ELECTRON-MICROSCOPIC ANALYSIS OF DROSOPHILA MIDLINE GLIA DURING EMBRYOGENESIS AND LARVAL DEVELOPMENT USING BETA-GALACTOSIDASE EXPRESSION ASENDOGENOUS CELL MARKER

To thoroughly study developmental problems it is often desirable to id entify specific cells at the resolution of the electron microscope (TE M). Specific antibodies, and immunogold and other antibody labelling t echniques can be successfully used with the TEM. But for these techniq ues to be successful there must be substantial adjustments for each an tibody and tissue analyzed. To develop a more generally applicable lab elling method we took advantage of the enhancer trap technique in Dros ophila. Enhancer trap fly strains show cell- and/or tissue-specific P- galactosidase expression which can be visualized by a simple X-gal sta ining procedure. To combine the power of the enhancer trap approach wi th electron microscopy, we have improved the fixation and staining con ditions, which allow detection of X-gal crystals (by TEM) and thus pro vide precise information on ultrastructural morphology. We have tested our technique using the well-known midline glial cells and examined t hese cells between late embryonic and pupal developmental stages. The four embryonic midline glial cells found in each neuromere reside vent rally and dorsally to the midline of the neuropile and are closely ass ociated with unpaired neurons, major commissures, and other types of g lial cells. During larval and pupal life dramatic cell growth and endo mitotic nuclear replication occur in midline glial cells. By the end o f larval life, the giant midline glial cells fragment to give rise to a variable number of small midline glial cells. Here we show that the combination of transmission electron microscopy with cytochemical dete ction of P-galactosidase expression represents a promising and valuabl e tool for the study of the morphology and development of specific cel l types. (C) 1996 Wiley-Liss, Inc.