Lawrence L. Wiseman

Self vs nonself in tissue assembly: Correlated changes in recognition behavior and tissue cohesiveness☆

Abstract Vertebrate embryonic cell populations of unlike kind, when combined in vitro, typically spread around and sort out from one another in combination-specific patterns, whereas like cell populations merely coalesce. These differing responses to self and nonself constitute one form of morphogenetic self-recognition behavior. Prolonged shaker-flask culturing and dissociation and reaggregation of embryonic chick heart tissue were both previously shown to reverse the tissues spreading behavior with liver. Here, we show that these treatments simultaneously initiate, in heart tissue, a “foreign” spreading reaction toward untreated heart. Moreover, the direction of this heart-heart spreading can be deduced from the change in direction of heart-liver spreading. This suggests that certain properties of heart tissue participate in the determination of both the foreign- and the self-recognition behaviors studied here. The differential adhesion hypothesis postulates that these properties are the intensities of tissue cohesion, with less cohesive tissues enveloping more cohesive ones. If so, our observations imply that heart fragments precultured 1 2 day should be more cohesive than 1 2 - day precultured heart reaggregates, but less cohesive than heart fragments precultured 2 1 2 days. With our centrifugation assay, in which relative tissue cohesiveness is assessed by the relative roundness of centrifuged aggregates at shape equilibrium, we confirm this prediction.

Algophagus pennsylvanicus-A new species of Hyadesidae from water-filled treeholes

ABSTRACT A new species of Hyadesidae, Algophagus pennsylvanicus, is established based on specimens collected from water-filled treeholes in Pennsylvania. A key to the species of the subfamily Algophaginae is provided.

Can the differential adhesion hypothesis explain how an aggregate of strongly cohesive cells can be penetrated by more weakly cohesive cells

Abstract The differential adhesion hypothesis, as advanced by Steinberg [Steinberg (1963) . Science 14, 401–408; (1964). In “Cellular Membranes in Development” (M. Locke, ed.), pp. 321–366. Academic Press, New York; (1970). J. Exp. Zool. 173, 395–434; (1975). J. Theor. Biol. 55, 431–443], predicts that, in an aggregate composed of cells from two different kinds of tissue, more cohesive cells will tend to become enveloped or covered by an external layer of less cohesive cells. Both embryonic chick heart and liver cells sorted out externally in every case to embryonic limb bud cells and are, therefore, according to the hypothesis, less cohesive than limb bud cells. However, when a few of the less cohesive heart or liver cells were seeded onto the surfaces of aggregates of the more cohesive limb bud cells, about half of the less cohesive cells assumed subsurface positions within several days of culture. The penetration of an aggregate of cohesive cells by less cohesive cells may indicate that the differential adhesion hypothesis will require modification for universal applicability to the cell level.