Density distribution analysis of <i>In vivo</i> and <i>In vitro</i> colony forming cells in developing fetal liver

Abstract

Abstract The technique of buoyant density separation in gradients of Bovine Serum Albumin has been used to separate in vivo and in vitro colony forming cells (C.F.C.'s) in hemopoietic tissue of mouse fetal liver. Differences in the density distribution profiles showed that the in vivo and in vitro C.F.C.'s were different cell populations but the existence of an “out‐of‐phase” density association suggested that the two cell types were closely related. Complex density heterogeneity of both cell populations was observed at later stages of liver development and was similar to that seen in adult marrow. A homogeneous population of in vivo and in vitro C.F.C.'s occupied a very light density position in 10.5 day fetal liver. The subsequent development of density heterogeneity was associated with progressive acquisition of higher density subpopulations. Transfer experiments showed the capacity of the lightest density cells from the earliest stage of liver hemopoiesis, to generate higher density colony forming cells in the environment of the adult marrow. Density determined differences in seeding efficiency of in vivo C.F.C.'s were observed but no evidence was obtained for differences in either in vivo or in vitro colony morphology in different density subpopulations.