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Morphogenetic Properties of Human Embryonic Cells: Aggregation of Dissociated Cells and Histogenesis in Cultured Aggregates

Extract: To test the hypothesis that the morphogenetic behavior of human embryonic cells can be characterized in vitro, human and mouse embryonic cells were compared by several variables which are thought to reflect morphogenetic cellular behavior. Trypsin-prepared cell suspensions of human (8–12 weeks) and mouse (13–18 days) embryonic organs were analyzed for (1) initial rate of aggregation, (2) aggregate size, (3) histogenesis in aggregates derived from a single organ, and (4) segregation of cells according to tissue type within mixed aggregates derived from different organs.The initial rate of aggregation followed strict first order kinetics for 40 min at 37°. The rate was identical (P > 0.05) for different cell types, for different ages of the same tissue, in the presence or absence of serum, and for mouse or human tissues. Aggregate size varied widely, regardless of the species, tissue type, or embryonic age. Thus, under the conditions employed, these variables are not worthwhile indices of morphogenetic cell behavior.On the other hand, histogenesis in human or mouse aggregates derived from a single organ was tissue specific. Mixed aggregates of human and mouse cells of the same organ behaved identically as aggregates derived from a single species, which indicates that species specificity is expressed less than tissue specificity. Regardless of species, cells from different organs within a single aggregate segregated from one another according to tissue type, which demonstrates that human embryonic cells show tissue-specific morphogenetic behavior.These findings confirm, for human embryonic cells, observations made with other species, that morphogenetic cell properties can be analyzed in vitro.Speculation: Demonstration that human embryonic cells maintain morphogenetic properties capable of analysis in a defined system in vitro opens the way for the direct study of human morphogenetic mechanisms and of possible genetic and environmental influences. Readily available normal or abnormal mouse embryonic cells could be used in combination with human embryonic cells to experimentally examine the pathogenesis of human developmental defects.