Absence of Erythroblast Macrophage Protein (Emp) Leads to Failure of Erythroblast Nuclear Extrusion

In mammals, the functional unit for definitive erythropoiesis is the erythroblastic island, a multicellular structure composed of a central macrophage surrounded by developing erythroblasts. Erythroblast-macrophage interactions play a central role in the terminal maturation of erythroblasts, including enucleation. One possible mediator of this cell-cell interaction is the protein Emp (erythroblast macrophage protein). We used targeted gene inactivation to define the function of Emp during hematopoiesis. Emp null embryos die perinatally and show profound alterations in the hematopoietic system. A dramatic increase in the number of nucleated, immature erythrocytes is seen in the peripheral blood of Emp null fetuses. In the fetal liver virtually no erythroblastic islands are observed, and the number of F4/80-positive macrophages is substantially reduced. Those present lack cytoplasmic projections and are unable to interact with erythroblasts. Interestingly, macrophages erythroblasts, Emp in a the and in in macrophage We Emp with and this interaction is in the of in and Emp to for and in the of the of Emp null a to the and to the function of macrophages in definitive In mammals, the functional unit for definitive erythropoiesis is the erythroblastic island, a multicellular structure composed of a central macrophage surrounded by developing erythroblasts. Erythroblast-macrophage interactions play a central role in the terminal maturation of erythroblasts, including enucleation. One possible mediator of this cell-cell interaction is the protein Emp (erythroblast macrophage protein). We used targeted gene inactivation to define the function of Emp during hematopoiesis. Emp null embryos die perinatally and show profound alterations in the hematopoietic system. A dramatic increase in the number of nucleated, immature erythrocytes is seen in the peripheral blood of Emp null fetuses. In the fetal liver virtually no erythroblastic islands are observed, and the number of F4/80-positive macrophages is substantially reduced. Those present lack cytoplasmic projections and are unable to interact with erythroblasts. Interestingly, macrophages erythroblasts, Emp in a the and in in macrophage We Emp with and this interaction is in the of in and Emp to for and in the of the of Emp null a to the and to the function of macrophages in definitive In mammals, erythropoiesis in the fetal liver in erythroblastic of a central macrophage surrounded by a of developing of with macrophages a central role in the of erythroblastic of islands the macrophage and cytoplasmic peripheral the macrophage and developing In to the interactions macrophages and erythroblasts, the and of erythroblastic structure interactions and of the and the interactions and a in are with macrophages in erythroblastic of the erythroblastic islands Emp used macrophage fetal liver used macrophage fetal liver (erythroblast macrophage in and macrophages in in of peripheral blood the of erythroblastic islands are to in in the In the of in erythroblastic islands and terminal maturation of in Emp the of with macrophages and this terminal maturation of In to the and macrophages interaction is the interaction interaction and macrophage a role in to structure of with in macrophage in to and a of central macrophages of the erythroblastic islands are to in the including and of and of enucleation. role of macrophages in for a gene in macrophages is for the to for of central macrophages in to immature by of the embryos profound in fetal liver macrophages interactions with the present gene to the in function of Emp null are and in and macrophage Emp is in and macrophage and interaction with the of the Emp null a to the in a gene in Emp of the gene for a Emp by of by of the Emp and with to by of with for the Emp Emp and for the the gene and by a the and embryos in the this and are and embryos blood peripheral blood embryos and with to in in and the and with for A used to of and of composed of and embryos in and in and for with the in of fetal and to to for in to the and for the in to macrophages with the in and for and in to erythroblasts. macrophages to in for the of to fetal embryos used the of erythroblasts. in for to the by and in in of for with macrophages the islands in to the for number of to macrophages by the number of present in a for and with and with erythroblasts, and the erythroblastic islands for in fetal and and for and of by with for by a of in embryos the A in with and of fetal macrophage and Emp null embryos and in with fetal a of and of the used for and the protein and to for by of Emp and macrophages and in and a for and the with the with by in and Emp used in of the Emp gene of the Emp in by a the gene the of the the is to with the and of the in show the the targeted of and and the One of the to to and the by of with for the Emp and and for the the gene and of and and and no Emp of the Emp Emp embryos during of embryos to the Emp embryos die of in a the of Emp and embryos and by Emp in and in of Emp the by of fetal liver the erythropoiesis is in the erythropoiesis is in the fetal liver and erythropoiesis by of the erythrocytes in are of fetal liver of definitive erythropoiesis in the fetal liver In the maturation in the of the the of erythroblastic islands the of Emp gene definitive embryos Emp embryos and Emp embryos and with the peripheral blood of and embryos a number of of embryos erythrocytes embryos erythrocytes with in the in the this to and In the embryos virtually no in the of erythrocytes the of in embryos is to a a of the number of and in the fetal in embryos number of with the a in terminal maturation and of in the of of and Emp null embryos of the peripheral blood and embryos and with and and embryos to in in and the and with the number of and erythrocytes in and with the null fetal number of in the peripheral blood of of is number of of peripheral blood embryos blood by and used to number of and and embryos and is number of of peripheral blood embryos blood by and used to number of and and embryos and in a fetal liver is the of definitive fetal liver and fetal a number of In the immature with erythrocytes erythrocytes in and in and in of the liver in the of in to of blood and to are for definitive erythropoiesis the of Emp of by the of the in a in the number of macrophages in of fetal liver with a of macrophages F4/80-positive the liver of In the number of F4/80-positive macrophages to of the Emp null and and to lack the cytoplasmic seen in immature by immature macrophage in and Emp fetal of Emp in terminal to the macrophage of in Emp null for and of and and fetal liver with and with is of and Emp null fetal with and with with with and the Emp is for erythroblastic used a in by and Emp null embryos with and in with and and by composed of to F4/80-positive macrophages in fetal virtually no seen to macrophages in Emp null fetal in the of erythroblastic is are with in Emp the of to macrophages in of Emp a in the of erythroblastic islands in the fetal erythroblastic islands and Emp fetal with and with is to erythroblastic in the of Emp is to in erythroblasts, erythroblastic islands and Emp null embryos in a and to the macrophages macrophages with Emp null fetal to in Emp null to macrophages with unable to to the Emp null macrophages by islands in and immature Emp null macrophages to with erythroblastic and erythroblastic islands with and in the to is erythroblastic islands of for and for and show Emp null the to to this to terminal erythroblastic islands of and Emp null in the of and to and of macrophages the of by and In a in the number of seen in Emp null to macrophages of the number of with Emp null erythroblasts. interaction with macrophages the of Emp null in and is the of the in Emp in with in the of the to this the and of in and Emp null erythroblasts. and embryos with to the and to the in the erythroblasts. In in Emp null erythroblasts. to the a the is to the and a number of of of by are in the is in and of of of Emp with the and cytoplasmic in in erythroblasts, Emp with seen in the the and a of Emp seen with the with the of Emp with the is with a by Emp and interact in erythroblasts, embryos used in with a in and Emp with and in is in and and with and with is with and with with by for Emp and used to of Emp and is by is macrophages and in and with with of the a the and is of macrophage of Emp the in of macrophage this macrophages the of and the of Emp and in a in the of the macrophages with and In macrophages and immature and of the in and with the macrophages of Emp the of a the is the Emp to a the and a cytoplasmic the Emp is to the in and macrophages of Emp in terminal maturation and of and of the in function of a functional Emp in the Emp are and die embryos are and with of peripheral blood a increase in the number of in in the of the are definitive erythrocytes the in the embryos to of definitive maturation of in the of macrophage is Emp null macrophages are and and lack cytoplasmic projections present in immature of in a to Emp is in the of erythroblastic in show the number of erythroblastic islands in null fetal is with fetal of erythroblastic islands the macrophages to and Emp null erythroblasts, macrophages are unable to of erythroblasts. the of erythroblastic islands the of Emp in macrophages in erythroblasts. is in of Emp in interactions and Emp the of and macrophages is possible Emp in in in the of the of of the in erythroblastic is is the Emp a function in Emp null to macrophages in erythroblastic islands to maturation and enucleation. to and erythroblastic with the of the terminal in the maturation of the A number of a to In the and is present in the of a in the to the of with the of is the and in erythroblasts. the of with enucleation. Interestingly, Emp is in the during and in a with in Emp with in and in the of and with a in the of of for and of in the erythroblasts, with Emp present the the In the erythroblasts, the no cytoplasmic in in the of the is in of Emp with in a role of Emp in enucleation. with this is the Emp with are in enucleation. the of Emp and in a of Emp with the with the with in to in function to the in Emp to the cytoplasmic and is a with the In of a the role of in protein during the of the of Emp to the during this role of Emp in in macrophage are unable to cytoplasmic of Emp null macrophages in of to and of are is the of show the of Emp null is to of null show immature and are unable to erythroblastic are the null with the Emp null Emp is for the of erythroblastic islands for the of and macrophage in the to the of Emp in the of the and in the of macrophage In mammals, erythropoiesis in the fetal liver in erythroblastic of a central macrophage surrounded by a of developing of with macrophages a central role in the of erythroblastic of islands the macrophage and cytoplasmic peripheral the macrophage and developing In to the interactions macrophages and erythroblasts, the and of erythroblastic structure interactions and of the and the interactions and a in are with macrophages in erythroblastic of the erythroblastic islands Emp used macrophage fetal liver used macrophage fetal liver (erythroblast macrophage in and macrophages in in of peripheral blood the of erythroblastic islands are to in in the In the of in erythroblastic islands and terminal maturation of in Emp the of with macrophages and this terminal maturation of In to the and macrophages interaction is the interaction interaction and macrophage a role in to structure of with in macrophage in to and a of central macrophages of the erythroblastic islands are to in the including and of and of enucleation. role of macrophages in for a gene in macrophages is for the to for of central macrophages in to immature by of the embryos profound in fetal liver macrophages interactions with In the present gene to the in function of Emp null are and in and macrophage Emp is in and macrophage and interaction with the of the Emp null a to the in a gene in Emp of the gene for a Emp by of by of the Emp and with to by of with for the Emp Emp and for the the gene and by a the and embryos in the this and are and embryos blood peripheral blood embryos and with to in in and the and with for A used to of and of composed of and embryos in and in and for with the in of fetal and to to for in to the and for the in to macrophages with the in and for and in to erythroblasts. macrophages to in for the of to fetal embryos used the of erythroblasts. in for to the by and in in of for with macrophages the islands in to the for number of to macrophages by the number of present in a for and with and with erythroblasts, and the erythroblastic islands for in fetal and and for and of by with for by a of in embryos the A in with and of fetal macrophage and Emp null embryos and in with fetal a of and of the used for and the protein and to for by of Emp and macrophages and in and a for and the with the with by in and in a gene in Emp of the gene for a Emp by of by of the Emp and with to by of with for the Emp Emp and for the the gene and by a the and embryos in the this and are and embryos blood peripheral blood embryos and with to in in and the and with for A used to of and of composed of and embryos in and in and for with the in of fetal and to to for in to the and for the in to macrophages with the in and for and in to erythroblasts. macrophages to in for the of to fetal embryos used the of erythroblasts. in for to the by and in in of for with macrophages the islands in to the for number of to macrophages by the number of present in a for and with and with erythroblasts, and the erythroblastic islands for in fetal and and for and of by with for by a of in embryos the A in with and of fetal macrophage and Emp null embryos and in with fetal a of and of the used for and the protein and to for by of Emp and macrophages and in and a for and the with the with by in and Emp used in of the Emp gene of the Emp in by a the gene the of the the is to with the and of the in show the the targeted of and and the One of the to to and the by of with for the Emp and and for the the gene and of and and and no Emp of the Emp Emp embryos during of embryos to the Emp embryos die of in a the of Emp and embryos and by Emp in and in of Emp the by of fetal liver the erythropoiesis is in the erythropoiesis is in the fetal liver and erythropoiesis by of the erythrocytes in are of fetal liver of definitive erythropoiesis in the fetal liver In the maturation in the of the the of erythroblastic islands the of Emp gene definitive embryos Emp embryos and Emp embryos and with the peripheral blood of and embryos a number of of embryos erythrocytes embryos erythrocytes with in the in the this to and In the embryos virtually no in the of erythrocytes the of in embryos is to a a of the number of and in the fetal in embryos number of with the a in terminal maturation and of in the of number of in the peripheral blood of of is number of of peripheral blood embryos blood by and used to number of and and embryos and is number of of peripheral blood embryos blood by and used to number of and and embryos and in a fetal liver is the of definitive fetal liver and fetal a number of In the immature with erythrocytes erythrocytes in and in and in of the liver in the of in to of blood and to are for definitive erythropoiesis the of Emp of by the of the in a in the number of macrophages in of fetal liver with a of macrophages F4/80-positive the liver of In the number of F4/80-positive macrophages to of the Emp null and and to lack the cytoplasmic seen in immature by immature macrophage in and Emp fetal of Emp in terminal to the macrophage of in Emp null for and of and and fetal liver with and with is of and Emp null fetal with and with with with and the Emp is for erythroblastic used a in by and Emp null embryos with and in with and and by composed of to F4/80-positive macrophages in fetal virtually no seen to macrophages in Emp null fetal in the of erythroblastic is are with in Emp the of to macrophages in of Emp a in the of erythroblastic islands in the fetal erythroblastic islands and Emp fetal with and with is to erythroblastic in the of Emp is to in erythroblasts, erythroblastic islands and Emp null embryos in a and to the macrophages macrophages with Emp null fetal to in Emp null to macrophages with unable to to the Emp null macrophages by islands in and immature Emp null macrophages to with erythroblastic and erythroblastic islands with and in the to is erythroblastic islands of for and for and show Emp null the to to this to terminal erythroblastic islands of and Emp null in the of and to and of macrophages the of by and In a in the number of seen in Emp null to macrophages of the number of with Emp null erythroblasts. interaction with macrophages the of Emp null in and is the of the in Emp in with in the of the to this the and of in and Emp null erythroblasts. and embryos with to the and to the in the erythroblasts. In in Emp null erythroblasts. to the a the is to the and a number of of of by are in the is in and of of of Emp with the and cytoplasmic in in erythroblasts, Emp with seen in the the and a of Emp seen with the with the of Emp with the is with a by Emp and interact in erythroblasts, embryos used in with a in and Emp with and in is in and and with and with is with and with with by for Emp and used to of Emp and is by is macrophages and in and with with of the a the and is of macrophage of Emp the in of macrophage this macrophages the of and the of Emp and in a in the of the macrophages with and In macrophages and immature and of the in and with the macrophages Emp Emp used in of the Emp gene of the Emp in by a the gene the of the the is to with the and of the in show the the targeted of and and the One of the to to and the by of with for the Emp and and for the the gene and of and and and no Emp of the Emp Emp embryos during of embryos to the Emp embryos die the of Emp and embryos and by Emp in and in of Emp the by of fetal liver Emp the erythropoiesis is in the erythropoiesis is in the fetal liver and erythropoiesis by of the erythrocytes in are of fetal liver of definitive erythropoiesis in the fetal liver In the maturation in the of the the of erythroblastic islands the of Emp gene definitive embryos Emp embryos and Emp embryos and with the peripheral blood of and embryos a number of of embryos erythrocytes embryos erythrocytes with in the in the this to and In the embryos virtually no in the of erythrocytes the of in embryos is to a a of the number of and in the fetal in embryos number of with the a in terminal maturation and of in the of fetal liver is the of definitive fetal liver and fetal a number of In the immature with erythrocytes erythrocytes in and in and in of the liver in the of in to of blood Emp and to are for definitive erythropoiesis the of Emp of by the of the in a in the number of macrophages in of fetal liver with a of macrophages F4/80-positive the liver of In the number of F4/80-positive macrophages to of the Emp null and and to lack the cytoplasmic seen in immature by immature macrophage in and Emp fetal of Emp in terminal to the macrophage Emp is for erythroblastic used a in by and Emp null embryos with and in with and and by composed of to F4/80-positive macrophages in fetal virtually no seen to macrophages in Emp null fetal in the of erythroblastic is are with in Emp the of to macrophages in to erythroblastic in the of Emp is to in erythroblasts, erythroblastic islands and Emp null embryos in a and to the macrophages macrophages with Emp null fetal to in Emp null to macrophages with unable to to the Emp null macrophages by islands in and immature Emp null macrophages to with erythroblasts. Emp show Emp null the to to this to terminal erythroblastic islands of and Emp null in the of and to and of macrophages the of by and In a in the number of seen in Emp null to macrophages of the number of with Emp null erythroblasts. interaction with macrophages the of Emp null erythroblasts. in and is the of the in Emp in with in the of the to this the and of in and Emp null erythroblasts. and embryos with to the and to the in the erythroblasts. In in Emp null erythroblasts. to the a the is to the and a number of of of by are in the is in and of of of Emp with the and cytoplasmic in in erythroblasts, Emp with seen in the the and a of Emp seen with the with the of Emp with the is with a by Emp and interact in erythroblasts, embryos used in with a in and Emp with and in erythroblasts. the and is of macrophage of Emp the in of macrophage this macrophages the of and the of Emp and in a in the of the macrophages with and In macrophages and immature and of the in and with the macrophages of Emp the of a the is the Emp to a the and a cytoplasmic the Emp is to the in and macrophages of Emp in terminal maturation and of and of the in function of a functional Emp in the Emp are and die embryos are and with of peripheral blood a increase in the number of in in the of the are definitive erythrocytes the in the embryos to of definitive maturation of in the of macrophage is Emp null macrophages are and and lack cytoplasmic projections present in immature of in a to Emp is in the of erythroblastic in show the number of erythroblastic islands in null fetal is with fetal of erythroblastic islands the macrophages to and Emp null erythroblasts, macrophages are unable to of erythroblasts. the of erythroblastic islands the of Emp in macrophages in erythroblasts. is in of Emp in interactions and Emp the of and macrophages is possible Emp in in in the of the of of the in erythroblastic is is the Emp a function in Emp null to macrophages in erythroblastic islands to maturation and enucleation. to and erythroblastic with the of the terminal in the maturation of the A number of a to In the and is present in the of a in the to the of with the of is the and in erythroblasts. the of with enucleation. Interestingly, Emp is in the during and in a with in Emp with in and in the of and with a in the of of for and of in the erythroblasts, with Emp present the the In the erythroblasts, the no cytoplasmic in in the of the is in of Emp with in a role of Emp in enucleation. with this is the Emp with are in enucleation. the of Emp and in a of Emp with the with the with in to in function to the in Emp to the cytoplasmic and is a with the In of a the role of in protein during the of the of Emp to the during this role of Emp in in macrophage are unable to cytoplasmic of Emp null macrophages in of to and of are is the of show the of Emp null is to of null show immature and are unable to erythroblastic are the null with the Emp null Emp is for the of erythroblastic islands for the of and macrophage in the to the of Emp in the of the and in the of macrophage of Emp the of a the is the Emp to a the and a cytoplasmic the Emp is to the in and macrophages of Emp in terminal maturation and of and of the in function of a functional Emp in the Emp are and die embryos are and with of peripheral blood a increase in the number of in in the of the are definitive erythrocytes the in the embryos to of definitive maturation of in the of macrophage is Emp null macrophages are and and lack cytoplasmic projections present in immature of in a to Emp is in the of erythroblastic in show the number of erythroblastic islands in null fetal is with fetal of erythroblastic islands the macrophages to and Emp null erythroblasts, macrophages are unable to of erythroblasts. the of erythroblastic islands the of Emp in macrophages in erythroblasts. is in of Emp in interactions and Emp the of and macrophages is possible Emp in in in the of the of of the in erythroblastic is is the Emp a function in Emp null to macrophages in erythroblastic islands to maturation and enucleation. to and erythroblastic with the of the terminal in the maturation of the A number of a to In the and is present in the of a in the to the of with the of is the and in erythroblasts. the of with enucleation. Interestingly, Emp is in the during and in a with in Emp with in and in the of and with a in the of of for and of in the erythroblasts, with Emp present the the In the erythroblasts, the no cytoplasmic in in the of the is in erythroblasts. of Emp with in a role of Emp in enucleation. with this is the Emp with are in enucleation. the of Emp and in a of Emp with the with the with in to in function to the in Emp to the cytoplasmic and is a with the In of a the role of in protein during the of the of Emp to the during this role of Emp in in macrophage are unable to cytoplasmic of Emp null macrophages in of to and of are is the of show the of Emp null is to of null show immature and are unable to erythroblastic are the null with the Emp null Emp is for the of erythroblastic islands for the of and macrophage in the to the of Emp in the of the and in the of macrophage We for this and for the