Chromatin structure in liver nuclei of Atlantic salmon after activation of the vitellogenin gene by 17-β estradiol

Sammanfattning: The present investigations were initiated to study changes in hepatic nucleiduring the 17-ß estradiol induced synthesis of vitellogenin in Atlantic salmon(Salmo salar). As a model system for the naturally maturing fish parr andsmoltified salmon were used and treated with the steroid hormone. Incubation ofliver nuclei with endonucleases made possible a separation of the chromatin intocondensed and dispersed structures. Information on the composition anddistribution of proteins was obtained after fractionation of the chromatin. Theorganization of the hepatic chromatin was altered after treatment of the fishwith 17-ß estradiol. The changes observed depended on the developmental stageof the fish. In parr larger portions of chromatin condensated than in smoltifiedsalmon. In both groups decondensation of the vitellogenin gene regions increasedupon hormone treatment, rendering the gene susceptible to attack by nucleases.The smoltified fish responded more readily than the parr.A protein with an apparent molecular weight of 21 kDa increased inconcentration by the hormone treatment. The protein was enriched in thedispersed chromatin and bound to nucleosomes. It was purified and the aminoacid composition and N-terminal sequence was established. The protein wasclassified as a member of the non-histone high mobility group proteins, involvedin the structure of transcriptionally active chromatin.The condensation of the chromatin was related to an increase in polyamineconcentration. The polyamines bound preferentially to condensed chromatinsupporting the view of a stabilizing effect of the polyamines on the structuralorganization of inactive chromatin.It was concluded that the 17-ß estradiol mediated alterations on hepaticchromatin structure involved a great number of factors among which proteinsand polyamines were predominant in function.

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