The role of bone marrow (BM)-derived precursor cells in tumor angiogenesis is not known. We demonstrate here that tumor angiogenesis is associated with recruitment of hematopoietic and circulating endothelial precursor cells (CEPs). We used the angiogenic defective, tumor resistant Id-mutant mice to show that transplantation of wild-type BM or vascular endothelial growth factor (VEGF)-mobilized stem cells restore tumor angiogenesis and growth. We detected donor-derived CEPs throughout the neovessels of tumors and Matrigel-plugs in an Id1+/-Id3-/- host, which were associated with VEGF-receptor-1-positive (VEGFR1+) myeloid cells. The angiogenic defect in Id-mutant mice was due to impaired VEGF-driven mobilization of VEGFR2+ CEPs and impaired proliferation and incorporation of VEGFR1+ cells. Although targeting of either VEGFR1 or VEGFR2 alone partially blocks the growth of tumors, inhibition of both VEGFR1 and VEGFR2 was necessary to completely ablate tumor growth. These data demonstrate that recruitment of VEGF-responsive BM-derived precursors is necessary and sufficient for tumor angiogenesis and suggest new clinical strategies to block tumor growth.

Higher order chromatin structure presents a barrier to the recognition and repair of DNA damage. Double-strand breaks (DSBs) induce histone H2AX phosphorylation, which is associated with the recruitment of repair factors to damaged DNA. To help clarify the physiological role of H2AX, we targeted H2AX in mice. Although H2AX is not essential for irradiation-induced cell-cycle checkpoints, H2AX −/− mice were radiation sensitive, growth retarded, and immune deficient, and mutant males were infertile. These pleiotropic phenotypes were associated with chromosomal instability, repair defects, and impaired recruitment of Nbs1, 53bp1, and Brca1, but not Rad51, to irradiation-induced foci. Thus, H2AX is critical for facilitating the assembly of specific DNArepair complexes on damaged DNA.The first 120 amino acids of the H2AX and the H2A1/2 bulk isoprotein species exhibit a high degree of similarity, but H2AX carries a unique COOH-terminal tail that contains the * To whom correspondence should be addressed. andre_nussenzweig@nih.gov. HHS Public Access Author Manuscript Author ManuscriptAuthor ManuscriptAuthor Manuscript consensus phosphatidyl inositol 3-kinase (PI-3 kinase) motif that is activated by DSBs (1, 2). Phosphorylation of H2AX (γ-H2AX) is induced by external genotoxic agents (2, 3) and is activated at physiological sites of recombination in lymphocytes (4, 5) and germ cells (6). Several essential DNA-repair factors implicated in homologous recombination (HR) (e.g., Brca1, Brca2, and Rad51) or that participate in both HR and nonhomologous end-joining (NHEJ) (e.g., Rad50, Mre11, Nbs1) form immunofluorescent foci that colocalize with γ-H2AX (7). However, the precise relation between focus formation and DNA repair is not understood.To determine the physiological role of H2AX in mammalian cells, we produced a targeted disruption of mouse H2AX (Web fig. 1A) (5,8). H2AX −/− mice were born at the expected frequency, and absence of H2AX protein was confirmed by two-dimensional gel electrophoresis and Western blotting (Web fig. 1, B to E) (8). Despite the loss of H2AX, treatment with γ-irradiation resulted in normal phosphorylation of Nbs1 (Web fig. 1E) (8).We conclude that H2AX is not essential for survival, or for irradiation-induced phosphorylation of Nbs1.H2AX −/− mice were growth retarded (Web fig. 2) (8), and H2AX −/− mouse embryo fibroblasts (MEFs) proliferated poorly in vitro (Fig. 1A). The difference in the growth of MEFs was partly due to a decrease in the number of dividing cells in H2AX −/− cultures as determined by incorporation of bromodeoxyuridine (BrdU) into DNA. During a 24-hour labeling period, only 44% of passage 1 H2AX −/− MEFs were actively cycling, compared with 72% for the controls, and the mitotic index of H2AX −/− MEFs was at least 50% lower than in wild-type cultures (see below; Fig. 1, D and F). By passage 4, H2AX −/− MEFS accumulated nondividing giant cells, suggesting premature entry into senescence. With continual passage, both H2AX −/− and wild-type MEFs went through crisis, after wh...

Little is known of the molecular mechanisms whereby spermatogonia, mitotic germ cells of the testis, self-renew and differentiate into sperm 1,2 . Here we show that Zfp145, encoding the transcriptional repressor Plzf, has a crucial role in spermatogenesis. Zfp145 expression was restricted to gonocytes and undifferentiated spermatogonia and was absent in tubules of W/W v mutants that lack these cells. Mice lacking Zfp145 underwent a progressive loss of spermatogonia with age, associated with increases in apoptosis and subsequent loss of tubule structure but without overt differentiation defects or loss of the supporting Sertoli cells. Spermatogonial transplantation experiments revealed a depletion of spermatogonial stem cells in the adult. Microarray analysis of isolated spermatogonia from Zfp145-null mice before testis degeneration showed alterations in the expression profile of genes associated with spermatogenesis. These results identify Plzf as a spermatogoniaspecific transcription factor in the testis that is required to regulate self-renewal and maintenance of the stem cell pool.

Id proteins may control cell differentiation by interfering with DNA binding of transcription factors. Here we show that targeted disruption of the dominant negative helix-loop-helix proteins Id1 and Id3 in mice results in premature withdrawal of neuroblasts from the cell cycle and expression of neural-specific differentiation markers. The Id1-Id3 double knockout mice also display vascular malformations in the forebrain and an absence of branching and sprouting of blood vessels into the neuroectoderm. As angiogenesis both in the brain and in tumours requires invasion of avascular tissue by endothelial cells, we examined the Id knockout mice for their ability to support the growth of tumour xenografts. Three different tumours failed to grow and/or metastasize in Id1+/- Id3-/- mice, and any tumour growth present showed poor vascularization and extensive necrosis. Thus, the Id genes are required to maintain the timing of neuronal differentiation in the embryo and invasiveness of the vasculature. Because the Id genes are expressed at very low levels in adults, they make attractive new targets for anti-angiogenic drug design.

Spo11, a protein first identified in yeast, is thought to generate the chromosome breaks that initiate meiotic recombination. We now report that disruption of mouse Spo11 leads to severe gonadal abnormalities from defective meiosis. Spermatocytes suffer apoptotic death during early prophase; oocytes reach the diplotene/dictyate stage in nearly normal numbers, but most die soon after birth. Consistent with a conserved function in initiating meiotic recombination, Dmc1/Rad51 focus formation is abolished. Spo11(-/-) meiocytes also display homologous chromosome synapsis defects, similar to fungi but distinct from flies and nematodes. We propose that recombination initiation precedes and is required for normal synapsis in mammals. Our results also support the view that mammalian checkpoint responses to meiotic recombination and/or synapsis defects are sexually dimorphic.

Nucleophosmin (also known as NPM, B23, NO38) is a nucleolar protein directly implicated in cancer pathogenesis, as the NPM1 gene is found mutated and rearranged in a number of haematological disorders. Furthermore, the region of chromosome 5 to which NPM1 maps is deleted in a proportion of de novo human myelodysplastic syndromes (MDS), and loss of chromosome 5 is extremely frequent in therapy-related MDS. NPM is a multifunctional protein, and its role in oncogenesis is controversial as NPM has been attributed with both oncogenic and tumour suppressive functions. To study the function of Npm in vivo, we generated a hypomorphic Npm1 mutant series (Npm1+/- < Npm1(hy/hy) < Npm1-/-) in mouse. Here we report that Npm is essential for embryonic development and the maintenance of genomic stability. Npm1-/- and Npm1(hy/hy) mutants have aberrant organogenesis and die between embryonic day E11.5 and E16.5 owing to severe anaemia resulting from defects in primitive haematopoiesis. We show that Npm1 inactivation leads to unrestricted centrosome duplication and genomic instability. We demonstrate that Npm is haploinsufficient in the control of genetic stability and that Npm1 heterozygosity accelerates oncogenesis both in vitro and in vivo. Notably, Npm1+/- mice develop a haematological syndrome with features of human MDS. Our findings uncover an essential developmental role for Npm and implicate its functional loss in tumorigenesis and MDS pathogenesis.

During meiotic prophase in male mammals, the X and Y chromosomes condense to form a macrochromatin body, termed the sex, or XY, body, within which X- and Y-linked genes are transcriptionally repressed. The molecular basis and biological function of both sex body formation and meiotic sex chromosome inactivation (MSCI) are unknown. A phosphorylated form of H2AX, a histone H2A variant implicated in DNA repair, accumulates in the sex body in a manner independent of meiotic recombination-associated double-strand breaks. Here we show that the X and Y chromosomes of histone H2AX-deficient spermatocytes fail to condense to form a sex body, do not initiate MSCI, and exhibit severe defects in meiotic pairing. Moreover, other sex body proteins, including macroH2A1.2 and XMR, do not preferentially localize with the sex chromosomes in the absence of H2AX. Thus, H2AX is required for the chromatin remodeling and associated silencing in male meiosis.

Androgen deprivation is the cornerstone of prostate cancer treatment. It results in involution of the normal gland to ~90% of its original size because of the loss of luminal cells. The prostate regenerates when androgen is restored, a process postulated to involve stem cells. Using single-cell RNA sequencing, we identified a rare luminal population in the mouse prostate that expresses stemlike genes (Sca1+ and Psca+) and a large population of differentiated cells (Nkx3.1+, Pbsn+). In organoids and in mice, both populations contribute equally to prostate regeneration, partly through androgen-driven expression of growth factors (Nrg2, Rspo3) by mesenchymal cells acting in a paracrine fashion on luminal cells. Analysis of human prostate tissue revealed similar differentiated and stemlike luminal subpopulations that likewise acquire enhanced regenerative potential after androgen ablation. We propose that prostate regeneration is driven by nearly all persisting luminal cells, not just by rare stem cells.