H1 Histone and nucleosome repeat length alterations associated with the in vitro differentiation of murine embryonal carcinoma cells to extra‐embryonic endoderm

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Abstract
The histone compositions and average distance between nucleosomes have been determined for F9.22 and PSA1 murine embryonal carcinoma cell lines, for primary extra‐embryonic endoderm derived from the in vitro differentiation of PSA1 embryonal carcinoma cells, and for two long‐term extra‐embryonic endodermal cell lines. A change in the relative proportions of two forms of the H1 histones (H1A and H1B) was found to correlate with the extra‐embryonic endodermal differentiated phenotype. The embryonal carcinoma cells had a ratio of H1A/H1B of 1.49 or greater. In contrast, extra‐embryonic endoderm from either cell lines or freshly isolated from differentiating embryonal carcinoma cell cultures had a ratio of H1A/H1B of less than 0.9. Partial peptide mapping of gel purified H1A and H1B suggest the two proteins differ in primary structure. The nucleosome repeat length of the embryonal carcinoma cell lines was 196 bp of DNA. Primary extra‐embryonic endoderm was found to have a value of 205 bp, but the long‐term extra‐embryonic endodermal cell lines had an average nucleosome repeat length of 187 bp. Since both freshly isolated primary endoderm and the long‐term endodermal cell lines express differentiated functions (basement membrane glycoproteins and plasminogen activator activity), there appears to be no simple correlation between the nucleosome repeat length and the expression of these differentiated functions.