title: Efficient production of chimeric mice from embryonic stem cells injected into 4- to 8-cell and blastocyst embryos.
abstract: BACKGROUND
  Production of chimeric mice is a useful tool for the elucidation of gene function. After successful isolation of embryonic stem (ES) cell lines, there are many methods for producing chimeras, including co-culture with the embryos, microinjection of the ES cells into pre-implantation embryos, and use of tetraploid embryos to generate the full ES-derived transgenic mice. Here, we aimed to generate the transgenic ES cell line, compare the production efficiency of chimeric mice and its proportion to yield the male chimeric mice by microinjected ES cells into 4- to 8-cell and blastocysts embryos with the application of Piezo-Micromanipulator (PMM), and trace the fate of the injected ES cells.
  
  
  RESULTS
  We successfully generated a transgenic ES cell line and proved that this cell line still maintained pluripotency. Although we achieved a satisfactory chimeric mice rate, there was no significant difference in the production of chimeric mice using the two different methods, but the proportion of the male chimeric mice in the 4- to 8-cell group was higher than in the blastocyst group. We also found that there was no tendency for ES cells to aggregate into the inner cell mass using in vitro culture of the chimeric embryos, indicating that they aggregated randomly.
  
  
  CONCLUSIONS
  These results showed that the PMM method is a convenient way to generate chimeric mice and microinjection of ES cells into 4- to 8-cell embryos can increase the chance of yielding male chimeras compared to the blastocyst injection. These results provide useful data in transgenic research mediated by ES cells.
authors.affiliation: Agricultural Animal Genomics and Molecular Breeding Key Lab of Guangdong, Province, College of Animal Science, South China Agricultural University, Guangzhou, 510642, China. sqzhang@scau.edu.cn.
authors.forename: Minhua
authors.initials: M
authors.lastname: Hu
authors.forename: Hengxi
authors.initials: H
authors.lastname: Wei
authors.forename: Jingfeng
authors.initials: J
authors.lastname: Zhang
authors.forename: Yinshan
authors.initials: Y
authors.lastname: Bai
authors.forename: Fenglei
authors.initials: F
authors.lastname: Gao
authors.forename: Li
authors.initials: L
authors.lastname: Li
authors.forename: Shouquan
authors.initials: S
authors.lastname: Zhang