Illegitimate pairing of the X and Y chromosomes in Sxr mice

X/Y male mice carrying the sex reversal factor, Sxr, on their Y chromosomes typically produce 4 classes of progeny (recombinant X/X Sxr male male and X/Y non-Sxr male male, and non-recombinant X/X female female and X/Y Sxr male male) in equal frequencies, these deriving from obligatory crossing over between the chromatids of the X and Y during meiosis. Here we show that X/Y males that, exceptionally, carry Sxr on their X chromosome, rather than their Y, produce fewer recombinants than expected. Cytological studies confirmed that X-Y univalence is frequent (58%) at diakinesis as in X/Y Sxr males, but among those cells with X-Y bivalents only 38% showed normal X-Y pseudo-autosomal pairing. The majority of such cells (62%) instead showed an illegitimate pairing between the short arms of the Y and the Sxr region located at the distal end of the X, and this can be understood in terms of the known homology between the testis-determining region of the Y short arm and that of the Sxr region. This pairing was sufficiently tenacious to suggest that crossing over took place between the 2 regions, and misalignment and unequal exchange were suggested by indications of bivalent asymmetry. Metaphase II cells deriving from meiosis I divisions in which the normal X-Y exchange had not occurred were also found. The cytological data are therefore consistent with the breeding results and suggest that normal pseudo-autosomal pairing and crossing over is not a prerequisite for functional germ cell formation.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Spermatogenesis in XO,Sxr mice: role of the Y chromosome

The goal of this investigation was to evaluate the role of the Y chromosome in spermatogenesis by a quantitative and qualitative analysis of spermatogenesis as it occurs in the absence of a significant portion of the Y chromosome, i.e., in XO,Sxr male mice. Although these mice have the testis-determining portion of the Y chromosome on their single X chromosome, they lack most of the Y chromosome. Since it was found that all sperm-specific structures were assembled in a normal spatial and temporal pattern in spermatids of XO,Sxr mice, the genes controlling these structures cannot be located on the Y chromosome outside of the Sxr region, and are more likely to be on autosomes or on the X chromosome. In spite of the assembly of the correct sperm-specific structures, spermatogenesis was not quantitatively normal in XO,Sxr mice and significantly reduced numbers of spermatids were found in the seminiferous tubules of these mice. Furthermore, two size classes of spermatids were found in the testes of XO,Sxr mice, normal and twice-normal size. These findings are suggestive of abnormalities of meiosis in XO,Sxr spermatocytes, which lack one of the two sex chromosomes, and may not implicate function of specific genes on the Y chromosome. Morphological abnormalities of spermatids, which were not unique to XO,Sxr mice, were observed and these may be due to either a defective testicular environment because of reduced numbers of germ cells or to the lack of critical Y chromosome-encoded products. Since pachytene spermatocytes of XO,Sxr mice exhibited a sex vesicle, it can be concluded that the assembly of this structure does not depend on the presence of either a complete Y chromosome or the pairing partner for the X chromosome.     

Meiosis in Sxr male mice

Cytological evidence for the existence of a Y-autosomal rearrangement in meiotic cells of Sxr mice has been sought. At pachytene, in silverstained light microscope spread preparations of XY, Sxr/+ and XO, Sxr/+ spermatocytes, evidence for pairing or association between a possible Y-bearing segment of a specific autosome and a sex chromosome could not, however, be found. Such sex chromosome-autosome associations as were seen were non-specific in nature, and occurred no more often in Sxr mice than in controls.     

Enzyme levels in testis and other tissues of genetically sex-reversed mice

The specific activity of G6PD and PGK were measured in the testes, seminal vesicles, and livers of Sxr/+,XX mice, their Sxr/+,XY littermates and normal mice. While G6PD activity was high in the testes of young normal mice and declined as the testes matured, in the testes of Sxr/+,XX mice activity remained high, suggesting a failure of the Sertoli cells to mature normally. The activity of PGK was low in the testes of young normal mice, and increased as the testes matured. The testes of young Sxr/+,XX mice had high activity of this enzyme which remained high into adulthood. The high activity in young mice suggests an abnormality in the somatic cells. The seminal vesicle and liver measurements of G6PD and PGK confirmed that the Sxr/+,XX mice were phenotypically normal males except with respect to the testis. The developmental patterns of both enzymes in testes lacking germinal cells indicate that the maturation of the somatic cells of the normal testis is influenced by the presence of germinal cells.     

Cytological evidence that the Sxr fragment of XY,Sxr mice pairs homologously at meiotic prophase with the proximal testis-determining region

Self-pairing of the Y chromosome at prophase of meiosis in XY,Sxr male mice appears to take place in many cells to the exclusion of pairing between the Y and the X. This phenomenon offers an explanation for the high level of X-Y separation seen in these males at prophase of meiosis, additional separations being evident, however, when metaphase I (MI) cells are examined. A minority of prophase cells show the Y paired both autologously and with a sub-terminal region of the X which could be the normal pairing region. The balloon-like configurations observed when self-pairing occurs suggest that the distal Sxr fragment is inverted on the Y chromosome of Sxr carrier males in relation to the normal proximal testis-determining (Td)-containing region.     

The Y-encoded gene zfy2 acts to remove cells with unpaired chromosomes at the first meiotic metaphase in male mice

During male but not female mammalian meiosis, there is efficient apoptotic elimination of cells with unpaired (univalent) chromosomes at the first meiotic metaphase (MI) [1]. Apoptotic elimination of MI spermatocytes is seen in response to the univalent X chromosome of XSxr(a)O male mice [2], in which the X chromosome carries Sxr(a) [3, 4], the Y-chromosome-derived sex-reversal factor that includes the testis determinant Sry. Sxr(b) is an Sxr(a)-derived variant in which a deletion has removed six Y short-arm genes and created a Zfy2/Zfy1 fusion gene spanning the deletion breakpoint [4, 5]. XSxr(b)O males have spermatogonial arrest that can be overcome by the re-addition of Eif2s3y from the deletion as a transgene; however, XSxr(b)OEif2s3y transgenic males do not show the expected elimination of MI spermatocytes in response to the univalent [6]. Here we show that these XSxr(b)OEif2s3y males have an impaired apoptotic response with completion of the first meiotic division, but there is no second meiotic division. We then show that Zfy2 (but not the closely related Zfy1) is sufficient to reinstate the apoptotic response to the X univalent. These findings provide further insight into the basis for the much lower transmission of chromosomal errors originating at the first meiotic division in men than in women [7].     

Linkage of the murine steroid sulfatase locus, Sts, to sex reversed, Sxr: a genetic and molecular analysis.

We present genetic and molecular data demonstrating linkage of the gene for steroid sulfatase (Sts) to the mutation sex reversed (Sxr) definitively showing the existance of a functional allele for Sts mapping to the pseudoautosomal region of the mouse Y chromosome. Thus, in mouse, functional Sts genes are present in the pseudoautosomal region of both the X and Y chromosomes. This is in contrast to man where Sts has been mapped to the short arm of the X just centromeric to the pseudoautosomal region. Only a single recombinant separating Sts and Sxr was found out of 103 male meioses analyzed; double recombinants were not found between sex (Tdy), Sts and Sxr. If the rate of recombination in the pseudoautosomal region in male mice is equivalent to that in man and thus 7-10X higher than normal, then our data suggest that the distance between Sts and Sxr (or the telomere of the Y) is approximately 100-200 kb in length. Our data is in contrast to a recent report of a recombination frequency separating Sts and Sxr of as high as 6.2-9.8%.     

Destruction of the main olfactory epithelium reduces female sexual behavior and olfactory investigation in female mice

We studied the contribution of the main olfactory system to mate recognition and sexual behavior in female mice. Female mice received an intranasal irrigation of either a zinc sulfate (ZnSO4) solution to destroy the main olfactory epithelium (MOE) or saline (SAL) to serve as control. ZnSO4-treated female mice were no longer able to reliably distinguish between volatile as well as nonvolatile odors from an intact versus a castrated male. Furthermore, sexual behavior in mating tests with a sexually experienced male was significantly reduced in ZnSO4-treated female mice. Vomeronasal function did not seem to be affected by ZnSO4 treatment: nasal application of male urine induced similar levels of Fos protein in the mitral and granule cells of the accessory olfactory bulb (AOB) of ZnSO4 as well as SAL-treated female mice. Likewise, soybean agglutinin staining, which stains the axons of vomeronasal neurons projecting to the glomerular layer of the AOB was similar in ZnSO4-treated female mice compared to SAL-treated female mice. By contrast, a significant reduction of Fos in the main olfactory bulb was observed in ZnSO4-treated females in comparison to SAL-treated animals, confirming a substantial destruction of the MOE. These results show that the MOE is primarily involved in the detection and processing of odors that are used to localize and identify the sex and endocrine status of conspecifics. By contrast, both the main and accessory olfactory systems contribute to female sexual receptivity in female mice.     

Manipulation of aggressive behavior in adult DBA/2/Bg and C57BL/10/Bg male mice implanted with testosterone in silastic tubing

Adult DBA/2/Bg and C57BL/10/Bg male mice were orchidectomized and implanted subcutaneously with one of two doses of testosterone (T) in Silastic tubing. Steroid doses which resulted in significant atrophy and hypertrophy of accessory sex tissues were determined for each strain. Relative to sham-castrated vehicle-implanted controls, both hypophysiological and hyperphysiological implants caused augmentation of aggression in C57BL/10/Bg males. In DBA/2/Bg mice, the hypophysiological dose reduced and the hyperphysiological implant increased aggression scores. The results demonstrate that agonistic behavior in male mice is influenced by the titer of circulating T and emphasize the importance of genetic variance in the study of hormones and behavior.     

Sex preference and species specificity of rodent (Mus musculus and Microtus arvalis pheromones.

The behavioural response to the sex pheromones in the externally voided urine of field voles (Microtus arvalis) and laboratory mice (CFLP, CBA strains) although specific for species showed no strain specificity. Bladder urine (free of accessory sex-gland secretions) and the preputial glands of CFLP and CBA mice contain sex attractants. Ether extracts made of blood of male CFLP mice attracted CFLP female mice.     

Epididymides of sex-reversed XX mice lack the initial segment

The genetic factor Sxr causes sex reversal of chromosomally female (XX or XO) mice to phenotypic maleness by inducing development of testes that produce androgens. It has been considered that these sex-reversed animals, called pseudomales, confirm the principle originally developed by Jost that adequate androgenization produces normal phenotypic maleness in mammals, irrespective of chromosomal sex. However, we previously discovered that the epididymis of sex-reversed XX mice (pseudomales of genotype XXSxr) lacks EH 9 cells (epididymal head, cell type No. 9, the "principal cell' of the initial segment). The purpose of the present study was to determine whether cell type EH 9 of XXSxr pseudomales is replaced by a principal cell of a different appearance, or whether the initial segment itself is actually absent. We made serial sections of entire epididymal heads and did microdissections to unravel the highly coiled epididymal duct. Using these two approaches, we studied the sequence of epididymal segments, and estimated lengths of the relevant portion of the epididymal duct; we found that the initial segment of XXSxr pseudomales is truly absent. This is the first report of a mutant genotype causing absence of a segment of the epididymis. The XXSxr mutant appears to be an exception to Jost's principle. This finding shows that, even in full androgenization, male phenotype may not always be independent of chromosomal sex.     

Molecular aspects of sex determination in mice: an alternative model for the origin of the Sxr region

Using a combination of in situ mapping and DNA analysis with recombinant DNA probes specific for the Sxr region of the mouse Y chromosome, we show that both the gene(s) controlling primary sex determination and the expression of the male-specific antigen H-Y (Tdy and Hya respectively) are located on the minute short arm of the mouse Y chromosome. We demonstrate that the H-Y- variant of Sxr (Sxr') arose by a partial deletion within the Sxr region and propose an alternative model for the generation of the original Sxr region.     

Correlation between sexual phenotype and X-chromosome inactivation pattern in the X*XY wood lemming

Replication patterns of the X chromosomes were studied in X*XY wood lemmings with male and female phenotypes. The wild-type X was late replicating (ie, inactivated) in all cells of the X*XY female, whereas the mutated X* was late replicating in all cells of the X*XY male. These findings are compared with those obtained in sex-reversed (Sxr) mice.     

Mosaic character of spermatogenesis in carriers of the sex reversed factor in the mouse

The "sex reversed" factor leads to development of XX male mice. It is inherited on one of the autosomes and transmitted through XY-Sxr carrier males. In the latter, spermatogenesis is studied under the aspect of gene dosis effects produced by the presence of the Sxr factor in addition to the Y chromosome. A mosaic pattern of normal and defective spermatogenesis is described. The defective areas are characterized by failure in late pachytene and metaphase I, and by appearance of spermatids with very large nuclei which degenerate in cap phase. The defects correspond to those observed in X0-Sxr spermatogenesis. Our interpretation is that in the normal areas only the Y chromosome, and in the defective areas the Sxr factor is expressed.     

烟夜蛾雄蛾性附腺因子对雌蛾性信 息素合成的抑制作用

烟夜蛾Helicoverpa assulta处女蛾在交配后1 h,其性信息素滴度即显著降低,72 h内未见恢复。生测结果表明,烟夜蛾性信息素合成抑制因子主要来源于雄蛾性附腺。不同日龄雄蛾性附腺提取物的抑制活性无显著差异。光暗期对其活性具显著影响,暗期中雄蛾的性附腺物质对雌蛾性信息素合成具有较强抑制作用,而光期中雄蛾的性附腺物质不具抑制活性。在暗期的不同时间处理,对处女蛾性信息素合成的抑制作用无显著差异。雄蛾性附腺提取物对雌蛾性信息素合成的抑制作用与注射剂量有明显的相关性,0.2 ME（雄蛾当量）是产生显著抑制作用的最小剂量。对交配雌蛾注射性信息素生物合成激活神经肽（PBAN）提取物后,其性信息素合成又可恢复,这说明雌蛾交配后,性信息素滴度降低的原因是由于缺少了PBAN的调控。     

Immunoregulation in the Peyer's patch microenvironment. Cellular basis for the enhanced responses by the B cells of X-linked immunodeficient CBA/N mice

The Peyer's patches (PP) of X-linked immunodeficient (xid) CBA/N and hemizygous (CBA/N X DBA/2)F1 (CDF1) male mice contain a B cell subpopulation that expresses the Lyb-5 maturational marker and is responsive to type 2 and T cell-dependent antigens in vitro, a B cell phenotype which is absent from the spleens of xid mice. Experiments reported here show that xid spleen B cells co-cultured with B cell-depleted PP cells from xid mice differentiated into specific plaque-forming cells in response to trinitrophenyl-Ficoll (type 2) and sheep erythrocytes (T cell-dependent). Two cell types were involved in this normalization of xid B cell responses. An accessory cell activity present in the PP, but not the spleens, of both CDF1 male (xid) and CDF1 female (normal) mice was required for the response to either the type 2 or T cell-dependent antigens. In the presence of this PP accessory cell, T cells from the PP of either xid or normal mice supported responses to both classes of antigens. In contrast, T cells from the spleens of xid mice did not support the response to trinitrophenyl-Ficoll, although the splenic T cells from normal mice did synergize with PP accessory cells in allowing plaque-forming cell development by xid B cells to this type 2 antigen. The xid PP T cell activity required for the type 2 response by xid B cells was present in the Ly-1+, Lyt-2- subpopulation, and the xid PP accessory cell activity was provided by an enriched population of dendritic accessory cells. These results demonstrate the the lymphoreticular cells comprising the PP microenvironment provide effective support for the differentiation of xid B cells in response to type 2 and T cell-dependent antigens.     

Age and strain dependence of O6-methylguanine DNA methyltransferase activity in mice

The activity of the DNA repair protein O6-methylguanine DNA methyltransferase (MT) was compared in liver extracts from female ICR and male C57BL/6 mice at various ages (3-130 weeks old). Similar patterns of overall enzyme activity were observed in both strains with O6-MT activity being relatively low in young mice (3 or 8 weeks old). However, the activity significantly increased after adolescence (middle age), thereafter decreasing with old age (over 100 weeks old) to a level equivalent to that found in young mice. In an additional strain difference study, O6-MT activities in liver extracts from 4 strains of mice were compared at 5 and 30 weeks of age. Although a similar age-associated increase of enzyme activity in adolescence was confirmed in all 4 strains investigated, the closed-colony ICR mice differed from the inbred strains in demonstrating significantly higher levels of O6-MT activity in females than in males. However, the same tendency was also observed in a comparison of the sexes in 30-week-old C3H/HeN, C57BL/6 and BALB/c mice.     

Possible modulation by male sex hormone of Th1/Th2 function in protection against Plasmodium chabaudi chabaudi AS infection in mice

Zhang, Z.-H., Chen, L., Saito, S., Kanagawa, O., and Sendo, F. 2000. Possible modulation by male sex hormone of Th1/Th2 function in protection against Plasmodium chabaudi chabaudi AS infection in mice. Experimental Parasitology 96, 121-129. We examined the mortality, survival time, and parasitemia in interferon gamma receptor (IFN-gamma R)-deficient (IFN-gamma R(-/-)) and IL-4-deficient (IL-4(-/-)) mice infected with Plasmodium chabaudi AS and compared them with the wild type counterparts (IFN-gamma R(+/+) and IL-4(+/+), respectively). (1) Mortality was higher and survival time was shorter in males of both IFN-gamma R(-/-) and IL-4(-/-) mice infected with P. chabaudi AS, compared with their wild type counterparts, whereas such a difference was not observed in female mice. (2) These differences between males and females were not observed when male mice were castrated; however, female castration had no effect on the data. (3) The rate of parasitemia in both male and female IFN-gamma R(-/-) and IL-4(-/-) mice was higher at some points during the observation than in the wild type counterparts. (4) These results on susceptibility vs resistance to P. chabaudi AS infection can be explained partially by the levels of expression of Th1/Th2 cytokine and chemokine mRNAs in the spleen cells of the infected mice. These results suggest that male sex hormones modulate the function of Th1/Th2 cells and that these T cells counteract the activity of these hormones in protection against P. chabaudi AS infection in mice.     

Properties of cloned T cells that mediate delayed-type hypersensitivity against ovalbumin in mice

Cloned T-cell lines that mediate delayed-type hypersensitivity (DTH) against soluble protein antigen, ovalbumin (OA), were established in (C57BL/6 X DBA/2)F1 mice and their properties were examined. They induced antigen-specific delayed-type footpad reactions, characterized histologically by a predominant mononuclear cell infiltration, when transferred intravenously into syngeneic mice. Morphologically, they were medium or large lymphoblasts with granules in the cytoplasm and expressed Lyt 1 cell surface antigens. One of them proliferated antigen specifically under the presence of both C57BL/6 and F1 accessory cells, while others proliferated antigen specifically only under the presence of F1 accessory cells. They also produced macrophage-activating factor (MAF) and substances which mediate a DTH-like footpad inflammatory reaction with a maximum 6 hr after injection into the footpad of normal mice, when incubated in the presence of specific antigen and specific accessory cells in a serum-free medium for 24 hr. These results demonstrate that cloned DTH-effector T cells, established here against soluble protein antigen, are Lyt 1-positive, large lymphoblasts and that they produce MAF and footpad-reactive inflammatory substances antigen specifically under the presence of specific accessory cells.