Although nutrients, including amino acids and their metabolites such as serotonin (5-HT), are strong modulators of anxiety-related behavior, the metabolic pathway(s) responsible for this physiological modulation is not fully understood. Regarding tryptophan (Trp), the initial ratelimiting enzymes for the kynurenine pathway of tryptophan metabolism are tryptophan 2,3-dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO). Here, we generated mice deficient for tdo (Tdo -/-). Compared with wild-type littermates, Tdo -/-mice showed increased plasma levels of Trp and its metabolites 5-hydroxyindoleacetic acid (5-HIAA) and kynurenine, as well as increased levels of Trp, 5-HT and 5-HIAA in the hippocampus and midbrain. These mice also showed anxiolytic modulation in the elevated plus maze and open field tests, and increased adult neurogenesis, as evidenced by double staining of BrdU and neural progenitor/neuronal markers. These findings demonstrate a direct molecular link between Trp metabolism and neurogenesis and anxiety-related behavior under physiological conditions.

The use of mutant mice plays a pivotal role in determining the function of genes, and the recently reported germ line transposition of the Sleeping Beauty (SB) transposon would provide a novel system to facilitate this approach. In this study, we characterized SB transposition in the mouse germ line and assessed its potential for generating mutant mice. Transposition sites not only were clustered within 3 Mb near the donor site but also were widely distributed outside this cluster, indicating that the SB transposon can be utilized for both region-specific and genome-wide mutagenesis. The complexity of transposition sites in the germ line was high enough for large-scale generation of mutant mice. Based on these initial results, we conducted germ line mutagenesis by using a gene trap scheme, and the use of a green fluorescent protein reporter made it possible to select for mutant mice rapidly and noninvasively. Interestingly, mice with mutations in the same gene, each with a different insertion site, were obtained by local transposition events, demonstrating the feasibility of the SB transposon system for region-specific mutagenesis. Our results indicate that the SB transposon system has unique features that complement other mutagenesis approaches.The analysis of mutant mice plays a key role in the understanding of gene functions, and the importance of this approach is expected to increase (2) with the recent availability of the mouse genome sequence (25). However, large-scale genetic screening for mice has been lagging far behind that for other model organisms, such as Drosophila melanogaster and Caenorhabditis elegans, because of the lack of a system allowing for both mutagenesis and subsequent rapid identification of the mutation. Large-scale generation of mutant mice has been conducted recently by using N-ethyl-N-nitrosourea (ENU), and a number of mutant mice with various phenotypes have been generated successfully (6, 26). The drawback of this approach is that identification of the causative point mutations is time-consuming. The embryonic stem (ES) cell-based gene trap is another effective approach (11,12,31). However, largescale generation of mutant mice, which is a prerequisite for genetic screening, is not easy because the ES cell-based methods involve labor-intensive processes such as tissue culture or embryo manipulation.Transposon-tagged mutagenesis has been used in a wide range of organisms, such as D. melanogaster (1, 32), C. elegans (13, 24), and plants (27). Although the mutation rate resulting from transposition is not as high as that in ENU mutagenesis, transposon-tagged mutagenesis has been used as an alternative genetic screening method for the following reasons. First, the genes responsible for the phenotypes can be identified rapidly by using the transposon sequence as a tag. Second, desired elements can be introduced into the transposon sequence to expand the application range of the mutant lines. This principle has been demonstrated in the P element of D. melanogaster, where various GAL4 en...

Recent consolidation of the whole-genome sequence with genome-wide transcriptome profiling revealed the existence of functional units within the genome in specific chromosomal regions, as seen in the coordinated expression of gene clusters and colocalization of functionally related genes. An efficient region-specific mutagenesis screen would greatly facilitate research in addressing the importance of these clusters. Here we use the 'local hopping' phenomenon of a DNA-type transposon, Sleeping Beauty (SB), for region-specific saturation mutagenesis. A transgenic mouse containing both transposon (acts as a mutagen) and transposase (recognizes and mobilizes the transposon) was bred for germ-cell transposition events, allowing us to generate many mutant mice. All genes within a 4-Mb region of the original donor site were mutated by SB, indicating the potential of this system for functional genomic studies within a specific chromosomal region.

. A new microscope technique, termed "W"