The olfactory neuroepithelium undergoes continual neurogenesis and, after extensive lesions, fully regenerates to maintain sensory function. The stem cell population underlying this regenerative capacity remains elusive. Here we show that mouse horizontal basal cells (HBCs) function as adult olfactory neuroepithelium neural stem cells and examine their distinct dynamics in olfactory neuroepithelium maintenance and regeneration. Fate-mapping analysis after olfactory neuroepithelium lesioning shows that HBCs are competent to regenerate both neuronal and non-neuronal olfactory neuroepithelium lineages. HBCs serve as a reservoir of long-lived progenitors that remain largely quiescent during normal neuronal turnover or even after acute, selective loss of mature neurons. Under these conditions, previously identified progenitors are largely responsible for tissue maintenance. Yet after extensive injuries that deplete resident neuronal precursors, HBCs transiently proliferate and their progeny fully reconstitute the neuroepithelium. Our data support a new model of adult neurogenesis in which distinct cell populations mediate normal neuronal turnover and neuronal replacement upon traumatic injury.

Centrosome amplification has long been recognized as a feature of human tumors, however its role in tumorigenesis remains unclear 1. Centrosome amplification is poorly tolerated by non-transformed cells, and, in the absence of selection, extra centrosomes are spontaneously lost 2. Thus, the high frequency of centrosome amplification, particularly in more aggressive tumors 3, raises the possibility that extra centrosomes could, in some contexts, confer advantageous characteristics that promote tumor progression. Using a three-dimensional model system and other approaches to culture human mammary epithelial cells, we find that centrosome amplification triggers cell invasion. This invasive behavior is similar to that induced by overexpression of the breast cancer oncogene ErbB2 4 and indeed enhances invasiveness triggered by ErbB2. We show that, through increased centrosomal microtubule nucleation, centrosome amplification increases Rac1 activity, which disrupts normal cell-cell adhesion and promotes invasion. These findings demonstrate that centrosome amplification, a structural alteration of the cytoskeleton, can promote features of malignant transformation.

Tumorigenesis is a clonal evolution process initiated from single cells within otherwise histologically normal tissue1. How single, sporadic mutant cells that have sustained oncogenic alterations evolve within tightly regulated tissue environment remains elusive. Here, we investigated the effects of inducing oncogene expression in single cells within organotypic mammary acini as a model to elucidate the processes by which oncogenic alterations initiate clonal progression from organized epithelial environments. We found that sporadic cells induced to overexpress oncogenes that specifically perturb cell-cycle checkpoints (HPV16-E7 and cyclinD1), deregulate c-Myc transcription, or activate AKT signaling, remain quiescent within growth-arrested acini. In contrast, single ErbB2-overexpressing cells initiate a cellular cascade involving cell translocation from the epithelial layer and luminal outgrowth characteristic of neoplastic progression in early-stage epithelial tumors. ErbB2-mediated luminal cell translocation is dependent on ERK and matrix metalloproteinase (MMP) activities, and genetic alterations that perturb local cell-matrix adhesion can drive cell translocation. We further provide evidence that luminal cell translocation may drive clonal selection by promoting either death or expansion of quiescent oncogene-expressing cells depending on whether preexisting alterations allow anchorage-independent survival and growth. Our data show that the initial outgrowth of single oncogene-expressing cells from organized epithelial structures is a highly regulated process, and we propose that a cell translocation mechanism allows sporadic mutant cells to evade suppressive microenvironments and provokes clonal selection for survival and proliferative expansion outside their native niches.

In the adult mammalian brain, new neurons and glia are continuously generated but molecular factors regulating their differentiation and lineage relationships are largely unknown. We show that Ascl1, a bHLH (basic helix-loop-helix) transcription factor, transiently labels neuronal and oligodendrocyte precursors in the adult brain. Using in vivo lineage tracing with inducible Cre recombinase, we followed the maturation of these precursors in four distinct regions.

A major barrier to conceptual advances in understanding the mechanisms and regulation of imprinting of a genomic region is our relatively poor understanding of the overall organization of genes and of the potentially important cis-acting regulatory sequences that lie in the nonexonic segments that make up 97% of the genome. Interspecies sequence comparison offers an effective approach to identify sequence from conserved functional elements. In this article we describe the successful use of this approach in comparing a ∼1-Mb imprinted genomic domain on mouse chromosome 7 to its orthologous region on human 11p15.5. Within the region, we identified 112 exons of known genes as well as a novel gene identified uniquely in the mouse region, termed Msuit, that was found to be imprinted. In addition to these coding elements, we identified 33 CpG islands and 49 orthologous nonexonic, nonisland sequences that met our criteria as being conserved, and making up 4.1% of the total sequence. These conserved noncoding sequence elements were generally clustered near imprinted genes and the majority were between Igf2 and H19 or within Kvlqt1.

Circulating tumor cells are responsible for seeding metastatic growth at distant sites. Kim et al. (2009) now discover that circulating tumor cells can reinfiltrate tumors at their primary organs and promote tumor progression.

VivosX is an in vivo disulfide crosslinking approach that utilizes a pair of strategically positioned cysteines on two proteins to probe physical interactions within cells. Histone H2A.Z, which often replaces one or both copies of H2A in nucleosomes downstream of promoters, was used to validate VivosX. Disulfide crosslinks between cysteine-modified H2A.Z and/or H2A histones within nucleosomes were induced using a membrane-permeable oxidant. VivosX detected different combinations of H2A.Z and H2A within nucleosomes in yeast cells. This assay correctly reported the change in global H2A.Z occupancy previously observed when the deposition and eviction pathways of H2A.Z were perturbed. Homotypic H2A.Z/H2A.Z (ZZ) nucleosomes accumulated when assembly of the transcription preinitiation complex was blocked, revealing that the transcription machinery preferentially disassembles ZZ nucleosomes. VivosX works in human cells and distinguishes ZZ nucleosomes with one or two ubiquitin moieties, demonstrating that it can be used to detect protein-protein interactions inside cells from different species.

The extent and importance of functional heterogeneity and crosstalk between tumor cells is poorly understood. Here, we describe the generation of clonal populations from a patient-derived ovarian clear cell carcinoma model which forms malignant ascites and solid peritoneal tumors upon intraperitoneal transplantation in mice. The clonal populations are engineered with secreted Gaussia luciferase to monitor tumor growth dynamics and tagged with a unique DNA barcode to track their fate in multiclonal mixtures during tumor progression. Only one clone, CL31, grows robustly, generating exclusively malignant ascites. However, multiclonal mixtures form large solid peritoneal metastases, populated almost entirely by CL31, suggesting that transient cooperative interclonal interactions are sufficient to promote metastasis of CL31. CL31 uniquely harbors ERBB2 amplification, and its acquired metastatic activity in clonal mixtures is dependent on transient exposure to amphiregulin, which is exclusively secreted by non-tumorigenic clones. Amphiregulin enhances CL31 mesothelial clearance, a prerequisite for metastasis. These findings demonstrate that transient, ostensibly innocuous tumor subpopulations can promote metastases via “hit-and-run” commensal interactions.