The E2A gene products, E12 and E47, are required for proper B cell dev
elopment. Mice lacking the E2A gene products generate only a very smal
l number of 8220(+) cells, which lack immunoglobulin DJ(H) rearrangeme
nts. We have now generated mice expressing either E12 or E47. B cell d
evelopment in mice expressing E12 but lacking E47 is perturbed at the
pro-B cell stage, and these mice lack IgM(+)B220(+) B cells in both bo
ne marrow and spleen. IgM(+)B220(+) B cells can be detected, albeit at
significantly reduced levels, in the bone marrow and spleen of mice l
acking E12. Ectopic expression of both E12 and E47 in a null mutant ba
ckground shows that E12 and E47 act in concert to promote B lineage de
velopment. Taken together, the data indicate that both E12 and E47 all
ow commitment to the B cell lineage and act synergistically to promote
B lymphocyte maturation.