Biochemical characterization of the adhesion-related differentiation antigen XT-1

The XT-1-molecule, an adhesion-related differentiation antigen of male mouse germ cells, is a 34 000 Mr glycoprotein with major charge isomer at pI 5.1 and is an integral component of the cell membrane. On large late pachytene spermatocyte, the molecule is present at a concentration of 2.5 X 10(3) molecules micron-2, which approximates HLA/ABC concentration on lymphocytes. By comparing the reactivity of four anti-XT-1 monoclonal antibodies, three of which elicit germ cell-germ cell adhesion, we have defined two distinct surface regions of the XT-1-molecule. The relationship of the XT-1-molecule with other known adhesion-related molecules and testicular antigens is discussed.