Turing in 1954 wrote his paper on Tessellation, the patterns we often see on animals and plants. The question is; is Turing’s approach the right way to understand these patterns? Namely Turing proposed a hypothetical method whereby cells communicate with one another and that this communications is akin to flows of some, as of 1954, yet to be defined chemical substance or substances. Depending on the concentrations of these substances the cells then turned, for example, black or white, as in a zebra, and that this flow being coordinated in some manner yielded a pattern, not just a mass of black and white hairs.
Turing hypothesized, for example, that there may be two
controlling molecules in varying densities and if one molecule was denser than
the other it would turn on white and otherwise it would turn on black. But
Turing said more, that the flow of the molecular density was not just random
but that cells somehow participated in a distributed manner so that the
densities flowed as waves, with peaks and valleys. Thus the Zebra stripes were
a reflection of this flow. When the black molecule was at a high the hairs were
black and when the white ones were high the hairs were white. The net result
looked like waves of white and black.
Now a second model that has become of recent popularity is
the explanation for the Calico Cat.
The explanation for this is dramatically different. Here
Calico Cats are all female. The way it works is the epigenetic silencing of one
of the X chromosomes. This allegedly is totally done at random. As seen above
this of course is hardly the case. If every hair cell were random then we would
expect to have a blend of two or more colors and not the patterns that we have
above. This means that if this is epigenetic that spatially there is some
mechanism that is not totally random. There is some form of cell to cell memory
and cell to cell thresholding. Namely the hair stays black, brown or white for
some spatial period and then switches to the other state. That is the Turing Tessellation
effect. What then does that?
Now consider a third example; the daylily. We show a typical
example below. Here we have an eyezone, the dark red around the milled and we
even have red on the edges. This is again a tessellation type as described by
Turing. There are areas where there is dark red and areas where there is light
red or pink. Is this epigenetic, genetic, or a Turing tessellation.
In fact daylilies can show dramatic patterning as they get
more sophisticated. The above is a simple form of patterning, a wave of dark
and light red.
Thus what enables these patterns? In epigenetics of cats, it
is the turning on and off of one X chromosome, but not really randomly, so
there must be some mechanism that selects which one gets wrapped in an lncRNA
and which does not. What is that activator? Not yet known.
In daylilies we know that color is driven by anthocyanin
production. More of one and we get one color and more of the other another
color. We also know that certain proteins, gene products, act as catalysts
facilitating one anthocyanin path or another. Thus if one gene is producing
then it may drive up pone anthocyanin or another. What turns these genes on and
off? Perhaps epigenetic methylation as we see in many other examples. But that
begs the question of what causes the methylation? It appears to be a pattern
like that of the Calico Cat.
Thus the Turing Tessellation is a process that explains
these patterns but the facilitator of that process, the extracellular or
intercellular molecule is not known. Thus we have an interesting area of
exploration. In addition we see similar effects in the field of metastatic
cancers, where we get clusters of metastatic cells, and not just random
aberrant one.
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