X-Y chromosome dissociation in mouse strains difering in efficiency of spermatogenesis: Elevated frequency of univalents in pubertal males

Dissociation of the X-Y chromosome bivalent in diakinesis-metaphase I spermatocytes of adult mice was significantly more frequent in the CBA strain (29%) than in C57, KP, or KE strains (7–11%). Autosome dissociatio (1–5%) involved only the smallest chromosome pairs. Eleyatedfrequency of X-Y dissociation in the CBA strain correlates with significantly lower testes weight and lower yield of spermatogenesis, which suggests that sex bivalent dissociation man be responsible for some loss of spermatogenic cells. However, sperm quality is not affected, the percentage of normal spermatozoa and their fertlizing capacity being higher in CBA thatn in the remaining strains. Two congenic strains, KE and KE. CBA (the latter with the Y chromosome introduced from CBA), had the same level of X-Y dissociatios, suggesting that the Y chromosome plays no rle in the determination of this character. In comparison with adult males pubertal (27–29 day-old) males had twice as hig a frequency of X-Y dissociation in KE an KP strains, and combined frequeicies of dissociated sex and autosome bivalents were significantly higher in pubertal males of all tested strains. Although te level of chromosome dissociation is not sufficient to explain increased mortality of germ cells observed in pubertal males, it could be one of the contributing factors.     

Sex-dependent frequency and type of autosomal univalency at the first meiotic metaphase in mouse germ cells

Univalents at the first meiotic metaphase in mouse spermatocytes occur mainly in the XY pair, making it difficult to compare the amounts of univalency in males and females. In this study, the amounts of autosomal univalency in male and female meiosis were compared using the model strain CBA-T6, in which univalency of the small marker autosome pair T6 has been shown to occur very frequently in spermatocytes. Mice from inbred CBA and DBA strains were also analysed. The total frequencies of univalency (sex chromosomes plus autosomes) in metaphase I spermatocytes were 45.6% in CBA, 36.9% in CBA-T6, and 37.3% in DBA males. The aneuploidy in metaphase II spermatocytes ranged from 1.4 to 3% in these strains, which was in agreement with previous findings that most primary spermatocytes with abnormal chromosome configurations are arrested in their development before metaphase II. In the CBA-T6 strain, autosomal univalency at metaphase I mostly involved chromosome pair T6; however, its frequency differed significantly between the sexes, amounting to 18.9% in spermatocytes and 4.3% in oocytes. In the CBA strain, autosomal univalents at metaphase I were seen in 7.7% of the spermatocytes and 1.4% of the oocytes and, in DBA mice, in 4.9% of the spermatocytes and 3.8% of the oocytes. However, in DBA oocytes, when univalency occurred it usually concerned a greater number of bivalents in one cell (range: 2-19 disjoined bivalents), a phenomenon very rare in males of this strain. This study shows that univalent formation differs between the male and female types of meiosis.     

Interstrain competition amongst mouse spermatozoa inseminated in various proportions, as affected by the genotype of the Y chromosome

Nonagouti (KP X C57BL)F1 hybrid females were artificially inseminated with a mixture of spermatozoa from males of the KE (nonagouti) and CBA (agouti) strains and the genotype of young was estimated by fur pigmentation. When KE and CBA spermatozoa mixed in the ratios of 1:1, 2:1 and 4:1 were inseminated after ovulation, 87%, 56% and 29% of progeny, respectively, were sired by CBA males, i.e. proportions of CBA progeny were significantly higher than ratios of CBA spermatozoa in the mixture. The surplus of CBA progeny was significantly less in females inseminated before ovulation, which may suggest that more rapid capacitation of CBA spermatozoa is partly responsible for their competitive advantage. In preparations from oviducal flushings of females killed 2-3 h after insemination, CBA spermatozoa (recognized by their shape) were found in similar proportions as in the inseminated mixture. There was therefore no evidence of their preferential selection at the uterotubal junction. No competitive advantage of CBA spermatozoa occurred when they were inseminated with spermatozoa from males of the KE.CBA strain, congenic with KE but with the Y chromosome derived from the CBA strain. This indicates that genetic factors linked with the Y chromosome may influence competitive ability of spermatozoa.     

Correlation of centromeric heterochromatin C-band polymorphism with breeding failure in mice

The aim of the present study was to test the hypothesis about the relation between segregation of chromosomes 14 and 18 and the deterioration of mouse fertility and vitality. The analysis was possible because C-banding on chromosome 14 and chromosome 18 of the CBA/Kw and KE strains show size polymorphism. A small sized C-band on chromosome 14 is characteristic for the CBA/Kw mice, while the KE mice show small C-bands on chromosomes 18. Thus, if fertility parameters are affected in a centromere-dependent manner, we should observe non-random inheritance of both chromosome pairs in recombinant inbred (RI) strains. The results showed statistically significant preferential segregation of chromosomes 14 and 18 with small C-bands. Most of the RI strains inherited chromosome 14 from the CBA/Kw strain and chromosome 18 from the KE strain, and did not manifest a deterioration of fertility and vitality. On the contrary, RI strains that inherited chromosomes 14 and 18 from one of the parental strains, particularly the KE strain, stopped breeding or had difficulties in producing the next generation.     

Analysis of oocyte quality in recombinant inbred mouse strains developed from KE and CBA strains that differ in fertilization efficiency

Recombinant inbred (RI) mouse strains were developed from reciprocal crosses between two inbred strains differing in the proportion of fertilized ova (CBA, 100%; KE, 77%), to analyse the underlying factors. A correlation (r = 0.83, P < 0.01) between fertilization efficiency within 22 RI strains and after mating RI females with KE males proved that oocyte quality was involved. The following oocyte parameters were analysed in RI and progenitor strains: time of meiotic maturation, rapidity of enzymatic removal of egg investments, and proportion of fertilized ova with supplementary spermatozoa in the perivitelline space. Among the RI strains, high incidence of supplementary spermatozoa was correlated with lower efficiency of fertilization (r = -0.58, P < 0.05) and with slow meiotic maturation (r = -64, P < 0.01), suggesting that delayed maturation may affect oocyte ability of being fertilized by the first penetrating spermatozoon. However, significant correlations were also found between characters which coexist within the progenitor strains, but are not likely to be physiologically related; this suggests that RI strains have inherited large blocks of progenitor genomes, not disrupted by recombination. The strain distribution pattern (SDP) of the analysed traits revealed CBA-like, KE-like, and intermediate phenotypes, indicating that they are polygenically determined. No linkages were found between the studied traits and 12 enzymatic markers. However, the SDP for fertilization efficiency showed a preponderance of non-matching strains (15/19) in relation to agouti locus; the known instability of this chromosome region makes it possible that a putative linkage was disrupted by recombination when RI strains were created.     

Radiation-induced and transposon-induced chromosome damage in Drosophila: translocations and transmission distortion

The possible interaction between X-ray- and transposon-induced chromosome damage was monitored in the P-M system of hybrid dysgenesis in Drosophila melanogaster. One- to two-day-old F1 dysgenic males originating from a cross between M strain females and P strain males were irradiated with 5.5 Gy (550 rad) or used as controls to monitor X-Y translocations and transmission ratio distortion. Two 3-day sperm broods were sampled for the former and two 4-day broods for the latter to detect damage induced in the most radiosensitive cells. F1 nondysgenic males derived from M female to M male crosses (controls) were treated identically. X-Y chromosome translocations induced by P element mobility alone declined sharply with a decrease in temperature (18 versus 21 degrees C) and they were significantly reduced with aging of hybrid males from brood 2, 4-8 days of age, to brood 3, 7-11 days of age. No significant increase in translocations was observed when X irradiation and P-M dysgenesis were combined, showing no interaction between damages induced by the two mutator systems. In contrast, interaction was observed in transmission ratio distortion which was significantly increased by X irradiation of hybrid males derived from both reciprocal M X P and P x M crosses. The preferential elimination of P element-bearing autosomes occurred when either spermatocytes or spermatids were irradiated. An aging effect was also observed, resulting in less distortion in 9- to 14-day-old dysgenic males compared to 5- to 10-day-old hybrids.     

Phenotype and fertilizing capacity of spermatozoa of chimaeric mice produced from two strains that differ in sperm quality

Spermatozoa of males from the inbred mouse strains, KE (albino) and CBA (agouti), are distinguishable by head shape and differ in quality: CBA spermatozoa show a lower percentage of abnormal heads and higher efficiency of fertilization. Aggregation chimaeras were produced to investigate whether these differences are intrinsic or extrinsic to spermatogenic cells. Among 24 overt chimaeras, 14 were males: 1 was sterile, 8 produced either KE or CBA spermatozoa, as recognized by shape and by progeny testing, and 5 (21%) were germ-line chimaeras. Both the level of abnormal sperm heads and the efficiency of fertilization of CBA and KE spermatozoa produced by chimaeric males (except two subfertile ones) were within the range characteristic for the respective strain. All 5 germ-line chimaeras, irrespective of their coat colour composition, produced about 98% KE and only 2% CBA spermatozoa, which indicated strong selection against CBA germ cells. However, mature CBA spermatozoa showed high competitive ability, because the proportion of agouti progeny (from the CBA component) sired by those males was significantly higher than the proportion of CBA spermatozoa, estimated from vaginal plug preparations after every mating. The fact that this difference was particularly striking for one chimaera with a preponderance of CBA somatic component may suggest some influences extrinsic to spermatogenic cells. We conclude from this study that sperm head shape, the level of sperm abnormalities and fertilizing capacity are determined largely autonomously by genes acting in the germ cells. The internal environment created by foreign somatic cells exerts only minor modifications, unless there has been deterioration beyond the range of 'normality'.     

Sex and H-2 haplotype control the resistance of CBA-BALB hybrids to the induction of T cell lymphoma by Moloney leukemia virus

CBA/N and CBA/CaHN have a significantly longer latent period than other inbred mouse strains between infection with Moloney murine leukemia virus and the appearance of T cell lymphoma. The genetic characteristics of this resistance have been analyzed in the F1 hybrids of CBA/N and CBA/CaHN with BALB H-2 congenic strains. Sexual phenotype and H-2 haplotype significantly influenced survival in the F1 hybrids of CBA/CaHN with BALB. In the F1 with BALB/cJ and BALB/cAnN (both H-2d), the males survived significantly longer than the females; but in the F1 with BALB.K (H-2k) and BALB.B (H-2b), the survival of males and females was the same. Survival was not prolonged by the recessive X-linked immunodeficiency gene xid or other genes on the CBA/N X-chromosome, because the (CBA/N X BALB/c)F1 male and the reciprocal (BALB/c X CBA/N)F1 male, which does not carry the CBA X-chromosome, were equally resistant. H-2 haplotype did not influence survival among the BALB H-2 congenics, and sex had little effect on the resistance of the CBA and BALB parents. These results demonstrate that a sex-dependent gene linked to H-2 significantly influences the expression of CBA genes for lymphoma resistance in the F1 hybrid with BALB.     

Modes of inheritance of X-Y dissociation in inter-subspecies hybrids between BALB/c mice and Mus musculus molossinus

Genetic analysis of the high frequency of X-Y chromosome dissociation found in primary spermatocytes of F1 hybrids between Japanese wild mice (Mus musculus molossinus) and inbred laboratory mice (BALB/c) was attempted. The frequency of X-Y dissociation (X//Y) in both BALB/c and M. m. molossinus was lower than 30% (Low X//Y), while the value was more than 70% (High X//Y) in their F1 hybrids. Two types of progeny (High X//Y and Low X//Y) appeared in the backcross between BALB/c and High X//Y males, although the frequency of Low X//Y progeny decreased with increasing numbers of backcross generations (26.5% at N2, 13.2% at N3, 5.3% at N4, and 0% at N5). Low X//Y sires produced only Low X//Y mice. We hypothesize that at least one heritable factor which is responsible for the end-to-end association of the sex chromosomes (temporally symbolized as Sxa) is located on the common part of the X and Y chromosomes. The Sxa allele of BALB/c is Sxaa and that of M. m. molossinus is Sxab. The genotype expected in High X//Y males is Sxaa/Sxab and in Low X//Y males and their parental stocks either Sxaa/Sxaa or Sxab/Sxab. The repeated segregation of Low X//Y progeny from High X//Y sires is interpreted simply by assuming that crossing-over has occurred between the X and Y chromosomes. The gradual decrease in the recombinant type mice (Low X//Y) during sequential backcrosses suggests the presence of some autosomal factors that suppress the crossing-over of the sex chromosomes and that do not seem to function in the inter-subspecies hybrids.     

An increased level of sperm abnormalities in mice with a partial deletion of the Y chromosome

Two congenic lines of mice, one with a partial deletion of the Y chromosome, differ in the percentage of spermatozoa with abnormal heads: B10.BR/SgSn males give 22.6% and B10.BR-Ydel/Ms males give 64.2% abnormal sperm. The F1s resulting from crosses of B10.BR/SgSn males with females of five common inbred strains exhibited significantly lower levels of abnormal sperm than the parental strains, as opposed to F1 hybrids sired by B10.BR-Ydel/Ms mutant males, where very high levels of abnormal spermatozoa were found. About 30% of abnormal spermatozoa, produced by males with deletion on the Y chromosome, were characterized by a flat acrosomal cap. This class of abnormality was never observed in non-mutant males, suggesting a mutant-specific defect. These results demonstrate the important role of the Y chromosome in spermatogenesis.     

The contribution of the y chromosome to hybrid male sterility in house mice

Hybrid sterility in the heterogametic sex is a common feature of speciation in animals. In house mice, the contribution of the Mus musculus musculus X chromosome to hybrid male sterility is large. It is not known, however, whether F(1) male sterility is caused by X-Y or X-autosome incompatibilities or a combination of both. We investigated the contribution of the M. musculus domesticus Y chromosome to hybrid male sterility in a cross between wild-derived strains in which males with a M. m. musculus X chromosome and M. m. domesticus Y chromosome are partially sterile, while males from the reciprocal cross are reproductively normal. We used eight X introgression lines to combine different X chromosome genotypes with different Y chromosomes on an F(1) autosomal background, and we measured a suite of male reproductive traits. Reproductive deficits were observed in most F(1) males, regardless of Y chromosome genotype. Nonetheless, we found evidence for a negative interaction between the M. m. domesticus Y and an interval on the M. m. musculus X that resulted in abnormal sperm morphology. Therefore, although F(1) male sterility appears to be caused mainly by X-autosome incompatibilities, X-Y incompatibilities contribute to some aspects of sterility.     

Preferential segregation of marker chromosomes 14 and 18 in mouse recombinant inbred strains derived from the KE and CBA/Kw strains

The segregation pattern of chromosomes 14 and 18 were analyzed in recombinant inbred strains of mice developed from KE and CBA/Kw strains. The analysis was possible owing to the fact that the C-band on chromosomes 14 of the CBA/Kw strain and that of chromosome 18 of the KE strain show size polymorphism: while the CBA/Kw mice have a small sized C-band on chromosome 14, the KE mice show small C-bands on chromosome 18. Chromosomes were identified by G-banding and FISH. The results show that the chromosomes with small centromeric chromatin segregate preferentially.     

Observations on the mutagenic power of hycanthone in mammals]

Male mice from the C57Bl strain were given 150 mg/kg of hycanthone, an antischistosomial drug. Spermatocytes derived from the treated spermatogonia as well as the spermatocytes from the F1 male offspring sired the first three weeks after treatment were examined for the presence of chromosome rearrangements. Since no reciprocal translocation was recorded, it is concluded that treatment with hycanthone is not susceptible to produce transmissible chromosome anomalies in male mammalian germ cells.     

Deficiency of X and Y chromosomal pairing at meiotic prophase in spermatocytes of sterile interspecific hybrids between laboratory mice (Mus domesticus) and Mus spretus

The normal association between the X and Y chromosomes at metaphase I of meiosis, as seen in air-dried light microscope preparations of mouse spermatocytes, is frequently lacking in the spermatocytes of the sterile interspecific hybrid between the laboratory mouse strains C57BL/6 and Mus spretus. The purpose of this work is to determine whether the separate X and Y chromosomes in the hybrid are asynaptic, caused by failure to pair, or desynaptic, caused by precocious dissociation. Unpaired X-Y chromosomes were observed in air-dried preparations at diakinesis, just prior to metaphase I. Furthermore, immunocytology and electron microscopy studies of surface-spread pachytene spermatocytes indicate that the X and Y chromosomes frequently fail to initiate synapsis as judged by the failure to form a synaptonemal complex between the pairing regions of the X and Y Chromosomes. Several additional chromosomal abnormalities were observed in the hybrid. These include fold-backs of the unpaired X or Y cores, associations between the autosome and sex chromosome cores, and autosomal univalents. The occurrence of abnormal autosomal and XY-autosomal associations was also correlated with cell degeneration during meiotic prophase. The primary breakdown in hybrid spermatogenesis occurs at metaphase I (MI), with the appearance of degenerated cells at late MI. In those cells, the X and Y are decondensed rather than condensed as they are in normal mouse MI spermatocytes. These results, in combination with the previous genetic analysis of spermatogenesis in hybrids and backcrosses with fertile female hybrids, suggest that the spermatogenic breakdown in the interspecific hybrid is primarily correlated with the failure of XY pairing at meiotic prophase, asynapsis, followed by the degeneration of spermatocytes at metaphase I. Secondarily, the failure of XY pairing can be accompanied by failure of autosomal pairing, which appears to involve an abnormal sex vesicle and degeneration at pachytene or diplotene.by C. Heyting     

Features of adrenal gland and gonadal reactions in mice with a genetic predisposition to dominance under zoo-social stress]

Intensity and duration of endocrine responses of adrenals and gonads in QT, CBA/Lac male mice and heir first generation reciprocal hybrids (F1) mice, social stress were studied. PT males had higher level of corticosterone in 1 h after stress, the adrenals and gonads reactions being some hrs shorter, as compared with CBA/Lac mice. No differences were observed in dynamics among reciprocal hybrids. They inherited not only high capacity to dominance in micropopulations but also reactions of adrenal activation and gonadal inhibition. Similar results were obtained, when these features were studied in dominant and subordinate males of PT strain mice.     

X-Y chromosome univalency in the testes of hyperthermic mice: II. Light and electron microscopic analysis of synaptonemal complexes

Hyperthermia-induced X-Y dissociation has been observed in diakinesis-metaphase I sper-matocytes but not in pachytene spermatocytes, which have been implicated as highly susceptible to heat stress. To determine X-Y dissociation in pachytene spermatocytes and to compare levels of dissociation between pachytene and diakinesis-metaphase I spermatocytes male ICR mice were exposed to 35°C ± 0.07°C and 65% ± 0.14% relative humidity for 2 or 4 days. Control mice were housed at 24°C ± 0.04°C and 43% ± 0.58% relative humidity. Mice were killed 0, 3, 5, 8, or 10 days after stress and the testes processed for meiotic chromosome display at diakinesis-metaphase I and synaptonemal complex display at pachynema. Twenty-five to thirty cells per mouse at both stages of meiosis were observed with light microscopy, and pachytene spreads with transmission electron microscopy to determine heat-stress effects on synaptonemal complex structure. Statistical analyses revealed significant linear increases in X-Y dissociation with prolonged exposure to heat at pachynema and diakinesis-metaphase I. Levels of pachytene dissociation were one-half the levels of dissociation at diakinesis-metaphase I. The resolvable structure of the lateral elements of the synaptonemal complex was not affected by heat stress.     

The Y Chromosome Effect on Intermale Aggression in Mice Depends on the Maternal Environment

Two parental strains of laboratory mice, NZB and CBA/H, were chosen for their differences in attack behavior. NZB have higher scores than CBA/H. An effect of the Y chromosome on attack behavior was determined for two maternal environments. Each male was tested once in a dyadic encounter with an A/J male as a standard opponent. The two reciprocal F1s and the four reciprocal backcrosses were used. In each group, the proportion of attacking males was used as the dependent variable. In the first experiment, the ovarian graft method was used to test for an effect of variation of the overall maternal environment: parental vs. F1. The results demonstrated an interaction between the Y chromosome and the maternal environment. By use of the adoption method, it was shown in the second experiment that this maternal effect was probably postnatal (and not prenatal).     

Fertility in first-generation hybrids of roach, Rutilus rutilus (L.), and silver bream, Blicca bjoerkna (L.)

Fertility in first‐generation hybrids of roach, Rutilus rutilus, and silver bream, Blicca bjoerkna, was investigated. Sperm and egg production of hybrids at first sexual maturity were examined. Eggs from female hybrids were artificially fertilized with the sperm of a corresponding hybrid male; a hybrid male from the reciprocal crossbreeding; a parental species male R. rutilus; and a parental species male B. bjoerkna. The results revealed that gametogenesis was normal in female hybrids. However, in male hybrids, a low efficiency of gametogenesis was observed. The semen of male hybrids was extremely dilute, with spermatozoa concentration lower than that in parental species. Nevertheless, these F1 hybrids (males and females) from reciprocal crossbreeding were fertile. F2 and backcross generations were produced, but F2 crosses from the female hybrid and corresponding hybrid male displayed a drastically slower hatching rate. Also higher proportions of deformed embryos were hatched than in other post‐F1‐generation crosses.     

X-Y chromosome univalency in the testes of hyperthermic mice: I. Concomitant formation of multinucleated giant cells

Exposure of mice to an environment of approximately 35°C and 65% relative humidity for 2–5 days caused dissociation of the X-Y chromosome bivalent in diakinesis-metaphase I (primary) spermatocytes. Dissociation of autosomal bivalents, chromosome fragmentation, aneuploidy, and polyploidy were not significantly affected by heat stress. Heat stress also caused formation of multinucleated giant cells in the mouse testis. Giant cell formation followed a distribution similar to X-Y dissociation, reaching highest levels 5 days after heat stress and returning to control levels 50–70 days after heat stress. Spermatogonial activity was not permanently damaged by these conditions, and the germinal epithelium was able to repopulate. We believe that cell aberration or cell death resulting from either or both of these anomalies causes much of the decreased fertility found after subjecting scrotal mammals to high temperatures.     

Localization of the gene for the vitamin B12 binding protein,transcobalamin II,near the centromere on mouse chromosome 11, linked with the hemoglobin alpha-chain locus

Somatic cell hybrids, recombinant inbred (RI) mouse strains, and backcross breeding experiments were used to locate the gene of transcobalamin II (Tcn-2), the vitamin B12 binding protein in mouse serum. TCN-2 was found to be a useful genetic marker in the somatic cell hybrids. Selected hybrid clones were derived from fusions between GR mouse cells and the Chinese hamster cell line E36. Analysis of mouse specific chromosomal enzyme markers in relationship to TCN-2 secretion, in the hybrid clones, provided provisional evidence for assignment of the Tcn-2 locus to chromosome 11. The strain distribution pattern of the TCN-2 variants S and F in the RI series CXS, constructed from the cross of BALB/cHeA (TCN-2S) with STS/A (TCN-2F), implied a close linkage with the hemoglobin alpha-chain locus (Hba) on chromosome 11. Backcross breeding using inbred strains confirmed these findings and located the Tcn-2 gene closest to the centromere, linked with waved 2 (wa-2) and Hba with recombination frequencies of 6.9 and 19.2% each. The linkage group Tcn-2/wa-2/Hba was established.This work was supported by Swiss National Science Foundation Grants 3.023-0.81 and 3.728-0.80, Fritz Hoffmann-La Roche Stiftung 173, the Prof. Dr. Max Cloëtta Foundation, and the Kantonale Zürcher Liga für krebsbekämpfung, Switzerland. M. Prochazka was supported by the Postgraduate Training Program for Experimental Medicine and Biology of the University of Zürich, Switzerland.