The pattern of expression of the """"""""early"""""""" histone genes during development of sea urchin embryos is characterized by a high level of transcription from the 16 to 200 cell stage, followed by diminishing transcription, mRNA turnover and cessation of expression after the 500 cell mesenchyme blastula stage. The regulation of changes in expression of these histone genes, and the description of expression of some non-histone chromatin protein genes, is the focal point of the proposed research. The influence of cytoplasm on gene expression will be studied by fusion of embryo blastomeres that display different modes of histone gene expression, and the level of transcription and persistence of cytoplasmic mRNA will be studied in the resultant heterokaryons by nucleic acid hybridization, in situ. The influence of altering the nueclear DNA/cytoplasmic rations by polyspermy and various inhibitors on the establishment of high mRNA synthesis rates will be studied. The cessation of early histone mRNA synthesis in embryos in which cell division and DNA synthesis have been inhibited will also be studied. The run-off transcription of histone genes will be studied in order to clarify the nature of the polymerase II-gene interaction at different stages of development. Some non-histone chromatin proteins are also synthesized at a high level during cleavage. Attempts will be made to isolate cDNA clones encoding some of these proteins, and the structure and expression of these sequences will be studied and compared to the histone genes. These studies should contribute to our understanding of how genes are turned on and off during normal and abnormal development.
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