論文

Mdm2 is the major inhibitor of the p53 tumor suppressor. Loss of Mdm2 in mice or in specific tissues of the mouse always yields p53-dependent lethal phenotypes. However, the role of Mdm2 in tissues with high turnover capacity is unknown. We have engineered mice lacking Mdm2 in the intestinal epithelium using the Cre/LoxP system. Loss of Mdm2 (Mdm2intΔ) results in viable animals, but neonates display multiple intestinal abnormalities such as hyperplasia, enterocyte vacuolization, and inflammation. These defects correlate with a drastic increase in p53-dependent apoptosis in highly proliferative and differentiated cells. Unexpectedly, the observed phenotypes disappear with age. The tissue selects against Mdm2-null cells and increases its proliferative capacity. Additionally, the intestinal stem and progenitor cell populations are enriched leading to an increase in crypt fission events. Enhanced proliferation is achieved by activation of the canonical Wnt and EGFR-mediated Ras/MAPK pathways. While Mdm2 is a critical inhibitor of p53 in the intestinal epithelium, the tissue employs a series of processes that compensate for cell death.

Transplantation of mature adipocyte-derived cells (dedifferentiated fat cells) led to marked functional recovery from spinal cord injury (SCI)-induced motor dysfunction in rats. When mature adipocytes were isolated from rat adipose tissue and grown in ceiling culture, transformation into fibroblast-like cells without lipid droplets occurred. These fibroblast-like cells, termed dedifferentiated fat cells (DFAT), could proliferate and could also differentiate back into adipocytes. DFAT expressed neural markers such as nestin, βIII tubulin, and GFAP. Allografting of DFAT into SCI-induced rats led to significant recovery from hindlimb dysfunction. Grafted cells were detected at the injection site, and some of these cells expressed βIII tubulin. DFAT expressed neurotrophic factors such as BDNF and GDNF prior to transplantation, and grafted cells were also positive for these factors. Therefore, these neurotrophic factors derived from grafted DFAT might have contributed to the promotion of functional recovery. These findings also suggest that mature adipocytes could become a new source for cell replacement therapy to treat central nervous system disorders. Copyright © 2008 Cognizant Comm. Corp.

Musashi protein is supposed to be involved in the regulation of differentiation of neural stem cells. Musashi binds to 3' untranslated region of target mRNA and represses the translation of mRNA. Musashi has two tandem RNA-binding domains (RBDs), RBD1 and RBD2. Both RBDs cooperatively bind to the target mRNA. Here, we determined the structure of RBD1-RBD2 in complex with target RNA. First, the structures of two RBDs in the complex were determined on the basis of short-range distance restrains derived from NOEs. However, the relative position of two RBDs was not determined due to the lack of long-range distance restraints across two RBDs. In order to overcome the situation, we introduced the paramagnetic center into Musashi by attaching MTSL carrying the NO radical. The long-range distance restraints (ca. 20-40 A) between two RBDs were derived from paramagnetic relaxation enhancement (PRE) caused by the paramagnetic center. The relative position of two RBDs was successfully determined on the basis of these long-range distance restraints. The change in the relative position of two RBDs on binding to the target RNA was also detected by PRE. The determined structure of RBD1-RBD2 in the complex has suggested how Musashi recognizes its target mRNA.

The radiological modalities that are currently utilized as critical components in clinical medicine have also been adapted to small-animal imaging, among which are ultrasound imaging, X-ray computerized tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), and singlephoton emission computed tomography (SPECT). Optical imaging techniques such as bioluminescence imaging (BLI) and fluorescence imaging (FLI) are approaches that are commonly used in small animals. Longitudinal surveys of living (i.e., nonsacrificed) animal models with these modalities provide some clues for the development of clinical applications. The techniques are absolutely essential for translational research. However, there are currently few tools available with sufficient spatial or temporal resolution ideal for all experimental studies. In this chapter, we provide a rationale and techniques for visualizing target cells in living small animals and an overview of the advantages and limitations of current imaging technology. Finally, we introduce a humanized mouse and a novel in vivo imaging system that we have developed. We also discuss real-time observations of reconstructs and clinical manifestations. © 2008 Springer-Verlag.