Analysis of Chromosomes of the Larval CNS by FISH and BrdU Labeling

The central nervous system (CNS) of the third instar larva is the most convenient tissue in which to examine both mitotic chromosomes and the diploid interphase nucleus. It contains a mixture of cell types at various degrees of differentiation. Here, methods for examining the diploid nuclei of the third instar larva are presented. One method employs BrdU incorporation to label nuclei during the S-phase. A second uses fluorescence in situ hybridization (FISH) to determine where certain sequences are located. Both can be used on either mitotic chromosomes or interphase nuclei. These two methods can be used by themselves or in combination. When used in combination, a researcher can identify which cells have recently undergone the S-phase and examine the specific positions of various chromosomal regions in the interphase nucleus.