In article <32f0j3$cg3 at agate.berkeley.edu>, frauwirt at mendel.Berkeley.EDU
(Ken Frauwirth (BioKen)) writes:
The example discussed above involving H-Y-directed MHC restricted
male-to-female graft rejection was also discussed in a rather "old" but
very provokative review in Immunological Reviews published in1977. The
author was Susumo Ohno. His contention was that the H-Y antigen is a
Y-chromosome encoded protein that is synthesized and secreted by most
nucleated Y chromosome bearing cells. Interestingly, cell-surface class I
MHC molecules serve as acceptors (receptors?) for cell-free H-Y, and
supposedly this complex then directs or somehow contributes to the sexual
differentiation of undifferentiated (?) embryonic gonads into what we
consider male sexual oragns. Thus, Ohno referred to H-Y/MHC as
organogenesis-directing proteins. What is interesting is that in birds
the H-Y antigen and by extension the Y chromosome is present in females
and not in males, unlike in mammals. Organ cultures of undifferentiated
H-Y-negative (male) bird embryos with bovine H-Y bearing (and also
MHC-positive) cells or extracts caused the change in the genetic
programming of otherwise male embryo to develop into a female bird
features (I suppose). This further extended support to Ohno's hypothesis
(at least in Ohno's mind) that MHC molecules are the
organopgenesis-directing proteins. It's been a while since I read this
review (1980), so there are likely to be some lapses in my recollection of
the details. I would appreciate knowing comments, ideas or thoughts of
the fellow immunologists / developmental biologists in this connection.
