Recently, we identified a novel gene, MJD1, which contains an expanded CAG triplet repeat in Machado-Joseph disease. Here we report the induction of apoptosis in cultured cells expressing a portion of the MJD1 gene that includes the expanded CAG repeats. Cell death occurs only when the CAG repeat is translated into polyglutamine residues, which apparently precipitate in large covalently modified forms. We also created ataxic transgenic mice by expressing the expanded polyglutamine stretch in Purkinje cells. Our results demonstrate the potential involvement of the expanded polyglutamine as the common aetiological agent for inherited neurodegenerative diseases with CAG expansions.

Although pharmacological doses of retinoic acid (RA) have a wide variety of actions in vivo, experimental difficulties have prevented a definitive assignment of its physiological functions. We recently made a dominant-negative retinoic acid receptor (RAR) by a single amino-acid substitution which creates a dominant-negative thyroid hormone receptor. The mutated RAR efficiently inhibited the endogenous activities of RARs (alpha, beta, gamma). Thus, targeted expression of the mutated receptor should reveal RA functions during organogenesis by blocking RA signalling in the tissues concerned. To address this possibility, we expressed the dominant-negative RAR in the epidermis, a potential target organ of RA. We report here that the resultant transgenic mice exhibited dramatic suppression of epidermal maturation, demonstrating the requirement of RA in normal skin development.

Interferon-y may play an important role in the immune response and in inflammatory diseases, including chronic active hepatitis. To understand the role of interferon-y in the regulation of inflammation and to establish a mouse model of chronic active hepatitis, we produced transgenic mice in which the mouse interferon-y gene was regulated by a liver-specific promoter, the serum amyloid P component gene promoter. Four transgenic mouse lines were generated, and two of these lines expressed mRNA of interferon-y in the liver. Levels of serum transaminases increased gradually as a function of age and were significantly higher than those of interferon--negative littermates after 4 weeks after birth. One transgenic mouse line showed a histology of chronic active hepatitis similar to that found in human patients, although cirrhotic changes such as fibrosis were scarce. Thus, the liver-specific production of interferon-y is sufficient to induce chronic inflammatory disease and this mouse is a transgenic model of chronic active hepatitis.Chronic hepatic diseases, such as chronic active hepatitis and liver cirrhosis, are public health problems of worldwide importance and are major causes of mortality in certain areas of the world. Clinical and epidemiological studies (1-4) have clearly shown the importance of hepatitis B and C viruses (HBV, HCV) in chronic active hepatitis as well as hepatocellular carcinoma (HCC). Furthermore, studies ofpathology revealed that HCC arises in a cirrhotic liver and that chronic hepatitis is prerequisite for the development of HCC. The mechanisms responsible for HBV-or HCV-induced hepatocellular injury are not well understood. However, it is generally accepted that HBV is not directly cytopathic and that liver cell necrosis is dependent upon the host's immune response, directed at viral determinants on the hepatocyte membrane (5, 6). This immune response is mainly mediated by cytotoxic T lymphocytes (7).Several transgenic models of hepatic disease have been described. Chisari et al. (8) (10) showed that transgenic mice expressing the albumin-plasminogen activator gene develop progressive degenerative change in the liver due to accumulation ofRER-bounded multivesicular bodies. However, the principal lesion in these models appears to involve the hepatocyte secretory pathway and thus is different from that found in human patients.A model of acute hepatitis can be produced by administration of chemicals. However, remaining hepatocytes are induced to proliferate until the liver regains its original weight. Shull et al. (11) produced transforming growth factor (TGF)-,81-deficient mice. These mice developed an inflammatory liver disease similar to that found in HBV infection. However, about 20 days after birth these mice died due to a wasting syndrome. Mori et al. (12) demonstrated that liver changes histologically mimicking human hepatitis were produced in the mouse liver after repeated immunization with syngeneic crude liver proteins. However, it is not known whether hepatitis continues l...

To elucidate the roles of SHP-2, we generated transgenic (Tg) mice expressing a dominant negative mutant lacking protein tyrosine phosphatase domain (⌬PTP). On examining two lines of Tg mice identified by Southern blot, the transgene product was expressed in skeletal muscle, liver, and adipose tissues, and insulin-induced association of insulin receptor substrate 1 with endogenous SHP-2 was inhibited, confirming that ⌬PTP has a dominant negative property. The intraperitoneal glucose loading test demonstrated an increase in blood glucose levels in Tg mice. Plasma insulin levels in Tg mice after 4 h fasting were 3 times greater with comparable blood glucose levels. To estimate insulin sensitivity by a constant glucose, insulin, and somatostatin infusion, steady state blood glucose levels were higher, suggesting the presence of insulin resistance. Furthermore, we observed the impairment of insulin-stimulated glucose uptake in muscle and adipocytes in the presence of physiological concentrations of insulin. Moreover, tyrosine phosphorylation of insulin receptor substrate-1 and stimulation of phosphatidylinositol 3-kinase and Akt kinase activities by insulin were attenuated in muscle and liver. These results indicate that the inhibition of endogenous SHP-2 function by the overexpression of a dominant negative mutant may lead to impaired insulin sensitivity of glucose metabolism, and thus SHP-2 may function to modulate insulin signaling in target tissues. SHP-2 (also referred to as PTP1D, PTP2C, SHPTP2, or SYP)is a ubiquitously expressed protein-tyrosine phosphatase (PTPase) 1 containing a single PTPase domain and two adjacent Src homology (SH) 2 domains near its N terminus which specifically associate with a variety of tyrosine-phosphorylated proteins upon growth factor stimulation (1-5). SHP-2 is the mammalian homologue of Drosophila Corkscrew, whose gene product potentiates the Drosophila homologue of mammalian c-raf to positively transmit signals downstream of the Torso receptor tyrosine kinase (6). Furthermore, SHP-2 has been reported to play an important role in mesodermal induction in oocyte by regulation of mitogen-activated protein (MAP) kinase activity (7).Regarding the roles of SHP-2 in tyrosine kinase signaling, several lines of evidence indicate that SHP-2 acts as a positive mediator in growth factor signaling such as that by plateletderived growth factor and epidermal growth factor (4,5,8,9). After stimulation by these ligands, SHP-2 is tyrosine-phosphorylated and bound to Grb2-SOS complex, resulting in activation of p21 ras and MAP kinase cascade. On the other hand, in the case of insulin signaling, SHP-2 is not tyrosine-phosphorylated in response to insulin stimulation. However, insulin induces the association of IRS-1 with SHP-2 (10, 11), and the expression of either a catalytically inactive mutant SHP-2 (Cys/Ser) or a deletion mutant lacking PTPase domain in Chinese hamster ovary cells overexpressing insulin receptors (CHO-IR) results in the attenuation of the insulin-stimulated MAP kinase activity, ...

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