Science: Self-Organizing Cells

Life among higher animals starts with a single fertilized cell. In a few days or weeks, it divides into billions or trillions of cells of different kinds, all arranged to help each other in the difficult business of life. How does this miracle happen? Scientists agree that the original cell contains genetic instructions that control the development of the embryo, but they are not sure how these instructions are brought to bear. One theory is that some central part of the embryo issues orders that make each tissue and organ develop. Another is that the multiplying cells, each of which has in its nucleus a set of instructions, organize themselves independently of any cellular high command.

This second theory has considerable evidence to support it, but in the Proceedings of the National Academy of Sciences, Dr. Paul Weiss and Dr. A. Cecil Taylor, both of the Rockefeller Institute, describe experiments to prove its validity beyond doubt. Weiss and Taylor took samples of different tissues, each containing many kinds of cells, from chick embryos 8 to 14 days old. They minced each sample finely and treated it with enzymes that made its cells separate without killing them. Straining the soupy stuff through a fine nylon filter, they removed all remaining cell clumps. Then they concentrated the isolated, mixed-up cells to a soft mush and deposited specks of it on the saclike “chorio-allantoic” membrane enclosing eight-day-old chick embryos.

After the bits of mush had been incubated for nine days, their jumbled cells arranged themselves in pretty good order. Getting nourishment from the blood supply of the membrane, they started to grow again. Kidney cells grew into a tiny kidney that seemed to be trying to purify the blood of a nonexistent chick. Liver cells developed into a miniature liver one-fifth of an inch long and apparently able to secrete bile to digest a chick’s food. The skin cells arranged themselves into a sheet, produced sprouting feathers about one-tenth of an inch long.

Weiss and Taylor do not know how a mush of isolated cells manages to rally and reassume its proper job in a developing embryo. But they are sure that no special guidance can come from the blood-supplying membrane, which acts the same in all cases. Therefore they say the individual cells of a partly formed organ must contain information that tells them what is expected of them. When they are separated and jumbled into a mush, they can reorganize and try to complete as best they can their part of the master plan of the vanished embryo.