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BACKGROUND: Key point for subculture of human embryonic stem cells (hESCs) is to inhibit spontaneous differentiation and make sure totipotency of cells. Although mouse embryonic fibroblasts (MEF) or human foreskin fibroblasts (HFF) used as the feeder layer can maintain undifferentiated state of embryonic stem cells, cell clone is still imperfect and parallel arranged. OBJECTIVE: To establish mixed feeder layer of mouse embryonic fibroblasts plus human foreskin fibroblasts and to observe the hESCs growth.DESIGN: Multi-sample observation and comparison.SETTING: Medical Center of Reproduction, the Affiliated Hospital of Hainan Medical College. MATERIALS: This study was performed at the Medical Center of Reproduction, the Affiliated Hospital of Hainan Medical College from April 2006 to July 2007. Foreskin was derived from the children who underwent circumcision and came from Urinary Surgery, the Affiliated Hospital of Haihan Medical College. The children's family members provided the informed consent, and the experiment received confirmed consent from the local ethic committee. hESCs line HN-1 was separated from human blastula. Eleven 12.5-14.5-day-old fetal mice of clean grade were selected in this study. The experimental animals were disposed according to ethical criteria. METHODS: Heads, four extremities, and viscera were removed from fetal mice under anesthesia. Subsequently, cell suspension was prepared using routine trypsinase digestion and inoculated. When cells were cultured in confluent monolayer, some primary cells were frozen, processed with mitocin-C for 2.0-3.0 hours, and inoculated based on the density of 1×108 L-1 in gelatin-coated dish, I.e., MEF feeder layer. The HFF separation and culture and the preparation of HFF feeder layer were the same as above-mentioned processing. In addition, the two fibroblasts were respectively counted and mixed together according to the ratios of 1∶0, 3∶1, 1∶1, 1∶3, and 0:1. And then, the mixture was inoculated based on the density of 1×108 L-1 in gelatin-coated dish, I.e., mixed feeder layer. The growth of subcultured hESCs in vitro was observed in three different feeder layers, and hESCs in the mixed feeder layer underwent alkaline phosphatase test, OCT-4 expression immunohistochemical measurement, and OCT-4 and telomerase mRNA expression RT-PCR detection. Finally, differentiation in vitro of hESCs was observed after removing the feeder layer.MAIN OUTCOME MEASURES: ① Growth of hESCs in the three different feeder layers; ② Growth of hESCs in the mixed feeder layer based on different mixed ratios; ③ undifferentiated state of hESCs in the mixed feeder layer; ④ differentiation in vitro.RESULTS: ① hESCs clone in the MEF and HFF feeder layers was thin and flat and imperfect, but hESCs clone in the mixed feeder layer was perfect and thick and solid. Apparently, the clone form in the mixed feeder layer was superior to MEF and HFF feeder layers. ② When MEF and HFF was mixed together according to the ratio of 1∶1, hESCs grew in apparent accumulation; clone border was clear; eminentia was apparent and perfect. However, there were no changes according to the ratio of 1∶3. The ratio of 1∶1 was superior to the ratios of 1∶0, 3∶1, and 0∶1. ③ Alkaline phosphatase staining and OCT-4 antigen expression were strongly positive. Specific straps of OCT-4 and telomerase mRNA expression were observed at 200-300 bp and 300-400 bp, respectively. ④ Embryoid bodies were formed. hESCs could differentiate into multi-morphological cells after attachment.CONCLUSION: ① The mixed feeder layer may well support in vitro subculture of hESCs to acquire excellent clone form compared to MEF or HFF feeder layer. ② The mixture of MEF and HFF has excellent effect according to the ratio of 1∶1.