gcm2 promotes glial cell differentiation and is required with glial cells missing for macrophage development in Drosophila

glial cells missing (gcm) is the primary regulator of glial cell fate in Drosophila. In addition, gcm has a role in the differentiation of the plasmatocyte/macrophage lineage of hemocytes. Since mutation of gcm causes only a decrease in plasmatocyte numbers without changing their ability to convert into macrophages, gcm cannot be the sole determinant of plasmatocyte/macrophage differentiation. We have characterized a gcm homolog, gcm2. gcm2 is expressed at low levels in glial cells and hemocyte precursors. We show that gcm2 has redundant functions with gcm and has a minor role promoting glial cell differentiation. More significant, like gcm, mutation of gcm2 leads to reduced plasmatocyte numbers. A deletion removing both genes has allowed us to clarify the role of these redundant genes in plasmatocyte development. Animals deficient for both gcm and gcm2 fail to express the macrophage receptor Croquemort. Plasmatocytes are reduced in number, but still express the early marker Peroxidasin. These Peroxidasin-expressing hemocytes fail to migrate to their normal locations and do not complete their conversion into macrophages. Our results suggest that both gcm and gcm2 are required together for the proliferation of plasmatocyte precursors, the expression of Croquemort protein, and the ability of plasmatocytes to convert into macrophages.     

A tissue-specific transcription enhancer from the Drosophila yolk protein 1 gene

The yolk protein 1 gene (yp1) of Drosophila melanogaster is expressed only in the ovarian follicle cells and the fat bodies of adult females. We have previously shown that a different cis-acting DNA region is required for each of these tissue specificities. In this paper we use germ line transformation to localize and characterized one of these tissue-specific regulatory regions. We demonstrate that a 125 bp segment of DNA located 196 bp upstream of the yp1 cap site is sufficient to determine the sex-, stage-, and fat body-specific expression of the yp1 gene. We also find that this region can confer yp1-specific expression on a heterologous Drosophila promoter. This specificity is retained when the region is in different orientations and at different distances from the heterologous promoter. Thus a small regulatory region acts in vivo as a positive enhancer to determine the fat body expression pattern of yp1.