Developmental expression of the mouse c-rel proto-oncogene in hematopoietic organs.

We have studied the expression of the c-rel proto-oncogene during mouse embryonic development and adult animals using in situ hybridization and immunocytochemical analysis. c-rel transcripts were detected late in development with an expression pattern that parallels the emergence and diversification of hematopoietic cells. In the embryo, c-rel is expressed first in the mesoderm-derived hematopoietic cells of the liver and later also in other hematopoietic tissues such as thymus and spleen. This correlation between c-rel expression and places of hematopoietic infiltration is conserved in the postnatal period, with expression of c-rel mRNA in the medullary region of the thymus and in splenic B cell areas, including the marginal zone and the outer region of the periarterial sheath. High levels of c-rel transcripts were also detected in the splenic germinal centers, lymph nodes and Peyer's patches. Using double immunofluorescence and cell preparations from different embryonic and adult hematopoietic organs, we have defined the pattern and cell types of c-rel expression in different hematopoietic cell lineages and in the stromal cell content of the thymus. By using electrophoretic mobility shift assays, we have also correlated c-Rel expression in spleen with kappa B-binding activity in the form of c-Rel/p50 and c-Rel/p52 heterodimers. The timing and pattern of expression of the c-rel proto-oncogene in the different cell lineages suggest that temporally regulated changes in c-Rel expression may be required for vertebrate hematopoiesis.