Analysis of Cellular Mosaicism in a Transgenic Mouse by Histological In Situ Hybridization: (Transgenic mice/mosaics/cell lineage/in situ hybridization).

One of the transgenic mice carrying a chicken δ-crystallin gene was found to be mosaic with regard to the distribution of the exogenous gene. Taking advantage of the exogenous DNA sequences as a cell lineage marker detectable by histological in situ hybridization technique, we studied cellular mosaicism in mouse 7-5. This mouse carried the exogenous gene in 20-40% of its cells, probably reflecting chromosomal integration of the exogenous DNA which occurred in a blastomere of around the 4-cell stage. The cells carrying the gene contributed to virtually any kind of tissue and their distribution varied from one tissue to another. For instance, in the neural retina, gene-positive cells formed columns several cells wide, indicating that migration of the cells derived from the founder cells is mainly along the radial axis. However, in other tissues we examined, clusters of the marked cells were less obvious, indicating the occurrence of extensive cell mixing during histogenesis. Thus, mosaic analysis of cell lineage in mouse ontogeny appears meaningful in early developmental stages or when clonal outgrowth takes place in a tissue.