Adult germline stem cells are capable of self-renewal, tissue regeneration and production of large numbers of differentiated progeny. We show here that the classical mouse mutant luxoid affects adult germline stem cell self-renewal. Young homozygous luxoid mutant mice produce limited numbers of normal spermatozoa and then progressively lose their germ line after birth. Transplantation studies showed that germ cells from mutant mice did not colonize recipient testes, suggesting that the defect is intrinsic to the stem cells. We determined that the luxoid mutant contains a nonsense mutation in the gene encoding Plzf, a transcriptional repressor that regulates the epigenetic state of undifferentiated cells, and showed that Plzf is coexpressed with Oct4 in undifferentiated spermatogonia. This is the first gene shown to be required in germ cells for stem cell self-renewal in mammals.The luxoid (lu) mutation arose spontaneously in 1950 and was initially characterized for its semidominant limb abnormalities and recessive skeletal and male infertility phenotypes 1,2 . A subsequent report suggested that luxoid mutant males had limited short-term production of normal-looking sperm followed by a rapid loss of all Plzf is required in adult male germ cells for stem cell self-renewal

Stem cells support tissue maintenance by balancing self-renewal and differentiation. In mice, it is believed that a homogeneous stem cell population of single spermatogonia supports spermatogenesis, and that differentiation, which is accompanied by the formation of connected cells (cysts) of increasing length, is linear and nonreversible. We evaluated this model using lineage-analysis and live-imaging and found that this putative stem cell population is not homogeneous. Instead, the stem cell pool that supports steady-state spermatogenesis is contained within a subpopulation of single spermatogonia. Also, cysts are not committed to differentiation and appear to recover stem cell potential by fragmentation. Lastly, the fate of individual spermatogonial populations was dramatically altered during regeneration following damage. Thus, there are multiple and reversible paths from stem cell to differentiation, which may also occur in other systems.Maintenance of adult tissues is supported by a small number of undifferentiated stem cells that self-renew to maintain their population and produce differentiating progeny for normal tissue function. It has generally been accepted that differentiating daughter cells progress unidirectionally towards terminal differentiation. This view has been recently challenged by data suggesting that under some circumstances differentiating cells can revert to the self-renewing stem cell pool (1-8). This apparent plasticity may add robustness to maintenance of the stem cell population during normal tissue maintenance and may play a crucial role in tissue regeneration following injury. However, the nature of the self-renewing stem cells and the plasticity of differentiating cells in the maintenance of tissue homeostasis and regeneration are mostly unknown, particularly in mammals.Germ cells share a characteristic feature across all animal species. While the most primitive cells in adult gonads are singly isolated, their differentiating progeny remain connected by intercellular bridges to form syncytial cysts of 2 n cells (9,10). Thus, the length of the cysts reflects their cell division history or lineage. This unique feature has made the germline one of the most tractable systems to study adult stem cell self-renewal and differentiation (2,3).* To whom correspondence should be addressed. shosei@nibb.ac.jp. The study of the spermatogenic stem cell compartment in mammals also relies on the heterogeneity in the cyst length (9,11,12 (Fig. S1).The prevailing rodent stem cell model (14,15) (Fig. 1A) assumes that the stem cell population resides in the A s population and that cyst length reflects the extent of differentiation in a linear manner (9,11). A corollary of this 'A s model' is that A s spermatogonia are functionally homogeneous, that all A s cells are stem cells, and that all cells are equivalent in each morphological category (9,10). This model, proposed in 1971, has provided the framework for years of germline stem cell research in mice and other animals. Despite its simplici...

Standardized and reproducible preclinical models that recapitulate the dynamics of prostate cancer are urgently needed. We established a bank of transplantable patient-derived prostate cancer xenografts that capture the biologic and molecular heterogeneity currently confounding prognostication and therapy development. Xenografts preserved the histopathology, genome architecture, and global gene expression of donor tumors. Moreover, their aggressiveness matched patient observations, and their response to androgen withdrawal correlated with tumor subtype. The panel includes the first xenografts generated from needle biopsy tissue obtained at diagnosis. This advance was exploited to generate independent xenografts from different sites of a primary site, enabling functional dissection of tumor heterogeneity. Prolonged exposure of adenocarcinoma xenografts to androgen withdrawal led to castration-resistant prostate cancer, including the first-in-field model of complete transdifferentiation into lethal neuroendocrine prostate cancer. Further analysis of this model supports the hypothesis that neuroendocrine prostate cancer can evolve directly from adenocarcinoma via an adaptive response and yielded a set of genes potentially involved in neuroendocrine transdifferentiation. We predict that these next-generation models will be transformative for advancing mechanistic understanding of disease progression, response to therapy, and personalized oncology. Cancer Res; 74(4); 1272-83. Ó2013 AACR.

The androgen-signaling pathway is important for the growth and progression of prostate cancer cells. The growth-promoting effects of androgen on prostate cells are mediated mostly through the androgen receptor (AR). There is increasing evidence that transcription activation by AR is mediated through interaction with other cofactors. ␤-Catenin plays a critical role in embryonic development and tumorigenesis through its effects on E-cadherin-mediated cell adhesion and Wnt-dependent signal transduction. Here, we demonstrate that a specific protein-protein interaction occurs between ␤-catenin and AR. Unlike the steroid hormone receptor coactivator 1 (SRC1), ␤-catenin showed a strong interaction with AR but not with other steroid hormone receptors such as estrogen receptor ␣, progesterone receptor ␤, and glucocorticoid receptor. The ligand binding domain of AR and the NH 2 terminus combined with the first six armadillo repeats of ␤-catenin were shown to be necessary for the interaction. Through this specific interaction, ␤-catenin augments the ligand-dependent activity of AR in prostate cancer cells. Moreover, expression of E-cadherin in E-cadherin-negative prostate cancer cells results in redistribution of the cytoplasmic ␤-catenin to the cell membrane and reduction of ARmediated transcription. These data suggest that loss of E-cadherin can elevate the cellular levels of ␤-catenin in prostate cancer cells, which may directly contribute to invasiveness and a more malignant tumor phenotype by augmenting AR activity during prostate cancer progression.

Cytokinesis in somatic cells concludes with the formation of a midbody, which is abscised to form individual daughter cells. In contrast, germ cell cytokinesis results in a permanent intercellular bridge connecting the daughter cells through a large cytoplasmic channel. During spermatogenesis, proposed roles for the intercellular bridge include germ cell communication, synchronization, and chromosome dosage compensation in haploid cells. Although several essential components of the midbody have recently been identified, essential components of the vertebrate germ cell intercellular bridge have until now not been described. Herein, we show that testis-expressed gene 14 (TEX14) is a novel protein that localizes to germ cell intercellular bridges. In the absence of TEX14, intercellular bridges are not observed by using electron microscopy and other markers. Spermatogenesis in Tex14 ؊/؊ mice progresses through the transit amplification of diploid spermatogonia and the expression of early meiotic markers but halts before the completion of the first meiotic division. Thus, TEX14 is required for intercellular bridges in vertebrate germ cells, and these studies provide evidence that the intercellular bridge is essential for spermatogenesis and fertility.cytoplasmic bridges ͉ knockout mouse ͉ male infertility ͉ male sterility ͉ ring canals

PI3K/Akt plays a critical role in prostate cancer cell growth and survival. Recent studies have shown that the effect of PI3K/Akt in prostate cells is mediated through androgen signaling. The PI3K inhibitor, LY294002, and a tumor suppressor, PTEN, negatively regulate the PI3K/Akt pathway and repress AR activity. However, the molecular mechanisms whereby PI3K/Akt and PTEN regulate the androgen pathway are currently unclear. Here, we demonstrate that blocking the PI3K/ Akt pathway reduces the expression of an endogenous AR target gene. Moreover, we show that the repression of AR activity by LY294002 is mediated through phosphorylation and inactivation of GSK3␤, a downstream substrate of PI3K/Akt, which results in the nuclear accumulation of ␤-catenin. Given the recent evidence that ␤-catenin acts as a coactivator of AR, our findings suggest a novel mechanism by which PI3K/Akt modulates androgen signaling. In a PTEN-null prostate cancer cell line, we show that PTEN expression reduces ␤-cateninmediated augmentation of AR transactivation. Using the mutants of ␤-catenin, we further demonstrate that the repressive effect of PTEN is mediated by a GSK3␤-regulated degradation of ␤-catenin. Our results delineate a novel link among the PI3K, wnt, and androgen pathways and provide fresh insights into the mechanisms of prostate tumor development and progression.

The androgen receptor (AR) is a hormone-dependent transcription factor that plays important roles in male sexual differentiation and development. Transcription activation by steroid hormone receptors, such as the androgen receptor, is mediated through interaction with cofactors. We recently identified a novel AR-interacting protein, provisionally termed PAK6, that shares a high degree of sequence similarity with p21-activated kinases (PAKs). PAK6 is a 75-kDa protein that contains a putative amino-terminal Cdc42/Rac interactive binding motif and a carboxyl-terminal kinase domain. A domainspecific and ligand-dependent interaction between AR and PAK6 was further confirmed in vivo and in vitro. Northern blot analysis revealed that PAK6 is highly expressed in testis and prostate tissues. Most importantly, immunofluorescence studies showed that PAK6 cotranslocates into the nucleus with AR in response to androgen. Transient transfection experiments showed that PAK6 specifically repressed AR-mediated transcription. This report identifies a novel function for a PAK-homologous protein and suggests a potential unique mechanism by which other signal transduction pathways may cross-talk with AR pathways to regulate AR function in normal and malignant prostate cells.

M.Sharma and X.Li contributed equally to this workThe androgen receptor (AR) plays a central role in male sexual development and in normal and malignant prostate cell growth and survival. It has been shown that transcriptional activation of AR is regulated through interaction with various co-factors. Here we identify a novel PIAS-like protein, hZimp10, as an AR-interacting protein. The transactivation domain (TAD) of AR and the central region of hZimp10 were found to be responsible for the interaction. A strong intrinsic transactivation domain was identi®ed in the C-terminal, proline-rich region of hZimp10. Endogenous AR and hZimp10 proteins were co-stained in the nuclei of prostate epithelial cells from human tissue samples. In human prostate cancer cells, hZimp10 augmented the transcriptional activity of AR. Moreover, hZimp10 co-localized with AR and SUMO-1 at replication foci throughout S phase, and it was capable of enhancing sumoylation of AR in vivo. Studies using sumoylation de®cient AR mutants suggested that the augmentation of AR activity by hZimp10 is dependent on the sumoylation of the receptor. Taken together, these data demonstrate that hZimp10 is a novel AR co-regulator.