Cell colony formation induced by Xenopus egg extract as a marker for improvement of cloned blastocyst formation in the pig

Treatment with cytoplasmic extracts from Xenopus laevis eggs represents a potential tool for universal cellular reprogramming. However, the biochemical activity and quality of the extract vary from batch to batch. This study aimed to evaluate three different extract batches prepared by the same method based on the colony formation of cells after extract treatment, and subsequent in vitro cloning efficiency using treated cells as chromatin donors. Porcine fetal fibroblasts were treated with each batch of extract, and cultured in embryonic stem cell (ES) medium for 12 days. The number of forming colonies in treated cells was counted on Day 7 after extract treatment and significant variability was detected between different batches of extract. Similarly, when using cells from colonies at Days 7 to 8 after treatment for handmade cloning, increased blastocyst formation rates were observed after the cells were treated with a batch showing higher colony formation. In conclusion, assessment of cell colony formation may be used as selection marker for Xenopus egg extract used for pretreatmentof donor cells prior to cloning.