Int..I. De'.lIiol. 35: 43-48 (1991) 43 Original Article Histone H1c decreases markedly in postreplicative stages of chicken spermatogenesis JACINT BOIX and CRISTOBAL MEZQUITA* Department of Physiological Sciences, Molecular Genetics Research Group, Faculty of Medicine, University of Barcelona, Spain ABSTRACT The relative proportions offour major chicken histone H1 subtypes (referred to as H1a, H1b, H1c and H1dJ 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. KEY WORDS: hislollf> III vflrianls, Hie, chromatin, sj)nmatogfllfsis Introduction Histones are involved in the packaging of DNA in the eukaryotic nuclei. Whereas histones H2A, H2B, H3 and H4 playa fundamental role in the formation of nucleosomes, histone Hi participates in all levels of DNA packaging: 1) Sealing off the two turns ofnucleosomal DNA, and thereby stabilizing the nucleosomal structure: 2) inducing the salt-dependent compaction of the nucleosomal strand; 3) folding the nucleosomal cores into a compact 30 nm fiber, and 4) aggregating the chromatin in vitro in a way that might be similar to the heterochromatic clumps observed in electron micrographs (McGhee and Fe1senfeld. 1980; Losa eJ al" 1984). In all species studied histone Hi is heterogeneous (Cole, 1987). In the chicken, six histone Hi subtypes and their corresponding genes have been sequenced (Coles et al., 1987; Shannon and Wells, 1987). Though little is known about the physiological role of histone Hi subtypes, it has been suggested that chromatin might be viewed as a mosaic of aggregation-resistant and aggregation-prone regions which differ in Hi content both qualitatively and quantitatively (Cole, 1987). During spermiogenesis chromatin undergoes one of the most dramatic changes observed in eukaryotes (Mezquita, 1985). The euchromatic and heterochromatic nuclear regions are replaced in elongating spermatids by fibers of uniform appearance. The chro- matin of elongated spermatids contains hyperacetylated histones and undergoes a structural change with a marked increment in DNA binding sites, followed by protamine deposition and the subsequent histone removal (Mezquita and Teng, 1977a, b; Oliva and Mezquita, 1982: Oliva and Mezquita, 1986; Oliva et al., 1987). The marked structural and functional transitions of chromatin during spermatogenesis offer an ideal system to study the involve- ment of histone Hi subtypes in these processes. We report here the characterization of histone Hi complement in postreplicative stages of spermatogenesis in comparison with the complement of replicative immature testis enriched in spermatogonia. The complement of chicken testis cells has also been compared with nonreplicating somatic tissues. such as liver, or erythrocytes. Results Changes in the relative proportions of H1. subtypes in different chicken tissues We have determined the relative proportions of histone H1 subtypes in different chicken tissues: immature testis, mature testis, liver, erythrocytes and reticulocytes. The four major histone Hi subcomponents quantified in this paper correspond to the main electrophoretic bands previously described in chick embryo and chicken testis cell nuclei at different stages of spermatogenesis Abbm.'iatiml5 IIst'd ill this papt'1: SDS. sodium dodl'cylsulfatl'; DNase I. deoxyribonuclease. -Address for reprints: Departamento de Fisiologia, Facultad de Medicina, Universidad de Barcelona, Casanova 143. 08036 Barcelona. FAX: 34-3- 490.93.46 0214-6282/91/S03.00 e UBC Pr~" Prin(~J;n Spain