Project

• Establishment of a Rett Syndrome Mouse Model Using the i-GONAD Method The MeCP2 (Methyl-CpG-binding protein 2) gene, the causative gene of Rett syndrome, contains a nuclear localization signal (NLS) that facilitates the translocation of the protein from the cytoplasm into the nucleus. The NLS domain of MeCP2 is a basic amino acid sequence spanning residues 255–271 (KSKRK...KKR), characteristic of a classical monopartite NLS, and is mainly believed to be transported into the nucleus via the importin-α/β pathway. Therefore, if the NLS does not function properly, MeCP2 cannot translocate to the nucleus, leading to dysfunction of MeCP2, which normally acts as a transcriptional repressor within the nucleus. In fact, Rett syndrome patients with mutations in the NLS domain (such as R255X and R270X) exhibit severe neurodevelopmental disorders, including prominent epilepsy, microcephaly, and loss of motor function. Previous studies using human MeCP2 proteins lacking the NLS and analyses of transgenic mice harboring PAC or BAC constructs suggested that MeCP2 nuclear localization is regulated by importin-α subtypes such as KPNA3 and KPNA4. However, other studies have reported that MeCP2 nuclear import may be regulated independently of its NLS domain, indicating ongoing debate about the functional importance of the MeCP2 NLS. To address this issue, we generated a Mecp2ΔNLS mouse model in which only amino acid residues 248–271 of the MeCP2 protein are deleted, to investigate the specific role of the NLS domain.
• Analysis of Nuclear Dynamics Using Human Chromosome Engineering Technology Under the guidance of Professor Mitsuo Oshimura at Tottori University, we have acquired chromosome transfer technology that allows us to introduce human chromosomes into various cell lines. In this study, we are using mouse hybrid cells carrying a single human chromosome to elucidate the regulatory mechanisms underlying parent-of-origin-specific expression of imprinted genes. Imprinted genes are typically regulated by epigenetic modifications such as promoter methylation and histone modifications, but they are also controlled at the chromosomal domain level by distal enhancers and non-coding RNAs. Focusing on genome organization within the nucleus, we are using techniques such as DNA-RNA FISH to investigate the molecular mechanisms of genomic imprinting mediated by nuclear chromatin dynamics. This research is part of a longstanding collaboration with Professor Janine LaSalle at the University of California, Davis.
• Analysis of ZFP57-Deficient Mice We have generated conditional knockout mice lacking ZFP57, a gene essential for the establishment and maintenance of genomic imprinting during gametogenesis, and are investigating its role in neuronal differentiation.
• Elucidating the Evolutionary Significance of Genomic Imprinting in the Brain Genomic imprinting is a phenomenon in which the parental origin of alleles is epigenetically remembered, playing a crucial role in placental development in mammals and seed development in angiosperms. Its evolutionary significance is often explained by the parental conflict hypothesis, in which the paternal genome promotes fetal and placental growth, while the maternal genome restricts it. However, this hypothesis does not sufficiently account for the presence of imprinting in the brain. We are exploring an alternative evolutionary explanation focused on postnatal maternal care, which is essential in mammals. In fact, we have conducted gene expression analyses in the brains of marmosets that were artificially reared by humans for three months after birth and those that were naturally reared by their parents, and have identified dysregulation in the expression of several imprinted genes. We are currently investigating how genomic imprinting contributes to the mother-infant relationship in the context of caregiving.