Mechanisms underlying human germ cell development are unclear, partly due to difficulties in studying human embryos and lack of suitable experimental systems. Here, we show that human induced pluripotent stem cells (hiPSCs) differentiate into incipient mesoderm-like cells (iMeLCs), which robustly generate human primordial germ cell-like cells (hPGCLCs) that can be purified using the surface markers EpCAM and INTEGRINα6. The transcriptomes of hPGCLCs and primordial germ cells (PGCs) isolated from non-human primates are similar, and although specification of hPGCLCs and mouse PGCs rely on similar signaling pathways, hPGCLC specification transcriptionally activates germline fate without transiently inducing eminent somatic programs. This includes genes important for naive pluripotency and repression of key epigenetic modifiers, concomitant with epigenetic reprogramming. Accordingly, BLIMP1, which represses somatic programs in mice, activates and stabilizes a germline transcriptional circuit and represses a default neuronal differentiation program. Together, these findings provide a foundation for understanding and reconstituting human germ cell development in vitro.

Sister chromatids, the products of eukaryotic DNA replication, are held together after their synthesis by the chromosomal cohesin complex. This allows the spindle in mitosis to recognise pairs of replication products for segregation into opposite direction1-6. Cohesin forms large protein rings that may bind DNA strands by encircling7, but the characterisation of cohesin binding to chromosomes in vivo has remained vague. Here, we present high resolution analysis of cohesin association along budding yeast chromosomes III -VI. Cohesin localises almost exclusively between genes transcribed in converging direction. We find that not the underlying sequence, but active transcription positions cohesin at these sites. Cohesin is initially loaded onto chromosomes at separate places, marked by the Scc2/Scc4 cohesin loading complex8, from where it appears to slide to its more permanent locations. But even after sister chromatid cohesion is established changes in transcription lead to repositioning of cohesin. Thus a key architectural feature of mitotic chromosomes, the sites of cohesin binding and therefore most likely sister chromatid cohesion, display surprising flexibility. Cohesin localisation to places of convergent transcription is conserved in fission yeast, suggesting that it is a common feature of eukaryotic chromosomes.Correspondence and requests for materials should be addressed to F.U. (e-mail: frank.uhlmann@cancer.org.uk).. * these authors contributed equally Supplementary Information accompanies the paper on Nature's website (http://www.nature.com). Cohesin association with yeast and human chromosomes has been studied4,9-15, but the defining characteristics of association sites, and how cohesin gets to these sites, remained unclear. We analysed cohesin binding to chromosome VI of the budding yeast Saccharomyces cerevisiae by chromatin immunoprecipitation (ChIP) followed by hybridisation to a high-density oligonucleotide array16. The pattern of association in metaphase was similar for all cohesin subunits analysed, Scc1, Scc3, Smc3, and Pds5 ( Fig. 1, and Supplementary Figure S1). It was also similar before the establishment of sister chromatid cohesion, in cells arrested with the replication inhibitor hydroxyurea (Ref. 9, and Supplementary Figure S1). Cohesin bound 28 distinct sites, each spanning 1-4 kilobases (kb) in width. The intensity of association varied, with the strongest peaks found around the centromere, consistent with previous analyses9-11. The distance between neighbouring cohesin association sites ranged from 2 to 35 kb. Almost all cohesin association sites were centred in intergenic regions where genes from opposite strands converged (Fig. 1a), as previously suggested17. Using an additional high-density array, we also mapped the association of Scc1 with chromosomes III, IV, and V (Supplementary Table 1 and Figure S2). 91% (276 of 304) cohesin association sites identified lie at intergenic regions between converging genes, and of 328 convergent intergene regions 84% were bound by cohes...

Fission yeast centromeres, like those of higher eukaryotes, are composed of repeated DNA structures and associated heterochromatin protein complexes, that have a critical function in the faithful segregation of chromosomes during cell division. Cohesin protein complexes, which are essential for sister-chromatid cohesion and proper chromosome segregation, are enriched at centromeric repeats. We have identified a functional and physical link between heterochromatin and cohesin. We find that the preferential localization of cohesins at the centromeric repeats is dependent on Swi6, a conserved heterochromatin protein that is required for proper kinetochore function. Cohesin is also enriched at the mating-type heterochromatic region in a manner that depends on Swi6 and is required to preserve the genomic integrity of this locus. We provide evidence that a cohesin subunit Psc3 interacts with Swi6 and its mouse homologue HP1. These data define a conserved function of Swi6/HP1 in recruitment of cohesin to heterochromatic regions, promoting the proper segregation of chromosomes.

Genomic imprinting regulates parental-specific expression of particular genes and is required for normal mammalian development. How imprinting is established during development is, however, largely unknown. To address this question, we studied the mouse Kcnq1 imprinted cluster at which paternal-specific silencing depends on expression of the noncoding RNA Kcnq1ot1. We show that Kcnq1ot1 is expressed from the zygote stage onward and rapidly associates with chromatin marked by Polycomb group (PcG) proteins and repressive histone modifications, forming a discrete repressive nuclear compartment devoid of RNA polymerase II, a configuration also observed at the Igf2r imprinted cluster. In this compartment, the paternal Kcnq1 cluster exists in a three-dimensionally contracted state. In vivo the PcG proteins Ezh2 and Rnf2 are independently required for genomic contraction and imprinted silencing. We propose that the formation of a parental-specific higher-order chromatin organization renders imprint clusters competent for monoallelic silencing and assign a central role to PcG proteins in this process.