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Biomedical subjects

G R Green

Publications and source records attributed to G R Green.

At least 55 records · Page 3Linked to original sources
PubMed1987

Transitions in histone variants during sea urchin spermatogenesis.

Transitions in the histone complement of nuclei during sea urchin spermatogenesis were investigated by two-dimensional gel electrophoresis. Nuclei were isolated from male gonads of individuals differing in degree of maturity. Unlike protamines, the sea urchin sperm-specific histone variants Sp H1 and Sp H2B appear early in spermatogenesis, well before spermatid differentiation, as the predominant representatives of their classes. Both proteins are phosphorylated from their first appearance until the last steps of spermiogenesis, when the highly condensed late spermatid nuclei become spermatozoan nuclei. Phosphorylation of serine occurs mostly (Sp H1) or entirely (Sp H2B) on the N-terminal portions of these molecules. We conclude that phosphorylated sperm-specific histone variants in the sea urchin function in spermatocytes during meiosis and are the major histones present during replication and transcription in some spermatogonia as well. We propose that the dephosphorylation of Sp H1 and Sp H2B in late spermatids is not primarily responsible for spermatid chromatin condensation but instead may act to stabilize the chromatin of the spermatozoon or aid in the final shaping of the sperm nucleus.

Animals↗
PubMed1986

Modification of verbal behavior of the mentally impaired elderly by their spouses.

Speaking disorders frequently result in serious consequences for mentally impaired elderly people. Two examples are presented illustrating the modification of both excess and deficit rates of talking via differential reinforcement procedures. Two men exhibiting verbal disorders severe enough to impair social interactions and lead to possible nursing home placement were treated by teaching their spouses to reinforce positive and ignore undesired verbal responses. Problem behaviors were reduced sufficiently to permit continued home care, and alternative positive behaviors were increased. These findings suggest that verbal behavior of the mentally impaired elderly can be affected by applying systematic consequences and can be modified by relatively simple procedures. These procedures provide an alternative to the negative effects of labels associated with either aversive or deficient verbal behaviors, promote more positive activities, and enable continued residence at home. Further, this research provides support for the generality of the utility of training spouses to serve as behavior therapists for the impaired elderly.

Aged↗
PubMed1985

Phosphorylation of sea urchin sperm H1 and H2B histones precedes chromatin decondensation and H1 exchange during pronuclear formation.

Immediately following fertilization in the sea urchin, sperm-specific histones Sp H1 and Sp H2B are phosphorylated. Then, in parallel with chromatin decondensation, nearly all phosphorylated Sp H1 is lost from the pronuclear chromatin, with the concurrent assimilation of the egg phosphoprotein CS H1. Chemical cleavage of in vivo labeled Sp H1 and Sp H2B shows that serine phosphorylation occurs in the unusually long N-terminal region of these proteins. These regions contain tandemly repeated tetra- and pentapeptide units each containing serine, proline, and two basic amino acids. It is proposed that sperm chromatin decondensation may require prior phosphorylation of these unusual N-terminal regions, whose function in the mature sperm may be to condense or stabilize its highly compact chromatin.

Amino Acid Sequence↗
PubMed1984

Remodeling of sperm chromatin following fertilization: nucleosome repeat length and histone variant transitions in the absence of DNA synthesis.

Within the first cell cycle following fertilization the average nucleosomal repeat length of sea urchin male pronuclear chromatin declines by 30-40 base pairs to a value typical of that found in the embryo. This decline occurs after a lag of about 30 min postfertilization, and is accompanied by replication of the male chromatin and accumulation of cleavage-stage (CS) core histone variants. When replication is inhibited by greater than 95% with aphidicolin, the decline in repeat length still occurs, although it is slightly retarded. The decline in repeat length also occurs when protein synthesis is blocked by greater than 98% and DNA synthesis by 60-70% with emetine. The adjustment of nucleosome repeat length therefore can occur in vivo without extensive movement of replication forks across the length of the chromatin, or normal progression of the cell cycle, and appears to require no proteins synthesized postfertilization. Blocking of DNA synthesis or protein synthesis also does not prevent the normal histone variant transitions involved in male pronuclear chromatin remodeling. Although their accumulation is slowed, CS core variants eventually become the predominant male pronuclear histones in their classes when replication is inhibited. Since a shortening of the average nucleosomal repeat length of approximately 10-20% is not sufficient to account for this large acquisition of CS variants, some of the sperm (Sp) core histones are probably displaced from the replication-blocked pronucleus. Therefore, accumulation of CS H2A and CS H2B are temporally correlated with the repeat length transition, whereas replication, normal progression of the cell cycle, and the early histone transitions involving SpH1 and SpH2B are not.

Animals↗
PubMed1983

Histone-like protein in the Archaebacterium Sulfolobus acidocaldarius.

The Archaebacterium Thermoplasma acidophilum contains a basic chromosomal protein remarkably similar to the histones of eukaryotes. Therefore, it was of interest to examine a different Archaebacterium for similar proteins. We chose to examine Sulfolobus acidocaldarius because it is thermophilic, like T. acidophilum, but nevertheless the two organisms are not particularly closely related. Two major chromosomal proteins were found in S. acidocaldarius. The smaller of these was soluble in 0.2 M H2SO4 and had a molecular weight of 14500. The larger was acid-insoluble and had a molecular weight of about 36000. Together, the proteins protected about 5% of the DNA against nuclease digestion and stabilized about 50% against thermal denaturation. Overall, the properties of these proteins were intermediate between those of the Escherichia coli protein HU and T. acidophilum protein HTa.

Amino Acids↗
PubMed1981

A histone-like protein (HTa) from Thermoplasma acidophilum. I. Purification and properties.

A histone-like protein (HTa) has been isolated from cell extracts of Thermoplasma acidophilum by column chromatography on DNA-cellulose, hydroxylapatite, and Sephadex G-75, HTa elutes from DNA-cellulose in two fractions, one of which contains an 80-residue form of the protein with an NH2-terminal sequence of Val-Gly. The other fraction apparently contains the 89-residue species, in addition to a 90-residue form of the protein with the NH2-terminal sequence Met-Val. The sequence of 47 residues from the NH2 terminus of the 89-residue protein was established by automated Edman degradation. HTa is characterized by the following properties: 22% of its residues are lysine and arginine; the lysine:arginine ratio is 2.33; the absorption spectrum of the protein is distinctive due to the lack of tryptophan and the presence of 1 tyrosine and 5 phenylalanine residues; and the protein stabilizes DNA against thermal denaturation (Stein, D. B., and Searcy, D. G. (1978) Science 202, 219-221) and condenses DNA into spherical particles. All of these characteristics indicate that HTa resembles eukaryotic histones, but there are distinctive differences.

Amino Acids↗
PubMed1981

Adhesion of particulate specimens to support films for electron microscopy: a model system for assessing the surface properties of support films, and its application to chromatin particles.

Silica microspheres bearing a known surface charge were used to test the adhesive properties of support films and support film treatments commonly used in the electron microscopy of particulate specimens. Adhesion was strongly correlated with surface charge, negatively charged microspheres binding well only to positively charged support films and vice versa in solutions of low ionic strength. This charge dependency could be overcome by increasing the ionic strength to about 100 mmol with monovalent cations; under these conditions, it was not necessary to provide an oppositely charged film surface to obtain adhesion. Chromatin particles (nucleosomes) which have a net negative charge, behaved very much like the negatively charged silica with respect to adhesion, confirming that the microspheres provided an accurate indication of support film surface properties. The chromatin particles showed dramatic structural changes under conditions when adhesion was either poor, or very strong, indicating the need for careful selection of binding conditions for delicate biological specimens. A new and simple method for pretreating carbon films to improve adhesion was developed, and a preliminary account of this technique is presented.

Carbon↗
PubMed1978

Somatotrophic diabetes: insulin release responses to arginine and glucagon in dogs.

Growth hormone injected daily in 6 dogs for 6 days caused a 20-fold elevation in fasting serum immunoreactive insulin (IRI) without appreciable change in serum glucose in 1 day. In the somatotrophic diabetes that occurred after 2 days, the hyperinsulinaemia was maintained and the serum IRI/glucose (I/G) ratio declined from the early high level but remained elevated. During this treatment, in response to glucose infusion, the rise in serum IRI above the initially high fasting level was 16 times the normal. In response to glucagon, the rise in IRI was twice the normal and the rise in glucose was more prolonged, resulting in a decline in the I/G ratio. In response to arginine infusion, the rise in serum IRI was 8 times the normal and the rise in the I/G ratio was twice normal. Following a meal, the rise in serum IRI was 8 times the normal. Thus, with growth hormone treatment the insulin secretory responses to these stimulating factors were magnified over the already elevated fasting level of secretion. The insulin content of the pancreas was reduced to less than 10% of normal by growth hormone treatment for 6 days, due apparently to elevation of the rate of secretion over the rae of formation of insulin.

Animals↗
PubMed1978

Phylogenetic affinities between eukaryotic cells and a thermophilic mycoplasma.

Thermoplasma acidophilum, a thermophilic mycoplasma, has several unusual features suggesting a possible relationship to eukaryotic cells. One feature is a histone-like protein that is associated with the DNA, condensing it into subunits similar to those in eukaryotic chromatin. A second feature is an association of cytoplasmic proteins that resembles eukaryotic actin and myosin. These two components are widely distributed in different groups of eukaryotic cells, but are typically lacking in prokaryotic cells. Furthermore, T. acidophilum lacks cytochromes and respires by enzymes that apparently are not coupled to oxidative phosphorylation. This primitive type of respiration resembles that of microbodies, another feature which is represented in the cytoplasm of all groups of eukaryotic cells. Furthermore, since T. acidophilum lacks a cell wall and appears to have a primitive correlate of endocytosis, it would appear to be mechanically capable of acquiring a symbiotic mitochondrion. Thus, our observations are consistent with the symbiotic hypothesis for the origin of eukaryotic cells. We suggest that an organism similar to T. acidophilum was the host cell for the original symbiosis, becoming the nucleus and cytoplasm of modern eukaryotic cells.

Actomyosin↗
PubMed1977

Mechanism of hypogonadism in cirrhotic males.

Men with chronic liver disease frequently develop clinical signs of hypogonadism and overt feminisation. Associated with these features, they have been found to have a reduced production of testosterone with low plasma concentrations, but only a minority of cirrhotic men would seem to have a marginal increase in circulating biologically potent oestrogens. Furthermore, this latter finding does not correlate with the presence of clinical feminisation. The original hypothesis to explain these changes now seems less likely to be true and no other single hypothesis has, on its own, been found to provide an adequate explanation for all the clinical and biochemical features found in cirrhotic men. It may be that the pathogenesis of endocrine changes in cirrhotic men is multifactorial--for instance, a combination of decreased hepatic clearance of some oestrogenic compounds, an autoimmune mediated primary testicular defect, and a specific potentiation effect by alcohol. Alternatively, it may be that none of these suggested mechanisms is of importance and that the endocrine changes are mediated instead by other mechanisms which remain, as yet, undiscovered or unconsidered. The fascination which this problem has held for clinicians and biochemists for many years seems likely to persist for some time to come.

Alcoholism↗