The development of the blood cells (haemocytes) of adult Drosophila occurs during larval development in a specialised organ called the lymph gland, but how haematopoiesis in flies is spatially and temporally regulated is poorly understood. On p. , Jung and co-workers remedy this by analysing the structure of the lymph gland and the expression of haematopoietic and pro-haemocytic markers within the gland. They describe two previously unrecognised zones in the larval lymph gland: the medullary zone, which contains quiescent, immature haemocytes; and the cortical zone, which contains proliferating haemocytes that express maturation markers. This finding indicates that in Drosophila, as in vertebrates, quiescent multipotent blood precursors give rise to various mature blood cells. Additional similarities between vertebrate and fly haematopoiesis, together with the researchers' detailed model for hemocyte maturation in the lymph gland, establish Drosophila as a genetic model for the study of haematopoiesis.
