Hematopoietic stem cells are acutely sensitive to Acd shelterin gene inactivation
Morgan Jones, Gail Osawa, Joshua A. Regal, Daniel N. Weinberg, James Taggart, Hande Kocak, Ann Friedman, David O. Ferguson, Catherine E. Keegan, Ivan Maillard
Morgan Jones, Gail Osawa, Joshua A. Regal, Daniel N. Weinberg, James Taggart, Hande Kocak, Ann Friedman, David O. Ferguson, Catherine E. Keegan, Ivan Maillard
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Research Article Hematology

Hematopoietic stem cells are acutely sensitive to Acd shelterin gene inactivation

Abstract

The shelterin complex plays dual functions in telomere homeostasis by recruiting telomerase and preventing the activation of a DNA damage response at telomeric ends. Somatic stem cells require telomerase activity, as evidenced by progressive stem cell loss leading to bone marrow failure in hereditary dyskeratosis congenita. Recent work demonstrates that dyskeratosis congenita can also arise from mutations in specific shelterin genes, although little is known about shelterin functions in somatic stem cells. We found that mouse hematopoietic stem cells (HSCs) are acutely sensitive to inactivation of the shelterin gene Acd, encoding TPP1. Homozygosity for a hypomorphic acd allele preserved the emergence and expansion of fetal HSCs but led to profoundly defective function in transplantation assays. Upon complete Acd inactivation, HSCs expressed p53 target genes, underwent cell cycle arrest, and were severely depleted within days, leading to hematopoietic failure. TPP1 loss induced increased telomeric fusion events in bone marrow progenitors. However, unlike in epidermal stem cells, p53 deficiency did not rescue TPP1-deficient HSCs, indicating that shelterin dysfunction has unique effects in different stem cell populations. Because the consequences of telomere shortening are progressive and unsynchronized, acute loss of shelterin function represents an attractive alternative for studying telomere crisis in hematopoietic progenitors.

Authors

Morgan Jones, Gail Osawa, Joshua A. Regal, Daniel N. Weinberg, James Taggart, Hande Kocak, Ann Friedman, David O. Ferguson, Catherine E. Keegan, Ivan Maillard

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Figure 7

Acd inactivation results in acute cell cycle arrest and induction of p53 target genes.

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Acd inactivation results in acute cell cycle arrest and induction of p5...
(A) Experimental design: Mx-Cre+Acd+/–, Mx-Cre+Acd+/–p53–/–, Mx-Cre+Acdfl/–, and Mx-Cre+Acdfl/–p53–/– mice were injected with a single dose of poly(I:C) followed by BrdU and sacrificed as indicated. (B) Relative abundance of p21 and Noxa transcripts in purified Lin–Sca-1hicKithi (LSK) progenitors demonstrating that Acd deletion induced a p53-dependent increase in p21 and Noxa mRNA (qRT-PCR; data are shown as the mean ± SEM and are representative of at least two independently sorted samples per group). (C) Flow cytometric analysis of progenitors for BrdU incorporation and icDAPI showing the accumulation of Mx-Cre+Acdfl/– and Mx-Cre+Acdfl/–p53–/– cells in G2/M phases of the cell cycle. Representative flow cytometry plots are shown from four independent experiments. (D) Quantification of data are shown in C (n = 3 mice per group). *P < 0.05; **P < 0.01; ***P < 0.001.