Polycomb genes in Drosophila maintain the repressed state of homeotic and other developmentally regulated genes by mediating changes in higher-order chromatin structure. M33, a mouse homologue of Polycomb, was isolated by means of the structural similarity of its chromodomain. The fifth exon of M33 contains a region of homology shared by Drosophila and Xenopus. In Drosophila, its deletion results in the loss of Polycomb function. Here we have disrupted M33 in mice by inserting a poly(A) capture-type neo(r) targeting vector into its fifth exon. More than half of the resultant M33cterm/M33cterm mutant mice died before weaning, and survivors showed male-to-female sex reversal. Formation of genital ridges was retarded in both XX and XY M33cterm/M33cterm embryos. Gonadal growth defects appeared near the time of expression of the Y-chromosome-specific Sry gene, suggesting that M33 deficiency may cause sex reversal by interfering with steps upstream of Sry. M33cterm/M33cterm mice may be a valuable model in which to test opposing views regarding sex determination.

These results suggest that hyperthermia using MCLs is an effective therapy for prostate cancer, since this treatment appears to kill the prostate cancer cells not only directly by heating but also by inducing an immune response. This therapy may cure not only the primary lesion but also metastatic lesions.

Previous studies have shown that the cyclin-dependent kinase inhibitor (CDKI) genes p15INK4B and p16INK4A are frequently inactivated by genetic alterations in many malignant tumors and that they are candidate tumor-suppressor genes. Although genetic alterations in these genes may be limited to lymphoid malignancies, it has been reported that their inactivation by aberrant methylation of 5′ CpG islands may be involved in various hematologic malignancies. In this study, we investigated the p15INK4B and p16INK4A genes to clarify their roles in the pathogenesis of myelodysplastic syndrome (MDS). Southern blotting analysis showed no gross genetic alterations in either of these genes. However, hypermethylation of the 5′ CpG island of the p15INK4B gene occurred frequently in patients with MDS (16/32 [50%]). Interestingly, the p15INK4B gene was frequently methylated in patients with high-risk MDS (refractory anemia with excess blasts [RAEB], RAEB in transformation [RAEB-t], and overt leukemia evolved from MDS; 14/18 [78%]) compared with patients with low-risk MDS (refractory anemia [RA] and refractory anemia with ring sideroblast [RARS]; 1/12 [8%]). Furthermore, methylation status of the p15INK4B gene was progressed with the development of MDS in most patients examined. In contrast, none of the MDS patients showed apparent hypermethylation of the p16INK4A gene. These results suggest that hypermethylation of the p15INK4B gene is involved in the pathogenesis of MDS and is one of the important late events during the development of MDS.

Thevarepsilon4 allele of apolipoprotein E (apoE) is associated with an increased risk of developing Alzheimer's disease (AD). To accurately determine the isoform-specific effects of human apoE on brain functions under physiological and pathological situations, we created mice expressing human apoE4 isoform in place of mouse apoE by utilizing the gene-targeting technique on the embryonic stem cells (knock-in). The homozygousvarepsilon4 (4/4) mice correctly expressed human apoE4 in the serum and the brain. The human apoE in the brain was found primarily in the astrocytes as was the mouse apoE in the wild-type (+/+) mice. In the 4/4 mice, the serum cholesterol level was 2.5-fold that of the +/+ littermate controls on a regular diet. This marked elevation was accounted for by an accumulation of very low and low density lipo-proteins. In the brains of the 4/4 mice, however, the amounts of total cholesterol and phospholipids were significantly decreased compared with the +/+ littermates. These findings indicate that cholesterol and lipid metabolism is markedly altered in the 4/4 mice. Our human apoE4 knock-in mice will be useful in clarifying the role of apoE in the etiologies of AD and cardiovascular diseases in relation to cholesterol and lipid metabolism.