56 CARDIOMYOCYTES FOR THE STUDY OF DEDIFFERENTIATION IN BOVINE NUCLEAR TRANSFER

Abstract

Nuclear transfer facilitates the study of the dedifferentiation process of differentiated somatic cells. Cardiomyocytes are a good model of terminally differentiated cells showing a unique gene expression pattern of cardiac marker genes. The purpose of this study was to test bovine cardiomyocytes as donor cells in nuclear transfer. Cardiomyocytes were isolated from fetal heart muscle (3–5 months of gestation), which were obtained at the abbatoir and immediately perfused with cold Custodiol (Dr. Franz Köhler Chemie, Germany) to reduce metabolism and protect the cells against ischaemia. Subsequently, hearts were perfused with collagenase in Krebs-Henseleit buffer (KHB) to dissociate the tissue and isolate single elongated, contractile cells. For nuclear transfer and fusion the cardiomyocytes were rounded up by exposure to increasing calcium concentrations (2.5–200 μM) in the culture medium before the cells were incubated in suspension for 46–48 hours in MEM medium plus 10% FCS. Nuclear transfer was performed as described earlier (Lucas-Hahn et al., 2002, Theriogenology 57, 433). As a control, adult female fibroblasts were employed. Fusion rate, cleavage (day 3 of in vitro culture) and development up to the morula/blastocyst (day 7 of in vitro culture) were recorded and statistically analysed with Student’s t-test. A total of 243 nuclear transfer complexes with cardiomyocytes and 127 with fibroblasts were produced. Fusion rates for cardiomyocyte complexes were significantly (P < 0.001) lower (28.8%) compared to fibroblasts (84.3%). Cleavage rates were 48.1% for cardiomyocytes and 62.8% for the fibroblast-derived embryos. The developmental capacity to the morula/blastocyst was significantly (P < 0.01) reduced for cardiomyocyte (9.4%) compared with the fibroblast-derived (32.4%) reconstructed embryos. Most of the Day 7 embryos were frozen for investigation of gene expression patterns of cardiac marker genes. Staining with Hoechst 33342 for counting total cell numbers revealed that 87.3 ± 20.9 blastocysts were derived from fibroblasts and 100 blastocysts from cardiomyocytes. These results indicate that nuclear transfer with terminally differentiated cardiomyocytes is possible, although with reduced rates. Studies are underway to analyze the gene expression of cardiac marker genes in reconstructed embryos to gain insight into dedifferentiation after nuclear transfer using cardiomyocytes as a model. This study was supported by Deutsche Forschungsgemeinschaft (DFG; Ni 256/16-1)