Jongseok Han

Establishment of a basic method for manipulating preantral follicles: effects of retrieval method on in vitro growth of preantral follicles and intrafollicular oocytes

The aim of this study was to establish a basic manipulation protocol of preantral follicles for deriving developmentally competent oocytes. Primary, early and late secondary follicles retrieved from the ovaries of 14-day-old F1 (C57BL/6 x DBA2) female mice mechanically or enzymatically were cultured singly and in vitro growth of the follicles and maturation of intrafollicular oocytes were subsequently monitored. A mechanical method retrieved more (p < 0.0001) follicles (339 +/- 48 vs. 202 +/- 28) than an enzymatic method. However, the enzymatic method collected more singly isolated follicles that could be provided for subsequent culture (102 +/- 26 vs. 202 +/- 28). When an enzymatic method was employed, early and late secondary follicles required 9 and 6 days for reaching the maximal incidence of the pseudoantral stage. However, primary follicles were not possible to develop into the pseudoantral stage. The optimal duration of oocyte maturation from the onset of follicle culture was 7 days and 5-7 days for early and late secondary follicles, respectively. A general decrease in oocyte diameter (65.2-65.53 microm vs. 75 microm) and zona thickness (5.41-5.74 microm vs. 7.76 microm) was detected in in vitro-derived compared with in vivo-derived matured oocytes. Pronuclear formation was detected in 86-94% of mature oocytes after parthenogenetic activation and no significant difference was detected among groups. These results showed that preantral follicles retrieved by an enzymatic method underwent step-by-step growth in vitro, which could yield mature oocytes.

Vertical organic light-emitting transistor showing a high current on/off ratio through dielectric encapsulation for the effective charge pathway

We demonstrate a vertical organic light emitting transistor (VOLET) showing a high current on/off ratio through dielectric encapsulation of a finger-like source electrode, which is placed between the bottom gate electrode and the top drain electrode. In such a VOLET configuration, the charge transport occurs largely from the source electrode to an underlying organic semiconductor (OSC) layer through the interface between the OSC and the gate insulator. Accordingly, the current leakage is greatly reduced and the transistor-type switching behavior with a high on/off current ratio is achieved. The on/off current ratio of our VOLET is about 100 times higher than that of an existing VOLET with no dielectric encapsulation. Numerical simulations of the spatial distributions of the charge densities and the charge pathways performed in the two different VOLET configurations are in good agreement with the experimental results. Our dielectric encapsulation approach will provide a versatile method for developing a ne...