Id4 is required for the correct timing of neural differentiation.

Complex intrinsic and extrinsic mechanisms determine neural cell fate during development of the nervous system. Using Id4 deficient mice, we show that Id4 is required for normal development of the central nervous system (CNS), timing neural differentiation in the developing forebrain. In the absence of Id4, the ventricular zone of the neocortex, future hippocampus as well as lateral and medial ganglionic eminences exhibited a 20-30% reduction in mitotic neural precursor cells (NPCs).

Retinoblastoma promotes definitive erythropoiesis by repressing Id2 in fetal liver macrophages.

In mammals, the fetal liver is the first site of definitive erythropoiesis-the generation of mature, enucleated red cells. The functional unit for definitive erythropoiesis is the erythroblastic island, a multicellular structure composed of a central macrophage surrounded by erythroblasts at various stages of differentiation. Targeted disruption of the retinoblastoma (Rb) tumour suppressor gene in the mouse leads to embryonic death caused by failure of erythroblasts to enucleate.