Anomalous nuclease digestion of Holothuria sperm chromatin containing histone H1 variants

Histones and nucleosomes in Cancer sperm (Decapod: Crustacea) previously described as lacking basic DNA-associated proteins: a new model of sperm chromatin

To date several studies have been carried out which indicate that DNA of crustacean sperm is neither bound nor organized by basic proteins and, contrary to the rest of spermatozoa, do not contain highly packaged chromatin. Since this is the only known case of this type among metazoan cells, we have re-examined the composition, and partially the structure, of the mature sperm chromatin of Cancer pagurus, which has previously been described as lacking basic DNA-associated proteins. The results we present here show that: (a) sperm DNA of C. pagurus is bound by histones forming nucleosomes of 170 base pairs, (b) the ratio [histones/DNA] in sperm of two Cancer species is 0.5 and 0.6 (w/w). This ratio is quite lower than the proportion [proteins/DNA] that we found in other sperm nuclei with histones or protamines, whose value is from 1.0 to 1.2 (w/w), (c) histone H4 is highly acetylated in mature sperm chromatin of C. pagurus. Other histones (H3 and H2B) are also acetylated, though the level is much lower than that of histone H4. The low ratio of histones to DNA, along with the high level of acetylation of these proteins, explains the non-compact, decondensed state of the peculiar chromatin in the sperm studied here. In the final section we offer an explanation for the necessity of such decondensed chromatin during gamete fertilization of this species.

Nucleosomal organization of chromatin in sperm nuclei of the bivalve mollusc Aulacomya ater

The sperm nuclei of Aulacomya ater, family Mitylidae, contain three proteins (X, Aa5 and Aa6) which are specific to this cell type coexisting with a set of five somatic-type histones. Information about the chromatin structure resulting from this kind of association is scarce. Therefore, we have probed the structure of this sperm chromatin through digestion with micrococcal nuclease in combination with salt fractionation. The data obtained have allowed us to propose a nucleosomal arrangement for this chromatin. However, two types of nucleosomes would be present in agreement with their protein components.

Sperm histones and chromatin structure of the "primitive" sea urchin Eucidaris tribuloides

The "primitive" sea urchin Eucidaris tribuloides resembles the advanced sea urchins (euechinoids) in many respects, yet some features of its biochemistry and morphogenesis are more similar to other echinoderms such as starfish or sea cucumbers. Two unique characteristics of the sperm chromatin of all known euechinoids are an extremely long average nucleosomal repeat length and the presence of two male germ-line-specific histone variants, Sp H1 and Sp H2B. Histone composition and nucleosomal repeat length of the sperm chromatin of Eucidaris were compared to those of several euechinoids and a starfish. Eucidaris sperm chromatin contained large H1 and H2B histone variants typical of euechinoids. The H1 was about nine amino acids smaller than Sp H1 of the advanced urchin Strongylocentrotus purpuratus. Its Sp H2B molecules were the same size as in the euechinoids. Peptide maps showed that N-terminal regions of Sp H1 and Sp H2B contained repeating basic amino acid motifs characteristic of euechinoids. The smaller size of Eucidaris H1 is accounted for by a smaller C-terminal region. The repeat length of Eucidaris sperm chromatin was slightly shorter than that of two euechinoids, but significantly larger than starfish, which lacks a large H2B. The Sp H2B gene of Eucidaris was expressed during spermatogenesis in the same cell types as for S. purpuratus. Thus Sp histone subtype expression and chromatin structure in this distantly related echinoid closely resemble the euechinoids. The presence of an Sp H2B and a very long repeat length appear to be characteristic of the echinoids only.

Purification and immunocytolocalization of protein phi 0 from sperm cells of the echinoderm Holothuria tubulosa

Histones in chromatin from germ cells of the echinoderm Holothuria tubulosa are retained throughout spermatogenesis. However, some alterations occur in the histone complement of the mature sperm, including the presence of a germ-line-specific H1 subcomponent unusually rich in arginine, and the appearance of a basic component termed phi 0. Histones from ripe sperm have been extracted in a preparative scale to allow for isolation and purification of protein phi 0. Polyclonal antibodies against phi 0 have been produced and purified by affinity chromatography. The specificity of the antibodies to phi 0 has been assessed by enzyme-linked immunosorbent assays, competition experiments, and Western immunoblotting analysis. No cross-reactivity of the antibodies with the remainder histone fractions has been observed. Immunocytolocalization of protein phi 0 by immunogold labeling has revealed that this protein is essentially confined to chromatin from ripe sperm, whereas it is wholly absent from less advanced germ cell types. From these observations, together with biochemical studies previously reported, it is inferred that protein phi 0 may well be instrumental in the known chromatin transitions occurring in this organism during germ cell development.

The interaction of the histone H1-related protein phi 0 with chromatin

Protein phi 0 is a unique protein which is present in the sperm of the sea cucumber, Holothuria tubulosa. It associates with histones, but its physiological role is unknown. From its amino acid composition and sequence, protein phi 0 can be considered as an H1-related protein. In this paper, we have studied its interaction with chicken erythrocyte chromatin particles of different complexity, from core particles to polynucleosomes. Addition of protein phi 0 results in marked chromatin insolubilization. The higher the molecular weight of the chromatin fragment, the lower is the phi 0/nucleosome molar ratio at which precipitation occurs, so that complete insolubilization of polynucleosomes is achieved at a phi 0/nucleosome molar ratio which is identical to that found in mature H. tubulosa spermatozoa. We have also found that the interaction of protein phi 0 with chromatin is cooperative. These findings contribute to clarification of the peculiar physico-chemical properties shown by H. tubulosa sperm chromatin and the role played by the phi 0 protein.