The segmentation gene runt is needed to activate Sex-lethal, a gene that controls sex determination and dosage compensation in Drosophila

SummaryIn Drosophila, sex is determined by the relative number of X chromosomes to autosomal sets (X: A ratio). The amount of products from several X-linked genes, called sisterless elements, is used to indicate to Sex-lethal the relative number of X chromosomes present in the cell. In response to the X: A signal, Sex-lethal is activated in females but remains inactive in males, being responsible for the control of both sex determination and dosage compensation. Here we find that the X-linked segmentation gene runt plays a role in this process. Reduced function of runt results in femalespecific lethality and sexual transformation of XX animals that are heterozygous for Sxl or sis loss-of-function mutations. These interactions are suppressed by SxlMI, a mutation that constitutively expresses female Sex-lethal functions, and occur at the time when the X: A signal determines Sex-lethal activity. Moreover, the presence of a loss-of-function runt mutation masculinizes triploid intersexes. On the other hand, runt duplications cause a reduction in male viability by ectopic activation of Sex-lethal. We conclude that runt is needed for the initial step of Sex-lethal activation, but does not have a major role as an X-counting element.

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Genetic evidence that the sans fille locus is involved in Drosophila sex determination.

Genetics ◽

10.1093/genetics/120.1.159 ◽

1988 ◽

Vol 120 (1) ◽

pp. 159-171

Author(s):

B Oliver ◽

N Perrimon ◽

A P Mahowald

Keyword(s):

Sex Determination ◽

Dosage Compensation ◽

Germ Line ◽

Ovarian Tumors ◽

Lethal Gene ◽

Nurse Cells ◽

Loss Of Function ◽

Wild Type ◽

Sex Lethal

Abstract Females homozygous for sans fille1621 (= fs(1)1621) have an abnormal germ line. Instead of producing eggs, the germ-line cells proliferate forming ovarian tumors or excessive numbers of nurse cells. The Sex-lethal gene product(s) regulate the branch point of the dosage compensation and sex determination pathways in the soma. The role of Sex-lethal in the germ line is not clear but the germ line of females homozygous for female sterile Sex-lethal alleles or germ-line clones of loss-of-function alleles are characterized by ovarian tumors. Females heterozygous for sans fille1621 or Sex-lethal are phenotypically wild type with respect to viability and fertility but females trans-heterozygous for sans fille1621 and Sex-lethal show ovarian tumors, somatic sexual transformations, and greatly reduced viability.

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Sex determination in the germ line of Drosophila depends on genetic signals and inductive somatic factors

Development ◽

10.1242/dev.107.3.505 ◽

1989 ◽

Vol 107 (3) ◽

pp. 505-518 ◽

Cited By ~ 15

Author(s):

R. Nothiger ◽

M. Jonglez ◽

M. Leuthold ◽

P. Meier-Gerschwiler ◽

T. Weber

Keyword(s):

Sex Determination ◽

Germ Cells ◽

Germ Line ◽

The State ◽

Loss Of Function ◽

X Chromosomes ◽

Constitutive Mutation ◽

Sex Lethal ◽

Double Sex ◽

State Of Activity

We have analyzed the mechanism of sex determination in the germ line of Drosophila by manipulating three parameters: (1) the ratio of X-chromosomes to sets of autosomes (X:A); (2) the state of activity of the gene Sex-lethal (Sxl), and (3) the sex of the gonadal soma. To this end, animals with a ratio of 2X:2A and 2X:3A were sexually transformed into pseudomales by mutations at the sex-determining genes Sxl (Sex-lethal), tra (transformer), tra-2 (transformer-2), or dsx (double-sex). Animals with the karyotype 2X;3A were also transformed into pseudofemales by the constitutive mutation SxlM1. The sexual phenotype of the gonads and of the germ cells was assessed by phase-contrast microscopy. Confirming the conclusions of Steinmann-Zwicky et al. (Cell 57, 157, 1989), we found that all three parameters affect sex determination in germ cells. In contrast to the soma in which sex determination is completely cell-autonomous, sex determination in the germ line has a non-autonomous component inasmuch as the sex of the soma can influence the sexual pathway of the germ cells. Somatic induction has a clear effect on 2X;2A germ cells that carry a Sxl+ allele. These cells, which form eggs in an ovary, can enter spermatogenesis in testes. Mutations that cause partial loss of function or gain of function of Sxl thwart somatic induction and, independently of the sex of the soma, dictate spermatogenesis or oogenesis, respectively. Somatic induction has a much weaker effect on 2X;3A germ cells. This ratio is essentially a male signal for germ cells which consistently enter spermatogenesis in testes, even when they carry SxlM1. In a female soma, however, SxlM1 enables the 2X;3A germ cells to form almost normal eggs. Our results show that sex determination in the germ line is more complex than in the soma. They provide further evidence that the state of Sxl, the key gene for sex determination and dosage compensation in the soma, also determines the sex of the germ cells, and that, in the germ line, the state of activity of Sxl is regulated not only by the X:A ratio, but also by somatic inductive stimuli.

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Differential effects of Sex-lethal mutations on dosage compensation early in Drosophila development.

Genetics ◽

10.1093/genetics/136.3.1051 ◽

1994 ◽

Vol 136 (3) ◽

pp. 1051-1061

Author(s):

M Bernstein ◽

T W Cline

Keyword(s):

Sex Determination ◽

X Chromosome ◽

Dosage Compensation ◽

Rna Splicing ◽

Lethal Gene ◽

Loss Of Function ◽

Developmental Pathway ◽

Pathway Choice ◽

Sex Lethal ◽

Blastoderm Stage

Abstract In response to the primary sex determination signal, X chromosome dose, the Sex-lethal gene controls all aspects of somatic sex determination and differentiation, including X chromosome dosage compensation. Two complementary classes of mutations have been identified that differentially affect Sxl somatic functions: (1) those impairing the "early" function used to set developmental pathway choice in response to the sex determination signal and (2) those impairing "late" functions involved in maintaining the pathway choice independent of the initiating signal and/or in directing differentiation. This "early vs. late" distinction correlates with a switch in promoter utilization from SxlPe to SxlPm at the blastoderm stage and a corresponding switch from transcriptional to RNA splicing control. Here we characterize five partial-loss-of-function Sxl alleles to explore a distinction between "early vs. late" functioning of Sxl in dosage compensation. Assaying for dosage compensation during the blastoderm stage, we find that the earliest phase of the dosage compensation process is controlled by products of the early Sxl promoter, SxlPe. Hence, in addition to triggering the sexual pathway decision of cells, products derived from SxlPe also control early dosage compensation, the first manifestation of sexually dimorphic differentiation. The effects of mutant Sxl alleles on early dosage compensation are consistent with their previous categorization as early vs. late defective with respect to their effects on pathway initiation. Results reported here suggest that the dosage compensation regulatory genes currently known to function downstream of Sxl, genes known as the "male-specific lethals," do not control all aspects of dosage compensation either at the blastoderm stage or later in development. In the course of this study, we also discovered that the canonical early defective allele, Sxlf9, which is impaired in its ability to establish the female developmental pathway commitment, is likely to be defective in the stability and/or functioning of products derived from SxlPe, rather than in the ability of SxlPe to respond to the chromosomal sex determination signal.

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The msl-2 dosage compensation gene of Drosophila encodes a putative DNA-binding protein whose expression is sex specifically regulated by Sex-lethal

Development ◽

10.1242/dev.121.10.3245 ◽

1995 ◽

Vol 121 (10) ◽

pp. 3245-3258 ◽

Cited By ~ 6

Author(s):

G.J. Bashaw ◽

B.S. Baker

Keyword(s):

Dna Binding ◽

X Chromosome ◽

Dosage Compensation ◽

Ring Finger ◽

The Other ◽

Male Specific Lethal ◽

Alternatively Spliced ◽

Sex Lethal ◽

Specific Regulation ◽

Male Specific

In Drosophila dosage compensation increases the rate of transcription of the male's X chromosome and depends on four autosomal male-specific lethal genes. We have cloned the msl-2 gene and shown that MSL-2 protein is co-localized with the other three MSL proteins at hundreds of sites along the male polytene X chromosome and that this binding requires the other three MSL proteins. msl-2 encodes a protein with a putative DNA-binding domain: the RING finger. MSL-2 protein is not produced in females and sequences in both the 5′ and 3′ UTRs are important for this sex-specific regulation. Furthermore, msl-2 pre-mRNA is alternatively spliced in a Sex-lethal-dependent fashion in its 5′ UTR.

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Both Loss-of-Function and Gain-of-Function Mutations in snf Define a Role for snRNP Proteins in Regulating Sex-lethal Pre-mRNA Splicing in Drosophila Development

Genetics ◽

10.1093/genetics/144.1.95 ◽

1996 ◽

Vol 144 (1) ◽

pp. 95-108

Author(s):

Helen K Salz ◽

Thomas W Flickinger

Keyword(s):

Sex Determination ◽

Rna Splicing ◽

Loss Of Function ◽

Functional Homology ◽

Snrnp Protein ◽

A Cell ◽

Sex Lethal ◽

Mutant Phenotypes ◽

Female Specific ◽

Male Specific

Abstract The Drosophila snf gene encodes a protein with functional homology to the mammalian UlA and U2B″ snRNP proteins. Studies, based on the analysis of three viable alleles, have suggested a role for snf in establishing the female-specific splicing pattern of the sex determination switch gene, Sex-lethal. Here, we show that the non-sex-specific lethal null allele is required for female sex determination, arguing against the formal possibility that the viable alleles disrupt a function unrelated to snf's wild-type function. Moreover, we find snf is required for normal cell growth and/or survival, as expected for a protein involved in a cell-vital process such as RNA splicing. We also show that of the three viable alleles only one, snfJA2, is a partial loss-of-function mutation. The other two viable alleles, snf1621 and snfe8H, encode antimorphic proteins. We find the antimorphic proteins are mislocalized and correlate their mislocalization with their molecular lesions and mutant phenotypes. Finally, we provide genetic evidence that the antimorphic alleles interfere with the autoregulatory splicing function of the Sex-lethal protein. Based on these studies we suggest a model in which the snRNP protein, Snf, functions with Sex-lethal to block recognition of the regulated male-specific exon.

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Identification of X chromosome regions in Caenorhabditis elegans that contain sex-determination signal elements.

Genetics ◽

10.1093/genetics/138.4.1105 ◽

1994 ◽

Vol 138 (4) ◽

pp. 1105-1125

Author(s):

C C Akerib ◽

B J Meyer

Keyword(s):

Caenorhabditis Elegans ◽

Sex Determination ◽

X Chromosome ◽

Dosage Compensation ◽

X Chromosomes ◽

Sensitive Region ◽

Signal Element ◽

Number Of Genes ◽

Mutant Phenotypes ◽

Chromosome Regions

Abstract The primary sex-determination signal of Caenorhabditis elegans is the ratio of X chromosomes to sets of autosomes (X/A ratio). This signal coordinately controls both sex determination and X chromosome dosage compensation. To delineate regions of X that contain counted signal elements, we examined the effect on the X/A ratio of changing the dose of specific regions of X, using duplications in XO animals and deficiencies in XX animals. Based on the mutant phenotypes of genes that are controlled by the signal, we expected that increases (in males) or decreases (in hermaphrodites) in the dose of X chromosome elements could cause sex-specific lethality. We isolated duplications and deficiencies of specific X chromosome regions, using strategies that would permit their recovery regardless of whether they affect the signal. We identified a dose-sensitive region at the left end of X that contains X chromosome signal elements. XX hermaphrodites with only one dose of this region have sex determination and dosage compensation defects, and XO males with two doses are more severely affected and die. The hermaphrodite defects are suppressed by a downstream mutation that forces all animals into the XX mode of sex determination and dosage compensation. The male lethality is suppressed by mutations that force all animals into the XO mode of both processes. We were able to subdivide this region into three smaller regions, each of which contains at least one signal element. We propose that the X chromosome component of the sex-determination signal is the dose of a relatively small number of genes.

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RNA Binding Protein Sex-Lethal (Sxl) and Control of Drosophila Sex Determination and Dosage Compensation

Microbiology and Molecular Biology Reviews ◽

10.1128/mmbr.67.3.343-359.2003 ◽

2003 ◽

Vol 67 (3) ◽

pp. 343-359 ◽

Cited By ~ 100

Author(s):

Luiz O. F. Penalva ◽

Lucas Sánchez

Keyword(s):

Sex Determination ◽

Dosage Compensation ◽

Target Genes ◽

Rna Binding ◽

Rna Binding Proteins ◽

Regulatory Gene ◽

Sex Lethal ◽

Male Specific ◽

Regulatory Functions ◽

And Control

SUMMARY In the past two decades, scientists have elucidated the molecular mechanisms behind Drosophila sex determination and dosage compensation. These two processes are controlled essentially by two different sets of genes, which have in common a master regulatory gene, Sex-lethal (Sxl). Sxl encodes one of the best-characterized members of the family of RNA binding proteins. The analysis of different mechanisms involved in the regulation of the three identified Sxl target genes (Sex-lethal itself, transformer, and male specific lethal-2) has contributed to a better understanding of translation repression, as well as constitutive and alternative splicing. Studies using the Drosophila system have identified the features of the protein that contribute to its target specificity and regulatory functions. In this article, we review the existing data concerning Sxl protein, its biological functions, and the regulation of its target genes.

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The dpy-30 gene encodes an essential component of the Caenorhabditis elegans dosage compensation machinery.

Genetics ◽

10.1093/genetics/137.4.999 ◽

1994 ◽

Vol 137 (4) ◽

pp. 999-1018 ◽

Cited By ~ 7

Author(s):

D R Hsu ◽

B J Meyer

Keyword(s):

Caenorhabditis Elegans ◽

Sex Determination ◽

X Chromosome ◽

Dosage Compensation ◽

The Other ◽

Temperature Sensitive ◽

Wild Type ◽

Phenotypic Analysis ◽

General Role ◽

Essential Component

Abstract The need to regulate X chromosome expression in Caenorhabditis elegans arises as a consequence of the primary sex-determining signal, the X/A ratio (the ratio of X chromosomes to sets of autosomes), which directs 1X@A animals to develop as males and 2X/2A animals to develop as hermaphrodites. C. elegans possesses a dosage compensation mechanism that equalizes X chromosome expression between the two sexes despite their disparity in X chromosome dosage. Previous genetic analysis led to the identification of four autosomal genes, dpy-21, dpy-26, dpy-27 and dpy-28, whose products are essential in XX animals for proper dosage compensation, but not for sex determination. We report the identification and characterization of dpy-30, an essential component of the dosage compensation machinery. Putative null mutations in dpy-30 disrupt dosage compensation and cause a severe maternal-effect, XX-specific lethality. Rare survivors of the dpy-30 lethality are dumpy and express their X-linked genes at higher than wild-type levels. These dpy-30 mutant phenotypes superficially resemble those caused by mutations in dpy-26, dpy-27 and dpy-28; however, detailed phenotypic analysis reveals important differences that distinguish dpy-30 from these genes. In contrast to the XX-specific lethality caused by mutations in the other dpy genes, the XX-specific lethality caused by dpy-30 mutations is completely penetrant and temperature sensitive. In addition, unlike the other genes, dpy-30 is required for the normal development of XO animals. Although dpy-30 mutations do not significantly affect the viability of XO animals, they do cause them to be developmentally delayed and to possess numerous morphological and behavioral abnormalities. Finally, dpy-30 mutations can dramatically influence the choice of sexual fate in animals with an ambiguous sexual identity, despite having no apparent effect on the sexual phenotype of otherwise wild-type animals. Paradoxically, depending on the genetic background, dpy-30 mutations cause either masculinization or feminization, thus revealing the complex regulatory relationship between the sex determination and dosage compensation processes. The novel phenotypes caused by dpy-30 mutations suggest that in addition to acting in the dosage compensation process, dpy-30 may play a more general role in the development of both XX and XO animals.

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sisterless A is required for the activation of Sex lethal in the germline

10.1101/2019.12.17.880070 ◽

2019 ◽

Cited By ~ 1

Author(s):

Raghav Goyal ◽

Ellen Baxter ◽

Mark Van Doren

Keyword(s):

Sex Determination ◽

X Chromosome ◽

Germ Cells ◽

Specific Expression ◽

Male Germ Cells ◽

X Chromosomes ◽

Dna Elements ◽

Sex Lethal ◽

Female Specific ◽

Necessary And Sufficient

ABSTRACTIn Drosophila, sex determination in somatic cells has been well-studied and is under the control of the switch gene Sex lethal (Sxl), which is activated in females by the presence of two X chromosomes. Though sex determination is regulated differently in the germline versus the soma, Sxl is also necessary and sufficient for the female identity in germ cells. Loss of Sxl function in the germline results in ovarian germline tumors, a characteristic of male germ cells developing in a female soma. Further, XY (male) germ cells expressing Sxl are able to produce eggs when transplanted into XX (female) somatic gonads, demonstrating that Sxl is also sufficient for female sexual identity in the germline. As in the soma, the presence of two X chromosomes is sufficient to activate Sxl in the germline, but the mechanism for “counting” X chromosomes in the germline is thought to be different from the soma. Here we have explored this mechanism at both cis- and trans-levels. Our data support the model that the Sxl “establishment” promoter (SxlPE) is activated in a female-specific manner in the germline, as in the soma, but that the timing of SxlPE activation, and the DNA elements that regulate SxlPE are different from those in the soma. Nevertheless, we find that the X chromosome-encoded gene sisterless A (sisA), which helps activate Sxl in the soma, is also essential for Sxl activation in the germline. Loss of sisA function leads to loss of Sxl expression in the germline, and to ovarian tumors and germline loss. These defects can be rescued by the expression of Sxl, demonstrating that sisA lies upstream of Sxl in germline sex determination. We conclude that sisA acts as an X chromosome counting element in both the soma and the germline, but that additional factors that ensure robust, female-specific expression of Sxl in the germline remain to be discovered.

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Regulation of domains and whole chromosomes

Epigenetics, Nuclear Organization & Gene Function ◽

10.1093/oso/9780198831204.003.0009 ◽

2019 ◽

pp. 104-122

Author(s):

John C. Lucchesi

Keyword(s):

X Chromosome ◽

Ribosomal Rna ◽

Dosage Compensation ◽

Sex Chromosomes ◽

Extreme Case ◽

The Other ◽

Histone Genes ◽

Mammalian Embryo ◽

X Chromosomes ◽

Coordinate Regulation

Clusters of genes that encode similar products, such as the β‎-globin, the ribosomal RNA (rRNA) and the histone genes, are regulated in a coordinated fashion. An extreme case of coordinate regulation—dosage compensation—involves the genes present on the sex chromosomes. In Drosophila males, a complex (MSL) associates with the X chromosome where it enhances the activity of most X-linked genes. In Caenorhabditis, a complex (DCC) decreases the level of transcription of both X chromosomes in the XX hermaphrodite. In mammals, dosage compensation is achieved by the inactivation, early during development, of most X-linked genes on one of the two X chromosomes in females. In the mammalian embryo, X inactivation of either X chromosome is random and clonally inherited. The mechanism involves the synthesis of an RNA (Tsix) that protects one of the two Xs from inactivation, and of another RNA (Xist) that coats the other X chromosome and recruits histone- and DNA-modifying enzymes.

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