gene expressions of Pcc-dmrt1s and cyp19a1a. Furthermore, the present study will be of great significance to broaden the understanding of masculinizing pathway during ovary development in gynogenetic teleost.

Sexually dimorphic and ontogenetic expression of dmrt1, cyp19a1a and cyp19a1b in Gobiocypris rarus

Fish have diverse sex determination and differentiation. DMRT1 and aromatase are conserved in the phyla and play pivotal roles in sex development. Gobiocypris rarus is a small fish used as a model in aquatic toxicology in China and has been used to study the effects of environmental endocrine disruptors on gene expression, but its sexual development remains elusive. Here, we report the full-length cDNA of G. rarus dmrt1 and its expression along with the expression of cyp19a1a and cyp19a1b, two genes encoding gonad and brain type aromatases, in adults and during ontogenesis. Both cyp19a1a and dmrt1 are expressed in the ovary and testis but show sexual dimorphism. Expression of cyp19a1a in the ovary is higher than in testes and dmrt1 follows the opposite pattern. Juvenile gonad histology changes at 15 days after hatching. The dimorphic expression of dmrt1 and cyp19a1a appears from 5 days after hatching, which is earlier than histological change. cyp19a1b is expressed coordinately with cyp19a1a until 15 days after hatching. These results show that dmrt1 and cyp19a1a play important roles in sex determination and sex differentiation in G. rarus.

Systems behavior: of male courtship, the nervous system and beyond in Drosophila

Male courtship in fruit flies is regulated by the same major regulatory genes that also determine general sexual differentiation of the animal. Elaborate genetics has given us insight into the roles of these master genes. These findings have suggested two separate and independent pathways for the regulation of sexual behavior and other aspects of sexual differentiation. Only recently have molecular studies started to look at the downstream effector genes and how they might control sex-specific behavior. These studies have confirmed the essential role of the previously identified male specific products of the fruitless gene in the neuronal circuits in which it is expressed. But there is increasing evidence that a number of non-neuronal tissues and pathways play a pivotal role in modulating this circuit and assuring efficient courtship.

Genomic and functional studies of Drosophila sex hierarchy regulated gene expression in adult head and nervous system tissues

The Drosophila sex determination hierarchy controls all aspects of somatic sexual differentiation, including sex-specific differences in adult morphology and behavior. To gain insight into the molecular-genetic specification of reproductive behaviors and physiology, we identified genes expressed in the adult head and central nervous system that are regulated downstream of sex-specific transcription factors encoded by doublesex (dsx) and fruitless (fru). We used a microarray approach and identified 54 genes regulated downstream of dsx. Furthermore, based on these expression studies we identified new modes of DSX-regulated gene expression. We also identified 90 and 26 genes regulated in the adult head and central nervous system tissues, respectively, downstream of the sex-specific transcription factors encoded by fru. In addition, we present molecular-genetic analyses of two genes identified in our studies, calphotin (cpn) and defective proboscis extension response (dpr), and begin to describe their functional roles in male behaviors. We show that dpr and dpr-expressing cells are required for the proper timing of male courtship behaviors.

The fruit fly Drosophila is an excellent model system to use to understand the molecular-genetic basis of male courtship behavior, as the potential for this behavior is specified by a well-understood genetic regulatory hierarchy, called the sex determination hierarchy. The sex hierarchy consists of a pre-mRNA splicing cascade that culminates in the production of sex-specific transcription factors, encoded by doublesex (dsx) and fruitless (fru). dsx specifies all the anatomical differences between the sexes, and fru is required for all aspects of male courtship behavior. In this study, we measure gene expression differences between males and females, and between sex hierarchy mutants and wild-type animals, to identify genes that underlie the differences between males and females. We have performed these studies on adult head and nervous system tissues, as these tissues are important for establishing the potential for behaviors. We have identified several genes regulated downstream of dsx and fru and more extensively characterized two genes that are more highly expressed in males. One gene regulated downstream of dsx is expressed in the retina and is known to have a function in visual transduction. The other gene, regulated downstream of fru, plays a role in the timing of male courtship behavior.

The creation of sexual dimorphism in the Drosophila soma

Animals have evolved a fascinating array of mechanisms for conducting sexual reproduction. These include producing the sex-specific gametes, as well as mechanisms for attracting a mate, courting a mate, and getting the gametes together. These processes require that males and females take on dramatically different forms (sexual dimorphism). Here, we will explore the problem of how sex is determined in Drosophila, and pay particular attention to how information about sexual identity is used to instruct males and females to develop differently. Along the way, we will highlight new work that challenges some of the traditional views about sex determination. In Drosophila, it is commonly thought that every cell decides its own sex based on its sex chromosome constitution (XX vs. XY). However, we now know that many cell types undergo nonautonomous sex determination, where they are told what sex to be through signals from surrounding cells, independent of their own chromosomal content. Further, it now appears that not all cells even "know" their sex, since key members of the sex determination pathway are not expressed in all cells. Thus, our understanding of how sex is determined, and how sexual identity is used to create sexual dimorphism, has changed considerably.

Vertebrate DM domain proteins bind similar DNA sequences and can heterodimerize on DNA

Background:

The DM domain is a zinc finger-like DNA binding motif first identified in the sexual regulatory proteins Doublesex (DSX) and MAB-3, and is widely conserved among metazoans. DM domain proteins regulate sexual differentiation in at least three phyla and also control other aspects of development, including vertebrate segmentation. Most DM domain proteins share little similarity outside the DM domain. DSX and MAB-3 bind partially overlapping DNA sequences, and DSX has been shown to interact with DNA via the minor groove without inducing DNA bending. DSX and MAB-3 exhibit unusually high DNA sequence specificity relative to other minor groove binding proteins. No detailed analysis of DNA binding by the seven vertebrate DM domain proteins, DMRT1-DMRT7 has been reported, and thus it is unknown whether they recognize similar or diverse DNA sequences.

Results:

We used a random oligonucleotide in vitro selection method to determine DNA binding sites for six of the seven proteins. These proteins selected sites resembling that of DSX despite differences in the sequence of the DM domain recognition helix, but they varied in binding efficiency and in preferences for particular nucleotides, and some behaved anomalously in gel mobility shift assays. DMRT1 protein from mouse testis extracts binds the sequence we determined, and the DMRT proteins can bind their in vitro-defined sites in transfected cells. We also find that some DMRT proteins can bind DNA as heterodimers.

Conclusion:

Our results suggest that target gene specificity of the DMRT proteins does not derive exclusively from major differences in DNA binding specificity. Instead target specificity may come from more subtle differences in DNA binding preference between different homodimers, together with differences in binding specificity between homodimers versus heterodimers.

Sex-, stage- and tissue-specific regulation by a mosquito hexamerin promoter

A portion of the 5'-flanking region of the female-specific hexamerin gene, Hex-1.2, from the mosquito Ochlerotatus atropalpus was used to drive expression of the luciferase reporter gene in Drosophila melanogaster. The proximal 0.7 kb of 5'-flanking DNA were sufficient to partially repress reporter gene activity in males and to drive tissue- and stage-specific expression comparable with that of the endogenous O. atropalpus Hex-1.2 gene. The Drosophila doublesex transcription factor (DSX), expressed in Escherichia coli, bound putative DSX sites of the Hex-1.2 gene differentially in vitro. Blocking expression of the female isoform of the Doublesex transcription factor in transgenic female flies resulted in reduction of luciferase expression to levels comparable with those in males, suggesting that Doublesex could contribute to regulation of female-specific expression of the O. atropalpus Hex-1.2 gene.

Regulation of sexual dimorphism: mutational and chemogenetic analysis of the doublesex DM domain

Doublesex (dsx) is a transcription factor in Drosophila that regulates somatic sexual differentiation. Male- and female-specific splicing isoforms of DSX share a novel DNA-binding domain, designated the DM motif. Broadly conserved among metazoan sex-determining factors, the DM domain contains a nonclassical zinc module and binds in the DNA minor groove. Here, we characterize the DM motif by site-directed and random mutagenesis using a yeast one-hybrid (Y1H) system and extend this analysis by chemogenetic complementation in vitro. The Y1H system is based on a sex-specific Drosophila enhancer element and validated through studies of intersexual dsx mutations. We demonstrate that the eight motif-specific histidines and cysteines engaged in zinc coordination are each critical and cannot be interchanged; folding also requires conserved aliphatic side chains in the hydrophobic core. Mutations that impair DNA binding tend to occur at conserved positions, whereas neutral substitutions occur at nonconserved sites. Evidence for a specific salt bridge between a conserved lysine and the DNA backbone is obtained through the synthesis of nonstandard protein and DNA analogs. Together, these results provide molecular links between the structure of the DM domain and its function in the regulation of sexual dimorphism.

Similarity of DNA binding and transcriptional regulation by Caenorhabditis elegans MAB-3 and Drosophila melanogaster DSX suggests conservation of sex determining mechanisms

Although most animals occur in two sexes, the molecular pathways they employ to control sexual development vary considerably. The only known molecular similarity between phyla in sex determination is between two genes, mab-3 from C. elegans, and doublesex (dsx) from Drosophila. Both genes contain a DNA binding motif called a DM domain and they regulate similar aspects of sexual development, including yolk protein synthesis and peripheral nervous system differentiation. Here we show that MAB-3, like the DSX proteins, is a direct regulator of yolk protein gene transcription. We show that despite containing different numbers of DM domains MAB-3 and DSX bind to similar DNA sequences. mab-3 mutations deregulate vitellogenin synthesis at the level of transcription, resulting in expression in both sexes, and the vitellogenin genes have potential MAB-3 binding sites upstream of their transcriptional start sites. MAB-3 binds to a site in the vit-2 promoter in vitro, and this site is required in vivo to prevent transcription of a vit-2 reporter construct in males, suggesting that MAB-3 is a direct repressor of vitellogenin transcription. This is the first direct link between the sex determination regulatory pathway and sex-specific structural genes in C. elegans, and it suggests that nematodes and insects use at least some of the same mechanisms to control sexual development.

DNA binding by the male and female doublesex proteins of Drosophila melanogaster

Drosophila yolk protein genes are regulated by doublesex male protein (DSXM) in males and doublesex female protein (DSXF) in females. Both proteins bind to the same DNA sites from which DSXM represses and DSXF activates transcription. The proteins are identical through 397 NH2-terminal amino acids that include domains for oligomerization and DNA binding. The remaining COOH termini are sex-specific and include an essential part of a second oligomerization domain. We report here mobility shift assays that examine the DNA binding properties of purified DSXM and DSXF. Dimers of DSXM and DSXF bind to a regulatory site, dsxA, with the same affinity (Kapp = 0.2 nM), specificity (specific/nonspecific approximately 1.2 x 10(4)), and dependence on monovalent and divalent cations. The DNA association rate constants also are indistinguishable (kon = 4.6 x 10(6) M-1 s-1) as are the several terms of the dissociation reaction. Dissociation has an intrinsic rate of koff = 5.1 x 10(-4) s-1 and other rate terms that depend on the free concentration of specific DNA binding sites (2.4 x 10(4) M-1 s-1) or nonspecific binding sites (2.4 M-1 s-1). This first order dependence on unbound DNA suggests that a direct transfer between DNAs is likely to occur when DSX proteins search for specific sites in the many short open DNA regions of chromatin. Overall, dimer binding to individual DNA sites appears to be determined by the sex-nonspecific part of the two proteins. We infer that the sex-specific oligomerization domains play roles in binding cooperativity to multiple DNA sites or in other protein:protein interactions.

Functional and genetic characterization of the oligomerization and DNA binding properties of the Drosophila doublesex proteins

The doublesex (dsx) gene of Drosophila melanogaster encodes both male-specific (DSXM) and female-specific (DSXF) polypeptides, which are required for normal differentiation of numerous sexually dimorphic somatic traits. The DSX polypeptides are transcription factors and have been shown previously to bind through a zinc finger-like domain to specific sites in an enhancer regulating sex-specific expression of yolk protein genes. We have determined the consensus target sequence for this DNA binding domain to be a palindromic sequence AGNNACTAAATGTNNTC composed of two half-sites around a central (A/T) base pair. As predicted by the symmetric nature of this site, we have found that the DSX proteins exist as dimers in vivo and have mapped two independent dimerization domains by the yeast two-hybrid method; one in the non-sex-specific amino-terminal region of the protein and one that includes the partially sex-specific carboxy-terminal domains of both the male and female polypeptides. We have further identified a missense mutation that eliminates dsx function in female flies, and shown that the same mutation prevents dimerization of DSXF in the yeast two-hybrid system, indicating a critical role for dimerization in dsx function in vivo.

Sex-specific and non-sex-specific oligomerization domains in both of the doublesex transcription factors from Drosophila melanogaster

The doublesex gene of Drosophila melanogaster encodes the alternatively spliced, sex-specific transcription factors DSXM and DSXF. These factors regulate male- and female-specific transcription of many genes. For example, female-specific transcription of the yolk protein 1 gene is regulated by DSXM repression in males and DSXF activation in females. In this study we used in vitro interaction assays and the in vivo yeast two-hybrid method to identify and examine oligomerization domains of the DSX proteins. A 66-amino-acid segment common to both proteins (amino acids 39 to 104) contains a sequence-specific DNA binding domain and an oligomerization domain (OD1). The OD1 domain oligomerizes up to at least a pentamer, but only dimers bound to a palindromic regulatory site in the yolk protein 1 gene are detected. Both subunits of the OD1 dimer are in contact with DNA. Another segment of each protein (amino acids 350 to 412 for DSXF and 350 to 427 for DSXM) contains a second oligomerization domain (OD2F and OD2M, respectively). The OD2 domains have both sex-specific and non-sex-specific sequences which are necessary for oligomerization. On the basis of sequence analysis, we predict that OD2 oligomerizes through coiled-coil interactions. We speculate that the common function of OD1 and OD2 is to oligomerize the full-length proteins, whereas their specialized functions are to form a dimeric DNA binding unit and a sex-specific transcriptional activation or repression unit.