Relationship between growth and meiotic maturation of the mouse oocyte

Oocytes of various sizes were isolated from trypsinized ovaries of juvenile mice, cultured in a chemically defined medium, and scored for the resumption and completion of meiotic maturation. Oocytes recovered from mice younger than 15 days remained in the germinal vesicle stage, whereas those from mice 15 days or older resumed meiosis at a frequency which increased with the age of the mice. The mean diameter of the oocytes recovered also increased with the age of the mice. Within individual litters, the mean diameter of oocytes which failed to mature (incompetent oocytes) was significantly less than that of oocytes which matured (competent oocytes). The frequency of premature metaphase I arrest decreased markedly as the age of the mice and oocyte volume increased. These results suggest that the ability to resume meiosis is acquired at a specific stage of oocyte growth in the juvenile mouse, and that the ability to complete meiotic maturation is acquired subsequently. These oocytes provide an in vitro system with which to study the control of meiosis in the mammal.     

Genetic relationship between the neurological (excitability thresholds) and the behavioral characteristics of mouse strains and their hybrids

The comparative genetic analysis of 16 inbred mouse strains was carried out for excitability thresholds of peripherical parts of the nervous system, viability to learning, short-term memory and exploratory activity in different experimental conditions. The high positive correlation was shown between excitability thresholds of different parts of the peripherical nervous system, the high negative correlation being established between excitability thresholds, viability to learning, short-term memory and exploratory activity. The data led to the conclusion about the existence of the pleiotropic effect of genes controlling the excitability thresholds, on peculiarities of behaviour. This was confirmed by the findings obtained in the study of various hybrids, which point to the similar way of inheritance of excitability thresholds and behavioural patterns.     

Genetic control of mammalian meiotic recombination. I. Variation in exchange frequencies among males from inbred mouse strains

Genetic background effects on the frequency of meiotic recombination have long been suspected in mice but never demonstrated in a systematic manner, especially in inbred strains. We used a recently described immunostaining technique to assess meiotic exchange patterns in male mice. We found that among four different inbred strains--CAST/Ei, A/J, C57BL/6, and SPRET/Ei--the mean number of meiotic exchanges per cell and, thus, the recombination rates in these genetic backgrounds were significantly different. These frequencies ranged from a low of 21.5 exchanges in CAST/Ei to a high of 24.9 in SPRET/Ei. We also found that, as expected, these crossover events were nonrandomly distributed and displayed positive interference. However, we found no evidence for significant differences in the patterns of crossover positioning between strains with different exchange frequencies. From our observations of >10,000 autosomal synaptonemal complexes, we conclude that achiasmate bivalents arise in the male mouse at a frequency of 0.1%. Thus, special mechanisms that segregate achiasmate chromosomes are unlikely to be an important component of mammalian male meiosis.     

Histological studies on male sterility of hybrids between laboratory and wild mouse strains

In this study the cellular mechanisms of male sterility in F1 hybrids (BNF1) between BALB/c and wild-derived M.MUS-NJL (NJL) was investigated. Cell proliferation and differentiation in the sterile testis were examined by bromodeoxyuridine-labeling and use of germ cell stage-specific antibodies. In BNF1 testes, spermatogonia actively proliferated with a seminiferous epithelial cycle, and were retained in the basal layer of the tubules. However, preleptotene, leptotene and zygotene spermatocytes moved to the adluminal region. Immunohistological data with germ cell stage-specific antibodies indicated the presence of few, if any, pachytene spermatocytes in BNF1 testes. Thus, spermatogenesis seemed to be blocked at the zygotene stage. For examination of germ cell-Sertoli cell interactions, testes of aggregation chimeras between BNF1 and C3H/HeN were analyzed immunohistologically with C3H-specific antibody. Results showed that spermatogenesis of C3H-germ cells was normal, even when these cells in contact with BNF1-Sertoli cells. Differentiation of BNF1-germ cells progressed from zygotene to pachytene stage spermatocytes when these cells were surrounded by C3H-Sertoli cells, but never proceeded beyond the pachytene stage. These observations suggest that at least two different cellular factors may be involved in spermatogenesis, one acting in the germ cells and the other mediated by Sertoli cells. Furthermore, mating experiments revealed that the degree of spermatogenesis varied in different F1 hybrids, and that the major sterility factor was closely linked to the T -locus on chromosome 17.     

Chromosome synapsis and genetic recombination: their roles in meiotic chromosome segregation

Chromosome synapsis and genetic recombination ensure the faithful segregation of chromosomes at meiosis I by establishing physical connections between homologs. Recent observations suggest that recombination may also play a role in the homology search process that precedes synapsis.     

Isozymes of NADP-dependent isocitrate dehydrogenase in normal and tumor tissues of various mouse strains and their hybrids

Normal tissues of DBA, CBA, CC57W, C3H, Balb/c, SHR mice and F1 hybrids CC57W/DBA appeared to differ in the ratios of mitochondrial and supernatant NADP-dependent isocitrate dehydrogenase (IDH). Tested inbred mice strains CC57W, C3H, SHR, Balb/c contain allelic form Idh-1a of supernatant IDH gene Idh-1, whereas allelic form Idh-1b is characteristic of mice strains DBA and CBA. In tumors IDH isozymes have the same mobility as do isozymes of homologous normal tissues; but their activity is lower. A high variability of each isozyme activity in the isozyme spectrum is revealed in various tissues of F1 hybrids CC57W/DBA. Allelic forms of gene Idh-1 were used as markers of normal and tumor cells for the experimental model: transplantation of sarcoma 37 (Idh-1a/Idh-1a) to subcutaneous tissue of the mouse strain DBA (Idh-1b/Idh-1b). It enables us to reveal isozymes of stromal cell in tumor IDH isozyme spectrum. The results indicate that the relation of normal and tumor isozymes vary in different tumors.     

A novel meiotic drive locus almost completely distorts segregation in mimulus (monkeyflower) hybrids

We report the discovery, mapping, and characterization of a meiotic drive locus (D) exhibiting nearly 100% nonrandom transmission in hybrids between two species of yellow monkeyflowers, outcrossing Mimulus guttatus and selfing M. nasutus. Only 1% of F(2) hybrids were M. nasutus homozygotes at the marker most tightly linked to D. We used a set of reciprocal backcrosses to distinguish among male-specific, female-specific, and zygote-specific sources of transmission ratio distortion. Transmission was severely distorted only when the heterozygous F(1) acted as the female parent in crosses to either parental species, ruling out pollen competition and zygote mortality as potential sources of drive. After four generations of backcrossing to M. nasutus, nearly isogenic lines were still >90% heterozygous at markers linked to D, suggesting that heterozygosity at the drive locus alone is sufficient for nonrandom transmission. A lack of dramatic female fitness costs in these lines rules out alternatives involving ovule or seed mortality and points to a truly meiotic mechanism of drive. The strength and direction of drive in this system is consistent with population genetic theory of selfish element evolution under different mating systems. These results are the first empirical demonstration of the strong female-specific drive predicted by new models of selfish centromere turnover.     

Chromosome-wide characterization of meiotic noncrossovers (gene conversions) in mouse hybrids

During meiosis, the recombination-initiating DNA double-strand breaks (DSBs) are repaired by crossovers or noncrossovers (gene conversions). While crossovers are easily detectable, noncrossover identification is hampered by the small size of their converted tracts and the necessity of sequence polymorphism. We report identification and characterization of a mouse chromosome-wide set of noncrossovers by next-generation sequencing of 10 mouse intersubspecific chromosome substitution strains. Based on 94 identified noncrossovers, we determined the mean length of a conversion tract to be 32 bp. The spatial chromosome-wide distribution of noncrossovers and crossovers significantly differed, although both sets overlapped the known hotspots of PRDM9-directed histone methylation and DNA DSBs, thus supporting their origin in the standard DSB repair pathway. A significant deficit of noncrossovers descending from asymmetric DSBs proved their proposed adverse effect on meiotic recombination and pointed to sister chromatids as an alternative template for their repair. The finding has implications for the molecular mechanism of hybrid sterility in mice from crosses between closely related Mus musculus musculus and Mus musculus domesticus subspecies.     

人精母细胞重组频率和年龄相关性的分析

减数分裂遗传重组对同源染色体的正确分离和单倍体的正确形成起至关重要的作用,但人们对人精母细胞减数分裂遗传重组机制了解的还很少。通过免疫荧光染色技术标记减数分裂I联会复合体上的MLH1(DNA错配修复蛋白)位点可以检测人精母细胞的重组。文章对10例可育男性进行分析,发现每个细胞中重组位点数平均为49.4士4.4,范围为33~63,具有显著的个体差异,只有0.4%(1/220)的常染色体SC上缺少MLH1位点。进一步通过Spearman相关性分析,分析了年龄因素与个体间重组位点差异的相关性,结果提示年龄因素对常染色体及性染色体的重组均无影响。     

Distinct frequencies balance segregation with interaction between different memory types within a prefrontal circuit

1. Download : Download high-res image (161KB)
2. Download : Download full-size image

     

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.     

Supermelanotic hybrids between mouse teratocarcinoma and mouse melanoma cells

Each of four kinds of teratocarcinoma cells, OTT6050P, PCC4, PSA1 and LT, derived from 129 or LT mouse strain, was fused with B16-CAPr melanoma cells derived from C57BL/6J by using Sendai virus. The resultant hybrids were morphologically melanotic melanoma cells which were larger and more heavily pigmented than the parental B16-CAPr melanoma cells. The chromosome analysis and GPI electrophoresis demonstrated that all hybrids were products of fusion between a single teratocarcinoma cell and a single melanoma cell. The pigmentation in the hybrids between a 129 teratocarcinoma cell and a melanoma cell was much stronger than that in hybrids between an LT teratocarcinoma cell and a melanoma cell. This phenomenon was consistent with the difference of coat color between 129 and LT mouse strain. From these results, it was suggested that the genes of teratocarcinoma cells involved in the pigmentation are activated in the hybrids with B16-CAPr melanoma cells.     

Mutation and reversion frequencies of different Sulfolobus species and strains

We have determined the apparent and actual spontaneous mutation frequencies and rates for different species and strains of the thermoacidophilic crenarchaeote Sulfolobus. The proportion of mutations caused by insertion sequences has also been analyzed. Mutation frequencies for S. islandicus (0.08–0.6 mutations per cell division and 10⁷ cells) were below those determined for S. solfataricus and comparable to or lower than those for S. acidocaldarius. The proportion of insertion sequence mutations for the S. islandicus strains REN1H1 (9 out of 230) and HVE10/4 (0 out of 24) was found to be considerably lower than in S. solfataricus P1 and P2 and also low in comparison to other S. islandicus strains. Mutants defective in either the pyrEF genes or the lacS gene have been isolated. Their growth phenotype on selective and non-selective medium was examined and the inactivating mutations in either of the genes were determined. In addition the reversion frequencies for these mutants were measured and found to be in the range of <0.6–1.5 mutations per cell division and 10⁸ cells. However, when being subjected to electroporation as a transformation procedure, increased reversion was observed.     

Relationship between topoisomerase II and radiosensitivity in mouse L5178Y lymphoma strains

The cytotoxic and mutagenic effects of topoisomerase II inhibitors were measured in closely related strains of mouse lymphoma L5178Y cells differing in their sensitivity to ionizing radiation. Strain LY-S is sensitive to ionizing radiation relative to strain LY-R and is deficient in the rejoining of DNA double-strand breaks induced by this agent, whereas 2 radiation-resistant variants of strain LY-S have regained the ability to rejoin these double-strand breaks. We have found that the sensitivity of these cells to m-AMSA, VP-16, and ellipticine is correlated to their sensitivity to ionizing radiation. However, this correlation did not extend to their sensitivities to novobiocin, camptothecin, hydrogen peroxide, methyl nitrosourea and UV radiation. Thus, there appears to be a unique correlation between sensitivity to ionizing radiation and to topoisomerase II inhibitors which stabilize the cleavable complex between the enzyme and DNA. It is possible either that (1) topoisomerase II is altered in strain LY-S and that this enzyme is involved in the repair of DNA double-strand breaks or (2) strain LY-S is deficient in a reaction which is necessary for the repair of DNA double-strand breaks induced by ionizing radiation as well as the repair of DNA damage induced by these topoisomerase II inhibitors. m-AMSA, VP-16, and ellipticine were found to be highly mutagenic at the tk locus in L5178Y strains which are heterozygous for the tk gene but not in a tk hemizygous strain, indicating that these inhibitors induce multilocus lesions in DNA, as does ionizing radiation. The differences in the sensitivity of strains LY-R and LY-S to the topoisomerase II inhibitors were paralleled by differences in the induction of protein-associated DNA double-strand breaks in the 2 strains. This correlation did not extend to the radiation-resistant variants of strain LY-S, however. The variants showed resistance to the cytotoxic effects of the inhibitors relative to strain LY-S, but exhibited DNA double-strand break induction similar to that observed in strain LY-S.     

Patterns of chromosome segregation in chinese hamster × mouse cell hybrids between permanent cell lines and thymus cells

Hybrids between a tumorigenic Chinese hamster cell line (DC3F-aza) and normal mouse thymus cells very rapidly lost most of their mouse chromosomes, whereas hybrids between tumorigenic mouse cell lines (either Cl.1D of L cell line origin, or PCC4-aza1 teratocarcinoma cells) and normal Chinese hamster thymus cells lost most of their hamster chromosomes. From three such fusion experiments, 20 cell lines were developed which all followed the same evolution, namely, the elimination of the majority of the chromosomes contributed by the normal thymus cell. In some hybrids, the elimination process resulted in the total absence of intact chromosomes contributed by the thymus cell parent. Such hybrids were distinguished from revertant parental cells growing in the selective hybrids were distinguished from revertant parental cells growing in the selective medium by the presence of at least one enzyme in their cell extracts which displayed the electrophoretic mobility of the enzyme of the thymus cell parent. These observations, together with data from other reports, suggest that, as a rule, interspecific cell hybrids which develop upon fusion between normal diploid cells and tumorigenic cell lines maintain the chromosomes of the latter and eliminate preferentially many or most of the chromosomes contributed by the normal cell parents, independent of the respective species of the parental cells.     

A test for meiotic drive in hybrids between Australian and Timor zebra finches

Meiotic drivers have been proposed as a potent evolutionary force underlying genetic and phenotypic variation, genome structure, and also speciation. Due to their strong selective advantage, they are expected to rapidly spread through a population despite potentially detrimental effects on organismal fitness. Once fixed, autosomal drivers are cryptic within populations and only become visible in between‐population crosses lacking the driver or corresponding suppressor. However, the assumed ubiquity of meiotic drivers has rarely been assessed in crosses between populations or species. Here we test for meiotic drive in hybrid embryos and offspring of Timor and Australian zebra finches—subspecies that have evolved in isolation for about two million years—using 38,541 informative transmissions of 56 markers linked to either centromeres or distal chromosome ends. We did not find evidence for meiotic driver loci on specific chromosomes. However, we observed a weak overall transmission bias toward Timor alleles at centromeres in females (transmission probability of Australian alleles of 47%, nominal p = 6 × 10^–5). While this is in line with the centromere drive theory, it goes against the expectation that the subspecies with the larger effective population size (i.e., the Australian zebra finch) should have evolved the more potent meiotic drivers. We thus caution against interpreting our finding as definite evidence for centromeric drive. Yet, weak centromeric meiotic drivers may be more common than generally anticipated and we encourage further studies that are designed to detect also small effect meiotic drivers.     

Chromosome relationships and meiotic mechanisms of certain morsitans group tsetse flies and their hybrids

There are three pairs of euchromatic components, the L₁ and L₂ autosomes and the X chromosome pair respectively, which are found in both G. austeni and the three forms of G. morsitans. Each species/sub-species also includes in its complement a group of heterochromatic autosomes (S) which have various morphologies and differ in number both within and between the species/sub-species. Several lines of evidence are outlined which point to these being supernumerary B chromosomes. Male meiosis is normally achiasmate and only L₁ and L₂ autosomes pair completely. X-Y association is restricted to a small pairing segment the position of which on the X is constant for all the species/sub-species. It is located in one of two positions on the Y chromosome according to the species/sub-species. The S chromosomes behave as hereditary univalents at first anaphase while the sex bivalent can undergo distance pairing best exemplified in G. austeni and G. submorsitans. A Y structural mutant line gives some indication of the size of the pairing segment and demonstrates that survival and maleness is possible even when two-thirds of the chromosome is missing. Meiotic and polytene chromosome studies connected with hybridisation experiments designed to test the sterility factor as a potential means of tsetse control assist in establishing the evolutionary relationship of the subspecies.     

Cerebellar protein expression in three different mouse strains and their relevance for motor performance

The present study uses a proteomic approach to link motor function to cerebellar protein expression in 129X1/SvJ, C57BL/6J and nNOS WT mice. Poor performance on the Rota rod, the standard test for motor coordination, was detected in 129X1/SvJ mice. No gross impairments of neurological, cognitive and behavioural functions were observed. Identification and quantification of 48 proteins revealed reduced expression of calbindin, septin 5 and syntaxin binding protein 1 in 129X1/SvJ. In nNos WT glucose-6-phosphate 1 dehydrogenase X was decreased whereas dihydropyrimidinase-related protein-4 was increased. In C57BL/6J stress-70 protein, alpha enolase, NAD-dependent deacetylase sirtuin 2, septin 2, dihydropyrimidinase-related protein-2 and brain derived neurotrophic factor showed elevated levels. Neurological examination, Rota rod test, Morris Water Maze, Multiple-T-Maze, Open field and Elevated plus-maze were employed to study motor, cognitive and behavioural function. Mice were sacrificed and cerebellar tissue was homogenized. Proteins were extracted and separated on two-dimensional gel electrophoresis with subsequent in-gel digestion followed by mass spectrometrical analysis of peptides (MALDI-TOF/TOF-TOF). Quantification of spots was carried out by specific software. A strong association of impaired motor function with altered cerebellar protein expression of calbindin, septin 5 and syntaxin binding protein 1in 129X1/SvJ was observed and is in agreement with previous observations of motor deficiencies in a calbindin knock-out mouse. These results have to be taken into account when using 129X1/SvJ for biochemical, toxicological or gene targeting experiments as well as when studying the above-mentioned proteins or corresponding pathways and cascades in this mouse strain.