Abstract: Objective To study whether the Axl and Mer receptors are involved in the regulation of erythroid differentiation. Methods Single and double mutant mice for AXL and MER were used in the study. Histological sections of bone marrows, livers and spleens, cellularity of bone marrow, hematologic parameters, and the expression of erythroid factors were analyzed to evaluate the function of Axl and Mer in erythropoiesis. Results Histological analysis showed that the sinusoids in wild-type bone marrows were filled with red blood cells, whereas those in the AXL–/–MER–/– bone marrows were largely empty and contained fewer red blood cells. The number of the total cells, the nuclearted cells and the red blood cells in an AXL–/–MER–/– femur were decreased. A compensatory extramedullary erythropoiesis occurred in AXL–/–MER–/– mice. The hematopoietic islands appeared in the liver, and the red pulp is expanded in the spleen. Mice lacking single AXL or MER exhibited normal erythropoiesis in steady-state conditions. The relative mRNA levels of EpoR and GATA-1 were significantly down-regulated in AXL–/–MER–/– erythroid cells. Conclusion Axl and Mer receptors may influence erythropoiesis through the regulation of GATA-1 and EpoR expression in erythroid cells.

Key words: Axl, Mer, gene knockout, erythropoiesis