Histone H1c decreases markedly in postreplicative stages of chicken spermatogenesis

The relative proportions of four major chicken histone H1 subtypes (referred to as H1a, H1b, H1c and H1d) change markedly in different chicken tissues. The relative amount of H1c is higher in nonreplicating somatic tissues, such as liver, than in replicating immature testis. The proportion of H1c sharply decreases as spermatogenesis proceeds, being much lower in mature than in immature testis. It has been proposed that the relative increment of H1c correlates with low rates of cell division in chicken tissues. It was assumed that the sharp decrease in H1c observed during maturation of chicken testis was a consequence of the intensification of proliferative activity in spermatogonia (Berdnikov et al., 1976). Our results, however, clearly show that the decrease of H1c during maturation is due to the low levels of this protein in postreplicative stages of spermatogenesis, where H1c is barely detectable. These results suggest that the presence of the arginine-rich H1c subtype would neither be compatible with the relaxed structure of acetylated chromatin present in active replicating cells nor with the hyperacetylated chromatin characteristic of postreplicative late spermatids undergoing the nucleohistone nucleoprotamine transition.