Immunological Specificities of Lysine-rich Histones from Tumors

Factors controlling the loss of immunoreactive somatic histone H1 from blastomere nuclei in oocyte cytoplasm: a potential marker of nuclear reprogramming

Nuclei of differentiated cells can acquire totipotency following transfer into the cytoplasm of oocytes. While the molecular basis of this nuclear reprogramming remains unknown, the developmental potential of nuclear-transfer embryos is influenced by the cell-cycle stage of both donor and recipient. As somatic H1 becomes immunologically undetectable on bovine embryonic nuclei following transfer into ooplasm and reappears during development of the reconstructed embryo, suggesting that it may act as a marker of nuclear reprogramming, we investigated the link between cell-cycle state and depletion of immunoreactive H1 following nuclear transplantation. Blastomere nuclei at M-, G1-, or G2-phase were introduced into ooplasts at metaphase II, telophase II, or interphase, and the reconstructed embryos were processed for immunofluorescent detection of somatic histone H1. Immunoreactivity was lost more quickly from donor nuclei at metaphase than at G1 or G2. Regardless of the stage of the donor nucleus, immunoreactivity was lost most rapidly when the recipient cytoplast was at metaphase and most slowly when the recipient was at interphase. When the recipient oocyte was not enucleated, however, immunoreactive H1 remained in the donor nucleus. The phosphorylation inhibitors 6-DMAP, roscovitine, and H89 inhibited the depletion of immunoreactive H1 from G2, but not G1, donor nuclei. In addition, immunoreactive H1 was depleted from mouse blastomere nuclei following transfer into bovine oocytes. Finally, expression of the developmentally regulated gene, eIF-1A, but not of Gapdh, was extinguished in metaphase recipients but not in interphase recipients. These results indicate that evolutionarily conserved cell-cycle-regulated activities, nuclear elements, and phosphorylation-linked events participate in the depletion of immunoreactive histone H1 from blastomere nuclei transferred in oocyte cytoplasm and that this is linked to changes in gene expression in the transferred nucleus.

Developmentally regulated loss and reappearance of immunoreactive somatic histone H1 on chromatin of bovine morula-stage nuclei following transplantation into oocytes

One difference between chromatin of bovine oocytes and blastomeres is that somatic subtypes of histone H1 are undetectable in oocytes and are assembled onto embryonic chromatin during the fourth cell cycle. We investigated whether this chromatin modification is reversed when nuclei containing somatic H1 are transplanted into ooplasts. Donor nuclei obtained from morula-stage bovine embryos were fused to ooplasts at different times before and after parthenogenetic activation of the ooplasts. After fusion, immunoreactive H1 became undetectable, and the loss occurred more rapidly when fusion was performed near the time of ooplast activation compared with several hours after activation, when the host oocytes were at a stage corresponding to interphase. Although the loss of immunoreactive H1 occurred independently of DNA replication and transcription, exposure of reconstructed oocytes to cycloheximide or 6-dymethylaminopurine (6-DMAP) delayed the loss of immunoreactive H1 from transplanted nuclei. During further development of nuclear-transplant embryos, somatic H1 remained undetectable at the 2- and 4-cell stages, and it reappeared on the chromatin at the 8- to 16-cell stage, as previously observed in unmanipulated embryos. We conclude that factors in oocyte cytoplasm are able to modify morula chromatin so that somatic H1 becomes undetectable, and that the amount or activity of these factors declines over time in activated ooplasts.

Chromatin modifications during oogenesis in the mouse: removal of somatic subtypes of histone H1 from oocyte chromatin occurs post-natally through a post-transcriptional mechanism

We examined the distribution of the somatic subtypes of histone H1 and the variant subtype, H1(0), and their encoding mRNAs during oogenesis and early embryogenesis in the mouse. As detected using immunocytochemistry, somatic H1 was present in the nuclei of oocytes of 18-day embryos. Following birth, however, somatic H1 became less abundant in both growing and non-growing oocytes, beginning as early as 4 days of age in the growing oocytes, and was scarcely detectable by 19 days. Together with previous results, this defines a period of time when somatic H1 is depleted in oocytes, namely, from shortly after birth when the oocytes are at prophase I until the 4-cell stage following fertilization. At the stages when somatic H1 was undetectable, oocyte nuclei could be stained using an antibody raised against histone H1(0), which suggests that this may be a major linker histone in these cells. In contrast to the post-natal loss of somatic H1 protein, mRNAs encoding four (H1a, H1b, H1d, H1e) of the five somatic subtypes were present, as detected using RT-PCR in growing oocytes of 9-day pups, and all five subtypes including H1c were present in fully grown oocytes of adults. All five subtypes were also present in embryos, both before and after activation of the embryonic genome. mRNA encoding H1(0) was also detected in oocytes and early embryos. Whole-mount in situ hybridization using cloned H1c and H1e cDNAs revealed that the mRNAs were present in the cytoplasm of oocytes and 1-cell embryos, in contrast to the sea urchin early embryo where they are sequestered in the cell nucleus. We suggest that, as in many somatic cell types, the chromatin of mouse oocytes becomes depleted of somatic H1 and relatively enriched in histone H1(0) postnatally, and that somatic H1 is reassembled onto chromatin in cleavage-stage embryos. The post-natal loss of somatic H1 appears to be regulated post-transcriptionally by a mechanism not involving nuclear localization.

Somatic histone H1 microinjected into fertilized mouse eggs is transported into the pronuclei but does not disrupt subsequent preimplantation development

We injected somatic subtypes of histone H1 into newly fertilized mouse eggs, which do not naturally contain this chromosomal protein, and examined the fate of the injected protein and its effect on preimplantation development of recipient eggs. Rhodamine-labelled H1 injected into the cytoplasm of 53 eggs was transported into the pronuclei in 51 cases, and this nuclear accumulation could be detected within 15 min of injection. Unlabelled histone H1, which was detected using immunofluorescence, was also transported following microinjection to the pronuclei, where it colocalized with the chromatin and remained associated with the nuclei following cleavage to the two-cell stage. Nuclear accumulation of injected H1 was inhibited when injected eggs were incubated in the presence of drugs that prevent mitochondrial electron transport or glycolysis, which indicates that nuclear transport occurs through an energy-dependent process, as previously observed in tissue culture cells. To determine whether the presence of somatic H1 in early embryonic nuclei would influence subsequent development, fertilized eggs were injected with an approximately physiological quantity (1-5 pg) of somatic H1 or, as controls, with another small basic protein, cytochrome c. Fifty-three eggs were injected with cytochrome c, of which 51 divided to the two-cell stage, and 32 (60%) reached the blastocyst stage, after 5 days in culture. One hundred and eleven eggs were injected with somatic H1, of which 95 divided to the two-cell stage, and 53 (48%) reached the blastocyst stage, after 5 days in culture. The two groups did not differ statistically (chi 2, P > 0.1) with respect to the fraction of injected embryos that developed to the blastocyst stage. These results show that, although mouse embryos lack the somatic subtypes of histone H1 until the four-cell stage of development, they are able to progress through preimplantation development when these subtypes are present beginning at the one-cell stage. This may imply that the distinctive chromatin composition that characterizes early embryos of a variety of species is not essential for early development in mammals.

Assembly of somatic histone H1 onto chromatin during bovine early embryogenesis

We have examined the distribution of somatic histone H1 in bovine oocytes and preimplantation embryos, using an antibody that recognizes histone H1 subtypes present in somatic cells. Immunoreactive H1 was not detectable on the chromosomes of metaphase II of meiosis nor in the nuclei of early cleavage-stage embryos. In most embryos, immunoreactive H1 was assembled onto embryonic chromatin during the fourth to sixth cell cycle after fertilization. No immunoreactive somatic histone H1 was detected, however, when embryos were incubated in the presence of alpha-amanitin beginning early during the fourth cell cycle. These results indicate that somatic subtypes of histone H1 are assembled onto embryonic chromatin in a developmentally regulated manner that requires embryonic transcription. Aphidicolin, an inhibitor of DNA replication, also inhibited the assembly of somatic histone H1 onto chromatin when present at early stages of the 4th cell cycle. It is suggested that, because the bulk of histone gene expression in proliferating cells occurs during DNA replication, expression of genes encoding immunoreactive H1 is inhibited in embryos blocked before or soon after entering the S-phase. These findings on the control of somatic histone H1 assembly onto chromatin in cattle show a remarkable similarity to those found in the mouse. Such evolutionary conservation suggests that the somatic histone H1 complement of chromatin may regulate critical aspects of chromatin activity during mammalian oogenesis or early embryogenesis.

Developmental regulation of chromatin composition during mouse embryogenesis: somatic histone H1 is first detectable at the 4-cell stage

We have examined the distribution of histone H1 in oocytes and preimplantation embryos of the mouse, using a polyclonal antibody raised against the histone H1 subtypes present in somatic cells. Immunofluorescence and immunoblotting analyses failed to detect somatic histone H1 in germinal vesicle (GV)-stage oocytes. In contrast, somatic histone H1 was detectable by immunofluorescence in the nuclei of GV oocytes previously injected with histone H1 as well as the nuclei of ovarian granulosa cells, and by immunoblotting in 8-cell embryos. 1- and 2-cell embryos examined by immunofluorescence did not contain detectable somatic histone H1. At the early 4-cell stage (54-56 hours post-hCG), 5 of 52 embryos contained somatic histone H1 in one or more nuclei. By the late 4-cell stage (66-68 hours post-hCG), however, 58 of 62 embryos contained somatic histone H1. In 8-cell embryos, morulae and blastocysts, all nuclei contained somatic histone H1 in every case. When embryos were exposed to the transcriptional inhibitor, alpha-amanitin, beginning at the late 2-cell stage, they cleaved to the 4-cell stage but fewer than 10% developed histone H1 immunoreactivity. When treatment began at the early 4-cell stage, the embryos that remained at the 4-cell stage in the presence of the drug developed histone H1 immunoreactivity in half of the cases. Embryos that reached the 5- to 8-cell stage in the presence of the drug developed histone H1 immunoreactivity in every case.(ABSTRACT TRUNCATED AT 250 WORDS)

Predictability of sequence homologies among lysine-rich histones by immunological distance

The relationship between immunological distance (I.D.) measured by microcomplement fixation and amino acid sequence difference for lysine-rich histones was tested using antisera to lysine-rich histones of known sequence, chicken H1 and H5, goose H5, and trout H1 as well as to trout H5. The best relationship between I.D. (y) and percent sequence difference (x) for lysine-rich histones, y = 2x, applies as well to other histones of known sequence but it differs from y = 5x, reported for other proteins and often used for histones. Although deviations indicate that I.D. is a poor predictor of primary sequence differences among histones, it suggests that trout H5 is more closely related to H1 than to chicken H5.

Histone phosphorylation in explants of mouse mammary glands and tumors

Rates of histone phosphorylation were measured in explants of mammary glands from mouse strains with high and low tumor incidence. Explants of hormone dependent and independent mouse mammary tumors were also investigated. All mouse strains studied showed predominant phosphorylation of H2A histone at serine and threonine residues. No differences in rates of H2A phosphorylation in glands were found between strains having different mammary tumor susceptibility. Hormone-dependent GR mouse mammary tumors also showed high H2A phosphorylation, but in some tumors also H1 and H3 were phosphorylated. Hormone-dependent GR tumors had 2-5 times higher histone phosphorylation at serine and threonine than hormone-independent tumors.

Comparison of nuclear proteins from DMBA-induced mammary tumors and lactating mammary glands by polyacrylamide gel electrophoresis

Nuclear proteins were extracted from purified nuclei of 7,12-dimethylbenz(a)anthracene(DMBA)-induced tumors and normal mammary glands of the rat by enzymatic treatment. Of the 34 bands indicated by one-dimensional polyacrylamide gel electrophoresis of nuclear proteins, 6 appeared in high concentration in tumors but were found as traces or undetectable in normal glands; 6 others were clearly shown in the latter but were not detectable or greatly reduced in the former. Two-dimensional electrophoresis identified about 130 and 92 non-histone proteins in normal mammary and tumor cell nuclei respectively. Marked differences in spot density were noted especially in spots (M.W. X 10(-3)/pI) 100/5.7 and 200/5.5 of tumors and 28/7.1, 32/5.4, 36/5.4, 38/6.9, and 68/6.0 of normal tissue. The relationship between these nuclear proteins and the development of mammary tumors is also discussed.

Anticentromere antibodies bind to trout testis histone 1 and a low molecular weight protein from rabbit thymus

Antibodies directed against centromeric chromatin characteristically occur in the sera of patients with the CREST variant of scleroderma. We have studied the in situ enzymatic sensitivity and solubility of the centromeric antigen and have isolated an antigenic moiety that reacts with anticentromere antibodies. The centromeric antigen in the human epithelial cell line, HEp-2, was sensitive to DNAase I and micrococcal nuclease but not affected by RNAase A, trypsin or amylase. It was insoluble in 0.15-4 M NaCl but was extracted from the HEp-2 cells by 4 M urea/2 M NaCl. Antigenic activity in a 4 M urea/2 M NaCl extract of rabbit thymus was demonstrated by immunoabsorption. Indirect immunofluorescence of the extract separated by polyacrylamide gel electrophoresis revealed a fluorescent band with a mol. wt of 33,000. Calf thymus and trout testis histone preparations were fractionated by gel electrophoresis and transferred by blotting techniques to diazobenzyloxymethyl cellulose paper for autoradiography. Anticentromere antibodies bound to and were absorbed by trout testis histone 1. We propose that the centromeric antigen may be a variant of histone 1 that is associated with condensed chromatin.

An initial step in the induction of cancer, the loss of histone H1 from chromosomes - a hypothesis

Unexpected blood group antigens of the P and ABO blood group systems have been found on gastric carcinoma cells of some individuals whose red cells did not possess the antigens and whose sera contained the corresponding antibodies. On the basis of the known biosynthetic pathways leading to the synthesis of the antigens, and on the concept that the blood group genes involved control the structure of glycosyltransferases, it seems that the individuals possess the respective glycosyltransferases structural genes which are not expressed in normal tissues. However, the genes have become expressed in the carcinoma cells.

Distribution of antigenicity in chicken erythrocyte histone H5

We have compared the inhibitory strengths of eight peptides from chicken histone H5 to that of the parent protein (189 residues) in complement fixation by guinea pig anti-H5 serum complexed with the homologous histone. Two precisely delineated regions (residues 59 to 65 and 94 to 99) and two less-defined regions (between 66 and 93; 100 and 189) are depicted. The sequences of particular consequences are quite conserved in avian histone H5 while the most variable N-terminal portion of 31 residues has no inhibitory effect.

Chromosomal proteins in hepatocarcinogenesis

The chromosomal proteins of rat liver were studied by SDS-gel electrophoresis during the process of nitrosomorpholine-induced hepatocarcinogenesis, in the primary hepatomas thus obtained, and in their metastases. It was found that an increased proteolytic activity was present in liver homogenates from carcinogen-fed animals which caused differences between the nonhistone chromosomal proteins of control and carcinogen-treated livers. These differences disappeared in the presence of the protease inhibitor PMSF. In the primary hepatomas slight quantative changes were observed: an increased amount of two proteins of 43000 and 63000 daltons molecular weight, respectively, and a decrease in the histone subfraction H 1 degrees. In the metastases both quantative and qualitative differences were detected: a strong decrease in the protein bands corresponding to the contractile proteins alpha-tubulin, beta-tubulin, and actin; an increased content of the 63000 dalton protein; the appearance of new proteins of approximately 60000, 90000, and 120000 daltons molecular weight, and the complete disappearance of histone H 1 degrees.

High multiplicity of H1 histones from mouse mammary tumors

Lysine-rich (H1) histones were isolated from mammary tumors of GR mice. Chromatography of the H1 histone class on a long column (130 X 1 cm) of Amberlite IRC-50 resin revealed the presence of nine components, designated 1-9 according to their order of elution. Amino acid analysis indicated that components 2-9 represented H1 class histones, but that peak 1 represented a nonhistone protein. Studies of three types of mouse mammary tumors, viz. hormone-dependent, hormone-responsive and hormone-independent, did not reveal significant differences in elution profiles of the H1 histones. In contrast, the H1 histone class from a dog mammary tumor differed chromatographically from that of mouse mammary tumors, indicating species specificity in elution patterns of mammary tumor H1 histones.

Exposure of histone antigenic determinants in chromatin

The exposure of antigenic determinants of histones present in "native" chromatin was studied by: (1) testing their ability to elicit anti-histone antibodies and (2) measuring their ability to interact with anti-histone sera. To this end, antisera specific to purified histone fractions and to purified rat liver chromatin were elicited in rabbits. The anti-chromatin sera did not react with pure histone fractions and pure histone fractions F2b, F3, F2a1, and F2a2 failed to inhibit the complement fixation resulting from the binding of anti-chromatin to chromatin. These results suggest that in native chromatin, determinants in these histones are not immunogenic. Histone F1, however, inhibited the reaction between chromatin and anti-chromatin. Antisera elicited by histone fractions reacted weakly with "native" chromatin. The maximal complement fixations (obtained with 5-10 mug of chromatin DNA) were as follows: 60% with anti-F2b, 20% with anti-F1 and anti-F3, and less than 5% with either anti-F2a1 or anti-F2a2. Studies of the interaction between anti-histone antibodies and chromatin in which chromatin was used as an immunoadsorbent indicated that antibodies against different histones were adsorbed to a different degree by the same amount of chromatin. Differences in the immunoadsorbing capacity between sonicated and nonsonicated chromatin were found. Quantitative adsorbtion studies revealed that in the "native" chromatin structure, antigenic determinants of F1 and F2b were more available to interact with homologous antibody than those of F3 and F2a1 and that determinants in F2a2 were the least available. It could be calculated that the "equivalent antigenicity" of the histones in chromatin was 9.6% for F1, 3.2% for F2b, and 0.90% for F3 and F2a1. Upon sonication these values did not change for F1 but increased two-, three-, and fourfold for F2b, F3, and F2a1, respectively. Digestion of chromatin with trypsin totally abolished the ability of chromatin to adsorb anti-histone antibodies.