RESUMO
Titanium dioxide (TiO2) nanotube and its hybrid nanotubes (with various metal oxides such as Ta2O5, Nb2O5, ZrO2, and SiO2) were fabricated by the sol-gel polymerization in the ethanol gels formed by simple l-lysine-based organogelator. The self-assembled nanofibers (gel fibers) formed by the gelator functioned as a template. The different calcination temperatures gave TiO2 nanotubes with various crystalline structures; e.g., anatase TiO2 nanotube was obtained by calcination at 600 °C, and rutile TiO2 nanotube was fabricated at a calcination temperature of 750 °C. In the metal oxide/TiO2 hybrid nanotubes, the metal oxide species were uniformly dispersed in the TiO2 nanotube, and the percent content of metal oxide species was found to correspond closely to the feed ratio of the raw materials. This result indicated that the composition ratio of hybrid nanotubes was controllable by the feed ratio of the raw materials. It was found that the metal oxide species inhibited the crystalline phase transition of TiO2 from anatase to rutile. Furthermore, the success of the hybridization of other metal oxides (except for TiO2) indicated the usefulness of the organogel route as one of the fabrication methods of metal oxide nanotubes.
RESUMO
The primordial germ cells (PGCs) in the oligochaete annelid Tubifex tubifex are descentants of the mesodermal (M) teloblast and are located in the two midbody segments X and XI in which they serve as germline precursors forming the testicular gonad and the ovarian gonad, respectively. During embryogenesis, vasa-expressing cells (termed presumptive PGCs or pre-PGCs) emerge in a variable set of midbody segments including the genital segments (X and XI); at the end of embryogenesis, pre-PGCs are confined to the genital segments, where they become PGCs in the juvenile. Here, using live imaging of pre-PGCs, we have demonstrated that during Tubifex embryogenesis, pre-PGCs (defined by Vasa expression) stay in segments where they have emerged, suggesting that it is unlikely that pre-PGCs move intersegmentally during embryogenesis. Thus, it is apparent that pre-PGCs derived from the 10th and 11th M teloblast-derived primary m blast cells (designated m10 and m11) that give rise, respectively, to segments X and XI are specified in situ as PGCs and that those born in other segments become undetectable at the end of embryogenesis. To address the mechanisms for this segment-specific development of PGCs, we have performed a set of cell-transplantation experiments as well as cell-ablation experiments. When m10 and m11 that are normally located in the mid region of the embryo were placed in positions near the anterior end of the host embryo, these cells formed two consecutive segments, which exhibited Vasa-positive PGC-like cells at early juvenile stage. This suggests that in terms of PGC generation, the fates of m10 and m11 remain unchanged even if they are placed in ectopic positions along the anteroposterior axis. Nor was the fate of m10 and m11 changed even if mesodermal blast cell chains preceding or succeeding m10 and m11 were absent. In a previous study, it was shown that PGC development in segments X and XI occurs normally in the absence of the overlying ectoderm. All this strongly suggests that irrespective of their surrounding cellular environments, m10 and m11 autonomously generate PGCs. We propose that m10 and m11 are exclusively specified as precursors of PGCs at the time of their birth from the M teloblast and that the M teloblast possesses a developmental program through which the sequence of mesodermal blast cell identities is determined.
