A novel linker histone-like protein is associated with cytoplasmic filaments inCaenorhabditis elegans

Abstract

The histone H1 complement of Caenorhabditis elegans contains a single unusual protein, H1.X. Although H1.X possesses the globular domain and the canonical three-domain structure of linker histones, the amino acid composition of H1.X is distinctly different from conventional linker histones in both terminal domains. We have characterized H1.X in C. elegans by antibody labeling, green fluorescent protein fusion protein expression and RNA interference. Unlike normal linker histones, H1.X is a cytoplasmic as well as a nuclear protein and is not associated with chromosomes. H1.X is most prominently expressed in the marginal cells of the pharynx and is associated with a peculiar cytoplasmic cytoskeletal structure therein, the tonofilaments. Additionally H1.X::GFP is expressed in the cytoplasm of body and vulva muscle cells, neurons, excretory cells and in the nucleoli of embryonic blastomeres and adult gut cells. RNA interference with H1.X results in uncoordinated and egg laying defective animals, as well as in a longitudinally enlarged pharynx. These phenotypes indicate a cytoplasmic role of H1.X in muscle growth and muscle function.

Characterization of Phosphorylation Sites on Histone H1 Isoforms by Tandem Mass Spectrometry

“…This protein can also be found in the cytoplasm as well as in the nucleus. Researchers have shown that H1.X is expressed in the cytoplasm of body and vulva muscles in C. elegans and may play a role in muscle growth and muscle function . Since the H1 analyzed in this report came from cervical cancer cells (a reproductive muscle cell), the presence of H1.X is not surprising.…”