03-P065 Identification and molecular characterisation of the hemangioblast in the early chick embryo

The Wilms’ tumour gene (Wt1) was originally identified as a gene involved in predisposition to the childhood kidney cancer Wilms tumour. Wt1 conventional KOs are embryonic lethal. The mutant embryos die before E13.5 days due to cardiac defects and spleen, kidney, and gonads fail to form. The role of Wt1 in haematopoiesis is controversial. Some evidence suggests that Wt1 is required for embryonic haematopoiesis while others suggest the opposite. The role of Wt1 in adult haematopoiesis has not been studied before. Here we wanted to address the function of Wt1 in adult haematopoiesis by using a tamoxifen-induced Wt1 deletion mouse line developed in the group. Knocking down Wt1 in the spleen in adult mice leads to massive atrophy. The spleen to body weight ratio is reduced in the mutant mice. FACS analysis shows that the mutant mice are unable to produce red blood cells in the spleen and in the bone marrow. The same result is obtained when the mutant spleen and bone marrow cells were cultured in methylcellulose-based medium for two weeks, suggesting the defect of forming red blood cells is caused by direct loss of Wt1. We also show that mouse embryonic stem cells (ES) lacking Wt1 fail to differentiate down the haematopoiesis lineage. Bone marrow transplantation experiment is currently being carried out to assess the importance of Wt1 in adult haematopoiesis. This study shows that there are differences in erythropoietic mechanisms between the fetuses and adults.