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

Genetics ◽  
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.

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

Genetics ◽  
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.

Dosage Compensation in Drosophila: Evidence That daughterless and Sex-lethal Control X Chromosome Activity at the Blastoderm Stage of Embryogenesis

Genetics ◽  
1987 ◽  
Vol 117 (3) ◽  
pp. 477-485
Author(s):  
J Peter Gergen
Keyword(s):  
X Chromosome ◽  
Dosage Compensation ◽  
Lethal Gene ◽  
Gene Products ◽  
Lethal Control ◽  
Eye Color ◽  
Phenotypic Assay ◽  
Sex Lethal ◽  
Blastoderm Stage

ABSTRACT Dosage compensation is a mechanism that equalizes the expression of X chromosome linked genes in males, who have one X chromosome, with that in females, who have two. In Drosophila, this is achieved by the relative hyperactivation of X-linked genes in males, as was first shown by Muller using a phenotypic assay based on adult eye color. Several genes involved in regulating dosage compensation have been identified through the isolation of mutations that are sex-specific lethals. However, because of this lethality it is not straightforward to assay the relative roles of these genes using assays based on adult phenotypes. Here this problem is circumvented using an assay based on embryonic phenotypes. These experiments indicate that dosage compensation is established early in development and demonstrate that the daughterless and Sex-lethal gene products are involved in regulating X chromosome activity at the blastoderm stage of embryogenesis.

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

1992 ◽  
Vol 59 (3) ◽  
pp. 189-198 ◽  
Author(s):  
Miguel Torres ◽  
Lucas Sanchez
Keyword(s):  
Sex Determination ◽  
Dosage Compensation ◽  
Relative Number ◽  
Initial Step ◽  
The Other ◽  
Loss Of Function ◽  
X Chromosomes ◽  
Segmentation Gene ◽  
Ectopic Activation ◽  
Sex Lethal

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.

scholarly journals 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 ◽  
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.

scholarly journals Transposon insertions causing constitutive Sex-lethal activity in Drosophila melanogaster affect Sxl sex-specific transcript splicing.

Genetics ◽  
1995 ◽  
Vol 139 (2) ◽  
pp. 631-648
Author(s):  
M Bernstein ◽  
R A Lersch ◽  
L Subrahmanyan ◽  
T W Cline
Keyword(s):  
Drosophila Melanogaster ◽  
X Chromosome ◽  
Dosage Compensation ◽  
Rna Splicing ◽  
Wild Type ◽  
Gain Of Function ◽  
Positive Regulators ◽  
Sex Lethal ◽  
Male Specific ◽  
Transposon Insertions

Abstract Sex-lethal (Sxl) gene products induce female development in Drosophila melanogaster and suppress the transcriptional hyperactivation of X-linked genes responsible for male X-chromosome dosage compensation. Control of Sxl functioning by the dose of X-chromosomes normally ensures that the female-specific functions of this developmental switch gene are only expressed in diplo-X individuals. Although the immediate effect of X-chromosome dose is on Sxl transcription, during most of the life cycle "on" vs. "off" reflects alternative Sxl RNA splicing, with the female (productive) splicing mode maintained by a positive feedback activity of SXL protein on Sxl pre-mRNA splicing. "Male-lethal" (SxlM) gain-of-function alleles subvert Sxl control by X-chromosome dose, allowing female Sxl functions to be expressed independent of the positive regulators upstream of Sxl. As a consequence, SxlM haplo-X animals (chromosomal males) die because of improper dosage compensation, and SxlM chromosomal females survive the otherwise lethal effects of mutations in upstream positive regulators. Five independent spontaneous SxlM alleles were shown previously to be transposon insertions into what was subsequently found to be the region of regulated sex-specific Sxl RNA splicing. We show that these five alleles represent three different mutant types: SxlM1, SxlM3, and SxlM4. SxlM1 is an insertion of a roo element 674 bp downstream of the translation-terminating male-specific exon. SxlM3 is an insertion of a hobo transposon (not 297 as previously reported) into the 3' splice site of the male exon, and SxlM4 is an insertion of a novel transposon into the male-specific exon itself. We show that these three gain-of-function mutants differ considerably in their ability to bypass the sex determination signal, with SxlM4 being the strongest and SxlM1 the weakest. This difference is also reflected in effects of these mutations on sex-specific RNA splicing and on the rate of appearance of SXL protein in male embryos. Transcript analysis of double-mutant male-viable SxlM derivatives in which the SxlM insertion is cis to loss-of-function mutations, combined with other results reported here, indicates that the constitutive character of these SxlM alleles is a consequence of an alteration of the structure of the pre-mRNA that allows some level of female splicing to occur even in the absence of functional SXL protein. Surprisingly, however, most of the constitutive character of SxlM alleles appears to depend on the mutant alleles' responsiveness, perhaps greater than wild-type, to the autoregulatory splicing activity of the wild-type SXL proteins they produce.

scholarly journals Conditional knockdown of transformer in sheep blow fly suggests a role in repression of dosage compensation and potential for population suppression

PLoS Genetics ◽  
2021 ◽  
Vol 17 (10) ◽  
pp. e1009792
Author(s):  
Megan E. Williamson ◽  
Ying Yan ◽  
Maxwell J. Scott
Keyword(s):  
X Chromosome ◽  
Dosage Compensation ◽  
Rna Splicing ◽  
Pupal Stage ◽  
Mrna Levels ◽  
Loss Of Function ◽  
Blow Fly ◽  
Female Development ◽  
Australian Sheep ◽  
Xx Males

The transformer (tra) gene is essential for female development in many insect species, including the Australian sheep blow fly, Lucilia cuprina. Sex-specific tra RNA splicing is controlled by Sex lethal (Sxl) in Drosophila melanogaster but is auto-regulated in L. cuprina. Sxl also represses X chromosome dosage compensation in female D. melanogaster. We have developed conditional Lctra RNAi knockdown strains using the tet-off system. Four strains did not produce females on diet without tetracycline and could potentially be used for genetic control of L. cuprina. In one strain, which showed both maternal and zygotic tTA expression, most XX transformed males died at the pupal stage. RNAseq and qRT-PCR analyses of mid-stage pupae showed increased expression of X-linked genes in XX individuals. These results suggest that Lctra promotes somatic sexual differentiation and inhibits X chromosome dosage compensation in female L. cuprina. However, XX flies homozygous for a loss-of-function Lctra knockin mutation were fully transformed and showed high pupal eclosion. Two of five X-linked genes examined showed a significant increase in mRNA levels in XX males. The stronger phenotype in the RNAi knockdown strain could indicate that maternal Lctra expression may be essential for initiation of dosage compensation suppression in female embryos.

Induction of female Sex-lethal RNA splicing in male germ cells: implications for Drosophila germline sex determination

Development ◽  
1997 ◽  
Vol 124 (24) ◽  
pp. 5033-5048 ◽  
Author(s):  
J.H. Hager ◽  
T.W. Cline
Keyword(s):  
Sex Determination ◽  
Germ Cells ◽  
Rna Splicing ◽  
Feedback Loop ◽  
Dose Effect ◽  
Male Germ Cells ◽  
Control Female ◽  
Sex Lethal ◽  
Specific Regulation ◽  
Female Specific

With a focus on Sex-lethal (Sxl), the master regulator of Drosophila somatic sex determination, we compare the sex determination mechanism that operates in the germline with that in the soma. In both cell types, Sxl is functional in females (2X2A) and nonfunctional in males (1X2A). Somatic cell sex is determined initially by a dose effect of X:A numerator genes on Sxl transcription. Once initiated, the active state of SXL is maintained by a positive autoregulatory feedback loop in which Sxl protein insures its continued synthesis by binding to Sxl pre-mRNA and thereby imposing the productive (female) splicing mode. The gene splicing-necessary factor (snf), which encodes a component of U1 and U2 snRNPs, participates in this RNA splicing control. Here we show that an increase in the dose of snf+ can trigger the female Sxl RNA splicing mode in male germ cells and can feminize triploid intersex (2X3A) germ cells. These snf+ dose effects are as dramatic as those of X:A numerator genes on Sxl in the soma and qualify snf as a numerator element of the X:A signal for Sxl in the germline. We also show that female-specific regulation of Sxl in the germline involves a positive autoregulatory feedback loop on RNA splicing, as it does in the soma. Neither a phenotypically female gonadal soma nor a female dose of X chromosomes in the germline is essential for the operation of this feedback loop, although a female X-chromosome dose in the germline may facilitate it. Engagement of the Sxl splicing feedback loop in somatic cells invariably imposes female development. In contrast, engagement of the Sxl feedback loop in male germ cells does not invariably disrupt spermatogenesis; nevertheless, it is premature to conclude that Sxl is not a switch gene in germ cells for at least some sex-specific aspects of their differentiation. Ironically, the testis may be an excellent organ in which to study the interactions among regulatory genes such as Sxl, snf, ovo and otu which control female-specific processes in the ovary.

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

Development ◽  
1995 ◽  
Vol 121 (10) ◽  
pp. 3245-3258 ◽  
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.

scholarly journals scute (sis-b) function in Drosophila sex determination.

1995 ◽  
Vol 15 (8) ◽  
pp. 4430-4440 ◽  
Author(s):  
G Deshpande ◽  
J Stukey ◽  
P Schedl
Keyword(s):  
Sex Determination ◽  
X Chromosome ◽  
Immunoblot Analysis ◽  
Lethal Gene ◽  
Helix Loop Helix ◽  
Nuclear Cycle ◽  
Early Embryos ◽  
Initial Activation ◽  
Activity State

The primary sex determination signal, the X chromosome-to-autosome (X/A) ratio, controls the choice of sexual identity in the Drosophila melanogaster embryo by regulating the activity of the early promoter of the Sex-lethal gene, Sxl-Pe. This promoter is activated in females (2X/2A), while it remains off in males (1X/2A). Promoter activation in females is dependent upon X-linked numerator genes. One of these genes, sisterless-b (sis-b), corresponds to the scute (sc) locus of the achaete-scute complex, and it encodes a helix-loop-helix transcription factor. In the studies reported here we have used monoclonal antibodies to study the expression and functioning of the sc(sis-b) protein. Sc is first detected at nuclear cycle 6 to 7, well before Sxl-Pe is first active. At this stage, the protein is in the cytoplasm, not the nucleus. Only after the formation of the syncytial blastoderm, at nuclear cycle 10 to 11, does a substantial fraction of the protein enter the nucleus, and this nuclear import closely coincides with the initial activation of Sxl-Pe. Consistent with the idea that the dose of sc(sis-b) is critical for its function as an X-chromosome counting element, wild-type syncytial blastoderm embryos could be grouped into two classes based on the level of protein. Western blot (immunoblot) analysis demonstrates that this difference in protein level correlates directly with the activity state of the Sxl gene. Finally, we provide the first direct evidence that Sc forms heteromeric complexes in vivo in early embryos with the maternally derived helix-loop-helix protein Daughterless. This in vivo complex is likely to be critical for Sc function in Sxl-Pe activation.

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