The oocyte is a highly structured cell in which it has been repeatedly demonstrated that there are localized regions which affect the developmental fate of cells that form from those regions. The molecules in the egg which regulate these developmental responses have been difficult to study. A new approach for studying maternal inheritance is presented here, in which stable isotopes are used to density label Drosophila egg proteins and RNAs so that maternal components can be physically separated from those synthesized later in development. This method also circumvents difficulties of a radiolabelling approach in which maternal components can turn over, be reutilized and obscure the initial maternal labelling. The number and stability of total maternal proteins will be monitored in whole animals during progressive stages of Drosophila development. Transport of egg cytoplasmic proteins into nuclei (and chromatin), as well as nucleoli, will be followed at the cellular blastoderm stage. At this stage the egg cytoplasm is known to affect gene activity in these nuclei, as well as cell determination. We will then ask whether there are specific subclasses of maternal proteins in determined cell types (imaginal discs or muscle cells). We will follow the assembly of maternal histones to form the nucleosomes of embryonic chromatin, and determine whether such nucleosomes are conserved and segregated from nucleosomal histones added to chromatin of dividing cells at later stages of development. The sequence complexity and stability of maternal RNAs will be analyzed in the same development stages, tissues and organelles to ascertain if there are specific maternal RNAs which are important in regulating early development. DNA copies of maternal RNA sequences will be inserted into bacterial plasmids to prepare a collection of bacterial clones which will be used to follow the fate of individual maternal RNA sequences during development.