The identification of testis-organizing H-Y antigen of man as hydrophobic polymers of a M.W. 18,000 subunit.
Mammalian testicular organogenesis initiated by male specific but ubiquitously expressed H-Y antigen can serve as the model of all other organogenesis. However, in order to understand the precise organizational role this plasma membrane antigen plays, it is essential to characterize H-Y antigen as a distinct molecular entity which would be extremely difficult if we have to deal directly with native H-Y antigen residing on the plasma membrane. Fortunately, we have previously found that in the mutational absence of H-Y antigen's proposed anchorage site, B2m (-), HLA (-) Daudi human male Burkitt lymphoma cells are incapable of stably maintaining H-Y antigen on their plasma membrane. B2m (-), HLA (-) Daudi human male Burkitt lymphoma cells excreted a group of several proteins that shared the three distinctive characteristics in common; their extreme hydrophobicity, their tendency beyond saturation to form irreversibly water insoluble aggregates by extensive interchain disulfide bridges, and their conspicuously slower turn over rates compared to other Daudi excreted proteins. After disruption of disulfide bridges, proteins of this group were resolved into at least seven distinct subunits of different molecular weights. M.W. 18,000 subunit of testis-organizing H-Y antigen was the smallest of the above. At the saturation, 0.7 to 0.9 microgram/ml of solubilized H-Y antigen uniformly assumed the form of very large aggregates of M.W. greater than 280,000. In more dilute solutions, however, the existence in much smaller trimeric and tetrameric forms of H-Y antigen was indicated. As these irreversibly water insoluble precipitates still retained H-Y antigenic determinants, they can be used in the future for the purification of H-Y antibody. When bound specifically to H-Y receptor sites residing on the plasma membrane of BFO cells, polymeric Daudi H-Y antigen apparently underwent the depolymerization process, thus, yielding the monomeric form of M.W. 18,000. It is likely that these six or more Daudi excreted proteins that shared the three distinct characteristics with testis-organizing H-Y antigen are also involved in various specific organogenesis.