Coordinated cell type differentiation is essential for morphogenesis duringDictyosteliumdevelopment. The specification of different cell types and the regulation of temporal and spatial patterns of expression of cell type-specific genes are important problems currently being addressed in many laboratories. Besides, determination of gene expression patterns provides significant information in the characterization of developmental mutants. Cell type-specific probes and well characterized promoters are available that allow the identification of most cell types duringDictyosteliumdevelopment. Expression patterns can be studied by whole-mountin situmessenger RNA (mRNA) detection and by the use of reporter genes under the control of specific promoters. The most commonin situhybridization technique, based on nonradioactive ribo-probes that are hybridized to fixed whole-mounts prepared at different developmental stages, is described. Several reporter genes have been used to characterize gene expression patterns and to determine functional promoter elements. ThelacZgene, coding for the β-galactosidase enzyme, is the reporter most frequently used inDictyosteliumbecause both temporal- and spatial-patterns of expression can be easily determined. Generally used β-galactosidase detection methods are described.
