Histone H1⁰ accumulates in growth-inhibited cultured cells

Abstract

The H1 class of histones contains several molecular species, even within a single organism ¹. The combination of these subtractions varies according to the state of terminal differentiation^2,3, embryonic development⁴ and hormonal induction⁵. One of the subtractions, H1⁰, occurs at levels that are inversely correlated with the rate of cell division in mammalian tissues⁶. Although H1⁰ might be functionally or even structurally distinct from the usual H1 histone, Panyim and Chalkley⁶ established that its size and amino acid composition resembled other H1 histones. The quantitative studies of its relationship to mitotic index were greatly extended by Marks et al.⁷, and others^8–12 have measured H1⁰ contents during processes such as tissue regeneration and selective tissue destruction. All these observations were consistent with the notion that histone H1⁰ suppresses gene replication. One limitation in these demonstrations of the inverse correlation between H1⁰ and cell division is that there are many variable parameters, other than mitotic index, when comparing one tissue to another. This problem is largely overcome by comparing regenerating tissues to their normal counterparts^8–11. In the latter situation, it is possible that cell types which always have low H1⁰ contents are preferentially replaced early in the regeneration process, while different cell types with high H1⁰ levels build up in the tissue later. If it could be demonstrated that H1⁰ accumulated along with the arrest of cell division in a single cell type, these ambiguities would be removed. We report here such a demonstration using cultured cells.