INTRODUCTION In the Drosophila adult midgut, multipotent intestinal stem cells (ISCs) produce two types of daughter cells: nutrient-absorbing enterocytes (ECs) and secretory enteroendocrine (ee) cells. Notch signaling between ISCs and their daughters directs the proper specification of both of these cell types. Previous work suggests that ISCs expressing high levels of the Notch ligand Delta (Dl) strongly activate the Notch signaling pathway in their daughters and result in their differentiation into ECs. By contrast, ISCs that express low levels of Dl direct their daughters to become ee cells. However, in this unidirectional Notch signaling model, the mechanisms regulating differential Dl expression in ISCs are poorly understood. RATIONALE During Drosophila pupal midgut development, pupal ISCs only make ee cells. Therefore, we examined how ee cells are made and evaluated the role of Notch signaling function during this developmental time window. On the basis of insights obtained from pupal development, we also asked whether similar mechanisms were used by ISCs in the adult midgut to generate ee cells. RESULTS The ee cell fate marker Prospero (Pros) appeared in pupal ISCs at 44 hours after pupal formation (APF). From 44 to 96 hours APF, ISCs first divided asymmetrically, generating one ISC and one ee cell, followed by symmetric division of both ISCs and ee cells, resulting in a pair of ISCs and a pair of ee cells. During ISC asymmetric divisions, Pros was asymmetrically segregated to the basal daughter cell, a process that depended on the function of the Par complex. After ISC asymmetric division, the ee daughter cell expressed the Notch ligand Dl and activated the Notch signaling pathway in ISCs. Loss of Notch signaling in pupal ISCs induced all stem cells to differentiate into ee cells, whereas low-level activation of Notch signaling in pupal ISCs blocked ee cell formation. During ee symmetric divisions, Pros distribution was symmetric; however, cell polarity and Notch signaling remained asymmetric. Loss of Notch signaling between progeny of ee symmetric divisions disrupted expression of peptide hormones in ee cells, indicating a role for Notch signaling in proper ee specification. We also investigated the Notch pathway in adult ISCs and confirmed that postmitotic Notch signaling from ee daughter cells also regulates ISC multipotency. CONCLUSION Consistent with previous work, high levels of Dl in ISCs activate high levels of Notch in the daughter cell, promoting EC differentiation. In contrast, after asymmetric localization of Pros, ISCs require a low Notch signal from their immediate ee cell daughters to maintain multipotency. Thus, Notch signaling is both bidirectional and context-dependent. Previous work also has suggested that ISCs remain basal during EC formation and that basal ISCs activate the Notch pathway in daughter cells. Our data show that ISCs are apically located during ee cell formation and that basal ee cells activate the Notch pathway in ISCs. Therefore, Notch signaling is always unidir...

Injury-induced BMP signaling in the midgut negatively regulates intestinal stem cell division, whereas regional constitutive BMP signaling promotes copper cell differentiation.

The ideal treatment of localized cancer should directly cause an irreversible and complete death of tumor cells without damage to surrounding normal tissue. High intensity focused ultrasound (HIFU) is such a potential treatment, which induces a complete coagulative necrosis of a tumor at depth through the intact skin. The idea that using an extracorporeal source of therapeutic ultrasound was introduced more than 50 years ago [J. Gen. Physiol. 26 (1942) 179]. However, up to now, most of the studies on HIFU have been dealing with animal experiments because this extracorporeal technique is very complicated in clinical applications. The purpose of this study is to introduce Chinese clinical experience of using extracorporeal HIFU for the treatment of patients with various kinds of solid tumor. From December 1997 to October 2001, a total of 1038 patients with solid tumors underwent HIFU ablation in China. Among them, 313 patients were treated at the Chongqing University of Medical Sciences, China. Pathological examination showed that the target region presented clear evidence of cellular destruction. Small blood vessels less than 2 mm in diameter were severely damaged. Follow-up diagnostic imaging revealed that there was no, or reduced, blood supply, and no uptake of radioisotope in the treated tumor after HIFU, both indicating a positive therapeutic response and an absence of viable tumor. Imaging at 6-12 months showed obvious regression of the lesion. Four-year follow-up data were significantly observed in patients with hepatocellular carcinoma, osteosarcoma, and breast cancer. An extremely low major complication rate was noted. It is concluded that HIFU ablation is a safe, effective, and feasible modality for the ablation of carcinomas.

The Drosophila ovary is an excellent system with which to study germline stem cell (GSC) biology. Two or three female GSCs are maintained in a structure called a niche at the anterior tip of the ovary. The somatic niche cells surrounding the GSCs include terminal filament cells, cap cells and escort stem cells. Mounting evidence has demonstrated that BMP-like morphogens are the immediate upstream signals to promote GSC fate by preventing the expression of Bam, a key differentiation factor. In contrast to their morphogenic long-range action in imaginal epithelia, BMP molecules in the ovarian niche specify GSC fate at single-cell resolution. How this steep gradient of BMP response is achieved remains elusive. In this study, we found that the glypican Dally is essential for maintaining GSC identity. Dally is highly expressed in cap cells. Cell-specific Dally-RNAi, mutant clonal analysis and cellspecific rescue of the GSC-loss phenotype suggest that Dally acts in the cap cells adjacent to the GSCs. We confirmed that Dally facilitated BMP signaling in GSCs by examining its downstream targets in various dally mutants. Conversely, when we overexpressed Dally in somatic cells outside the niche, we increased the number of GSC-like cells apparently by expanding the pro-GSC microenvironment. Furthermore, in a genetic setting we revealed a BMP-sensitivity distinction between germline and somatic cells, namely that Dally is required for short-range BMP signaling in germline but not in somatic cells. We propose that Dally ensures high-level BMP signaling in the ovarian niche and thus female GSC determination.