No red cell is an island

摘要

Red blood ceils develop in the bone marrow in 'islands' nurtured by a central white blood cell, Work in mice shows that the retinoblastoma protein is crucial for these white celis to mature and form islands. As adults, we make more than 2 million redblood cells (erythrocytes) in our bone marrow every second to replace those lost through normal attrition. The mammalian erythrocyte is unique among the blood celis of the animal kingdom because it discards its nucleus (enucleates) and all its internal organelles before enter ing the circulation. This matui a-tion of red cells is aided by white blood cells called macrophages, and somehow requires the letinoblastoma protein (Rb) On page 1040 of this issue, lavarone et al tease out some of the mechanismsinvolved. Surprisingly, it seems that Rb regulates the maturation of macrophages, which bind to immature nucleated erythrocytes (erythro-blasts) to form 'islands' that nurture red-cell synthesis.