Sex determination in polyploids of Caenorhabditis elegans.

Abstract In Caenorhabditis elegans triploid animals with two X chromosomes (symbolized 3A;2X) are males. However, these triploid males can be feminized by making them mutant for recessive dosage compensation mutations, by adding X chromosome duplications or by microinjecting particular DNA sequences termed feminizing elements. None of these treatments affects diploid males. This study explores several aspects of these treatments in polyploids. The dosage compensation mutants exhibit a strong maternal effect, such that reduction of any of the dosage compensation gene functions in the mother leads to sex reversal of 3A;2X animals. Likewise, all X chromosome duplications tested cause both sex reversal and intersexual development of many 3A;2X animals. Microinjected feminizing element DNA does not cause extensive sex reversal, but does result in intersexual development in 3A;2X animals. Neither X chromosome duplications nor microinjected feminizing elements show that extreme maternal effect of the dosage compensation mutants, although there is indirect evidence for a maternal effect of the feminizing elements. In particular, very little feminizing element DNA needs to be microinjected in order to feminize triploid males, far less than what is needed for stable inheritance, implying that feminizing elements can work within the mother's gonad. However, even very high concentrations of microinjected feminizing elements do not affect sex determination in diploid males, suggesting that they are not part of the numerator of the X/A ratio. In addition, no pair of X chromosome duplications feminizes diploid males, suggesting that none of these duplications contains a numerator of the X/A ratio. Instead, I infer that an X-linked locus, as yet undefined, must be present in two copies for hermaphrodite development to ensue or that the two X chromosomes might interact.

Download Full-text

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.

Download Full-text

The Caenorhabditis elegans Dosage Compensation Machinery Is Recruited to X Chromosome DNA Attached to an Autosome

Genetics ◽

10.1093/genetics/156.4.1603 ◽

2000 ◽

Vol 156 (4) ◽

pp. 1603-1621

Author(s):

Jason D Lieb ◽

Carlos Ortiz de Solorzano ◽

Enrique Garcia Rodriguez ◽

Arthur Jones ◽

Michael Angelo ◽

...

Keyword(s):

Caenorhabditis Elegans ◽

X Chromosome ◽

Dosage Compensation ◽

Dna Sequences ◽

Three Dimensional ◽

Dosage Compensation Complex ◽

X Chromosomes ◽

Cis Acting ◽

Recognition Elements ◽

The Right

Abstract The dosage compensation machinery of Caenorhabditis elegans is targeted specifically to the X chromosomes of hermaphrodites (XX) to reduce gene expression by half. Many of the trans-acting factors that direct the dosage compensation machinery to X have been identified, but none of the proposed cis-acting X chromosome-recognition elements needed to recruit dosage compensation components have been found. To study X chromosome recognition, we explored whether portions of an X chromosome attached to an autosome are competent to bind the C. elegans dosage compensation complex (DCC). To do so, we devised a three-dimensional in situ approach that allowed us to compare the volume, position, and number of chromosomal and subchromosomal bodies bound by the dosage compensation machinery in wild-type XX nuclei and XX nuclei carrying an X duplication. The dosage compensation complex was found to associate with a duplication of the right 30% of X, but the complex did not spread onto adjacent autosomal sequences. This result indicates that all the information required to specify X chromosome identity resides on the duplication and that the dosage compensation machinery can localize to a site distinct from the full-length hermaphrodite X chromosome. In contrast, smaller duplications of other regions of X appeared to not support localization of the DCC. In a separate effort to identify cis-acting X recognition elements, we used a computational approach to analyze genomic DNA sequences for the presence of short motifs that were abundant and overrepresented on X relative to autosomes. Fourteen families of X-enriched motifs were discovered and mapped onto the X chromosome.

Download Full-text

Major sex-determining genes and the control of sexual dimorphism in Caenorhabditis elegans

Genome ◽

10.1139/g89-116 ◽

1989 ◽

Vol 31 (2) ◽

pp. 625-637 ◽

Cited By ~ 4

Author(s):

Jonathan Hodgkin ◽

Andrew D. Chisholm ◽

Michael M. Shen

Keyword(s):

Caenorhabditis Elegans ◽

Sex Determination ◽

X Chromosome ◽

Germ Line ◽

Cell Lineage ◽

Regulatory Genes ◽

Nematode Caenorhabditis Elegans ◽

X Chromosomes ◽

The Many ◽

Lineage Analysis

Sex determination in Caenorhabditis elegans involves a cascade of major regulatory genes connecting the primary sex determining signal, X chromosome dosage, to key switch genes, which in turn direct development along either male or female pathways. Animals with one X chromosome (XO) are male, while animals with two X chromosomes (XX) are hermaphrodite: hermaphrodite development occurs because the action of the regulatory genes is modified in the germ line so that both sperm and oocytes are made inside a completely female soma. The regulatory genes are being examined by both genetic and molecular means. We discuss how these major genes, in particular the last switch gene in the cascade, tra-1, might regulate the many different sex-specific events that occur during the development of the hermaphrodite and of the male.Key words: nematode, Caenorhabditis elegans, sex determination, sexual differentiation, cell lineage analysis.

Download Full-text

The Caenorhabditis elegans gene sdc-2 controls sex determination and dosage compensation in XX animals.

Genetics ◽

10.1093/genetics/122.3.579 ◽

1989 ◽

Vol 122 (3) ◽

pp. 579-593 ◽

Cited By ~ 4

Author(s):

C Nusbaum ◽

B J Meyer

Keyword(s):

Caenorhabditis Elegans ◽

Sex Determination ◽

X Chromosome ◽

Dosage Compensation ◽

Apparent Effect ◽

Linked Gene ◽

Male Development ◽

Coordinate Control

Abstract We have identified a new X-linked gene, sdc-2, that controls the hermaphrodite (XX) modes of both sex determination and X chromosome dosage compensation in Caenorhabditis elegans. Mutations in sdc-2 cause phenotypes that appear to result from a shift of both the sex determination and dosage compensation processes in XX animals to the XO modes of expression. Twenty-eight independent sdc-2 mutations have no apparent effect in XO animals, but cause two distinct phenotypes in XX animals: masculinization, reflecting a defect in sex determination, and lethality or dumpiness, reflecting a disruption in dosage compensation. The dosage compensation defect can be demonstrated directly by showing that sdc-2 mutations cause elevated levels of several X-linked transcripts in XX but not XO animals. While the masculinization is blocked by mutations in sex determining genes required for male development (her-1 and fem-3), the lethality, dumpiness and overexpression of X-linked genes are not, indicating that the effect of sdc-2 mutations on sex determination and dosage compensation are ultimately implemented by two independent pathways. We propose a model in which sdc-2 is involved in the coordinate control of both sex determination and dosage compensation in XX animals and acts in the regulatory hierarchy at a step prior to the divergence of the two pathways.

Download Full-text

LETHALS, STERILES AND DEFICIENCIES IN A REGION OF THE X CHROMOSOME OF CAENORHABDITIS ELEGANS

Genetics ◽

10.1093/genetics/92.1.99 ◽

1979 ◽

Vol 92 (1) ◽

pp. 99-115 ◽

Cited By ~ 8

Author(s):

Philip M Meneely ◽

Robert K Herman

Keyword(s):

Caenorhabditis Elegans ◽

X Chromosome ◽

Maternal Effect ◽

Mutant Allele ◽

Temperature Sensitive ◽

Wild Type ◽

Nematode Caenorhabditis Elegans ◽

X Chromosomes ◽

X Ray ◽

Chromosome Duplication

ABSTRACT Twenty-one X-linked recessive lethal and sterile mutations balanced by an unlinked X-chromosome duplication have been identified following EMS treatment of the small nematode, Caenorhabditis elegans. The mutations have been assigned by complementation analysis to 14 genes, four of which have more than one mutant allele. Four mutants, all alleles, are temperature-sensitive embryonic lethals. Twelve mutants, in ten genes, are early larval lethals. TWO mutants are late larval lethals, and the expression of one of these is influenced by the number of X chromosomes in the genotype. Two mutants are maternal-effect lethals; for both, oocytes made by mutant hermaphrodites are rescuable by wild-type sperm. One of the maternal-effect lethals and two larval lethals are allelic. One mutant makes defective sperm. The lethals and steriles have been mapped by recombination and by complementation testing against 19 deficiencies identified after X-ray treatment. The deficiencies divide the region, about 15% of the X-chromosome linkage map, into at least nine segments. The deficiencies have also been used to check the phenotypes of hemizygous lethal and sterile hermaphrodites.

Download Full-text

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.

Download Full-text

X chromosome duplications affect a region of the chromosome they do not duplicate in Caenorhabditis elegans.

Genetics ◽

10.1093/genetics/119.2.365 ◽

1988 ◽

Vol 119 (2) ◽

pp. 365-375

Author(s):

P M Meneely ◽

K D Nordstrom

Keyword(s):

Gene Expression ◽

Caenorhabditis Elegans ◽

Sex Determination ◽

X Chromosome ◽

Dosage Compensation ◽

Linked Gene ◽

Hypomorphic Mutation ◽

Level Of Activity

Abstract X chromosome duplications have been used previously to vary the dose of specific regions of the X chromosome to study dosage compensation and sex determination in Caenorhabditis elegans. We show here that duplications suppress and X-linked hypomorphic mutation and elevate the level of activity of an X-linked enzyme, although these two genes are located in a region of the X chromosome that is not duplicated. The effects do not depend on the region of the X chromosome duplicated and is stronger in strains with two doses of a duplication than in strains with one dose. This is evidence for a general elevation of X-linked gene expression in strains carrying X-chromosome duplications, consistent with the hypothesis that the duplications titrate a repressor acting on many X-linked genes.

Download Full-text

Two Classes of Dosage Compensation Complex Binding Elements along Caenorhabditis elegans X Chromosomes

Molecular and Cellular Biology ◽

10.1128/mcb.01448-08 ◽

2009 ◽

Vol 29 (8) ◽

pp. 2023-2031 ◽

Cited By ~ 6

Author(s):

Timothy A. Blauwkamp ◽

Gyorgyi Csankovszki

Keyword(s):

Caenorhabditis Elegans ◽

X Chromosome ◽

Dosage Compensation ◽

Gene Products ◽

Dosage Compensation Complex ◽

X Chromosomes ◽

Linked Gene ◽

Unknown Mechanism

ABSTRACT Dosage compensation equalizes X-linked gene products between the sexes. In Caenorhabditis elegans, the dosage compensation complex (DCC) binds both X chromosomes in XX animals and halves the transcription from each. The DCC is recruited to the X chromosomes by a number of loci, rex sites, and is thought to spread from these sites by an unknown mechanism to cover the rest of the chromosome. Here we describe a novel class of DCC-binding elements that we propose serve as “way stations” for DCC binding and spreading. Both rex sites and way stations comprise strong foci of DCC binding on the native X chromosome. However, rex sites maintain their ability to bind large amounts of DCC even on X duplications detached from the native X, while way stations do not. These results suggest that two distinct classes of DCC-binding elements facilitate recruitment and spreading of the DCC along the X chromosome.

Download Full-text

Isolation of dominant XO-feminizing mutations in Caenorhabditis elegans: new regulatory tra alleles and an X chromosome duplication with implications for primary sex determination.

Genetics ◽

10.1093/genetics/141.2.527 ◽

1995 ◽

Vol 141 (2) ◽

pp. 527-542

Author(s):

J Hodgkin ◽

D G Albertson

Keyword(s):

Caenorhabditis Elegans ◽

Sex Determination ◽

X Chromosome ◽

Chemical Mutagenesis ◽

The Novel ◽

X Chromosomes ◽

Inverted Orientation ◽

Fertile Female ◽

Fertile Male ◽

Selection Of

Abstract A strain of Caenorhabditis elegans was constructed that permits selection of dominant or sex-linked mutations that transform XO animals (normally male) into fertile females, using a feminizing mutation, tra-2(e2046gf), which by itself does not sexually transform XO males. Twenty-three mutations were isolated after chemical mutagenesis and found to fall into both expected classes (four dominant tra-1 mutations and eight recessive xol-1 mutations) and novel classes. The novel mutations include 10 second-site mutations of tra-2, which are called eg mutations, for enhanced gain-of-function. The tra-2(gf, eg) alleles lead to complete dominant transformation of XO animals from fertile male into fertile female. Also isolated was a duplication of the left end of the X chromosome, eDp26, which has dominant XO lethal and feminizing properties, unlike all previously isolated duplications of the X chromosome. The properties of eDp26 indicate that it carries copies of one or more numerator elements, which act as part of the primary sex-determination signal, the X:A ratio. The eDp26 duplication is attached to the left tip of the X chromosome in inverted orientation and consequently can be used to generate unstable attached-X chromosomes.

Download Full-text

POLYPLOIDS AND SEX DETERMINATION IN CAENORHABDITIS ELEGANS

Genetics ◽

10.1093/genetics/93.2.393 ◽

1979 ◽

Vol 93 (2) ◽

pp. 393-402 ◽

Cited By ~ 11

Author(s):

James E Madl ◽

Robert K Herman

Keyword(s):

Caenorhabditis Elegans ◽

Sex Determination ◽

X Chromosome ◽

Sex Chromosomes ◽

Chromosome Constitution ◽

Diploid Males ◽

C Elegans

ABSTRACT Tetraploid stocks of Caenorhabditis elegans var. Bristol carrying autosomal and X-linked markers have been produced. Tetraploid hermaphrodites fall into two categories: those that give about 1% male self-progeny and those that give 25 to 40% male self-progeny, The former are basically 4A;4X—four sets of autosomes and four sex chromosomes—and the latter are 4A;3X. Males are 4A;2X. (Diploid hermaphrodites are 2A;2X; males are 2A;IX.) Triploids wsre produced by crossing tetraploid hermaphrodites and diploid males. Triploids of composition 3A;3X are hermaphrodites; 3A;2X animals are fertile males. Different X-chromosome duplications were added to a 3A;2X chromosome constitution to increase the X-to-autosome ratio. Based on the resulting sexual phenotypes, we conclude that there exists on the C. elegans X chromosome at least three (and perhaps many mare) dose-sensitive sites that act cumulatively in determining sex.

Download Full-text