Hematopoietic stem cells (HSC) must engage in a life-long balance between self-renewal and differentiation to sustain hematopoiesis. The highly conserved PIWI protein family regulates proliferative states of stem cells and their progeny in diverse organisms. A Human piwi gene (for clarity, the non-italicized “piwi” refers to the gene subfamily), HIWI (PIWIL1), is expressed in CD34+ stem/progenitor cells and transient expression of HIWI in a human leukemia cell line drastically reduces cell proliferation, implying the potential function of these proteins in hematopoiesis. Here, we report that one of the three piwi genes in mice, Miwi2 (Piwil4), is expressed in primitive hematopoetic cell types within the bone marrow. Mice with a global deletion of all three piwi genes, Miwi, Mili, and Miwi2, are able to maintain long-term hematopoiesis with no observable effect on the homeostatic HSC compartment in adult mice. The PIWI-deficient hematopoetic cells are capable of normal lineage reconstitution after competitive transplantation. We further show that the three piwi genes are dispensable during hematopoietic recovery after myeloablative stress by 5-FU. Collectively, our data suggest that the function of the piwi gene subfamily is not required for normal adult hematopoiesis.
References
[1]
Baum CM, Weissman IL, Tsukamoto AS, Buckle AM, Peault B (1992) Isolation of a candidate human hematopoietic stem-cell population. Proc Natl Acad Sci U S A 89: 2804–2808.
[2]
Bhatia M, Wang JC, Kapp U, Bonnet D, Dick JE (1997) Purification of primitive human hematopoietic cells capable of repopulating immune-deficient mice. Proc Natl Acad Sci U S A 94: 5320–5325.
[3]
Civin CI, Strauss LC, Brovall C, Fackler MJ, Schwartz JF, et al. (1984) Antigenic analysis of hematopoiesis. III. A hematopoietic progenitor cell surface antigen defined by a monoclonal antibody raised against KG-1a cells. J Immunol 133: 157–165.
[4]
Krause DS, Ito T, Fackler MJ, Smith OM, Collector MI, et al. (1994) Characterization of murine CD34, a marker for hematopoietic progenitor and stem cells. Blood 84: 691–701.
[5]
Sharma AK, Nelson MC, Brandt JE, Wessman M, Mahmud N, et al. (2001) CD34(+) stem cells express the hiwi gene, a human homologue of the Drosophila gene piwi. Blood 97: 426–434.
[6]
Chen L, Shen R, Ye Y, Pu XA, Liu X, et al. (2007) Precancerous stem cells have the potential for both benign and malignant differentiation. PLoS One 2: e293.
[7]
Aravin A, Gaidatzis D, Pfeffer S, Lagos-Quintana M, Landgraf P, et al. (2006) A novel class of small RNAs bind to MILI protein in mouse testes. Nature 442: 203–207.
[8]
Aravin AA, Sachidanandam R, Bourc'his D, Schaefer C, Pezic D, et al. (2008) A piRNA pathway primed by individual transposons is linked to de novo DNA methylation in mice. Mol Cell 31: 785–799.
[9]
Brennecke J, Aravin AA, Stark A, Dus M, Kellis M, et al. (2007) Discrete small RNA-generating loci as master regulators of transposon activity in Drosophila. Cell 128: 1089–1103.
[10]
Girard A, Sachidanandam R, Hannon GJ, Carmell MA (2006) A germline-specific class of small RNAs binds mammalian Piwi proteins. Nature 442: 199–202.
[11]
Grivna ST, Beyret E, Wang Z, Lin H (2006) A novel class of small RNAs in mouse spermatogenic cells. Genes Dev 20: 1709–1714.
[12]
Houwing S, Kamminga LM, Berezikov E, Cronembold D, Girard A, et al. (2007) A role for Piwi and piRNAs in germ cell maintenance and transposon silencing in Zebrafish. Cell 129: 69–82.
[13]
Kim VN (2006) Small RNAs just got bigger: Piwi-interacting RNAs (piRNAs) in mammalian testes. Genes Dev 20: 1993–1997.
[14]
Lau NC, Seto AG, Kim J, Kuramochi-Miyagawa S, Nakano T, et al. (2006) Characterization of the piRNA complex from rat testes. Science 313: 363–367.
[15]
Lin H (2007) piRNAs in the germ line. Science 316: 397.
[16]
O'Donnell KA, Boeke JD (2007) Mighty Piwis defend the germline against genome intruders. Cell 129: 37–44.
[17]
Juliano C, Wang J, Lin H (2011) Uniting germline and stem cells: the function of Piwi proteins and the piRNA pathway in diverse organisms. Annu Rev Genet 45: 447–469.
[18]
Sasaki T, Shiohama A, Minoshima S, Shimizu N (2003) Identification of eight members of the Argonaute family in the human genome small star, filled. Genomics 82: 323–330.
[19]
Sugimoto K, Kage H, Aki N, Sano A, Kitagawa H, et al. (2007) The induction of H3K9 methylation by PIWIL4 at the p16Ink4a locus. Biochem Biophys Res Commun 359: 497–502.
[20]
Liu X, Sun Y, Guo J, Ma H, Li J, et al. (2006) Expression of hiwi gene in human gastric cancer was associated with proliferation of cancer cells. Int J Cancer 118: 1922–1929.
[21]
Qiao D, Zeeman AM, Deng W, Looijenga LH, Lin H (2002) Molecular characterization of hiwi, a human member of the piwi gene family whose overexpression is correlated to seminomas. Oncogene 21: 3988–3999.
[22]
Grochola LF, Greither T, Taubert H, Moller P, Knippschild U, et al. (2008) The stem cell-associated Hiwi gene in human adenocarcinoma of the pancreas: expression and risk of tumour-related death. Br J Cancer 99: 1083–1088.
[23]
He G, Chen L, Ye Y, Xiao Y, Hua K, et al. (2010) Piwil2 expressed in various stages of cervical neoplasia is a potential complementary marker for p16. Am J Transl Res 2: 156–169.
[24]
Lee JH, Jung C, Javadian-Elyaderani P, Schweyer S, Schutte D, et al. (2010) Pathways of proliferation and antiapoptosis driven in breast cancer stem cells by stem cell protein piwil2. Cancer Res 70: 4569–4579.
[25]
Lee JH, Schutte D, Wulf G, Fuzesi L, Radzun HJ, et al. (2006) Stem-cell protein Piwil2 is widely expressed in tumors and inhibits apoptosis through activation of Stat3/Bcl-XL pathway. Hum Mol Genet 15: 201–211.
[26]
Liu JJ, Shen R, Chen L, Ye Y, He G, et al. (2010) Piwil2 is expressed in various stages of breast cancers and has the potential to be used as a novel biomarker. Int J Clin Exp Pathol 3: 328–337.
[27]
Siddiqi S, Terry M, Matushansky I (2012) Hiwi mediated tumorigenesis is associated with DNA hypermethylation. PLoS One 7: e33711.
[28]
Taubert H, Greither T, Kaushal D, Wurl P, Bache M, et al. (2007) Expression of the stem cell self-renewal gene Hiwi and risk of tumour-related death in patients with soft-tissue sarcoma. Oncogene 26: 1098–1100.
[29]
Ye Y, Yin DT, Chen L, Zhou Q, Shen R, et al. (2010) Identification of Piwil2-like (PL2L) proteins that promote tumorigenesis. PLoS One 5: e13406.
[30]
Williams RT, Sherr CJ (2008) The INK4-ARF (CDKN2A/B) locus in hematopoiesis and BCR-ABL-induced leukemias. Cold Spring Harb Symp Quant Biol 73: 461–467.
[31]
Carmell MA, Girard A, van de Kant HJ, Bourc'his D, Bestor TH, et al. (2007) MIWI2 is essential for spermatogenesis and repression of transposons in the mouse male germline. Dev Cell 12: 503–514.
[32]
Deng W, Lin H (2002) miwi, a murine homolog of piwi, encodes a cytoplasmic protein essential for spermatogenesis. Dev Cell 2: 819–830.
[33]
Kuramochi-Miyagawa S, Kimura T, Ijiri TW, Isobe T, Asada N, et al. (2004) Mili, a mammalian member of piwi family gene, is essential for spermatogenesis. Development 131: 839–849.
[34]
Akashi K, Traver D, Miyamoto T, Weissman IL (2000) A clonogenic common myeloid progenitor that gives rise to all myeloid lineages. Nature 404: 193–197.
[35]
Pronk CJ, Rossi DJ, Mansson R, Attema JL, Norddahl GL, et al. (2007) Elucidation of the phenotypic, functional, and molecular topography of a myeloerythroid progenitor cell hierarchy. Cell Stem Cell 1: 428–442.
[36]
Van Zant G (1984) Studies of hematopoietic stem cells spared by 5-fluorouracil. J Exp Med 159: 679–690.
[37]
Lerner C, Harrison DE (1990) 5-Fluorouracil spares hemopoietic stem cells responsible for long-term repopulation. Exp Hematol 18: 114–118.
[38]
Attema JL, Papathanasiou P, Forsberg EC, Xu J, Smale ST, et al. (2007) Epigenetic characterization of hematopoietic stem cell differentiation using miniChIP and bisulfite sequencing analysis. Proc Natl Acad Sci U S A 104: 12371–12376.
[39]
Pal-Bhadra M, Leibovitch BA, Gandhi SG, Rao M, Bhadra U, et al. (2004) Heterochromatic silencing and HP1 localization in Drosophila are dependent on the RNAi machinery. Science 303: 669–672.
[40]
Sarot E, Payen-Groschene G, Bucheton A, Pelisson A (2004) Evidence for a piwi-dependent RNA silencing of the gypsy endogenous retrovirus by the Drosophila melanogaster flamenco gene. Genetics 166: 1313–1321.
[41]
Yin H, Lin H (2007) An epigenetic activation role of Piwi and a Piwi-associated piRNA in Drosophila melanogaster. Nature 450: 304–308.
