Spleen Colonies in Mice: Karyotypic Evidence of Multiple Colonies from Single Cells

Abstract

IF mice are heavily irradiated, injected intravenously with an appropriate suspension of haematopoietic cells and killed 1–2 weeks later, prominent nodules can be seen on the surface of the spleen¹. Microscopically, the nodules are foci of intense cellular proliferation and are commonly termed colonies. The linear relationship between the numbers of cells injected and the numbers of colonies observed¹ and the exponential reduction of numbers of colonies with increasing dose when irradiated cells are injected^1,2 suggested that each colony could be a clone of cells derived from a single progenitor cell in the inoculum¹. Becker et al.³ provided direct evidence of clonal origin by irradiating recipients before and after injection, then finding individual colonies in which most mitotic cells had the same uniquely abnormal karyotype. This result has been supported by other experiments using marker chromosomes^4–6. We now offer evidence that a single cell from the donor may give rise to two, three or four colonies in the irradiated recipient.