Vesicular transport to and from the lysosome and late endosome is defective in patients with Chediak-Higashi syndrome (CHS) and in mutant beige (bg) mice. CHS and bg cells have giant, perinuclear vesicles with characteristics of late endosomes and lysosomes that arise from dysregulated homotypic fusion. CHS and bg lysosomes also exhibit compartmental missorting of proteins, such as elastase, glucuronidase and cathepsin G. Lyst, a candidate gene for bg, was identified by direct complementary DNA selection from a yeast artificial chromosome (YAC) clone containing a 650-kilobase segment of the bg-critical region on mouse chromosome 13. Lyst is disrupted by a 5-kilobase deletion in bg mice, and Lyst messenger RNA is markedly reduced in bg homozygotes. The homologous human gene, LYST, is highly conserved with mouse Lyst, and contains a frame-shift mutation at nucleotides 117-118 of the coding domain in a CHS patient. Thus bg mice and human CHS patients have homologous disorders associated with Lyst mutations. Lyst encodes a protein with a carboxy-terminal prenylation motif and multiple potential phosphorylation sites. Lyst protein is predicted to form extended helical domains, and has a region of sequence similar to stathmin, a coiled-coil phosphoprotein thought to act as a relay integrating cellular signal response coupling.

Prader-Willi syndrome (PWS) is a neurogenetic disease characterized by infantile hypotonia, gonadal hypoplasia, obsessive behaviour and neonatal feeding difficulties followed by hyperphagia, leading to profound obesity. PWS is due to a lack of paternal genetic information at 15q11-q13 (ref. 2). Five imprinted, paternally expressed genes map to the PWS region, MKRN3 (ref. 3), NDN (ref. 4), NDNL1 (ref. 5), SNRPN (refs 6-8 ) and IPW (ref. 9), as well as two poorly characterized framents designated PAR-1 and PAR-5 (ref. 10). Imprinting of this region involves a bipartite 'imprinting centre' (IC), which overlaps SNRPN (refs 10,11). Deletion of the SNRPN promoter/exon 1 region (the PWS IC element) appears to impair the establishment of the paternal imprint in the male germ line and leads to PWS. Here we report a PWS family in which the father is mosaic for an IC deletion on his paternal chromosome. The deletion chromosome has acquired a maternal methylation imprint in his somatic cells. We have made identical findings in chimaeric mice generated from two independent embryonic stem (ES) cell lines harbouring a similar deletion. Our studies demonstrate that the PWS IC element is not only required for the establishment of the paternal imprint, but also for its postzygotic maintenance.

Platelets are known to play a role in blood borne metastasis. Previous experimental studies have suggested that platelet GpIIb/IIIa may be a therapeutic target. However, the need for intravenous administration limits the potential application of current GpIIb/IIIa inhibitors to cancer therapy. The aim of the present study was to assess the efficacy of a novel, non-peptide oral GpIIb/IIIa antagonist (XV454) on tumor cell-induced platelet aggregation in vivo and on experimental metastasis. A Lewis lung carcinoma (LL2) mouse model of experimental metastasis was used in this study. XV454 (100 micro g) was administered intravenously (via tail vein) or orally (gavages) to 20 g mice. To determine the effect of XV454 on platelet aggregation, blood samples were collected by cardiac puncture 10 minutes after intravenous and 1-24 hrs after oral XV454, and platelet function was assessed by aggregometry, thrombelastography and the Platelet Function Analyzer (PFA100). The effect of XV454 on tumor cell-induced thrombocytopenia was determined 10 minutes after intravenous and 3 hrs after oral XV454 administration. Tumor cells (2 x 10(6)) were injected intravenously and 15 minutes after cell injection, platelet count was measured and compared to baseline (pre-injection) counts. To assess the effect on metastasis, XV454 was administered intravenous or orally 10 minutes and 3 hrs before tumor cell injection, respectively. Eighteen days later, surface lung tumor nodules were counted and the total lung tumor burden assessed. In a fourth group, in addition to the initial oral dose (before tumor cell injection), oral XV454 was given daily for the first week and three times in the second week. Administration of XV454 (5 mg/kg) completely inhibited platelet aggregation and this effect persisted for at least 24 hrs after oral delivery. Both intravenous and oral XV454 significantly inhibited tumor cell-induced thrombocytopenia (P < 0.01), the number of surface lung tumor nodules (80-85%; P < 0.001) and total tumor burden (83% for intravenous group; 50% oral [single treatment] group; 91% oral [multiple treatment] group, P < 0.001). Overall, these data provide further evidence for the effect of oral and intravenous GpIIb/IIIa antagonism on tumor cell-platelet interaction and metastasis.

Juvenile myelomonocytic leukemia (JMML) is a disease that occurs in young children and is associated with a high mortality rate. In most patients, JMML has a progressive course leading to death by virtue of infection, bleeding, or progression to acute myeloid leukemia (AML). As it is known that children with neurofibromatosis type 1 syndrome have a markedly increased risk of developing JMML, we have previously developed a mouse model of JMML through reconstitution of lethally irradiated mice with hematopoietic stem cells homozygous for a loss-of-function mutation in the Nf1 gene (D. L. Largaespada, C. I. Brannan, N. A. Jenkins, and N. G. Copeland, Nat. Genet. 12:137-143, 1996). In the course of these experiments, we found that all these genetically identical reconstituted mice developed a JMML-like disorder, but only a subset went on to develop more acute disease. This result strongly suggests that additional genetic lesions are responsible for disease progression to AML. Here, we describe the production of a unique tumor panel, created using the BXH-2 genetic background, for identification of these additional genetic lesions. Using this tumor panel, we have identified a locus, Epi1, which maps 30 to 40 kb downstream of the Myb gene and appears to be the most common site of somatic viral integration in BXH-2 mice. Our findings suggest that proviral integrations at Epi1 cooperate with loss of Nf1 to cause AML.Juvenile myelomonocytic leukemia (JMML) is a disease characterized by a young age of onset, a tendency to affect boys, prominent enlargement of the liver and spleen, leukocytosis, and the absence of the Philadelphia chromosome. JMML has a poor prognosis, with either progression to acute myeloid leukemia (AML) or death from bleeding or infection (36). It has been estimated that at least 10% of children with JMML also have neurofibromatosis type 1 (NF1) syndrome, an autosomal dominant disorder found in 1/3500 individuals (1,7,14,32). However, the actual frequency of children with NF1 and JMML is likely higher than 10% as the peak incidence of childhood leukemia occurs at an age when NF1 often goes undiagnosed (13, 34). In fact, one study found that 15% of JMML patients had mutations in the NF1 gene even though there was no previous clinical diagnosis of NF1 (33), suggesting that approximately 25% of JMML cases are associated with NF1.While RAS gene point mutations are commonly found in JMML patients without NF1, they are not found in JMML patients with NF1 (20), providing genetic evidence that NF1 and RAS are involved in the same pathway. This idea is supported by the fact that neurofibromin, the protein product of NF1, contains a region that has extensive homology with the catalytic domain of GTPase activating proteins that are known to accelerate the intrinsic GTPase activity of Ras, thereby negatively regulating Ras GTP levels (15). This suggests that inactivating mutations in NF1 are equivalent to activating mutations in RAS. Consistent with the hypothesis, analysis of bone marrow taken from children with ...