Effects of molecular size fraction of DOM on photodegradation of aqueous methylmercury.

This study investigated the photodegradation kinetics of MeHg in the presence of various size fractions of dissolved organic matter (DOM) with MW < 3.5 kDa, 3.5 < MW < 10 kDa, and MW > 10 kDa. The DOM fraction with MW < 3.5 kDa was most effective in MeHg photodegradation. Increasing UV intensity resulted in the increase of photodegradation rate of the MeHg in all size of DOM fractions. Higher rates of MeHg degradation was observed at higher pH. For the portion of MW < 3.5 kDa, the photodegradation rate of MeHg increased with increasing DOM concentration, indicating that radicals such as singlet oxygen (1O2) radicals can be effectively produced by DOM. At higher portion of MW > 3.5 kDa, the inhibition of MeHg degradation was observed due to the effect of DOM photo-attenuation. Our result indicates that radical mediated reaction is the main mechanism of photodegradation of MeHg especially in the presence of MW < 3.5 kDa. Our results imply that the smaller molecular weight fraction (MW < 3.5 kDa) of DOM mainly increased the photodegradation rate of MeHg.

Development of a decoy immunization strategy to identify cell-surface molecules expressed on undifferentiated human embryonic stem cells.

Little is known about the cell-surface molecules that are related to the undifferentiated and pluripotent state of human embryonic stem cells (hESCs). Here, we generated a panel of murine monoclonal antibodies (MAb) against undifferentiated hESCs by a modification of a previously described decoy immunization strategy. H9 hESCs were differentiated in the presence of retinoic acid and used as a decoy immunogen. Twelve Balb/c mice were immunized in the right hind footpads with differentiated H9 cells and in the left hind footpads with undifferentiated H9 cells. After immunization, the left popliteal lymph node cells were collected and were fused with mouse myeloma cells. The fusion resulted in 79 hybridomas secreting MAbs that bound to the undifferentiated H9 cells as shown by flow cytometric analysis. Of these, 70 MAbs bound to the undifferentiated H9 cells, but only weakly or not at all to the differentiated H9 cells. We characterized 37 MAbs (32 IgGs, 5 IgMs) recognizing surface molecules that were down-regulated during embryoid body cell formation. One of the MAbs, L125-C2, was confirmed to immunoprecipitate CD9, previously known as a surface molecule on the undifferentiated hESCs. To investigate the relationship between the MAbs and hESC-specific antibodies, two representative MAbs, viz., L125-C2 and 291-D4, were selected and studied by multi-color flow cytometric analysis. This showed that more than 60% of L125-C2- and 291-D4-positive cells were also positive for the expression of hESC-specific surface molecules such as SSEA3, SSEA4, TRA-1-60, and TRA-1-81, indicating the close relationship between the two MAbs and the hESC-specific surface molecules. Our results suggest that the decoy immunization strategy is an efficient method for isolating a panel of MAbs against undifferentiated hESCs, and that the generated MAbs should be useful for studying the surface molecules on hESCs in the pluripotent and undifferentiated state.