In situ hybridization as a rapid means to assess meiotic pairing and detection of alien DNA transfers in interphase cells of wide crosses involving wheat and rye

Summary The objectives of this study were to determine if biotin-labelled total genomic DNA of rye (Secale cereale L.) could be used to (i) preferentially label rye meiotic chromosomes in triticale and (ii) detect translocation stocks at interphase and/or early prophase by in situ hybridization. Welsh triticale, a wheat-rye segmental amphiploid, and Kavkaz wheat, a wheat-rye translocation were used. The results indicated that labelled chromosomes of rye and unlabelled chromosomes of wheat could be observed throughout all meiotic stages in the triticale. For Kavkaz wheat, the presence of the translocated 1RS chromosome arm of rye was detected at the interphase or very early prophase stage. Rapid assessment of feasibility of gene transfers and detection of alien DNA in somatic cells at the interphase stage by in situ hybridization allows for rapid decision-making and saves time and expense in plant breeding programs.Plant Research Centre Contribution No. 1276     

Effects of gonadotropins and granulosa cell secretions on the maturation and fertilization of rat oocytes in vitro

Fully grown germinal vesicle-stage oocytes are induced to resume meiosis and acquire the capacity to undergo fertilization in response to a surge of gonadotropins. The present study examined possible direct and indirect roles of gonadotropins in the maturation and fertilization of rat oocytes by determining 1) the effect of exogenous administration of gonadotropins (priming) to immature rats prior to oocyte collection on the capacity of oocytes to undergo maturation and fertilization in vitro, 2) the effect of follicle-stimulating hormone (FSH) in the maturation media on the resumption of meiosis and subsequent capacity of oocytes to undergo fertilization, and 3) the capacity of oocytes to undergo maturation and fertilization following culture in preovulatory follicular fluid or in conditioned media obtained from gonadotropin-stimulated granulosa cell (GC) cultures. In the first experiment, oocytes from unprimed rats underwent spontaneous meiotic maturation in vitro and 17% underwent subsequent fertilization. Priming increased the proportion of oocytes undergoing fertilization. Maturation of oocytes in media supplemented with various concentrations of FSH or for various lengths of time (6-16 h) in medium with 500 ng FSH/ml indicated that FSH slowed the rate of meiotic maturation, but had no effect on the capacity of the oocytes to be fertilized. Oocytes obtained from primed animals and cultured in the presence of preovulatory follicular fluid were fertilized in proportions similar to those cultured in serum-containing medium. In the third experiment, medium conditioned by FSH-stimulated GC for 40 h slowed the rate of meiotic maturation; the addition of luteinizing hormone (LH) to the FSH-stimulated cells produced a medium in which the rate of oocyte maturation was not different from that of control oocytes (in medium from unstimulated cells). Medium conditioned by FSH- or LH-stimulated GC, but not fibroblasts, increased the proportions of oocytes undergoing fertilization following maturation in those media. FSH + LH stimulation of GC increased the fertilization of oocytes to proportions significantly higher than with either gonadotropin alone. These data suggest that GC respond to gonadotropin stimulation by providing a factor(s) that regulates the rate of oocyte maturation and promotes the capacity of oocytes to undergo fertilization.     

Observations on the division characterization of diploid nuclear in <Emphasis Type="Italic">Porphyra</Emphasis> (Bangiales,Rhodophyta)

Nuclear divisions of carpospores, conchocelis and conchospores of Porphyra yezoensis, P. haitanensis, P. katadai var. hemiphylla and P. oligospermatangia from China were investigated. The observations showed diploid chromosome numbers of 2n = 6 for P. yezoensis and P. oligospermatangia, and 2n = 10 for P. haitanensis and P. katadai var. hemiphylla. For all four species, somatic pairing of chromosome sets was observed in late prophase. Sister chromosomes separated at anaphase as mitosis took place in carpospores, conchocelis filamentous cells, conchosporangial branch cells and sporangial cells (conchospore formation). Chromosome configurations of tetrad and ring-shaped in conchospore germination were observed, demonstrating the occurrence of meiosis. The characteristics of diploid nuclear division in 2n = 6 species are the same as those of 2n = 10 species. The influence of somatic pairing on nuclear division of diploid cells in Porphyra was discussed.     

Identification of <Emphasis Type="Italic">Porphyra yezoensis</Emphasis> (Rhodophyta) meiosis by DNA quantification using confocal laser scanning microscopy

Conchospore germlings of Porphyra yezoensis were stained with a fluorescent dye for DNA and observed with confocal laser scanning microscopy (CLSM). Relative DNA values of the germling nuclei were obtained by measuring fluorescence intensities of nuclear regions of the optically sliced specimens, using the mean value of the smallest blade cells as a reference of the genomic n value. Such quantification revealed that the nuclear DNA amounts of the one-cell, two-cell, and four-cell-stage germlings are approximately 4 × n, 2 × n, and n ∼2 × n values respectively; these values agreed well with the expected ones from the hypothesis that meiosis corresponds to the first successive cell divisions after the conchospore germination. These results are consistent with a previous study on cytogenetic analysis of the chimaera blade formation (Ohme and Miura 1988, Plant Sci 57:135–140) and not consistent with a recent microscopic study (Wang et al. 2006, Phycol Res 54:201–207) which proposed that the first meiotic division occurs at the conchospore formation and the second division at the germination.     

The characterization of color mutations in Bangiaceae (Bangiales, Rhodophyta)

The color mutations in Bangiaceae were investigated by treating the blades, conchocelis and conchospores phase of Bangia sp., Porphyra yezoensis, and P. haitanensis sampled in China with mutagen N-methyl-N′-nitro-N-nitrosoguanidine (MNNG). A high percentage of mutation in different expression characteristics in all three phases were shown within optimum mutagen concentrations. Among mutagenized blades, mutations occurred on single cells, which is a direct outcome of mutation of haploid cells. The mutation of mutagenized conchocelis resulted in a two-step process: low-level expression in conchocelis phase, and high-level expression in progeny, explaining that mutation took place in diploid cells. The mutations of conchospores were expressed immediately at germination of spores, indicating a change in ploidy. This paper reports the process of meiosis and its effect on frond development, and the relation between color mutations and morphological characteristics expressed by mutations in Bangiaceae.     

木兰科含笑的细胞学研究

对含笑Michelia figo(Lour．)Spreng进行了细胞学研究。证实其染色体数目为2n=2x=38,最大与最小染色体长度比率为2．2,没发现st染色体和随体。首次观察和描述了其减数分裂行为。     

Kinesin-dependent transport results in polarized migration of the nucleus in oocytes and inward movement of yolk granules in meiotic embryos

During female meiosis, meiotic spindles are positioned at the oocyte cortex to allow expulsion of chromosomes into polar bodies. In C. elegans, kinesin-dependent translocation of the entire spindle to the cortex precedes dynein-dependent rotation of one spindle pole toward the cortex. To elucidate the role of kinesin-1 in spindle translocation, we examined the localization of kinesin subunits in meiotic embryos. Surprisingly, kinesin-1 was not associated with the spindle and instead was restricted to the cytoplasm in the middle of the embryo. Yolk granules moved on linear tracks, in a kinesin-dependent manner, away from the cortex, resulting in their concentration in the middle of the embryo where the kinesin was concentrated. These results suggest that cytoplasmic microtubules might be arranged with plus ends extending inward, away from the cortex. This microtubule arrangement would not be consistent with direct transport of the meiotic spindle toward the cortex by kinesin-1. In maturing oocytes, the nucleus underwent kinesin-dependent migration to the future site of spindle attachment at the anterior cortex. Thus the spindle translocation defect observed in kinesin-1 mutants may be a result of failed nuclear migration, which places the spindle too far from the cortex for the spindle translocation mechanism to function.     

Meiosis and retrotransposon silencing during germ cell development in mice

In mammals, germ cells derive from the pluripotent cells that are present early in embryogenesis, and then differentiate into male sperm or female eggs as development proceeds. Fusion between an egg and a sperm at fertilization allows genetic information from both parents to be transmitted to the next generation, and produces a pluripotent zygote to initiate the next round of embryogenesis. Meiosis is a central event in this self-perpetuating cycle that creates genetic diversity by generating new combinations of existing genetic alleles, and halves the number of chromosomes in the developing male and female germ cells to allow chromosome number to be maintained through successive generations. The developing germ cells also help to maintain genetic and chromosomal stability through the generations by protecting the genome from excessive de novo mutation. Several mouse mutants have recently been characterised whose germ cells exhibit defects in silencing the potentially mutagenic endogenous retroviruses and other retrotransposons that are prevalent in mammalian genomes, and these germ cells also exhibit defects in progression through meiosis. Here we review how mouse germ cells develop and proceed through meiosis, how mouse germ cells silence endogenous retroviruses and other retrotransposons, and discuss why silencing of endogenous retroviruses and other retrotransposons may be required for meiotic progression in mice.