We report differential expression of the RB1 tumor suppressor gene and the homologous genes p107 and p130 during embryogenesis. Abundant RB1 transcripts were detected during neurogenesis, hematopoiesis, myogenesis, lens development and in the ganglion cell layer of the embryonic retina, prior to and during differentiation. The expression pattern of RB1 mirrored the defects in RB1 mutant mice (RB-/-). In the heart, lung, kidney and intestine, p107, but not RB1, was expressed. In the liver and the central nervous system p107 and RB1 were co-expressed, consistent with the accelerated cell death observed in RB-/-; p107-/- double knock-out mice. In the central nervous system, p107 expression was restricted to proliferating cells surrounding the ventricles, while RB1 was expressed in areas of both proliferating and differentiating cells. In contrast to RB1 and p107, expression of p130 was low throughout embryogenesis. In situ hybridization and Western blot analyses showed that the expression of p107 and p130 was not markedly altered in RB-/- embryos compared to control littermates. Our results suggest that members of RB1 gene family have distinct, but overlapping roles in embryogenesis, with p107 and RB1 possibly having redundant functions in the central nervous system and liver.