Mature monocytic cells enter tissues and engraft

The goal of this study was to identify the circulating cell that is the immediate precursor of tissue macrophages. ROSA 26 marrow mononuclear cells (containing the β-geo transgene that encodes β-galactosidase and neomycin resistance activities) were cultured in the presence of macrophage colony-stimulating factor and flt3 Ligand for 6 days to generate monocytic cells at all stages of maturation. Expanded monocyte cells (EMC), the immature (ER-MP12+) and more mature (ER-MP20+) subpopulations, were transplanted into irradiated B6/129 F2 mice. β-gal staining of tissue sections from animals 15 min after transplantation demonstrated that the donor cells landed randomly. By 3 h, donor cells in lung and liver were more frequent in animals transplanted with ER-MP20+ (more mature) EMC than in animals transplanted with unseparated EMC or fresh marrow mononuclear cells, a pattern that persisted at 3 and 7 days. At 3 days, donor cells were found in spleen, liver, lung, and brain (rarely) as clusters as well as individual cells. By 7 and 14 days, the clusters had increased in size, and the cells expressed the macrophage antigen F4/80, suggesting that further replication and differentiation had occurred. PCR for the neogene was used to quantitate the amount of donor DNA in tissues from transplanted animals and confirmed that ER-MP20+ EMC preferentially engrafted. These data demonstrate that a mature monocytic cell gives rise to tissue macrophages. Because these cells can be expanded and manipulated in vitro, they may be a suitable target population for gene therapy of lysosomal storage diseases.

A modifier screen in the eye reveals control genes for Krüppel activity in the Drosophila embryo

Irregular facets (If) is a dominant mutation of Drosophila that results in small eyes with fused ommatidia. Previous results showed that the gene Krüppel (Kr), which is best known for its early segmentation function, is expressed ectopically in If mutant eye discs. However, it was not known whether ectopic Kr activity is either the cause or the result of the If mutation. Here, we show that If is a gain-of-function allele of Kr. We then used the If mutation in a genetic screen to identify dominant enhancers and suppressors of Kr activity on the third chromosome. Of 30 identified Kr-interacting loci, two were cloned, and we examined whether they also represent components of a natural Kr-dependent developmental pathway of the embryo. We show that the two genes, eyelid (eld) and extramacrochaetae (emc), which encode a Bright family-type DNA binding protein and a helix-loop-helix factor, respectively, are necessary to achieve the singling-out of a unique Kr-expressing cell during the development of the Malpighian tubules, the excretory organs of the fly. The results indicate that the Kr gain-of-function mutation If provides a tool to identify genes that are active during eye development and that a number of them function also in the control of Kr-dependent developmental processes.