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Balancing stem cell self-renewal and initiation of lineage specification programs is essential for the development and homeostasis of the hematopoietic system. We have specifically ablated geminin in the developing murine hematopoietic system and observed profound defects in the generation of mature blood cells, leading to embryonic lethality. Hematopoietic stem cells (HSCs) accumulated in the fetal liver following geminin ablation, while committed progenitors were reduced. Genome-wide transcriptome analysis identified key HSC transcription factors as being upregulated upon geminin deletion, revealing a gene network linked with geminin that controls fetal hematopoiesis. In order to obtain mechanistic insight into the ability of geminin to regulate transcription, we examined Hoxa9 as an example of a key gene in definitive hematopoiesis. We demonstrate that in human K562 cells geminin is associated with HOXA9 regulatory elements and its absence increases HOXA9 transcription similarly to that observed in vivo. Moreover, silencing geminin reduced recruitment of the PRC2 component SUZ12 to the HOXA9 locus and resulted in an increase in RNA polymerase II recruitment and H3K4 trimethylation (H3K4me3), whereas the repressive marks H3K9me3 and H3K27me3 were reduced. The chromatin landscape was also modified at the regulatory regions of HOXA10 and GATA1. K562 cells showed a reduced ability to differentiate to erythrocytes and megakaryocytes upon geminin silencing. Our data suggest that geminin is indispensable for fetal hematopoiesis and regulates the generation of a physiological pool of stem and progenitor cells in the fetal hematopoietic system.

Estradiol (E2) is believed to modulate physiological functions relevant to osteoblast biology through the actions of estrogen receptors (ERs) that in turn regulate the expression of target genes. The molecular effects of estrogen action in bone remain to be fully elucidated. This study reports a genome-wide molecular and computational analysis of the interaction between ER and regulatory elements on the DNA of target genes in human primary osteoblasts. Of approximately 54,000 gene probes surveyed in this study, a total of 375 genes were up-regulated and 418 genes were down-regulated on exposure to E2, with only 46 of these being direct target genes after 24 h, as determined by concomitant cycloheximide treatment. Computational analysis discovered several pathways where E2 co-regulates multiple functionally linked components. Examination of the genomic sequence of IGF binding protein 4 located ER response elements within the first intron. Using by chromatin immunoprecipitation, we show a site- and cell-specific recruitment of transcription factors to this newly identified regulatory region. Transient transfection studies revealed that this intronic region acts as a functional promoter in human osteoblasts. Taken together, this analysis provides a comprehensive gene transcription profile and identifies several genes of potential physiological importance in controlling estrogen-mediated signaling in primary osteoblasts.

By detecting several new differentially expressed genes in the human corneal limbus, this study further expands current knowledge on the molecular signature of limbal epithelial stem cells. Plasma membrane localization of IFITM1 and ITM2A suggests their potential usefulness as targets to select stem cell-enriched populations from the limbal epithelium.

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