The polycystic kidney disease 1 gene encodes a 14 kb transcript and lies within a duplicated region on chromosome 16

Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disorder that frequently results in renal fallure due to progressive cyst development. The major locus, PKD1, maps to 16p13.3. We identified a chromosome translocation associated with ADPKD that disrupts a gene (PBP) encoding a 14 kb transcript in the PKD1 candidate region. Further mutations of the PBP gene were found in PKD1 patients, two deletions (one a de novo event) and a splicing defect, confirming that PBP is the PKD1 gene. This gene is located adjacent to the TSC2 locus in a genomic region that is reiterated more proximally on 16p. The duplicate area encodes three transcripts substantially homologous to the PKD1 transcript. Partial sequence analysis of the PKD1 transcript shows that it encodes a novel protein whose function is at present unknown

The role of the polycomb complex in silencing α-globin gene expression in nonerythroid cells

Although much is known about globin gene activation in erythroid cells, relatively little is known about how these genes are silenced in nonerythroid tissues. Here we show that the human α- and β-globin genes are silenced by fundamentally different mechanisms. The α-genes, which are surrounded by widely expressed genes in a gene dense region of the genome, are silenced very early in development via recruitment of the Polycomb (PcG) complex. By contrast, the β-globin genes, which lie in a relatively gene-poor chromosomal region, are not bound by this complex in nonerythroid cells. The PcG complex seems to be recruited to the α-cluster by sequences within the CpG islands associated with their promoters; the β-globin promoters do not lie within such islands. Chromatin associated with the α-globin cluster is modified by histone methylation (H3K27me3), and silencing in vivo is mediated by the localized activity of histone deacetylases (HDACs). The repressive (PcG/HDAC) machinery is removed as hematopoietic progenitors differentiate to form erythroid cells. The α- and β-globin genes thus illustrate important, contrasting mechanisms by which cell-specific hematopoietic genes (and tissue-specific genes in general) may be silenced

Identification and Single-Cell Functional Characterization of an Endodermally Biased Pluripotent Substate in Human Embryonic Stem Cells.

Human embryonic stem cells (hESCs) display substantial heterogeneity in gene expression, implying the existence of discrete substates within the stem cell compartment. To determine whether these substates impact fate decisions of hESCs we used a GFP reporter line to investigate the properties of fractions of putative undifferentiated cells defined by their differential expression of the endoderm transcription factor, GATA6, together with the hESC surface marker, SSEA3. By single-cell cloning, we confirmed that substates characterized by expression of GATA6 and SSEA3 include pluripotent stem cells capable of long-term self-renewal. When clonal stem cell colonies were formed from GATA6-positive and GATA6-negative cells, more of those derived from GATA6-positive cells contained spontaneously differentiated endoderm cells than similar colonies derived from the GATA6-negative cells. We characterized these discrete cellular states using single-cell transcriptomic analysis, identifying a potential role for SOX17 in the establishment of the endoderm-biased stem cell state

The chromatin remodelling factor ATRX suppresses R-loops in transcribed telomeric repeats

ATRX is a chromatin remodelling factor found at a wide range of tandemly repeated sequences including telomeres (TTAGGG)n. ATRX mutations are found in nearly all tumours that maintain their telomeres via the alternative lengthening of telomere (ALT) pathway, and ATRX is known to suppress this pathway. Here we show that recruitment of ATRX to telomeric repeats depends on repeat number, orientation and, critically, on repeat transcription. Importantly, the transcribed telomeric repeats form RNA-DNA hybrids (Rloops) whose abundance correlates with the recruitment of ATRX. Here we show loss of ATRX is also associated with increased R-loop formation. Our data suggest that the presence of ATRX at telomeres may have a central role in suppressing deleterious DNA secondary structures that form at transcribed telomeric repeats, and this may account for the increased DNA damage, stalling of replication and homology directed repair previously observed upon loss of ATRX function

Editing an α-globin enhancer in primary human hematopoietic stem cells as a treatment for β-thalassemia

β-thalassemia is characterised by the presence of an excess of α-globin chains, which contribute to erythrocyte pathology. Here the authors use CRISP/Cas9 to reduce α-globin expression in hematopoietic precursors, and show effectiveness in xenograft assays in mice

Lineage-specific combinatorial action of enhancers regulates mouse erythroid Gata1 expression

Precise spatiotemporal control of Gata1 expression is required in both early hematopoietic progenitors to determine erythroid/megakaryocyte versus granulocyte/monocyte lineage output and in the subsequent differentiation of erythroid cells and megakaryocytes. An enhancer element upstream of the mouse Gata1 IE (1st exon erythroid) promoter, mHS−3.5, can direct both erythroid and megakaryocytic expression. However, loss of this element ablates only megakaryocytes, implying that an additional element has erythroid specificity. Here, we identify a double DNaseI hypersensitive site, mHS−25/6, as having erythroid but not megakaryocytic activity in primary cells. It binds an activating transcription factor complex in erythroid cells where it also makes physical contact with the Gata1 promoter. Deletion of mHS−25/6 or mHS−3.5 in embryonic stem cells has only a modest effect on in vitro erythroid differentiation, whereas loss of both elements ablates both primitive and definitive erythropoiesis with an almost complete loss of Gata1 expression. Surprisingly, Gata2 expression was also concomitantly low, suggesting a more complex interaction between these 2 factors than currently envisaged. Thus, whereas mHS−3.5 alone is sufficient for megakaryocytic development, mHS−3.5 and mHS−25/6 collectively regulate erythroid Gata1 expression, demonstrating lineage-specific differences in Gata1 cis-element use important for development of these 2 cell types