Targeted mutagenesis analysis has shown that the Cmyb proto-oncogene, which encodes a sequence-specific DNA binding protein, is required for normal murine fetal liver erythropoiesis and myelopoiesis. To identify novel genes involved in hematopoiesis, differential display analysis was conducted using total liver RNA isolated from 14.5-day postcoitus Cmyb wildtype, heterozygous, and homozygous mutant littermates. Using 4 oligo(dT) 3' primers and 5 arbitrary decamers as 5' primers, 22 differentially expressed genes have been identified. Eight putatively novel genes were identified from 12 cDNAs that were sequenced. One gene, initially designated DD7A5-7, is primarily expressed in cells of the myeloid lineage. The full-length DD7A5-7 cDNA is 3239 nucleotides, encoding a putative protein of 931 amino acids. The protein is a member of a family of hormone receptors containing 7 transmembrane segments. The receptor also contains 7 epidermal growth factor-like (Egf-like) motifs at the amino terminal of the predicted protein. The gene is alternatively spliced, resulting in the deletion of one or more copies of the Egf-like motif. DD7A5-7 maps to mouse Chromosome 17 and is the putative homologue of EMR1, a recently described Egf-like module containing mucin-like hormone receptor with 7 transmembrane segments in humans. Our results indicate that the Cmyb mutant fetuses represent a unique resource for identifying genes involved in hematopoiesis.