Identification and genetic localization of mRNAs from ovarian follicle cells of Drosophila melanogaster

RNA synthesis in ovarian follicles of Drosophila melanogaster was studied by methods which eliminate experimentally induced alterations in gene expression. Gel electrophoresis of follicular RNA, labeled after injection of precursors into females, revealed qualitative and quantitative differences in synthesis during the course of oogenesis. A highly heterogeneous group of poly(A)-containing RNAs is produced during much of the course of follicular development. However, post-vitellogenic stages synthesize a small number of stage-specific poly(A)-containing RNAs. During this period, RNA synthesis is known to take place primarily in the follicle cells, which are engaged in the production of the endochorion and exochorion. Two intense bands of nonmitochondrial poly(A)⁺ RNA are labeled between stage 11 and early stage 13. The synthesis of a more heterogeneous group of very small poly(A)-containing RNAs characterizes the last part of oogenesis, stages 13 and 14. Evidence is presented to show that these RNAs are specifically localized in the follicle cells of the egg chamber. We propose that they represent mRNAs for chorion proteins. In situ hybridization of preparations of late stage poly(A)-containing RNA to salivary gland chromosomes revealed two major sites of complementarity, 7E11 and 12E, as well as several minor sites. Experiments in which RNAs were separated on gels prior to hybridization in situ suggested that both the major stage 12-specific RNA bands contained molecules which were complementary to DNA in the 7E11 region. It is particularly interesting that this site is within a small chromosomal interval known to contain the gene ocelliless. Females homozygous for ocelliless have been shown to produce structurally abnormal chorions (Johnson and King, 1974).