Pratt, C.,Crippen, Craig Alexander.2009-03-252009-03-2519971997Source: Masters Abstracts International, Volume: 36-04, page: 1026.9780612263123http://hdl.handle.net/10393/9528http://dx.doi.org/10.20381/ruor-7843RAR$\beta$ has been shown to be expressed in the developing heart at the 8 somite stage. Differentiation of EC cells with DMSO produces a mixture of embryonic cardiac, skeletal, endodermal and other mesodermal derivatives. The RAR$\beta$-2 isoform is predominantly expressed in the differentiated cardiac muscle cells. RT-PCR with isoform specific primers has been used to identify RAR$\beta$-2 as the predominant isoform. These results show, that like RA-treated EC cells, expression of the RAR$\beta$-2 isoform in DMSO differentiated P19 cells predominates. Stable transformants of the RARE$\beta$-2-CAT reporter gene construct were pooled and differentiated with either RA or DMSO. The results obtained demonstrate that RA induced CAT activities increased to a maximum of 188 fold by day 3. The increase in RAR$\beta$-2 mRNA levels was not due to another enhancer element as evidenced by nuclear run-on analysis. RAR$\beta$2 mRNA levels seem to be regulated by a post-transcriptional mechanism. The stability of the DMSO induced RAR$\beta$2 message was determined using the transcriptional inhibitor actimomycin-D on day 4 and 7 of differentiation. The half life of the message was found to be approximately equal on both days. We postulate that stabilization of the message occurs at an earlier time point, and that accumulation of the message occurs up until Day 7 of differentiation. Simultaneous administration of RA and DMSO to aggregating P19 cells blocked the up-regulation of Brachyury expression in these cells. No beating cardiac muscle was formed, however neuroectoderm was found to be the predominant cell type, indicating that the DMSO differentiating effect was usurped by the presence of RA. (Abstract shortened by UMI.)112 p.Biology, Molecular.Thesis