XO Males Research Articles

Fertile XO males and females in the varying lemming, Dicrostonyx torquatus pall. (1779)

In the varying lemming, only some of the females exhibit a conventional sex chromosome constitution, XX. Many fertile females as well as all males have one X chromosome. The Y chromosome was not revealed by the methods employed. It has been shown that the sex of XO specimens depends on a genetic factor which displays two alternative forms. The XO lemmings possessing the m-form develop as males; those carrying the f-form develop as females. This factor is most likely X-linked. The XX females are heterozygous for this factor or homozygous for the m-form. In progeny of the XO and heterozygous XX females an excess of daughters is observed, the secondary sex ratio being 0·67 and 0·75 respectively. Two or three mutational events must have given rise to this complex system of sex determination. The possible adaptive significance of the relevant system is discussed.

NONDISJUNCTION MUTANTS OF THE NEMATODE CAENORHABDITIS ELEGANS

The frequency of males (5AA; XO) among the self progeny of wild-type Caenorhabditis elegans hermaphrodites (5AA; XX) is about one in 500. Fifteen him (for "high incidence of males") mutations have been identified that increase this frequency by a factor of ten to 150, as a result of increased X-chromosome nondisjunction. The mutations define ten complementation groups, which have been mapped: nine are autosomal, and one sex linked. Most of the mutants are superficially wild type in anatomy and behavior; however, him-4 mutants display gonadal abnormalities, and unc-86 mutants, which have a Him phenotype, exhibit a variety of anatomical and behavioral abnormalities. All the mutants segregate fertile 3X hermaphrodite progeny as well as XO male progeny. Some produce large numbers of inviable zygotes. Mutants in all ten genes produce diplo-X and nullo-X exceptional ova, and in the four strains tested, diplo-X and nullo-X exceptional sperm are produced by 2X "transformed" males. It appears likely that most of the mutants have defects in both gamete lines of the hermaphrodite. XO males of him strains other than him-4 and unc-86 are similar to wild-type males in anatomy and behavior, and all produce equal or almost equal numbers of haplo-X and nullo-X sperm, and no diplo-X sperm. Male fertility is reduced to varying extents in all him mutants. In four of the strains, nondisjunction during oogenesis has been shown to occur at a reductional division, and in three of these strains, abnormalities in recombination have been demonstrated. One mutant also exhibits autosomal nondisjunction, but many of the others probably do not. Therefore, the X chromosome of C. elegans may differ from the autosomes in the mechanisms controlling its meiotic behavior.--3X hermaphrodites are shorter and less fertile than 2X hermaphrodites, and they produce many inviable zygotes among their self progeny: these are probably 4X zygotes. Haplo-X and diplo-X ova are produced in 2:1 ratio by 3X hermaphrodites. him mutations are expressed in these animals, increasing the frequency of self-progeny males and 2X hermaphrodites.

The Role of H-Y Antigen in Primary Sex Determination

The basic embryonic plan of mammals is inherently feminine. Male development is due to two-step interventions of this basic plan: the Y chromosome directs the embryonic indifferent gonad to organize a testis instead of an ovary; the Y-organized testis synthesizes and secretes testosterone, which induces all the extragonadal masculine development. The Y chromosome plays no direct and appreciable role in extragonadal masculine development. Testicular organization, normally under the direction of the Y, is the function of the evolutionary conserved plasma membrane protein serologically detectable as H-Y antigen. Under specific circumstances, H-Y antigen may be expressed in the absence of the Y chromosome, thus producing XO and XX males. If H-Y antigen is not expressed, XY individuals develop as females. H-Y antigen is the first plasma membrane or cell surface protein to which a specific organogenesis function has been assigned.

Meiotic studies in mice carrying the sex reversal (Sxr) factor.

A sex reversal factor (Sxr) that causes mice having apparently normal X chromosomes to become phenotypically male is transmitted in an autosomal pattern. The origin of the Sxr factor is still unknown. It seems most likely that it has originated from an autosomal gene mutation or is the result of a translocation of part of the Y chromosome to one of the autosomes. Chromosomes from four XY and six XO mice carrying this sex reversal factor were examined in the diakinesis stage of meiosis. The following unusual observations were noted: (1) in XY males carrying the Sxr factor, the X and Y chromosomes were separated more often than in controls. (2) The Y chromosome tends to be closer to an autosome when the X and Y are separate than when the X and Y are attached. (3) A chromosome fragment was present in 4/226 cells from two XO males and a single cell from an XY, Sxr carrier. Although there is no direct evidence, these observations seem to favor the possibility that the Sxr factor involves a chromosomal rearrangement rather than a single gene mutation.

Studies on the ribosomal RNA cistrons in interspecific Drosophila hybrids : I. Nucleolar dominance

Interspecific hybrids between Drosophila melanogaster and Drosophila simulans were examined for patterns of secondary constriction formation at the nucleolus-organizer regions. In neuroblast tissue taken from F 1 interspecific hybrids, a nucleolar constriction was normally absent from the D. simulans X chromosome, while a secondary constriction was always associated with the D. melanogaster sex chromosome, regardless of the origin of maternal egg cytoplasm. When hybrids lacking a D. melanogaster sex chromosome were constructed, however, the resulting XO males were viable and displayed a constriction at the D. simulans nucleolus organizer. These results suggest a preferential transcription of ribosomal DNA from the D. melanogaster genome when nucleolus organizers from both species are present in conjunction, a phenomenon termed nucleolar dominance. In addition, rDNA redundancy in regular interspecific F 1 progeny was monitored by RNA-DNA hybridization. Parental values conformed to previously reported measurements, but hybrid rDNA values were nonadditive with respect to the parental contributions. Hybrid females possessed rDNA levels approximately 73 genes in excess of predicted values. Since F 1 hybrid progeny presumably inherit wild-type levels of rDNA, this disproportionate increase may represent a response to a functional, rather than a physical, deficiency.

Gene expression and the control of spermatid morphogenesis in Drosophila melanogaster

The genetic control of spermatid morphogenesis was studied by light microscopy through the analysis of meiotic and premeiotic lesions. Sperm disfunction-type male-sterile mutations were screened for novel “early effect” mutations: (1) timing mutations, in which mitochondrial aggregation occurs before instead of after meiosis; (2) mutations which affect the spindle structure, e.g., a mutant with second-division monoastral spindle; (3) mutations which cause deformations in primary spermatocyte structures. It is shown, in addition to the examples cited above, that normal meiosis may often serve as an early marker for normal differentiation, and that approximately 20% of male-sterile mutations are meiotic mutants. The role of the Y chromosome was reexamined. The interaction between Y factors and X-linked male steriles is in many cases additive, indicating that Y gene products are essential for normal development of the primary spermatocytes. Furthermore, XO males are shown to be extreme meiotic mutants. It is argued that spermatid morphogenesis is totally dependent on developmental processes in the primary spermatocyte stage. The relations among developmental processes in early spermatogenesis are discussed in terms of gene activity.

MUTATIONS CAUSING TRANSFORMATION OF SEXUAL PHENOTYPE IN THE NEMATODE CAENORHABDITIS ELEGANS

Ten mutations are described that transform genotypic hermaphrodites of the nematode Caenorhabditis elegans into phenotypic males. These fall into three autosomal complementation groups, termed tra-1, tra-2, and tra-3. Two alleles of tra-1 produce almost complete transformation, to a fertile male phenotype; such transformed animals are useful for analyzing sex-linked genes. All alleles of tra-1 and tra-2 are recessive; the one known allele of tra-3 is both recessive and maternal in effect. Where tested, both XX and XXX hermaphrodites are transformed into males, but XO males (true males) are unaffected by these mutations. It is suggested that these genes are actually involved in hermaphrodite development and have no role in male development.

Testis-determining H-Y antigen in XO males of the mole-vole (Ellobius lutescens)

The XO sex chromosome constitution has been found in both sexes of the mole-vole (Ellobius lutescens) belonging to the rodent family Microtinae. This enigmatic species has apparently been enduring a 50% zygotic lethality. The current serological study revealed the presence in XO males and the absence from XO females of H-Y (histocompatibility Y) antigen. In all the mammalian species studied thus far, the expression of H-Y antigen strictly coincided with the presence of testicular tissue and not necessarily with the presence of the Y chromosome. The testis-organizing function of the H-Y gene appears to have been confirmed. In the mole-vole, X linkage of the testis-organizing H-Y gene is favored over its autosomal inheritance. Only X linkage of the H-Y gene creates a compelling evolutionary need to change the female sex chromosome constitution from XX to XO, and to abandon the dosage compensation by an X inactivation mechanism, so that the nonproductive X H-YX zygote can be eliminated as an embryonic lethal. With regard to the electrophoretic mobilities of three X-linked marker enzymes, however, a genetic difference between the male-specific X H-Y and the female-specific X was not detected. This might reflect a relatively recent speciation.

Characterisation of male meiotic-sterile mutations in Drosophila melanogaster

Male meiotic sterile mutations were selected among X-linked male-steriles by detection of micronuclei in early spermatids. Despite severe defects in the 1st or 2nd meiotic spindles in all mutants, no effect on mitosis was observed. Various features of spindle structure, chromosome segregation, and centriole movements were compared in seven meitoic steriles and in XO males. Chromosome behaviour and centriole movement were always affected concomitantly, and were both shown to be genetically independent of "centre" formation in the meiotic spindles. Precocious and delayed centromere separation was observed in the various mutants in both divisions, and similarly attributed to basic spindle lesions rather than chromosome defects. Attachment of the centriole body to the membrane of the spermatid nucleus was normal only in mutants where second division nuclei were formed. The role of the centriole body was shown to be independent of membrane attachment.--The phenomena observed in this study were discussed mainly with regard to genetic interdependence of morphogenetic processes during male meiosis. A common base for the pleiotropic defects of meiotic steriles and XO males is suggested, and the genetic control of meiosis is re-evaluated in the light of comparison with fertile meiotic mutants.

Karyotypes and Meiosis of the Morabine Grasshoppers. I. Introduction and Genera Moraba, Spectriforma and Filoraba.

Moraba, with four species, has two showing the primitive 2nB = 17 karyotype and two in which the large metacentric AB autosome has undergone dissociation into separate acrocentrics. Spectriforma, also with four species (one cytologically unknown) shows the primitive karyotype. The single species of Filoraba likewise shows 2nB = 17, but its karyotype is distinctive, since one of the small autosomes has undergone an evolutionary diminution in size and is exceedingly minute. Members of these genera all have XO males. No cytological material of Drysdalopila, the fourth genus of the tribe Morabini (Key 1977), was available.

The induction of aneuploidy by colcemid fed to Drosophila melanogaster females

Colcemid, a chemical closely related to colchicine, was fed to Drosophila melanogaster females (0.0001 and 0.0005%, respectively). In the F 1 the frequency of aneuploid males (XO karyotype) and aneuploid females (either of the XXY or of the XXXY karyotype, with 2 and 3 sets of autosomes, respectively) was significantly higher than in the controls as shown by genetical methods supplemented by cytological tests. A consistent brood pattern effect was observed, possibly but not necessarily reflecting differential stage sensitivity to the action of colcemid. It seems plausible to assume that most of the aneuploid exceptions were produced via colcemid-induced spindle defects leading to lagging of the X-chromosome. Exclusion of the lagging X from the pronucleus (or its precursors) would yield XO males, its inclusion would yield XXY females. Definitely more XO than XXY exceptions were observed.

The induction of aneuploidy by colcemid fed to Drosophila melanogaster females

Colcemid, a chemical closely related to colchicine, was fed to Drosophila melanogaster females (0.0001 and 0.0005%, respectively). In the F1 the frequency of aneuploid males (XO karyotype) and aneuploid females (either of the XXY or of the XXXY karyotype, with 2 and 3 sets of autosomes, respectively) was significantly higher than in the controls as shown by genetical methods supplemented by cytological tests. A consistent brood pattern effect was observed, possibly but not necessarily reflecting differential stage sensitivity to the action of colcemid. It seems plausible to assume that most of the aneuploid exceptions were produced via colcemid-induced spindle defects leading to lagging of the X-chromosome. Exclusion of the lagging X from the pronucleus (or its precursors) would yield XO males, its inclusion would yield XXY females. Definitely more XO than XXY exceptions were observed.

Radiosensitization of Drosophila sperm by commonly used food additives--butylated hydroxyanisole and butylated hydroxytoluene.

SummaryThe radiosensitivity of sperm of Drosophila melanogaster was enhanced by a factor of about two by commonly-used food additives. Neither butylated hydroxyanisole (BHA) nor butylated hydroxytoluene (BHT), with and without gamma-irradiation (0, 1·2, 2·4 and 3·6 krads), had any noticeable effect on the sex-ratio. At the concentration used (0·001 per cent BHA; 0·001 per cent BHT), the two phenolic antioxidants seem to induce XB-chromosome loss in the sperm (XO males in F1) and sex-linked recessive lethal mutations in F2, although these effects were not statistically significant. However, both agents proved to be potent radiosensitizers for the sex-linked recessive lethals.

The nucleolus in primary spermatocytes of Drosophila hydei.

Transcribing ribosomal RNA genes in primary spermatocyte nucleoli of Drosophila hydei have been visualized by electron microscopy using a microspreading technique. The length of the transcribing unit is in agreement with the length of the ribosomal RNA precursor as determined by acrylamide gel electrophoresis (2.6×106 daltons). The length of the non-transcribed spacer is approximately 1.0×106 daltons. The maximum number of active cistrons in wild type (XY) males only approaches one half the estimated number of ribosomal cistrons of the replicated diploid genome (∼300) of D. hydei and is found to vary between 120 and 320 cistrons in different developmental stages of spermatocytes. There is also some variation between different males. In a few cases a variation in the transcriptional activity of different cistrons has been observed. The synthesis of ribosomal RNA therefore seems to be regulated primarily by the activation or inaetivation of varying numbers of ribosomal cistrons. Groups of adjacent cistrons seem to be under coordinated control. Inhibition of RNA synthesis by actinomycin, in contrast, follows a random pattern. The frequent observation of a bipartite nucleolus indicates that the nucleolus organizer regions of the two sex chromosomes are both active in transcription. The number of active ribosomal eistrons found in some X-Y translocation stocks and in XO males deviates considerably from that expected on the basis of DNA/RNA hybridization data. We conclude that, in agreement with the observations of other authors, a mechanism adjusting the number of ribosomal cistrons may be operating in these cases.

Sex-reversed mice: XX and XO males.

An autosomally inherited condition is described in the mouse which causes genetic females to develop as phenotypic males. XX males are phenotypically normal with the exception of small testes, which, in the adult, are devoid of germ cells. During late fetal and early postnatal development, male-type germ cells are present but progressively become lost, so that none is present by 10 days of age. XO males are also phenotypically normal, but spermatogenesis is active in the testis, and spermatozoa are produced. Cytological evidence of a Y-autosome translocation was completely lacking, and it is proposed that an autosomal dominant gene mutation, analogous to that found in other mammalian species, is responsible for the sex reversal.

The mutagenic activity of the pyrrolizidine alkaloid heliotrine in Drosophila melanogaster II. Chromosome rearrangements

The occurrence of chromosomal damage produced by the pyrrolizidine alkaloid heliotrine in Drosophila has been demonstrated using the frequencies of induced dominant lethals, partial and complete sex-chromosome loss, translocations and sex-ratio shifts as measures of the resulting damage. It has been shown that the frequency of XO males induced by the alkaloid is insufficient to account for the observed deviation in the sex-ratio even on the unlikely assumption that all XO males result from X-chromosome loss. Therefore it is proposed that the remaining deviation is due to the differential production of dominant lethals in the X- and Y-bearing sperm. Assuming that all XO males result from X-chromosome loss, and dominant lethals are produced in a ratio of 1:0.85 for the X- and Y-bearing sperms respectively, then a close fit with the experimentally observed sex-ratios is obtained. Translocations are produced with a low frequency. Evidence is discussed which indicates that there is a close relationship between the frequencies of induced translocations and asymmetrical exchanges. On this basis it is concluded that the latter made an insignificant contribution to dominant lethality in Drosophila following heliotrine treatment. It is suggested that most dominant lethals arise as a result of intrachromosomal rearrangements with lethal effect, or to isochromatid aberrations. It is further proposed that the different sensitivities of the X-ray and Y-bearing sperms must be due to the different frequencies of lethals occurring in the X- and Y-chromosomes.

Radiation-induced loss of ring-X chromosomes in the germ cells of Drosophila melanogaster males

A comparison was made between teh sensitivities of spermatocytes and postmeiotic germ cells, for the induction of XO males and sex-ratio shift. Adult males were irradiated and the treated germ cells were samples in a brooding scheme. In post-meiotic germ cells there was a uniform sensitivity for the induction of XO males. Within the range of exposured given, teh frequencies of XO males increased linearly with increasing exposure. In spermatocytes, which were themost sensitive germ-cell stage for the induction of XO males, the frequencies of XO males increased nonlinearly with increasing exposure. Significant sex-ratio shifts were found only when germ cells were samples on the first six days after irradiation. It was not possible to establishe a common relationship between the inductino of XO males and sec-ratio shift when post-meiotic germ cells were irradated. The highest frequenceis of XO males were found in the progeny from sperm samples on the eight day after irradiation. This was also the period when the fertlity of the irradiated males was most reduced. It is suggested that induced crossing-over may be the mechanism which is largely responsible for the production of high frequencies of XO males when spermatocytes are irradiated.

Experiments on the mechanisms of X-ray induced chromosome loss

The influence of dose fractionation and dose protraction on the induction of X-chromosome loss (leading to viable XO males) after irradiation of mature (stageI4) and immature (stage 7) oocytes of Drosophila melanogaster has been investigated. 150 kV X-rays were used witj a dose rate of 850 R/min or—in the protracted treatments—100 R/min and 50 R/min. In the fractionation experiments the doses were halved and separated by irradiation-free intervals of 20 min or 60 min. Fractionation and protraction of the dose decreases the X-loss frequency when immature, but not when mature oocytes are irradiated. This finding fits the (almost) linear relationship between X-loss frequency and X-ray dose when mature oocytes are irradiated, and the multi-hit curve obtained after treatment of immature oocytes. From the close parallel existing between the radiation response (as regards stage sensitivity, dose dependence and dose-rate dependence) of X-chromosome loss and dominant lethality, common principal causes of these two radiation effects are postulated: on the basis of the experimental data so far available, single chromatid breakage after irradiation of mature oocytes and sister-chromatid breakage after irradiation of immature oocytes are considered as the main mechanisms of both X-chromosome loss and dominant lethality.

Differential mutagenicity of the amine and amide derivatives of nitroso compounds in Drosophila melanogaster

The mutagenicity of N-diethyl- N-nitrosamine (DEN) was compared with that of N-ethyl- N-nitrosourethane (ENU) as regards: non-disjunction, XO males, translocations, induced crossing-over in the male, sex-linked recessive lethals and the elimination of y + and B from a marked Y-chromosome. All phenomena were followed in daily sperm samples from injected males (30 ± 5 h old) bred at unity mating pressure (equal male to female ratio). The various genetic effects were simultaneously determined on the same sample of treated cells or testes, so as to enable the assessment of the relative yield of different mutations. Activity as regards non-disjunction was low with both compounds, but there were occasional indications of some rise in its frequency within the 11th–14th days, thus marking the period of utilization of the meiotic spermatocytes. Induced crossing-over was first sampled on the 10th or 11th day; small clusters of identical or complementary recombinants occurred on the 12th–14th days and the larger ones from the 15th day. Accordingly, the post-meiotic sector of the germ line (sperm and spermatids) was sampled during the first 9 days and the pre-meiotic (spermatocytes and spermatogonia) from the 10th day onwards, with the gonia mainly starting on the 15th day. The yield of the sex-linked recessive lethals was roughly the same for the pre- a and post-meiotic stages with DEN, but was considerably higher for the more mature stages with ENU. There was virtually no activity with either compound as regards the induction of chromosome breaks: both did not induce XO males, and were inactive for translocations. Deletion of the Y-markers occurred with both compounds, but was almost restricted to the pre-meiotic stages with DEN, while extending to the post-meiotic sector with ENU. The induction of deletions relative to lethals with both compounds was higher for the pre- than for the post-meiotic sector, but the degree of this differential response was more marked with DEN. The differences in the mutagenicity of the tested compounds were discussed in relation to their biochemical properties and carcinogenic effects.

Adenosine triphosphate: protection against radiation-indued chromosome loss in Drosophila.

Injection of 5 milligrams of adenosine triphosphate per milliliter into adult Drosophila melanogaster X(e2) yB/sc(8) y(+) 4 to 8 hours old either immediately before or after administration of 2000 roentgens of x-rays protected those cells in spermatogenesis which were in or near meiosis from the loss of the ring X or the y(+) portion of Y chromosome. The loss of the chromosomes was determined by appearance of exceptional XO males in the offspring.