Expression of proteasome subunit isoforms during spermatogenesis in Drosophila melanogaster

In this study, we sought to identify and characterize all the proteasome genes of Drosophila melanogaster. Earlier work led to the identification of two genes encoding alpha4-type 20S proteasome subunit isoforms that are expressed exclusively in the male germline. Here we extend these results and show that six of the 20S proteasome subunits, and four of the 19S regulatory cap subunits, have gene duplications encoding male-specific isoforms. More detailed analyses of two of these male-specific subunits (Prosalpha3T and Prosalpha6T), using GFP-tagged reporter transgenes, revealed that they are predominantly localized to the nucleus at later stages of spermatogenesis and are present there in mature, motile sperm. These results suggest a possible role of a 'spermatogenesis-specific' proteasome in sperm differentiation and/or function.

Temperature-dependent gene silencing by an expressed inverted repeat in Drosophila

Posttranscriptional gene silencing (PTGS) induced by double-stranded RNA (dsRNA) is an intriguing phenomenon that has been observed in a variety of organisms, including Drosophila melanogaster. Although PTGS in Drosophila is typically observed following direct injection of the dsRNA into embryos, it is theoretically possible that the in vivo transcription of an inverted repeat transgene might also produce a dsRNA "hairpin" that is capable of triggering PTGS. Here we test this idea, and show that an expressed inverted repeat of a portion of the sex differentiation gene, transformer-2, (tra-2), driven by a GAL4-dependent promoter, does genetically repress the endogenous wild-type tra-2 function, producing a dominant loss-of-function mutant phenotype. Remarkably, this effect is temperature-sensitive, with phenotypic consequences seen at 29 degrees, but not at 22 degrees. Moreover, by altering the dosage of either the transgenes or the endogenous tra2(+) loci, one can vary the effect over a wide range of mutant phenotypes.

Subunit compositions and catalytic properties of proteasomes from developmental temperature- sensitive mutants of Drosophila melanogaster

Two dominant temperature-sensitive (DTS) Drosophila mutants are missense mutations of proteasome genes encoding beta-type subunits beta6/C5 (DTS5) and beta2/Z (DTS7). At nonpermissive temperature (29 degrees C), heterozygotes (DTS5/+ and DTS7/+) develop normally until metamorphosis; pupae fail to mature and die before eclosion. Proteasomes were purified from wild-type (WT) and heterozygous adult flies raised at permissive temperature (25 degrees C). Two-dimensional gel electrophoresis separated at least 28 proteins, 13 of which were identified with monospecific antibodies to alpha6/C2 (five species), alpha2/C3 (three species), alpha7/C8 (three species), alpha5/zeta, and beta1/Y subunits. Both quantitative and qualitative differences were observed between WT and DTS/+ proteasomes, with DTS5/+ deviating more from WT than DTS7/+ proteasomes. In DTS5/+ there was a shift to more acidic species of C2 and C3 and a shift to less acidic species of 32-kDa subunits (#3-#7) recognized by an anti-alpha subunit monoclonal antibody (MCP222) and were losses of two 32-kDa subunits (#2 and #3), decreases in Y (25 kDa; 2-fold) and 31-kDa (#9; 2-fold) subunits, and increases in 52-kDa (#1; 1.9-fold) and 24-kDa (#13; 2.3-fold) subunits. In DTS7/+ there was a less pronounced shift to acidic species of C3 and no pI shift in C2 species and subunits #3-#7 and were decreases in #9 (2.5-fold) and #14 (3-fold) and a loss of #2. The three C8 species were similar between WT, DTS5/+, and DTS7/+ proteasomes. Qualitatively, the most dramatic difference was the appearance of a new 24-kDa subunit (#16) in DTS/+ preparations, with about a 14-fold greater amount of #16 in DTS7/+ than in DTS5/+ proteasomes. Catalytically, WT and DTS/+ proteasomes had similar peptidase activities, although the DTS/+ proteasomes were slightly more sensitive to SDS and elevated temperatures in vitro. The incorporation of DTS subunits apparently altered proteasome assembly and/or processing at permissive temperature with little effect on catalytic activities. These data suggest that at nonpermissive temperature, assembly/processing is more severely affected, producing DTS-containing complexes that lack functions essential for cellular proliferation and differentiation at metamorphosis.

The dominant temperature-sensitive lethal DTS7 of Drosophila melanogaster encodes an altered 20S proteasome beta-type subunit

Proteasomes are multicatalytic complexes that function as the major proteolytic machinery in regulated protein degradation. The eukaryotic 20S proteasome proteolytic core structure comprises 14 different subunits: 7 alpha-type and 7 beta-type. DTS7 is a dominant temperature-sensitive (DTS) lethal mutation at 29 degrees that also acts as a recessive lethal at ambient temperatures. DTS7 maps to cytological position 71AB. Molecular characterization of DTS7 reveals that this is caused by a missense mutation in a beta-type subunit gene, beta2. A previously characterized DTS mutant, l(3)73Ai1, results from a missense mutation in another beta-type subunit gene, beta6. These two mutants share a very similar phenotype, show a strong allele-specific genetic interaction, and are rescued by the same extragenic suppressor, Su(DTS)-1. We propose that these mutants might act as "poison subunits," disrupting proteasome function in a dosage-dependent manner, and suggest how they may interact on the basis of the structure of the yeast 20S proteasome.

Evolutionary conservation of a testes-specific proteasome subunit gene in Drosophila

Proteasomes are large multisubunit particles that act as the proteolytic machinery for the ubiquitin-dependent proteolytic pathway. The core of this complex, the 20S proteasome, is made up of seven alpha-type and seven beta-type subunits, arranged in an (alpha1-alpha7)(beta1-beta7)(beta1-beta7)(alpha1-al pha7) configuration. Previous work had shown that there exist alternative isoforms of the Drosophila melanogaster alpha4-type subunit, encoded by two distinct genes, alpha4t1_dm and alpha4t2_dm, and that these are expressed exclusively in the germline of the testes. We sought to investigate the evolutionary conservation of this phenomenon by screening for orthologs of the alpha4-type gene family in the distantly related Drosophila species, D. virilis. We isolated the D. virilis orthologs of the somatically expressed gene, alpha4_dm, and the testes-specific gene, alpha4t2_dm. We failed to find an ortholog of the other testes-specific gene, alpha4t1_dm. The alpha4_dv gene maps to the X chromosome at 12A-C, its product shares 90% amino acid identity with alpha4_dm, and it is expressed at high levels in both males and females. The other gene, alpha4t_dv, encodes a protein most similar to the testes-specific alpha4t2_dm proteasome subunit (59% a.a. identity), and it maps to position 27 on chomosome 2. The expression of the alpha4t_dv gene is testes-specific, like that of alpha4t2_dm. The existence of testes-specific alpha4-type subunits in two widely diverged subgenera of Drosophila suggests that these subunit isoforms have important functional roles in spermatogenesis.

Cloning of Drosophila GCN5: conserved features among metazoan GCN5 family members

PCAF and hGCN5 are distinct human genes that encode proteins related to the yeast histone acetyltransferase and transcriptional adapter GCN5. The PCAF protein shares extensive similarity with the 439 amino acids of yGCN5, but it has an approximately 350 amino acid N-terminal extension that interacts with the transcriptional co-activator p300/CBP. Adenoviral protein E1a can disrupt PCAF-CBP interactions and prevent PCAF-dependent cellular differentiation. In this report, we describe the cloning and initial characterization of a Drosophila homolog of yGCN5. In addition to the homology to yGCN5, the Drosophila protein shares sequencesimilarity with the N-terminal portion of human PCAF that is involved in binding to CBP. In the course of characterizing dGCN5, we have discovered that hGCN5 also contains an N-terminal extension with significant similarity to PCAF. Interestingly, in the case of the h GCN5 gene, alternative splicing may regulate the production of full-length hGCN5. The presence of the N-terminal domain in a Drosophila GCN5 homolog and both human homologs suggests that it was part of the ancestral form of metazoan GCN5.

Molecular cloning of the Drosophila melanogaster gene alpha5_dm encoding a 20S proteasome alpha-type subunit

Proteasomes are large, multisubunit particles that act as the proteolytic machinery for most regulated intracellular protein breakdown in eukaryotic cells. The core proteinase of this complex, known as the 20S proteasome, is a hollow barrel-shaped structure made up of four stacked rings of seven subunits each, with the outer two rings each being made up of seven distinct alpha-type subunits, and the two inner rings composed of seven different beta-type subunits. Here we present the cloning, sequencing and genetic mapping of a Drosophila melanogaster gene, alpha5_dm, encoding one of the proteasome alpha subunits. This gene, which is homologous to the yeast PUP2 and the human Zeta genes, maps to chromosome 2 at position 54B3-5. The map positions of the previously cloned proteasome genes Pros25 and Pros29 were also determined, and found to lie at positions 87B and 57B, respectively. A search for other D. melanogaster alpha5_dm-like genes encoding potential isoforms of this subunit failed to identify any closely related genes.

Duplicated proteasome subunit genes in Drosophila melanogaster encoding testes-specific isoforms

Using the previously cloned proteasome alpha-type subunit gene Pros28.1, we screened a Drosophila melanogaster genomic library using reduced stringency conditions to identify closely related genes. Two new genes, Pros28.1A (map position 92F) and Pros28.1B (map position 60D7), showing high sequence similarity to Pros28.1, were identified and characterized. Pros28.1A encodes a protein with 74% amino acid identity to PROS28.1, while the Pros28.1B gene product is 58% identical. The Pros28.1B gene has two introns, located in exactly analogous positions as the two introns in Pros28.1, while the Pros28.1A gene lacks introns. Northern blot analysis reveals that the two new genes are expressed only in males, during the pupal and adult stages. Tissue-specific patterns of expression were examined using transgenic flies carrying lacz-fusion reporter genes. This analysis revealed that both genes are expressed in germline cells during spermatogenesis, although their expression patterns differed. Pros28.1A expression is first detected at the primary spermatocyte stage and persists into the spermatid elongation phase of spermiogenesis, while Pros28.1B expression is prominent only during spermatid elongation. These genes represent the most striking example of cell-type-specific proteasome gene expression reported to date in any system and support the notion that there is structural and functional heterogeneity among proteasomes in metazoans.

Protein-protein interactions among components of the Drosophila primary sex determination signal

Sex determination in Drosophila melanogaster is initiated in the early embryo by a signal provided by three types of genes: (1) X-linked numerator elements [e.g., sisterless-a (sis-a) and sisterless-b (sis-b)], (2) autosomally linked denominator elements [e.g., deadpan (dpn)], and (3) maternal factors [e.g., daughterless (da)]. This signal acts to stimulate transcription from an embryo-specific promoter of the master regulatory gene Sex-lethal (Sxl) in embryos that have two X chromosomes (females), while it fails to activate Sxl in those with only one X (males). It has been previously proposed that competitive dimerizations among the components of this signal might provide the molecular basis for this sex specificity. Here, we use the yeast two-hybrid system to demonstrate specific protein-protein interactions among the above-mentioned factors, and to delimit their interacting domains. These results support and extend the model of the molecular basis of the X/A ratio signal.

Isolation of the rat F1-ATPase inhibitor gene and its pseudogenes

Multiple mitochondrial ATPase inhibitor genes have been identified in the rat-genome. The sequences of two genomic clones indicate that one encodes the functional gene, and the other is a processed pseudogene. The ATPase inhibitor gene isolated is about 1.5 kb long and the coding region contains three exons and two introns. The presence of multiple pseudogenes in the rat is suggested by this study and this is unique since in the bovine genome only a single gene has been found, which is also confirmed here. The presence of multiple inhibitor transcripts in the rat suggests that the functional gene might have multiple transcriptional start sites.

Determination of the molecular lesions associated with loss-of-function transformer alleles of Drosophila melanogaster

Three mutant alleles of the transformer locus, trav1, trav2 and traenu, were analyzed genetically, and all were found to be functionally null alleles. The DNA sequences of these mutants revealed that they represent nonsense mutations that potentially encode truncated Tra polypeptides of 12, 61, and 90 amino acids, respectively.

Identification of an essential gene, l(3)73Ai, with a dominant temperature-sensitive lethal allele, encoding a Drosophila proteasome subunit

Proteasomes are multicatalytic proteinase complexes that function as a major nonlysosomal proteolytic system in all eukaryotes. These particles are made up of 13-15 nonidentical subunits, and they exhibit multiple endopeptidase activities that promote the intracellular turnover of abnormal polypeptides and short-lived regulatory proteins. Although the biochemical characterization of proteasomes has been quite extensive, and although a number of the genes encoding proteasome subunits have been cloned from various organisms, there is still much to be learned about their function in vivo and what role(s) they might play during development. Here, we report the identification of the l(3)73Ai1 allele of Drosophila melanogaster as a dominant temperature-sensitive lethal mutation in a gene encoding a component of the proteasome, thus opening the way for future genetic and developmental studies on this important proteolytic system in a higher eukaryote.

Interspecific comparison of the transformer gene of Drosophila reveals an unusually high degree of evolutionary divergence

The transformer (tra) gene of Drosophila melanogaster occupies an intermediate position in the regulatory pathway controlling all aspects of somatic sexual differentiation. The female-specific expression of this gene's function is regulated by the Sex lethal (Sxl) gene, through a mechanism involving sex-specific alternative splicing of tra pre-mRNA. The tra gene encodes a protein that is thought to act in conjunction with the transformer-2 (tra-2) gene product to control the sex-specific processing of doublesex (dsx) pre-mRNA. The bifunctional dsx gene carries out opposite functions in the two sexes, repressing female differentiation in males and repressing male differentiation in females. Here we report the results from an evolutionary approach to investigate tra regulation and function, by isolating the tra-homologous genes from selected Drosophila species, and then using the interspecific DNA sequence comparisons to help identify regions of functional significance. The tra-homologous genes from two Sophophoran subgenus species, Drosophila simulans and Drosophila erecta, and two Drosophila subgenus species, Drosophila hydei and Drosophila virilis, were cloned, sequenced and compared to the D. melanogaster tra gene. This comparison reveals an unusually high degree of evolutionary divergence among the tra coding sequences. These studies also highlight a highly conserved sequence within intron one that probably defines a cis-acting regulator of the sex-specific alternative splicing event.

Cytogenetic analysis of chromosome region 73AD of Drosophila melanogaster

The 73AD salivary chromosome region of Drosophila melanogaster was subjected to mutational analysis in order to (1) generate a collection of chromosome breakpoints that would allow a correlation between the genetic, cytological and molecular maps of the region and (2) define the number and gross organization of complementation groups within this interval. Eighteen complementation groups were defined and mapped to the 73A2-73B7 region, which is comprised of 17 polytene bands. These complementation groups include the previously known scarlet (st), transformer (tra) and Dominant temperature-sensitive lethal-5 (DTS-5) genes, as well as 13 new recessive lethal complementation groups and one male and female sterile locus. One of the newly identified lethal complementation groups corresponds to the molecularly identified abl locus, and another gene is defined by mutant alleles that exhibit an interaction with the abl mutants. We also recovered several mutations in the 73C1-D1.2 interval, representing two lethal complementation groups, one new visible mutant, plucked (plk), and a previously known visible, dark body (db). There is no evidence of a complex of sex determination genes in the region near tra.

The control of sexual development in Drosophila melanogaster: genetic and molecular analysis of a genetic regulatory hierarchy--a minireview

Genetic analyses of mutants affecting the sexual development of the fruitfly, Drosophila melanogaster, have led to a genetic model that describes how the wild-type genes interact with one another as parts of a single regulatory pathway. More recent molecular studies on some of these sex differentiation regulatory genes have lent support to this genetic model, and have defined the molecular nature of some of these genetic interactions. One surprising feature of the regulatory hierarchy to emerge from these molecular studies is that many of the sex-specific genetic switches in this pathway are not transcriptional regulation events but, rather, are based on sex-specific alternative RNA processing events (pre-mRNA splicing and/or polyadenylation site selection).

Sex-specific alternative splicing of RNA from the transformer gene results from sequence-dependent splice site blockage

Sex-specific alternative splicing of RNA from the Drosophila transformer gene involves competition between two 3' splice sites. In the absence of Sex-lethal activity (as in males), only one site functions; in the presence of Sex-lethal activity (as in females), both sites function. Information for sex-specific splice site choice is contained within the intron itself. Deletions of the splice site used in males lead to Sex-lethal-independent use of the otherwise female-specific site. The relative amounts of unspliced and spliced RNA derived from these mutant genes do not change with changes in Sex-lethal activity. Specific nucleotide changes in the non-sex-specific splice site do not affect splicing activity but eliminate Sex-lethal-induced regulation. A deletion removing material between the two splice sites does not eliminate sex-specific regulation, while a deletion of the female splice site leads to a female-specific increase in unspliced RNA. These results are consistent with a model in which female-specific factors block the function of the non-sex-specific 3' splice site.

Cloning and characterization of the scarlet gene of Drosophila melanogaster

DNA from the scarlet (st) region of Drosophila melanogaster has been cloned by chromosome walking, using the breakpoints of a new X-ray-induced third chromosome inversion (In(3LR)st-a27) which breaks in the scarlet (73A3.4) and rosy (87D13-14) regions. Two spontaneous mutants of st(st1 and stsp) contain insertions of non-st DNA located within 3.0 kb of the site of the inversion breakpoint used to isolate the gene, and a second scarlet inversion breaks within 6.5 kb of this site. However no changes detectable by Southern blotting were found in 5 X-ray-induced st mutants with cytologically normal third chromosomes. A 2.3-kb transcript arising from the st gene region (as defined by mutant analysis and DNA transformation) has been detected. This transcript is present throughout development at low levels, with a peak level during the early to mid-pupal stage. The size and amount of this transcript is altered in st1, and its amount is drastically reduced in stsp. Flies carrying the white1 mutation show normal levels of expression of the st transcript, suggesting that the w+ gene does not regulate transcription of the st+ gene. Nucleotide homology between sequences from the st transcription unit and a fragment carrying coding information from the white gene has been detected. This suggests that the st and w proteins are related; they appear to belong to a family of membrane-spanning, ATP-binding proteins involved in the transport of pigment precursors into cells.

Molecular genetics of transformer, a genetic switch controlling sexual differentiation in Drosophila

The transformer gene is one of a set of regulatory genes that form the hierarchy controlling all aspects of somatic sexual differentiation in Drosophila melanogaster. The gene transformer occupies an intermediate position in this hierarchy. Analysis of this gene has allowed us to determine the mechanism by which it is regulated in a sex-specific manner and to examine the way in which the regulatory hierarchy is organized. The female-specific expression of the tra gene, previously inferred from genetic observations, is based on sex-specific alternative splicing of tra pre-mRNA and is not the result of sex-specific transcriptional activation. The female-specific RNA produced by this alternative splicing is the functional mediator of tra activity. Multiple genetic, molecular, and transformation experiments show that female-specific activation of genes or gene products occurs in the order Sex lethal greater than transformer greater than transformer-2 greater than doublesex greater than or equal to intersex greater than female differentiation. The results do not distinguish the level at which transformer might regulate the downstream gene transformer-2. Neither transformer nor any of the down-stream genes feedback on, or participate in, alternative splicing of transformer RNA. The mechanism by which Sex lethal regulates transformer splicing appears to be a repression of the use of one of a pair of splice acceptor sites.

Ectopic expression of the female transformer gene product leads to female differentiation of chromosomally male Drosophila

The transformer (tra) gene of Drosophila is necessary for all aspects of female somatic sexual differentiation. tra uses a single set of precursor RNAs to produce female- and non-sex-specific RNAs by alternative splicing. Ectopic expression of the female-specific RNA causes chromosomal males to develop as females, indicative of a linear pathway of regulated genes controlling sex. Genetic and molecular tests with this ectopically expressed gene are consistent with the following order of gene action: X chromosome to autosome ratio----Sex lethal----transformer----transformer-2----doublesex----intersex--- - terminal differentiation. Expression of the female-specific tra RNA in tra mutants is sufficient to lead to female differentiation. Expression of the non-sex-specific tra RNA in tra mutants is not sufficient to lead to female differentiation. The tra female-specific activity is not required for female-specific splicing of the tra precursor RNAs.

The control of alternative splicing at genes regulating sexual differentiation in D. melanogaster

The transformer (tra) and doublesex (dsx) genes produce sex-specific transcripts that are generated by differential RNA processing. We have examined the effects of mutants in other regulatory genes controlling sexual differentiation on the patterns of processing of the tra and dsx RNA transcripts. Our results demonstrate that the genes suggested by genetic studies to act upstream of tra or dsx in the sex determination hierarchy regulate these two loci at the level of RNA processing. Our data suggest that the order of interaction of the factors controlling sex is X:A greater than Sxl greater than tra greater than tra-2 greater than dsx greater than or equal to ix greater than terminal differentiation. While these results cannot preclude regulatory interactions at other levels, the regulation of RNA splicing revealed by these experiments is sufficient to account for all of the known functional interactions between the regulatory genes in this hierarchy.

Sexual behavior: its genetic control during development and adulthood in Drosophila melanogaster

Courtship behavior in Drosophila melanogaster males is an innate behavior pattern. Whether or not a fly will display male courtship behavior is governed by the action of a set of regulatory genes that control all aspects of somatic sexual differentiation. The wild-type function of one of these regulatory genes, transformer-2 (tra-2), is necessary for female sexual differentiation; in the absence of tra-2+ function XX individuals differentiate as males. A temperature-sensitive tra-2 allele has been used to investigate, by means of temperature shifts, when and how male courtship behavior is specified during development. The removal of tra-2ts function in the adult (by a shift of the tra-2ts mutant flies to the restrictive temperature) can lead to the appearance of male courtship behavior in flies that otherwise would not display these behaviors. These experiments suggest that the regulatory hierarchy controlling sexual differentiation is functioning in the adult central nervous system. More importantly, these results suggest that the adult central nervous system has some functional plasticity with respect to the innate behavioral pattern of male courtship and is maintained in a particular state of differentiation by the active control of gene expression in the adult.

Regulation of sexual differentiation in D. melanogaster via alternative splicing of RNA from the transformer gene

The transformer (tra) gene regulates female somatic sexual differentiation and has no known function in males. It gives rise to two sizes of RNA, one non-sex-specific and one female-specific. These two RNAs are shown to be present throughout the life cycle, and related by the use of alternative first intron splice acceptor sites. The non-sex-specific RNA has a 73 base first intron, while that in the female-specific RNA is 248 bases. The non-sex-specific RNA has no long open reading frame, while the female-specific RNA has a single long open reading frame beginning at the first AUG. Substitution of a heat shock promoter for the tra promoter still leads to female-specific differentiation of otherwise tra-females. We suggest a mechanism by which Sex-lethal controls itself and tra.

A molecular analysis of transformer, a gene in Drosophila melanogaster that controls female sexual differentiation

The transformer (tra) gene regulates all aspects of somatic sexual differentiation in Drosophila melanogaster females and has no function in males. We have isolated the tra gene as part of a 200 kb chromosomal walk. The 25 kb region around tra contains four genetically identified complementation groups and at least six transcriptional units. Germ-line transformation experiments indicate that a fragment of 2 kb is sufficient to supply tra+ function. Mapping of cDNAs from tra and from the adjacent genes indicates that the tra+ transcription unit is 1.2 kb or less. This transcription unit gives rise to a 1.0 kb RNA that is female-specific and a 1.2 kb RNA that is present in both sexes. tra+ and the gene at the 3' side overlap slightly in the 3' ends of their RNA coding sequences. These results suggest that tra+ function is regulated at the level of production of the female-specific tra RNA. The fact that a tra transcript is found in males raises interesting possibilities for how tra expression is controlled.

Sequences expressed sex-specifically in Drosophila melanogaster adults

To obtain probes for sex-specific gene regulation during development in D. melanogaster, sequences expressed sex-specifically in adult flies were isolated by differential cDNA hybridization screens of a genomic library. Ten clones define new sex-specifically expressed genes. The remaining three isolates correspond to previously cloned genes encoding female-specific yolk proteins and chorion proteins. The pattern of expression of these genes in sex determination mutants and in germlineless flies, as well as their tissue specificities, permitted us to distinguish transcripts whose expression is dependent on correct sexual development of the soma or the germline. One of the female transcripts is expressed in nurse cells and oocytes. Five of the male-specific sequences are expressed in the testis during spermatogenesis: the remaining one is expressed in the soma. Experiments using a temperature-sensitive allele of tra-2 show that the presence of this male-specific transcript, found only in the adult paragonia, is not affected by temperature shift of X/X; tra-2ts2 adults. This is in contrast to yolk protein genes, which require tra-2 function in the adult for their expression in the female fat body.

Sex-specific regulation of yolk protein gene expression in Drosophila

Many of the genes in the regulatory hierarchy controlling sex determination in Drosophila melanogaster are known. Here we examine how this regulatory hierarchy controls the expression of the structural genes encoding the female-specific yolk polypeptides. Temperature shift experiments with a temperature-sensitive allele of the sex determination regulatory gene transformer-2 (tra-2) showed that tra-2+ function is required in the adult for both the sex-specific initiation and maintenance of YP synthesis. Control of the YP genes by this regulatory hierarchy is at the level of transcription, or transcript stability. The results of temperature shift experiments with abdomens isolated from tra-2ts homozygotes support the notion that the tra-2+ function acts in a cell-autonomous manner to control YP synthesis. These results provide a paradigm for the way this regulatory hierarchy controls the terminal differentiation functions for sexually dimorphic development.

MALE-SPECIFIC LETHAL MUTATIONS OF DROSOPHILA MELANOGASTER. II. PARAMETERS OF GENE ACTION DURING MALE DEVELOPMENT

The male-specific lethal mutations (msl's) identify loci whose wild-type gene products are essential for male, but not female, viability. Earlier studies in which X-linked gene activities were monitored in msl/msl male larvae demonstrated that these genes are responsible for setting and/or maintaining the level of X chromosome transcription in males (i.e., they are necessary for proper dosage compensation). The present study examines several important questions concerning their mode of action during development—The results of an examination of the effects of an msl-1 deficiency on male-lethal phase and female viability suggest that this mutation is an amorph, or a severe hypomorph. The effects of rendering a fly mutant for more than one male-lethal mutation were also examined. Multiply mutant flies were no more severely affected than singly mutant ones. A gynandromorph analysis revealed that the male-limited lethality associated with msl-2 has no single lethal focus. Somatic clones of homozygous msl-2 cells were initiated at various times during development by X-ray-induced mitotic recombination. An examination of the viability, growth patterns and morphology of marked clones demonstrated that: (1) msl-2  + acts in a cell autonomous manner, (2) msl-2  + function is required not only in larval (polytene) cells as was shown in previous work but is also needed in the diploid cells that give rise to adult structures, (3) the msl-2  + gene is needed fairly late in development and perhaps continuously, (4) the msl-2 mutation does not affect sexual differentiation.

The dual functions of a sex determination gene in Drosophila melanogaster

The wild-type function of the sex transforming gene transformer-2 (tra-2) is shown to be required for normal spermatogenesis in XY males. A temperature-shift experiment using the tra-2ts2 allele suggests that tra-2+ must function during the middle stages of spermatogenesis to ensure development of functional sperm. Our results, taken together with those of T. Schüpbach (1982, Dev. Biol. 89, 117-127) indicate that the tra-2+ gene functions in the male germ line and thus, in contrast to all other sex determination loci examined to date (doublesex, intersex, transformer), its action is not limited to the soma. Orcein-stained testis preparations from tra-2 males reveal a spermiogenic defect similar to that associated with dominant male sterile (X; autosome) translocations.

Sex determination in Drosophila melanogaster: analysis of transformer-2, a sex-transforming locus

The transformer-2 (tra-2) locus is one of a set of regulatory loci that control sex determination in Drosophila melanogaster. Temperature-shift experiments with temperature-sensitive tra-2 mutants demonstrate that within single cell lineages tra-2+ function is required at several times, and probably continuously, during development for the occurrence of a series of determinative decisions necessary for female sexual differentiation. Analysis of the effects of tra-2 in the genital disc demonstrates that the tra-2+ function is necessary in females both to prevent male sexual differentiation and to permit female differentiation. These and other results support the model that the tra-2+ and tra+ loci act to control the expression of the bifunctional doublesex (dsx) locus.

Male-specific lethal mutations of Drosophila melanogaster

A total of 7,416 ethyl methanesulfonate (EMS)-treated second chromosomes and 6,212 EMS-treated third chromosomes were screened for sex-specific lethals. Four new recessive male-specific lethal mutations were recovered. When in homozygous condition, each of these mutations kills males during the late larval or early pupal stages, but has no detectable effect in females. One mutant, mlets, is a temperature sensitive allele of maleless, mle (Fukunaga, Tanaka and Oishi 1975), while the other three mutants identify two new loci: male-specific lethal-1 (msl-1) (two alleles) at map position 2-53.3 and male-specific lethal-2 (msl-2) at 2-9.0----The male-specific lethality associated with these mutants is not related to the sex per se of the mutant flies, since sex-transforming genes fail to interact with these mutations. Moreover, the presence or absence of a Y chromosome in males or females has no influence on the male-specific lethal action of these mutations. Finally, no single region of the X chromosome, when present as a duplication, is sufficient to rescue males from the lethal effects of msl-1 or msl-2. These results suggest that the number of complete X chromosomes determines whether a fly homozygous for a male-specific lethal mutation lives or dies.

Control of X chromosome transcription by the maleless gene in Drosophila

In Drosophila, a large group of structural genes exhibit coordinate regulation, not because they function in a common developmental pathway but because they happen to reside on the X chromosome. These genes are subjected to the regulatory mechanism of dosage compensation which insures that their phenotypic products are identical in the sex with one and in the sex with two X chromosomes. This equilization of gene products is achieved by regulating the level of transcription of both X chromosomes in females and of the single X chromosome in males. We report here that, reasoning that sex-specific lethal mutations may represent lesions in the processes controlling the transcription of X-linked loci, we sought and recovered several male-specific lethal mutations and noted that they affect the levels of X-linked enzyme activities in crude extracts of homozygous male larvae. Autoradiographic monitoring of RNA synthesis in larval polytene chromosomes of males homozygous for one of these mutations, mlets, reveals a significant reduction in the rate of X chromosome transcription.