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Evidence for erythrocyte-specific histone modification and structural changes in chromatin during goose erythrocyte maturation.

Regenerating blood of geese suffering from phenylhydrazine anaemia was separated into ‘mature’ and ‘immature’ cell populations by centrifugation through a barrier of BSA. Socalled ‘mature cells’ consisted of mainly mature erythrocytes and ‘immature cells’ included two-thirds polychromatic and younger erythroblasts. Histone proteins, dissociated from isolated nuclei of both populations of cells by sequential extraction with citric acid and hydrochloric acid, were compared and the nuclei were examined by electron microscopy. Erythrocyte-specific histone V (f2c) was fully extracted from immature nuclei at pH 2.0, but only partially extracted at the same pH from mature nuclei. An inverse correlation was found between relative case of extraction and alkali-labile phosphate content of purified samples of histone V. The more readily dissociated fraction of histone V from immature nuclei had a higher phosphate content than the less readily dissociated component V from immature and mature nuclei. Chromatin in mature nuclei became tightly congealed after only partial extraction of histone V at pH 2.0, but loosened visibly after subsequent full extraction of histone V at pH 1.8. In contrast, chromatin in immature nuclei never became totally congealed. Histone V may be a tissue-specific agent involved in packing of DNA within chromatin fibrils. During erythropoiesis, progressive decrease of histone V phosphate may lead to its increased binding affinity for chromatin and thus to the gradual transformation of the erythrocyte genome into a permanently repressed state.