worms with eyes

David H. A. Fitch fitch at ACF2.NYU.EDU
Fri Sep 29 10:10:11 EST 1995


Yes, there are worms with eyespots (ocelli), such as the freeliving soil
Adenophorea of the genus Mermis.  Jay Burr (Dept. of Biol. Sci., Simon
Fraser Univ., Burnaby, BC  V5A 1S6 Canada) will ship them to you on ice if
you ask him (604-291-3496; burr at sfu.ca).  The species he works with is
Mermis nigrescens.

My rhetorical question to you is why bother sequencing pax-6 from these
worms?  We already know the gene must exist in those worms--a simple
phylogenetic deduction.  A much more interesting question would be the
origin of the pax-6 gene, not in nematodes, but in even lower metazoa (e.g.
hydra), or perhaps protozoa.  If we only look for the pax-6 gene in species
with photoreceptors, we may never understand the 'preadaptation(s)' that
allowed its (presumably) convergent use for photoreceptor development in
many different evolutionary lineages.

Of course, the interesting question about the Mermis pax-6 would not be
just what its sequence is, but how it is expressed (i.e., is it expressed
in a manner consistent with a specific role in eyespot development, or is
it expressed in Mermis in a manner similar to that of Caenorhabditis
vab-3/mab-18?).

Perhaps Walter Gehring would also like to know whether such work has
already been proposed by another group, such as the Burr or Emmons groups?

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