In article <Pine.ULT.3.91.960315014238.163B-100000 at essex.UCHSC.edu>
Teresa Binstock <binstoct at essex.UCHSC.edu> writes:
>1. Yeast's alpha-factor is functionally homologous to mammalian GnRH.
The term "functional homology" is an oxymoron. Evolutionary homology is
based upon structure, not function. For example, a bird's wing is not
homologous to a bat's because they have very different structures. On
the other hand, several jaw bones of cartilagenous fish are homologous to
mammalian inner ear ossicles--structural similarity not functional. Homology
is defined as a structural similarity than can be traced back phylogenetically
to a common ancestor. The correct term you are looking for in terms of functio
is "analogous."
> . GnRH and GnRH receptors are in the thymus and are expressed on
>T-cells; in other words, a mammalian functional-homologue of alpha-factor
>is present in the thymus and in T-cells.
>As many of us who work with neuropeptides/neurohoromones are aware, any
given peptide can exist in many places throughout the brain while having little
to no similar functions. Just because yeast Ste2/3 stimulates gonadotrope
release does not mean it has anything to do with GnRH. Many things stimulate
GnRH, among them: neuropeptide Y, Galanin, norepinephrine, some opiods,
glutamate, and many others. None of these are necessarily related. Besides,
you state that the yeast Ste2/3 are membrane spanning receptors. If so, then
how can they have any relationship to a blood-bound hormone?? Also, GnRH
receptors are G protein linked so stimulating gonadotropes by a yeast G
protein may have no more significance than stimulating gonadotropes with K+.
>4. Just as one class of yeast cells generally produces GnRH-like
>alpha-factor, so too do human T-cells produce GnRH.
Yes, human T-cells are immunoreactive for GnRH. So are C cells of the
sympathetic ganglia. GnRH receptors also are found in the hippocampus
and in the central gray of the midbrain. Again, just because the stuff is
there, may or may not have any relationship to its function in reproduction.
I have no problems really with the idea of a genetic component to mate
selection. Many pheromones are metabolites of several gonadal hormones.
Different genetic phenotypes may have these various metabolites in defferent
proportions which other individuals may find more or less attractive. This
differing phenotypes in pheromone constitution may also be revealed by the
MHC. So differeing MHC may be revealed in mate selection I cannot see how
it is causal. If for no other reason then I cannot see how a potential mate's
MHC is getting from her to my nose. Pheromones..yes, perfume...yes, but a
membrane bound MHC molecule??
I have been following this thread since its inception and I finally felt the
need to add my two cents. No offense intended, just trying to add to the
pool of information here and throw in an additional question or two regarding
your postulates.
--GS Fraley
"They say there's no devil, Jim...but there is!"
