Outline history of cell sorting discoveries and debates
H. V. Wilson
(of UNC) notices that living sponge tissues become disorganized when in poor culture
conditions, but can reorganize if conditions are improved. (Plus, he must have known about gemmules in
fresh water sponges)
Wilson tries mixing physically dissociated cells from different species of salt water sponges; (Explicitly
hoping to make chimeric sponges that could be economically useful) But discovers rapid sorting-out by
species, into separate masses of cells.
repeats sponge dissociation, using kinds of sponges that have larger cells, that are easier to
watch and distinguish. He proposes that rearrangement according to differentiated cell type is the means by
which functional individuals are re-formed.
Wilson dissociated cells of soft corals (Phylum Cnideria), and these also re-form functional organisms.
In this paper, Wilson concludes that it is more likely that cells are changing from one differentiated cell type
to another, instead of rearranging (contrary to Huxley's proposal).
Wilson later decides that maybe the new sponges are formed by cells that had previously not been
differentiated (archeocytes) and publishes papers describing cells that seem to be in intermediate stages of
uses slightly acidic and low calcium water to cause early embryos of salamanders and
frogs to separate into their individual cells, which he then mixes randomly. In contrast to what happened in
sponges, cells of different species of amphibian DO NOT sort out from each other; therefore, their color
differences can be used to track cell fates.
Holtreter (chemically) dissociates amphibian cells of mesoderm, endoderm, neural ectoderm, skin ectoderm,
and other embryonic subdivisions, mixes different combinations of these into random mixtures, and
discovers that cells sort out by "germ layer" (for example, ectoderm sorts out from ectoderm, and skin
ectoderm sorts out from neural ectoderm), but that instead of sorting into different piles of cells (as did cells
of different species of sponges), the amphibian cells sort out with one kind of cell forming an inner core,
surrounded by cells of the other kind of cell.
Holtfreter concludes that sorting is caused by differences in "tissue affinity", by which he meant to include
not just selective adhesiveness but also differences in chemotaxis, or any other behavior or property that
could rearrange cells. But almost everyone interprets his paper to have proposed differences in adhesiveness,
only. He resented that.
Townes and Holtfreter publish a classic (long!) paper in J. Experimental Zoology, with a few photographs,
and lots of drawings of what happens for every different random mixture of dissociated amphibian cells of
different germ layers and other embryonic subdivisions. This was Townes MD/PhD thesis research, and took
him nine years to do!