Expression of bone marrow stromal cell specific antigen during murine development:Its expression in embryonic hematopoietic tissues as well as in other developing tissues

Monoclonal antibody R4-A9 demonstrated specificity for a cell surface antigen of stromal cells in murine bone marrow and spleen. In order to Identify patterns of expression that may elucidate the potential role of R4-A9 antigen, the developmental expression of this antigen in mouse embryos from 8 days post-coitum to 5 days post-partum was investigated by immunohistochemistry. At an early developmental stage, weak staining for R4-A9 antigen could be detected in the yolk sac. At later stages, strong staining of this antigen was detected predominantly in the embryonic liver, the main site of embryonic hematopoiesis. However, concomitant with the decreased staining in the liver, increased expression of this antigen was observed in bone marrow and spleen. Therefore, the changes in expression in those hematopofetic tissues suggest that its expression is coordinately regulated during the developmental stage of the sites of embryonic hematopoiesis. Compared with the distribution of R4-A9 antigen in adult tissues as previously reported, the expression of this antigen in fetal tissues was more widespread during the period of organogenesis, and was most abundant in other developing tissues, including the heart, skin, and lung. In contrast, fetal expression detected in hematopoietic and other developing tissues was lost after birth. These results taken together show a marked gradient of R4-A9 antigen expression, with the highest level at the peak of organ development, raising the possibility that this molecule may act as a growth/differentiation factor both in hematopoietic and other developing tissues in a fetus.