Chromosome 9 of Ellobius lutescens is the X chromosome

Ellobius lutescens carries an apparently identical karyotype (2n = 17) in both sexes. On the basis of indirect evidence the unpaired chromosome 9 has been considered to represent the X chromosome of this species. We have obtained data to substantiate this view by four different techniques. After fusion of HPRT^– RAG cells with E. lutescens fibroblasts we demonstrated that the enzymes HPRT and G6PD are localized on the presumptive X chromosome. By analysis of pachytene figures after silver staining we showed by electron microscopy that the single chromosome exhibits the typical features of an X chromosome in male meiosis. Hybridization of (GATA)₄ and (GACA)₄ oligonucleotide probes to E. lutescens DNA revealed several distinct bands in the high molecular weight range some of which appeared to be specific for the individual but not for the sex of the animal. Hybridization in situ of the (GATA)₄ probe on metaphase spreads of E. lutescens did not highlight any particular chromosome segment but showed a significant deficit of these sequences in chromosome 9. These observations are discussed with respect to their bearing on X chromosome determination. Finally it is concluded that E. lutescens should be an ideal tool for testing candidate genes assumed to be involved in primary sex determination.     

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.     

Characterization of Pisrt1/Foxl2 in Ellobius lutescens and exclusion as sex-determining genes

The rodent Ellobius lutescens is an exceptional mammal which determines male sex constitutively without the SRY gene and, therefore, may serve as an animal model for human 46,XX female-to-male sex reversal. It was suggested that other factors of the network of sex-determining genes determine maleness in these animals. However, some sex-determining genes like SOX9 and SF1 have already been excluded by segregation analysis as primary sex-determining factors in E. lutescens. In this work, we have cloned and characterized two genes of the PIS (polled intersex syndrome) gene interval, which were reported as candidates in female-to-male sex reversal in hornless goats recently. The genes Foxl2 and Pisrt1 from that interval were identified in E. lutescens DNA and mapped to Chromosome 8. We have excluded linkage of Foxl2 and Pisrt1 loci with the sex of the animals. Hence, the involvement of this gene region in sex determination may be specific for goats and is not a general mechanism of XX sex reversal or XX male sex determination.The nucleotide sequence data reported in this article have been submitted to GenBank and have been assigned the accession number AY623815.     

The repeated DNA sequences of Microtinae : I. Microtus agrestis, Microtus pennsylvanicus and Ellobius lutescens

A comparison has been made of the repeated nucleotide sequences from 3 Microtinae which possess varying amounts of constitutive heterochromatin per cell nucleus. Eight repetitive fractions of DNA, ranging in C_ot values from 10⁻³ to 10⁻³, were obtained by reassociation of sheared, denatured DNA and fractionation on hydroxyapatite. At C_ot values of less than 1, 3 fractions were isolated that amounted to 18.7, 10.0 and 7.4 % of the total DNA of Microtus agrestis, Microtus pennsylvanicus and Ellobius lutescens, respectively, in agreement with the amounts of heterochromatin in these species. At C_ot values higher than 1, the amounts of repeated sequences were more comparable and constituted about 12 to 14 % of the DNA. Thermal denaturation profiles of all the repetitive fractions showed a good deal of order in the reassociated duplexes, with an average hyperchromicity of 20 %. Upon density gradient centrifugation in neutral CsCl, the fractions from M. pennsylvanicus and E. lutescens yielded almost identical patterns and differed significantly from those of M. agrestis. In M. agrestis a fraction of fast-intermediate repetitiveness (reassociating at C_ot values between 10⁻² and 1) was isolated, amounting to about 12 % of the total DNA. This fraction has a base composition comparable to that of total DNA and represents the major component of the constitutive heterochromatin of giant sex chromosomes that have been isolated by the disruption of brain and liver nuclei and differential centrifugation.     

The reliability of osteometric techniques for the sex determination of burned human skeletal remains

The influence of heat-induced shrinkage on the osteometric sexual dimorphism of human skeletons is still poorly known. In order to investigate this issue, a sample composed of 84 Portuguese individuals cremated at a modern crematorium was examined using standard measurements from the femur, the talus and the calcaneus. In addition, sex determination of the sample was attempted by using osteometric standards developed from the Coimbra collection of identified skeletons. This was carried out to assess the extent of the effect of heat-induced shrinkage on the correct classification of known-sex skeletons while using standards developed on unburned skeletons.Results demonstrated that sexual dimorphism was still observable in the sample of calcined bones despite shrinkage. However, the application of conventional osteometric standards was unsuccessful. As expected, shrinkage caused most females to be correctly classified according to sex, but the sex allocation of males was very poor for all standard measurements.The results were obtained on a small sample but suggest that univariate metric techniques specifically developed for calcined bones may be valuable for sex determination. This would bring new methodological possibilities for biological anthropology and would enlarge the set of techniques regarding sex determination of burned skeletal remains.     

The primary sex ratio under environmental sex determination

The ESS primary sex ratio (male/female) under environmental sex determination (ESD) is shown to be equal to the ratio of the average fertility of a female to the average fertility of a male. Thus, depending upon how male and female fertility change over the environmental variable causing ESD, the primary sex ratio may be either male or female biased, or neither. The primary sex ratio thus contains information as to how male and female fertilities change with the environment.     

Ultrastructure,meiotic behavior,and evolution of sex chromosomes of the genus Ellobius

The whole-mount SC preparations from males of three species of the genus Ellobius (Ellobius fuscocapillus, Ellobius lutescens), and Ellobius tancrei were studied by electron microscopy. In the males of Ellobius fuscocapillus, behavioral peculiarities of the sex bivalent (viz. the normal male heterozygosity) are characterized by early complete desynapsis of sex chromosomes (X, Y), occurring at late pachytene-early diplotene. The karyotype of species Ellobius lutescens is unique for mammals. In both sexes it is characterized by an odd number of chromosomes (2n=17). At prophase I the unpaired chromosome 9 is not involved in synapsis with other chromosomes and forms a sex body at the end of pachytene.The complete Robertsonian fan has been described for superspecies Ellobius tancrei. As shown on the basis of G-band patterns the male and female sex chromosomes are cytologically indistinguishable.Analysis of whole-mount SC preparations revealed the formation of a closed sex SC bivalent and showed some morphological differences in the axes of sex chromosomes at meiotic prophase I. A number of assumptions are made about the relationship between the behavior of sex chromosomes, their evolution and the sex determination system in the studied species of genus Ellobius.

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The biochemical role of SRY in sex determination

The human sex-determining gene on the Y chromosome, termed SRY, has recently been isolated by positional cloning; compelling evidence now exists equating SRY with the testis-determing factor, TDF. The SRY gene product is an HMG box protein whose DNA-binding activity is vital for testis formation as sex-reversed patients with SRY mutations lack this activity in vitro. The in vivo DNA target for SRY, however, remains elusive. Here, we show, by gel retardation analysis, that SRY recognises specific DNA sequences and that such sequences exist upstream of the AMH promoter, a potential downstream target for SRY. We also describe the DNA bending and cruciform DNA-binding functions of SRY and propose a model for the potential action of SRY in the “HMG-1-rich” mammalian nucleus. © 1994 Wiley-Liss, Inc.     

The mechanism of sex determination in Rumex acetosella

Summary Cytogenetic studies were made with particular emphasis on the sex-determining mechanism in Rumex acetosella (6 x = 42) and its hybrids (F ₁, F ₂, BC ₁ and BC ₂) with R. hastatulus (synthetic 4 x = 16 = 4 A +4 X = and 4 x = 18 = 4 A + 2 (X Y ₁ Y ₂) = ). Rumex acetosella was almost strictly dioecious with 5050 male and female. Breeding tests revealed that the males were heterogametic. The longest chromosomes (S), usually two, are the sex chromosomes of this hexaploid species. The S chromosomes are homomorphic in both male and female. The sex chromosome: autosome ratios, and the strong epistatic male effect of the S ^M chromosome in the polyploid dioecious species and in the hybrids, are evidence of an X/Y Melandrium type sex-determining mechanism controlled by a single pair of homomorphic sex chromosomes. Thus, the sex chromosome formula of the males was S ^F S ^M and that of females was S ^F S ^F. The present approach is a new method for resolving the sex-determining mechanism in a dioecious species.     

The evolution of sex determination in isopod crustaceans

Sex is determined by non-Mendelian genetic elements overriding the sex factors carried by the heterochromosomes in some species of terrestrial isopods. A bacterium Wolbachia and a non-bacterial feminizing factor (f) can both force chromosomal males of Armadillidium vulgare to become phenotypic functional females. The f factor is believed to be a genetic element derived from the Wolbachia genome that becomes inserted into the host nuclear genome. The feminizing factors can be considered to be selfish genetic elements because they bias their host's sex ratio to increase their own transmission. New sex-determining genes are selected (genes resisting the feminizing effects, or the transmission of feminizing elements) as a consequence of the conflict between these elements and the rest of the host's genome. These events drive the sex-determining mechanisms to evolve, and may explain the polymorphism of sex factors and the poor differentiation of the heterochromosomes in isopods.     

The end of gonad-centric sex determination in mammals

The 20th-century theory of mammalian sex determination states that the embryo is sexually indifferent until the differentiation of gonads, after which sex differences in phenotype are caused by the differential effects of gonadal hormones. However, this theory is inadequate because some sex differences precede differentiation of the gonads and/or are determined by non-gonadal effects of the sexual inequality in the number and type of sex chromosomes. In this article, I propose a general theory of sex determination, which recognizes multiple parallel primary sex-determining pathways initiated by genes or factors encoded by the sex chromosomes. The separate sex-specific pathways interact to synergize with or antagonize each other, enhancing or reducing sex differences in phenotype.     

Plant sex determination and sex chromosomes

Sex determination systems in plants have evolved many times from hermaphroditic ancestors (including monoecious plants with separate male and female flowers on the same individual), and sex chromosome systems have arisen several times in flowering plant evolution. Consistent with theoretical models for the evolutionary transition from hermaphroditism to monoecy, multiple sex determining genes are involved, including male-sterility and female-sterility factors. The requirement that recombination should be rare between these different loci is probably the chief reason for the genetic degeneration of Y chromosomes. Theories for Y chromosome degeneration are reviewed in the light of recent results from genes on plant sex chromosomes.     

Bird sex determination

During the evolution, sex determination occurred early. Sex determining factors were progressively isolated from other genes in sexual chromosomes, or gonosomes. Among vertebrates, evolution took two opposite pathways : in mammals, the system of XX:XY sex determination, with Y chromosome, induces male differentiation. In contrast, in birds, the system ZZ:ZW, with the W chromosome, induces female differentiation. But comparative studies show that the two pathways are not so simple. In the chicken as in the lower vertebrates, estrogens play a central role in gonadal sex differentiation. Several genes, show to be critical for mammalian determination, are also expressed in the chicken but their expression pattern differs, indicating functional plasticity. The W-linked female determinants remains still unknown. But comparative studies of the two pathways, with conserved and divergent elements, are broadening our understanding of sex determination.     

Age and sex biases in the preservation of human skeletal remains

Inaccuracies introduced through biases in preservation are a major source of error in paleodemographic reconstructions. Although it is generally assumed that such biases exist, little is known about their magnitude. To investigate this problem, we studied age and sex differences in the preservation of skeletal remains from Mission La Purisima and a prehistoric cemetery (Ca-Ven-110). Comparison of mortality profiles obtained through analysis of skeletal remains and burial records from the mission indicates that biases in preservation can be very significant in poorly preserved skeletal collections. The Purisima burial records show that most of the people interred in the cemetery were either infants or elderly adults. The skeletal remains, in contrast, are predominantly those of young adults. The burial records and skeletal collection produced comparable sex ratios. These results show that age biases in preservation are much more important than sex biases. This conclusion is supported by data on the completeness of the skeletons from La Purisima and Ca-Ven-110. At both sites, the remains of young adults were better preserved than those of children or elderly adults, and the completeness of male and female skeletons was comparable.     

The role of the Y-chromosome in sex determination.

The basic plan of gonadal development in both sexes is female unless testes are induced by factor(s) of the Y chromosome, known as testis determining factor(s) (TDF). It is not clearly established whether the Y chromosome control is autonomous or under the control of a gene on the X chromosome or autosomes. A gene for the H-Y antigen (Histocompatibility-Y antigen) has been postulated to be the factor determining testicular differentiation. Recent studies have demonstrated that the gene for testis determination and the H-Y determinant are two separate entities. Although earlier cytogenetic observations localized TDF on the pericentric region of the short arm of the Y chromosome, subsequent findings by high-resolution chromosome banding and molecular analysis localise TDF to the distal part of the short arm of the Y chromosome, adjacent to the pseudoautosomal region. A candidate for TDF, the ZFY, was localised within the 140 kb interval where the position of TDF was defined, and considered as the TDF gene. However, a smaller gene sequence of 35 kb, the SRY, situated outside the 140 kb ZFY region, has recently been isolated and proved to be the only and the smallest part of the Y chromosome necessary for male sex determination.