Biology subjects

Joyce, C. E.

Publications and source records attributed to Joyce, C. E..

3 recordsLinked to original sources

bioRxiv2019

Lfc/Arhgef2 regulates mitotic spindle orientation in hematopoietic stem and progenitor cells and is essential for productive hematopoiesis

How hematopoietic stem cells (HSCs) coordinate their divisional axis relative to supportive niche cells and whether or not their divisional orientation is important for stem cell-driven hematopoiesis is poorly understood. Single cell RNA sequencing data from patients with the inherited bone marrow failure Shwachman-Diamond syndrome (SDS) show that ARHGEF2, a RhoA-specific guanine nucleotide exchange factor (GEF) and determinant of mitotic spindle orientation, is one of a restricted group of genes specifically downregulated in SDS HSCs and multipotent progenitors. Here, we describe Lfc/Arhgef2 as an important regulator of hematopoiesis in vivo. Transplanted Lfc/Arhgef2-/- bone marrow shows impaired hematopoietic recovery and a production deficit of long-term HSCs. These phenotypes cannot be explained by differences in numbers of transplanted HSCs, their cell cycle status, level of apoptosis, progenitor output or homing ability. Using live imaging of dividing hematopoietic stem and progenitor cells (HSPCs), we show an increased frequency of misoriented divisions in the absence of Lfc/Arhgef2. Functional ARHGEF2 knockdown in human HSCs also impairs their ability to regenerate hematopoiesis, culminating in significantly smaller hematopoietic xenografts. Together, these data provide evidence demonstrating a conserved role for Lfc/Arhgef2 in orienting HSPC division and suggest that HSCs divide in certain orientations to establish hematopoiesis, the loss of which leads to their exhaustion in a mechanism that may underlie certain bone marrow failure syndromes.

cell biology↗

bioRxiv2018

Human bone marrow disorders recapitulated in vitro using organ chip technology

Understanding human bone marrow (BM) pathophysiology in the context of myelotoxic stress induced by drugs, radiation, or genetic mutations is of critical importance in clinical medicine. However, study of these dynamic cellular responses is hampered by the inaccessibility of living BM in vivo. Here, we describe a vascularized human Bone Marrow-on-a-Chip (BM Chip) microfluidic culture device for modeling bone marrow function and disease states. The BM Chip is comprised of a fluidic channel filled with a fibrin gel in which patient-derived CD34+ cells and bone marrow-derived stromal cells (BMSCs) are co-cultured, which is separated by a porous membrane from a parallel fluidic channel lined by human vascular endothelium. When perfused with culture medium through the vascular channel, the BM Chip maintains human CD34+ cells and supports differentiation and maturation of multiple blood cell lineages over 1 month in culture. Moreover, it recapitulates human myeloerythroid injury responses to drugs and gamma radiation exposure, as well as key hematopoietic abnormalities found in patients with the genetic disorder, Shwachman-Diamond Syndrome (SDS). These data establish the BM Chip as a new human in vitro model with broad potential utility for studies of BM dysfunction.

bioengineering↗

bioRxiv2018

Saccharomyces cerevisiae H2A copies differentially contribute to recombination and CAG/CTG repeat maintenance, with a role for H2A.1 threonine 126

DNA are sites of genomic instability. Long CAG/CTG repeats form hairpin structures, are fragile, and can expand during DNA repair. The chromatin response to DNA damage can influence repair fidelity, but the knowledge of chromatin modifications involved in maintaining repair fidelity within repetitive DNA is limited. In a screen for CAG repeat fragility in Saccharomyces cerevisiae, histone 2A copy 1 (H2A.1) was identified to protect the repeat from increased rates of breakage. To address the role of H2A in CAG repeat instability, we tested the effect of deleting each histone H2 subytpe. Whereas deletion of HTA2, HTZ1, HTB1, and HTB2 did not significantly affect CAG repeat maintenance, deletion of HTA1 resulted in increased expansion frequency. Notably, mutation of threonine 126, unique to H2A.1, to a non-phosphorylatable alanine increased CAG repeat instability to a similar level as the hta1{Delta} mutant. CAG instability in the absence of HTA1 or mutation to hta1-T126A was dependent on the presence of the homologous recombination (HR) repair proteins Rad51, Rad52, and Rad57, and the Pol{delta} subunit Pol32. In addition, sister chromatid recombination (SCR) was suppressed in the hta1{Delta} and hta1-T126A mutants and this suppression was epistatic to pol32{Delta}. Finally, break-induced replication (BIR) is impaired in the hta1{Delta} mutant, resulting in an altered repair profile. These data reveal differential roles for the H2A subtypes in DNA repair and implicate a new role for H2A.1 threonine-126 phosphorylation in mediating fidelity during HR repair and promoting SCR. Using a fragile, repetive DNA element to model endogenous DNA damage, our results demonstrate that H2A.1 plays a greater role than H2A.2 in promoting homology-dependent repair, suggesting H2A.1 is the true homolog of mammalian H2AX, whereas H2A.2 is functionally equivalent to mammalian H2A.\n\nAuthor SummaryCAG/CTG trinuncleotide repeats are fragile sequences that when expanded can cause human disease. To evaluate the role of S. cerevisiae histone H2A copies in DNA repair, we have measured instability of an expanded CAG/CTG repeat tract and repair outcomes in H2A mutants. Although the two copies of H2A are nearly identical in amino acid sequence, we found that the CAG repeat is more unstable in the absence of H2A copy 1 (H2A.1) than H2A copy 2, and that this role appears to be partially dependent on a phosphorylatable threonine at residue 126 in the C-terminal tail of H2A.1. Further, we show through a series of genetic assays that H2A.1 plays a role in promoting homologous recombination events, including sister chromatid recombination and break-induced replication. Our results uncover a role for H2A.1 in mediating fidelity of repair within repetitive DNA, and demonstrate that modification of its unique Thr126 residue plays a role in regulating SCR. Given the dependence of HR repair on H2A.1 but not H2A.2, we conclude that H2A.1 plays a greater repair-specific role in the cell and therefore would be the true homolog of mammalian H2AX.

genetics↗