メダカにおける同一パートナーとの性行動の経験が雌雄の性行動の活性に与える行動学的研究

Tohoku University竹内秀明課

Mating experiences with the same partner enhanced mating activities of naive male medaka fish

Mating experience shapes male mating behavior across species, from insects, fish, and birds, to rodents. Here, we investigated the effect of multiple mating experiences on male mating behavior in "naive" (defined as sexually inexperienced) male medaka fish. The latency to mate with the same female partner significantly decreased after the second encounter, whereas when the partner was changed, the latency to mate was not decreased. These findings suggest that mating experiences enhanced the mating activity of naive males for the familiar female, but not for an unfamiliar female. In contrast, the mating experiences of "experienced" (defined as those having mated > 7 times) males with the same partner did not influence their latency to mate. Furthermore, we identified 10 highly and differentially expressed genes in the brains of the naive males after the mating experience and revealed 3 genes that are required for a functional cascade of the thyroid hormone system. Together, these findings suggest that the mating experience of naive male medaka fish influences their mating behaviors, with neural changes triggered by thyroid hormone activation in the brain

Strict De Novo Methylation of the 35S Enhancer Sequence in Gentian

A novel transgene silencing phenomenon was found in the ornamental plant, gentian (Gentiana triflora × G. scabra), in which the introduced Cauliflower mosaic virus (CaMV) 35S promoter region was strictly methylated, irrespective of the transgene copy number and integrated loci. Transgenic tobacco having the same vector did not show the silencing behavior. Not only unmodified, but also modified 35S promoters containing a 35S enhancer sequence were found to be highly methylated in the single copy transgenic gentian lines. The 35S core promoter (−90)-introduced transgenic lines showed a small degree of methylation, implying that the 35S enhancer sequence was involved in the methylation machinery. The rigorous silencing phenomenon enabled us to analyze methylation in a number of the transgenic lines in parallel, which led to the discovery of a consensus target region for de novo methylation, which comprised an asymmetric cytosine (CpHpH; H is A, C or T) sequence. Consequently, distinct footprints of de novo methylation were detected in each (modified) 35S promoter sequence, and the enhancer region (−148 to −85) was identified as a crucial target for de novo methylation. Electrophoretic mobility shift assay (EMSA) showed that complexes formed in gentian nuclear extract with the −149 to −124 and −107 to −83 region probes were distinct from those of tobacco nuclear extracts, suggesting that the complexes might contribute to de novo methylation. Our results provide insights into the phenomenon of sequence- and species- specific gene silencing in higher plants

A Histological Evaluation of Adventitious Bud Formation in Cotyledons in Crotalaria juncea L.

In Crotalaria juncea L., adventitious buds were formed in cotyledonary expiants cultured on 0.8% agar-solidified 1/2 MS basal medium containing B5 vitamins, 1.0 or 0.5 mg L–1 NAA, 5.0 or 10.0 mg L–1 BA and 3% sucrose. The frequency of adventitious bud formation was 30-45% in all combinations of NAA and BA. In histological observations, prominent mitotic figures were observed in several cells of the subepidermal palisade layers on the adaxial side of the expiants in contact with medium after 3 days of culture. Calli were formed within 6 days of culture. After 10 days of culture, numerous mature tracheary elements were produced at random in the proliferated regions, and cell divisions at the superficial region led to the formation of the meristematic structure. The shoot apex of the seedling produced numerous trichomes from superficial cells, but the adventitious bud formed on the cotyledon produced no trichomes. Initiation of the meristematic region in the expiant could be used as a target site for gene transfer experiments