Use of a repetitive mouse B2 element to identify transplanted mouse cells in mouse-chick chimeras

Monitoring the migrations of cells during embryonic development requires a system in which cells can be identified in situ during locomotion. One prom ising system involves the generation of chimeras by transplanting mouse cel ls into chick embryos in ovo to exploit the wealth of mouse genetic variant s. The success of this technique relies on the ability to detect individual mouse cells in a chick environment with high specificity. The murine B2 fa mily of short interspersed elements is present in the mouse genome at copy numbers in excess of 10(5), whereas this sequence is absent in the chick ge nome based on hybridization techniques. This differential of five orders of magnitude produces signals in mouse cells that are easily identified, even in an environment that is predominantly chick. Thus, the B2 repeat probe i s highly effective for the purpose of identifying mouse cells in mouse-chic k chimeras. (C) 1999 Academic Press.