Alternative linker histone permits fast paced nuclear divisions in early Drosophila embryo.

László Henn,Imre M Boros,Balázs Vedelek,Ádám Román,László Imre,Péter Nánási,Andrea Ábrahám,Anikó Szabó

doi:10.1093/nar/gkaa624

Abstract

In most animals, the start of embryogenesis requires specific histones. In Drosophila linker histone variant BigH1 is present in early embryos. To uncover the specific role of this alternative linker histone at early embryogenesis, we established fly lines in which domains of BigH1 have been replaced partially or completely with that of H1. Analysis of the resulting Drosophila lines revealed that at normal temperature somatic H1 can substitute the alternative linker histone, but at low temperature the globular and C-terminal domains of BigH1 are essential for embryogenesis. In the presence of BigH1 nucleosome stability increases and core histone incorporation into nucleosomes is more rapid, while nucleosome spacing is unchanged. Chromatin formation in the presence of BigH1 permits the fast-paced nuclear divisions of the early embryo. We propose a model which explains how this specific linker histone ensures the rapid nucleosome reassembly required during quick replication cycles at the start of embryogenesis.

Highlights

In eukaryotic cells, genomic DNA is arranged in a highly ordered chromatin structure consisting of nucleosomes as its basic units
Chromatin structure on nucleosome level is similar in wild type and have H1 linker histone (HHH) mutant we focused on exploring phenotypic differences of wild type and HHH mutant embryos at optimal temperature (25◦C) in order to gather information on the specific function of BigH1 in the early embryo
Results of QINESIn assays showed that in nuclei obtained from embryos with linker histone BigH1, nucleosomes were more resistant toward salt elution than nucleosomes containing H1 (HHH)

Summary

Introduction

Genomic DNA is arranged in a highly ordered chromatin structure consisting of nucleosomes as its basic units. Nucleosomes are formed by an octamer core of small, positively charged histone proteins (each composed of dimers of H2A, H2, H3 and H4) wrapped around nearly twice by 145–147 bp DNA. A fifth histone protein, linker histone H1 seals the nucleosome by binding to the entry and exit site of DNA, stabilizing a structure called the chromatosome. Linker histones possess the typical tripartite structure [1] of histone proteins. The central domain has a globular structure, while the lysine-rich N- and C-terminal regions are intrinsically disordered. The globular domain interacts with the nucleosome and the entering/exiting DNA. The Cterminal end is involved in DNA binding [1,2,3], while the N-terminus may contribute to the binding affinity [4]

Methods

Results

Conclusion