ABSTRACT
The AML1:CBFbeta transcription factor complex is essential for definitive hematopoiesis. Null mutations in mouse AML1 result in midgestational lethality with a complete lack of fetal liver hematopoiesis. While the cell autonomous nature and expression pattern of AML1 suggest an intrinsic role for this transcription factor in the developing hematopoietic system, no direct link to a functional cell type has been made. Here, we examine the consequences of AML1 loss in hematopoietic stem cells (HSC) of the mouse embryo. We demonstrate an absolute requirement for AML1 in functional HSCs. Moreover, haploinsufficiency results in a dramatic change in the temporal and spatial distribution of HSCs, leading to their early appearance in the normal position in the aorta-gonad-mesonephros region and also in the yolk sac.
Subject(s)
DNA-Binding Proteins/genetics , Embryo, Mammalian/physiology , Hematopoietic Stem Cells/physiology , Proto-Oncogene Proteins , Transcription Factors/genetics , Animals , Aorta/embryology , Aorta/transplantation , Cell Aggregation/genetics , Cell Aggregation/immunology , Cell Aggregation/physiology , Cell Differentiation/genetics , Cell Differentiation/immunology , Colony-Forming Units Assay , Core Binding Factor Alpha 2 Subunit , DNA-Binding Proteins/administration & dosage , DNA-Binding Proteins/physiology , Embryo Transfer , Embryo, Mammalian/cytology , Female , Gestational Age , Gonads/embryology , Gonads/transplantation , Haplotypes/genetics , Hematopoiesis/genetics , Hematopoiesis/immunology , Hematopoietic Stem Cells/immunology , Male , Mesonephros/embryology , Mesonephros/transplantation , Mice , Mice, Inbred C57BL , Mice, Mutant Strains , Organ Culture Techniques , Transcription Factors/administration & dosage , Transcription Factors/physiology , Yolk Sac/embryology , Yolk Sac/transplantationABSTRACT
The aorta-gonad-mesonephros (AGM) region is a potent hematopoietic site in the midgestation mouse conceptus and first contains colony-forming units-spleen day 11 (CFU-S(11)) at embryonic day 10 (E10). Because CFU-S(11) activity is present in the AGM region before the onset of hematopoietic stem cell (HSC) activity, CFU-S(11) activity in the complex developing vascular and urogenital regions of the AGM was localized. From E10 onward, CFU-S(11) activity is associated with the aortic vasculature, and is found also in the urogenital ridges (UGRs). Together with data obtained from organ explant cultures, in which up to a 16-fold increase in CFU-S(11) activity was observed, it was determined that CFU-S(11) can be increased autonomously both in vascular sites and in UGRs. Furthermore, CFU-S(11) activity is present in vitelline and umbilical vessels. This, together with the presence of CFU-S(11) in the UGRs 2 days before HSC activity, suggests both temporally and spatially distinct emergent sources of CFU-S(11). (Blood. 2000;96:2902-2904)
Subject(s)
Aorta/embryology , Gonads/embryology , Hematopoiesis, Extramedullary , Hematopoietic Stem Cells/cytology , Mesonephros , Animals , Animals, Outbred Strains , Cell Lineage , Crosses, Genetic , Female , Gestational Age , Male , Mice , Mice, Inbred C57BL , Mice, Inbred CBA , Microscopy, Electron, Scanning , Radiation ChimeraABSTRACT
Fragile X syndrome is caused by the absence of expression of the FMR1 gene. Both FXR1 and FXR2 are autosomal gene homologues of FMR1. The products of the three genes are belonging to a family of RNA-binding proteins, called FMRP, FXR1P, and FXR2P, respectively, and are associated with polyribosomes as cytoplasmic mRNP particles. The aim of the present study is to obtain more knowledge about the cellular function of the three proteins (Fxr proteins) and their interrelationships in vivo. We have utilized monospecific antibodies raised against each of these proteins and performed Western blotting and immunolabeling at the light-microscopic level on tissues of wild-type and Fmr1 knockout adult mice. In addition, we have performed immunoelectron microscopy on hippocampal neurons of wild-type mice to study the subcellular distribution of the Fxr proteins. A high expression was found in brain and gonads for all three proteins. Skeletal muscle tissue showed only a high expression for Fxr1p. In the brain the three proteins were colocalized in the cytoplasm of the neurons; however, in specific neurons Fxr1p was also found in the nucleolus. Immunoelectronmicrsocopy on hippocampal neurons demonstrated the majority of the three proteins in association with ribosomes and a minority in the nucleus. The colocalization of the Fxr proteins in neurons is consistent with similar cellular functions in those specific cells. The presence of the three proteins in the nucleus of hippocampal neurons suggests a nucleocytoplasmic shuttling for the Fxr proteins. In maturing and adult testis a differential expression was observed for the three proteins in the spermatogenic cells. The similarities and differences between the distribution of the Fxr proteins have implications with respect to their normal function and the pathogenesis of the fragile X syndrome.