Mature mammary epithelial cells are generated from undifferentiated precursors through a hierarchical process, but the molecular mechanisms involved, particularly in the human mammary gland, are poorly understood. To address this issue, we isolated highly purified subpopulations of primitive bipotent and committed luminal progenitor cells as well as mature luminal and myoepithelial cells from normal human mammary tissue and compared their transcriptomes obtained using three different methods. Elements unique to each subset of mammary cells were identified, and changes that accompany their differentiation in vivo were shown to be recapitulated in vitro. These include a stage-specific change in NOTCH pathway gene expression during the commitment of bipotent progenitors to the luminal lineage. Functional studies further showed NOTCH3 signaling to be critical for this differentiation event to occur in vitro. Taken together, these findings provide an initial foundation for future delineation of mechanisms that perturb primitive human mammary cell growth and differentiation.

Analysis of transcript representation on gene microarrays requires microgram amounts of total RNA or DNA. Without amplification, such amounts are obtainable only from millions of cells. However, it may be desirable to determine transcript representation in few or even single cells in aspiration biopsies, rare population subsets isolated by cell sorting or laser capture, or micromanipulated single cells. Nucleic-acid amplification methods could be used in these cases, but it is difficult to amplify different transcripts in a sample without distorting quantitative relationships between them. Linear isothermal RNA amplification has been used to amplify as little as 10 ng of total cellular RNA, corresponding to the amount obtainable from thousands of cells, while still preserving the original abundance relationships. However, the available procedures require multiple steps, are labor intensive and time consuming, and have not been shown to preserve abundance information from smaller starting amounts. Exponential amplification, on the other hand, is a relatively simple technology, but is generally considered to bias abundance relationships unacceptably. These constraints have placed beyond current reach the secure and routine application of microarray analysis to single or small numbers of cells. Here we describe results obtained with a rapid and highly optimized global reverse transcription#150;PCR (RT-PCR) procedure. Contrary to prevalent expectations, the exponential approach preserves abundance relationships through amplification as high as 3 x 10(11)-fold. Further, it reduces by a million-fold the input amount of RNA needed for microarray analysis, and yields reproducible results from the picogram range of total RNA obtainable from single cells.

Sustained blood cell production depends on divisions by hematopoietic stem cells (HSCs) that yield both differentiating progeny as well as new HSCs via self-renewal. Differentiating progeny remain capable of self-renewal, but only HSCs sustain self-renewal through successive divisions securely enough to maintain clones that persist life-long. Until recently, the first identified next stage consisted of "short-term" reconstituting cells able to sustain clones of differentiating cells for only 4-6 weeks. Here we expand evidence for a numerically dominant "intermediate-term" multipotent HSC stage in mice whose clones persist for 6-8 months before becoming extinct and that are separable from both short-term as well as permanently reconstituting "long-term" HSCs. The findings suggest that the first step in stem cell differentiation consists not in loss of initial capacity for serial self-renewal divisions, but rather in loss of mechanisms that stabilize self-renewing behavior throughout successive future stem cell divisions.

Src homology 2 domain-containing phosphatase 2 (Shp2), encoded by Ptpn11, is a member of the nonreceptor proteintyrosine phosphatase family, and functions in cell survival, proliferation, migration, and differentiation in many tissues. Here we report that loss of IntroductionHematopoiesis is maintained by a small number of multipotent long-term hematopoietic stem cells (LT-HSCs) with extensive self-renewal capability. These cells give rise to lineage-committed progenitors, which produce various types of mature blood cells. Cytokine and growth factor signaling is critical for the sustained production of HSCs and progenitors and directs cellular survival, migration, and differentiation. 1,2 Src homology 2 (SH2) domain-containing phosphatase 2 (Shp2) is a ubiquitously expressed nonreceptor protein-tyrosine phosphatase (PTP), encoded by the Ptpn11 gene, which regulates signaling networks and cell fates in many organisms. Shp2 is composed of 2 SH2 domains (N-SH2 and C-SH2), a PTP domain, a C-terminal tail with tyrosyl phosphorylation sites that modulate some RTK signaling pathways, and a proline-rich motif of unknown function. In multiple tissues, Shp2 positively regulates Ras/Erk signaling downstream of receptor tyrosine kinases (RTKs) and cytokine receptors. 3 Shp2 also appears to have cell-type-and/or agonistdependent effects on the activation of Akt, Jnk, NF-B, Rho, and Nfat. 3 Germline PTPN11 mutations underlie approximately 50% of Noonan syndrome, which is characterized by short stature, skeletal abnormalities, cardiac defects, learning disabilities, and a predisposition to hematologic abnormalities, particularly juvenile myelomonocytic leukemia. Somatic gain-of-function mutations in PTPN11 also are the most common cause of sporadic juvenile myelomonocytic leukemia. 4 Although Shp2 is required for normal Ras/Erk activation in many contexts, 3 the underlying mechanism shows great diversity and depends on the precise cell type and stimulus involved. Epistasis studies in Caenorhabditis elegans and Drosophila show that activated Ras/let-60/ras1 suppresses the effects of Shp2/ptp-2/ csw loss, 5,6 arguing that Shp2 acts upstream of Ras in these signaling pathways. However, in C elegans vulva development and Drosophila R7 photoreceptors and muscle precursors, Shp2/ptp-2/ csw appears to act downstream of Ras/let-60/ras1 in some contexts. 5,7-9 Furthermore, in the EGL-15/Egfr signaling pathway, ptp-2 may act parallel to let-60. 10 In mice, expression of activated Kras (Kras G12D ) does not completely restore defective lens proliferation and lacrimal gland development caused by the loss of Ptpn11. 11 Collectively, these results indicate that Shp2 can act upstream, downstream, or parallel to Ras in different systems, and imply that the consequences and the mediators of Shp2 action must be specifically delineated in particular biologic contexts.Homozygous inactivation of murine Shp2 results in early embryonic lethality 12-14 because of a critical role of Shp2 in trophoblast stem cell survival. 14 Loss of Shp2 also reduces...

Gata3 is expressed and required for differentiation and function throughout the T lymphocyte lineage. Despite evidence it may also be expressed in multipotent hematopoietic stem cells (HSC), any role in these cells has remained unclear. Here we show GATA3 was cytoplasmic in quiescent long-term stem cells from steady state bone marrow, but relocated to the nucleus when HSC cycle. Relocation depended on p38-MAPK signaling and was associated with diminished capacity for long-term reconstitution upon transfer to irradiated mice. Deletion of Gata3 enhanced repopulating capacity and augmented self-renewal of long term HSC in cell-autonomous fashion, without affecting cell cycle. These observations position Gata3 as a regulator of the balance between self-renewal and differentiation in HSC acting downstream of the p38 signaling pathway.

No abstract

We described a 32-year-old man who developed severe drug-induced liver injury after using Ligandrol (LGD-4033). The diagnosis was confirmed by a liver biopsy that showed cholestatic hepatitis with a mild portal, periportal, and perisinusoidal fibrosis. Ligandrol is a selective androgen receptor modulator that is available over the counter and via the internet.

Although hematopoiesis is known to proceed from stem cells through a graded series of multipotent, oligopotent, and unipotent precursor cells, it has been difficult to resolve these cells physically one from another. There is, therefore, corresponding uncertainty about the exact distribution and timing of the expression of genes known to be important in hematopoietic differentiation. In earlier work, the generation of a set of amplified complementary DNAs (cDNAs) from single precursor cells was described, whose