The colonic and intestinal epithelium are renewed every 3 days. In the intestine there are at least two principal stem cell pools. The first contains rapid cycling crypt based columnar (CBC) Lgr5+ cells, while the second is comprised of slower cycling Bmi1-expressing cells at the +4 position above the crypt base. In the colon, however, the identification of Lgr5-negative stem cell pools has proven more challenging. Here, we demonstrate that the intermediate filament, keratin-19 (Krt19), marks long-lived, radiation resistant cells above the crypt base that generate Lgr5+ CBCs in the colon and intestine. In colorectal cancer models, Krt19+ cancer initiating cells are also radioresistant while Lgr5+ stem cells are radiosensitive. Moreover, Lgr5+ stem cells are dispensable in both the normal and neoplastic colonic epithelium, as ablation of Lgr5+ stem cells results in their regeneration from Krt19 expressing cells. Thus, Krt19+ stem cells are a discrete target relevant for cancer therapy.

In the central nervous system (CNS), oligodendrocyte maturation and axonal myelination occur on a predictable schedule, but the underlying timing mechanisms are largely unknown. In the present study, we demonstrate that Nkx2.2 homeodomain transcription factor is a key regulator for the timing of oligodendrocyte differentiation during development. Whereas induced expression of Nkx2.2 in early oligodendrocyte precursor cells (OPCs) causes precocious differentiation of oligodendrocytes, conditional ablation of Nkx2.2 temporally delays oligodendrocyte maturation. Moreover, Nkx2.2 can directly bind to the promoter of platelet-derived growth factor receptor alpha (Pdgfra) and repress its gene expression. Genetic ablation of Pdgfra mimics the effect of Nkx2.2 overexpression in accelerating OPC differentiation in the developing spinal cord. Together, our findings strongly suggest that Nkx2.2 functions as a major 'switch' to turn off Pdgfra signaling in OPCs and initiate the intrinsic program for oligodendrocyte differentiation. KEY WORDS: Spinal cord, Tet-on, Transcription factor, Mouse INTRODUCTIONA requisite component of nervous system development is the achievement of proper axonal myelination for rapid and accurate transmission of electric activities. In the central nervous system (CNS), myelin sheaths are elaborated by oligodendrocytes (OLs), and the myelination process is preceded by molecular and morphological differentiation of oligodendrocyte precursor cells (OPCs). It was observed that OPCs differentiate on a predictable schedule both in vivo and in vitro, but the molecular pathways that control the timing of OPC differentiation have not been clearly defined.It has been recently shown that multiple classes of transcription factors are involved in the regulation of the OL differentiation process. They include the negative differentiation regulators Id2, Id4 and Hes5 (Kondo and Raff, 2000; Liu et al., 2006;Wang et al., 2001), and positive regulators such as Olig1 (Lu et al., 2002), Mrf (Myrf -Mouse Genome Informatics) (Emery, 2010), Mash-1 (Ascl1 -Mouse Genome Informatics) (Sugimori et al., 2008), Sip1 (Gemin2 -Mouse Genome Informatics) (Weng et al., 2012), Nkx2.2 (Qi et al., 2001 and Sox10 (Soula et al., 2001). Among these transcription factors, Nkx2.2 (Nkx2-2 -Mouse Genome Informatics) is uniquely positioned as a candidate regulator for the timing of OL differentiation. In the developing mouse spinal cord, Nkx2.2 expression is upregulated in OPCs immediately before their differentiation but rapidly downregulated after OPC differentiation (Fu et al., 2002;Soula et al., 2001;Xu et al., 2000;Zhou et al., 2001). Thus, Nkx2.2 expression in differentiating OPCs correlates seamlessly with the onset of OL differentiation. Functional analyses revealed that Nkx2.2 plays an essential role in the terminal differentiation of OLs (Qi et al., 2001;Zhou et al., 2001). However, because of the neonatal lethality of Nkx2.2 mutants, it has remained unknown whether Nkx2.2 is absolutely required for OPC maturation or simp...

from alternative islet cell fates. Furthermore, β cells appeared to transdifferentiate to acquire other non-β cell endocrine identities. Deletion of Nkx2.2 in fully differentiated adult β cells also resulted in the very rapid onset of diabetes, and the islets of these mice were also characterized by a loss of β cell identity and the acquisition of δ cell characteristics, confirming the importance of NKX2.2 ration and/or function, we generated mouse models that allowed constitutive and inducible deletion of the Nkx2.2 gene. Disruption of Nkx2.2 in maturing β cells resulted in the rapid development of diabetes, with a significant decrease in insulin expression and content. Strikingly, the loss of genes associated with β cell identity and function was accompanied by increased expression of genes ΔBeta compared with control mice at 4 weeks of age. The white boxes indicate regions of the islet that are shown in higher magnification in E and F. (G) Ad libitum blood glucose levels in 2-week-old male Nkx2.2ΔBeta mice compared with controls (n = 3-16), in 3-week-old mice (n = 5-22), and in 11-week-old mice (n = 6-18). **P ≤ 0.01, ***P ≤ 0.001; 2-tailed Student's t test. Each control genotype was examined separately to ensure that the individual Cre and floxed alleles did not cause metabolic phenotypes. (H) Higher fasting blood glucose levels are evident in 11-week-old Nkx2.2ΔBeta mice compared with controls (3-week-old mice: n = 6-23; 11-week-old mice: n = 8-21). *P ≤ 0.05; 2-tailed Student's t test. (I) Glucose intolerance is observed in Nkx2.2ΔBeta male mice compared with controls at 3 weeks of age (n = 6-23). *P ≤ 0.05, ***P ≤ 0.001; 2-tailed Student's t test. (J) Glucose intolerance becomes more severe at 11 weeks of age in Nkx2.2ΔBeta male mice compared with control mice (n = 8-21). *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001; 2-tailed Student's t test.

Tumor development from an early lesion through to invasive disease is not a clearly defined progression in the breast. Studies of invasive lobular carcinoma have reported mutations, loss of heterozygosity (LOH) and loss of protein expression in epithelial (E)-cadherin, a protein involved in cell adhesion. Our study examines in situ lobular neoplastic lesions without concurrent invasive carcinoma for E-cadherin gene alterations and protein expression, beta-catenin, alpha-catenin and p120-catenin protein expression, and LOH at the chromosome 16q locus, with the goal of determining the events occurring at the stage of lobular neoplasia. In all, 13 atypical lobular hyperplasia lesions and 13 lobular carcinoma in situ lesions from archived cases were examined. E-cadherin sequence alterations were evaluated using single strand conformation polymorphism and DNA sequencing, and PCR-based LOH analysis was carried out for the 16q locus. Using immunohistochemistry, we assessed protein expression. A total of 23 of 24 lesions evaluated by immunohistochemistry were negative for both E-cadherin and beta-catenin protein expression, and 21 of 23 lesions were negative for alpha-catenin. Cytoplasmic (rather than membrane) localization of p120-catenin was observed in 20 of 21 cases. Lobular carcinoma in situ cases were characterized by mutations; however, atypical lobular hyperplasia cases were not. LOH at 16q was an infrequent event. From our study, we conclude that an altered E-cadherin adhesion complex is an early event affecting atypical lobular hyperplasia as well as lobular carcinoma in situ and occurs prior to progression to invasive disease. However, the loss of protein expression is accompanied by E-cadherin DNA alterations in lobular carcinoma in situ but not in atypical lobular hyperplasia. These cases lacking both protein expression and gene alterations suggest that another mechanism is involved, possibly as early as at the hyperplastic stage, causing silencing of the E-cadherin complex.