SURFACE TENSIONS OF EMBRYONIC-TISSUES PREDICT THEIR MUTUAL ENVELOPMENT BEHAVIOR

During embryonic development, certain tissues stream to their destinat ions by liquidlike spreading movements, According to the 'differential adhesion hypothesis', these movements are guided by cell-adhesion-gen erated tissue surface tensions (sigma s), operating in the same manner as surface tensions do in the mutual spreading behavior of immiscible liquids, among which the liquid of lower surface tension is always th e one that spreads over its partner, In order to conduct a direct phys ical test of the 'differential adhesion hypothesis', we have measured the sigma s of aggregates of five chick embryonic tissues, using a par allel plate compression apparatus specifically designed for this purpo se, and compared the measured values with these tissues' mutual spread ing behaviors, We show that aggregates of each of these tissues behave for a time as elasticoviscous liquids with characteristic surface ten sion values, Chick embryonic limb bud mesoderm (sigma = 20.1 dyne/cm) is enveloped by pigmented epithelium (sigma = 12.6 dyne/cm) which, in turn, is enveloped by heart (sigma = 8.5 dyne/cm) which, in turn, is e nveloped by liver (sigma = 4.6 dyne/cm) which, in turn, is enveloped b y neural retina (sigma = 1.6 dyne/cm), Thus, as predicted, the tissues ' surface tension values fall in the precise sequence required to acco unt for their mutual envelopment behavior.