The actions of prolactin (PRL) are characterized by cellular differentiation and the changes of gene expression that underlie that differentiation. This research is directed toward understanding the induction of altered gene expression in pigeon crop tissue by prolactin. This model is especially useful because the tissue organization and development is relatively simple, and the changes prolactin induces are profound and rapid. Various molecular approaches are used. Specific prolactin-induced gene products have been identified by us through in vivo and in vitro protein synthesis, cloning, differential hybridization, immunochemical probes, and hybridization with known genes. The mechanisms responsible for PRL-induced gene expression will be the subject of the experiments described in this proposal. Sequencing of the major PRL-inducible cDNAs from the crop will be completed to examine possible relationships of these genes with genes of known function. These data will also be useful later in making predictions about sequences involved in the regulation of the genes. Nuclear run-off transcription assays and mRNA turnover measurements will be used to determine whether the regulation of PRL- inducible mRNAs is primarily at a transcriptional or post- transcriptional level. Based on data thus far it is expected that a large part of the regulation will be post-transcriptional. If so, the biochemical nature of the factors responsible for controlling PRL-inducible mRNA decay will be studied by reconstituting either native or cloned PRL-inducible transcripts with cytosolic factors from crop tissues. Decay of the products will be measured by either hybridization or electrophoresis of end-labelled transcripts. If transcription is the primary mechanism of PRL control, the genomic structure of one or more of the PRL-inducible genes will be determined by Southern analysis, genomic cloning, S1 mapping and sequencing. The proposed experiments will provide an understanding of the mechanisms and substrates of prolactin stimulation in the crop tissue model, and will contribute to the general understanding of the mechanism of action of this important hormone.
