Cell contacts and sorting out in vivo: the behaviour of some embryonic tissues implanted into the developing chick wing.

The interaction of cells from embryonic liver, neural retina and mesonephros with cells from limb-bud mesenchyme has been investigated in vivo by grafting these tissues into the developing chick wing-bud. The implanted cells were in all cases from quail tissue which can be recognized histologically. As embryonic liver and neural tube are tissues that sort externally to limb-bud mesenchyme in mixed aggregates, it would be expected, from a differential adhesiveness hypothesis, that heterotypic adhesions along the borders of graft and host would be favoured over cell-cell adhesions in the graft. No morphological signs of this were evident: rather the grafted cells maximized like-like contacts. The cells of the grafts, including those from control mesenchyme, did not invade into the wing. The results were the same irrespective of whether the graft was a fragment of tissue or a pellet of reaggregated cells. This supports the idea that cells within tissues are not actively moving around and also provides controls for assaying the invasiveness of other cell types, such as malignant cells into the wing.