55 LIVE PLASMA MEMBRANE ANALYSIS OF EARLY APOPTOTIC CELL DEATH IN PORCINE ADULT DERMAL FIBROBLASTS PRIOR TO SOMATIC CELL CLONING

Abstract

The aim of our study was to determine the in vitro developmental capability of porcine nuclear-transferred (NT) embryos reconstructed with adult dermal fibroblast cells, which had been analyzed for apoptosis by live plasma membrane fluorescent labelling. Frozen/thawed fibroblasts, which had been in vitro cultured to confluency, were used for analysis. To detect the early apoptotic changes in the plasma membrane involving the externalization of phosphatidylserine molecules and the subsequent loss of lipid composition asymmetry, the fibroblasts were tagged using a conjugate of annexinV with enhanced green fluorescent protein (eGFP). In the somatic cell cloning procedure, enucleated in vitro-matured oocytes were reconstituted with non-apoptotic dermal fibroblast cell nuclei. Afterwards, NT-derived oocytes were stimulated with a combination of electrical and chemical activation. Simultaneous fusion and electrical activation were induced by application of two successive DC pulses of 1.2 kV cm^–1 for 60 ¼s. A two-step chemical activation procedure was initiated after a 1.5–2 h delay. The cybrids were exposed to 15 µm calcium ionomycin for 5 to 7 min and then incubated in the culture medium supplemented with 10 µg mL^–1 cycloheximide for 3 h. Reconstructed embryos were in vitro cultured in NCSU-23 medium for 6–7 days. Fluorescence analysis of the adult dermal fibroblast cells revealed that a relatively high proportion of donor cells exhibited proapoptotic changes in the plasma membrane. The percentage of late apoptotic cells with advanced morphological changes did not exceed 30%. Moreover, an extremely low rate (ranging from 0 to 2%) of early apoptotic cells, with a morphologically normal, i.e., smooth (non-corrugated) and intact (non-blebbing), plasmolemma but which emitted the green eGFP-derived chemiluminescence, was detected. A total of 219 enucleated oocytes were subjected to reconstruction and 185/219 (84.5%) were successfully fused with non-apoptotic nuclear donor cells. Out of 185 cultured NT embryos, 108 (58.4%) cleaved. The frequencies of cloned embryos, that reached the morula and blastocyst stages, were 84/185 (45.4%) and 26/185 (14.0%), respectively. In conclusion, annexin V-eGFP is a sensitive method able to detect the early phases of apoptosis in cultured adult dermal fibroblast cells, because it identified that very small proportion of morphologically normal cells (without shrinkage of the plasmolemma) that also emitted the annexin V-eGFP-derived biochemiluminescence. Nonetheless, the probability of their random erroneous selection for somatic cell cloning appears to be extremely low. It was also found that the preimplantation developmental potential of NT embryos originating from non-apoptotic adult dermal fibroblast cells is relatively high.

This work was supported by the Scientific Net of Animal Reproduction Biotechnology.