IntroductionCells of sexually reproducing eukaryotes normally contain two equal (homologous) sets of chromosomes, one contributed by the father and the other by the mother during the fusion of gametes and the formation of a zygote. Meiosis is the cell division that reduces the number of chromosomes by half. It produces gametes or their precursor cells, each of which contains a haploid set consisting of randomly assorted parental chromosomes. These chromosomes are mosaics, because the original parental homologues have exchanged corresponding pieces by crossing-over. Thus, the function of meiosis is twofold -it compensates for the doubling of the chromosome number at fertilization and it provides the progeny with newly assorted sets of alleles, which is the basis of their genetic diversity.Crossing-over is initiated at multiple sites in recombining chromosomes by the enzymatic induction of double-strand breaks (DSBs). The resection of single strands at DSBs leads to the formation of gaps in the DNA. The missing bases are replenished by using the complementary sequence from the homologous chromosome as the template. This process is recombinogenic; that is, it can lead to the reciprocal exchange of DNA between the chromosomes involved (for review, see Keeney, 2001).In order to allow crossing-over, homologous parental chromosomes must pair during meiotic prophase via a ladderlike proteinaceous structure, the synaptonemal complex (SC) (for reviews, see Loidl, 1990;Zickler and Kleckner, 1999). The SC consists of two parallel axes (the lateral elements), to each of which the two chromatin threads of a single replicated chromosome are attached. The lateral elements are connected and kept at a distance of ~100 nm by the so-called transversal filaments. The ultrastructure of the SC is evolutionarily well conserved from protists to humans, although its molecular composition is far more heterogeneous.The fission yeast Schizosaccharomyces pombe features a meiosis that is unique in several respects. Most remarkably, it lacks an SC. Instead, so-called linear elements (LEs) appear during meiotic prophase (Olson et al., 1978;Bähler et al., 1993). LEs appear in the electron microscope (EM) as single lines of variable length, networks of interconnected lines or bundles of lines. These different morphological classes were found to prevail at different stages of meiotic prophase (Bähler et al., 1993), which suggests that their change in appearance is functionally related to chromosome pairing and/or recombination.Because a rec10 mutant lacks LEs, a structural or regulatory role of the Rec10 protein in LE formation has been proposed (Molnar et al., 2003). Apart from this indirect evidence, information on the molecular composition of LEs is scarce. Neither topoisomerase II nor Rec8 [which, in other organisms, constitute the cores along which lateral elements form (Klein et al., 1992;Klein et al., 1999)] delineate entire LEs (Hartsuiker et al., 1998;Parisi et al., 1999;Watanabe and Nurse, 1999), and S. pombe homologues of proteins prese...

Identifying cancer-specific biomarkers represents an ongoing challenge to the development of novel cancer diagnostic, prognostic and therapeutic strategies. Cancer/testis (CT) genes are an important gene family with expression tightly restricted to the testis in normal individuals but which can also be activated in cancers. Here we develop a pipeline to identify new CT genes. We analysed and validated expression profiles of human meiotic genes in normal and cancerous tissue followed by meta-analyses of clinical data sets from a range of tumour types resulting in the identification of a large cohort of highly specific cancer biomarker genes, including the recombination hot spot activator PRDM9 and the meiotic cohesin genes SMC1beta and RAD21L. These genes not only provide excellent cancer biomarkers for diagnostics and prognostics, but may serve as oncogenes and have excellent drug targeting potential.

The modification of yeast artificial chromosomes through homologous recombination has become a useful genetic tool for studying gene function and enhancer͞promoter activity. However, it is difficult to purify intact yeast artificial chromosome DNA at a concentration sufficient for many applications. Bacterial artificial chromosomes (BACs) are vectors that can accommodate large DNA fragments and can easily be purified as plasmid DNA. We report herein a simple procedure for modifying BACs through homologous recombination using a targeting construct containing properly situated Chi sites. To demonstrate a usage for this technique, we modified BAC clones containing the zebrafish GATA-2 genomic locus by replacing the first coding exon with the green f luorescent protein (GFP) reporter gene. Molecular analyses confirmed that the modification occurred without additional deletions or rearrangements of the BACs. Microinjection demonstrated that GATA-2 expression patterns can be recapitulated in living zebrafish embryos by using these GFP-modified GATA-2 BACs. Embryos microinjected with the modified BAC clones were less mosaic and had improved GFP expression in hematopoietic progenitor cells compared with smaller plasmid constructs. The precise modification of BACs through Chi-stimulated homologous recombination should be useful for studying gene function and regulation in cultured cells or organisms where gene transfer is applicable.