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G Childs

Publications and source records attributed to G Childs.

At least 55 records · Page 3Linked to original sources
PubMed1985

Comparison of endogenous murine leukemia virus proviral organization and RNA expression in 3-methylcholanthrene-induced and spontaneous thymic lymphomas in RF and AKR mice.

3-Methylcholanthrene-induced T-cell thymic lymphomas in RF mice were examined for involvement of murine leukemia virus (MuLV)-related sequences in leukemogenesis. Both the expression of MuLV-related RNA species and the organization of endogenous MuLV proviral DNA were analyzed. Of 27 primary tumors examined, only 5 exhibited elevated MuLV-related RNA species homologous to xenotropic specific env DNA. None of these RNA species hybridized with ecotropic p15E DNA sequences. Only two of these five tumors contained MuLV-like RNA species that hybridized with ecotropic MuLV long terminal repeat sequences, despite the probe's ability to detect both ecotropic MuLV and mink cell focus-inducing viral RNA. No muLV resembling mink cell focus-inducing virus whose expression could be correlated with lymphomagenesis was detected in either preleukemic thymocytes, primary 3-methylcholanthrene-induced thymic tumors, tumors passaged in vivo, or cell lines derived from tumors. Restriction endonuclease analysis of DNA from both primary tumors and cell lines failed to reveal either proviral DNA with recombinant env genes or rearrangement of endogenous MuLV proviruses. Therefore, chemically induced lymphomagenesis in RF mice appears different from the spontaneous lymphomagenic process in AKR mice with respect to the involvement of endogenous MuLV sequences.

AKR murine leukemia virus↗
PubMed1984

A new family of tandem repetitive early histone genes in the sea urchin Lytechinus pictus: evidence for concerted evolution within tandem arrays.

We have isolated and characterized a third nonallelic tandemly arrayed histone cluster (LpE) from the sea urchin Lytechinus pictus. Although this tandem array is not intermingled with the other two early histone gene families also found in the L. pictus genome, the order and polarity of the five histone coding sequences in this family are the same as every other well characterized sea urchin early histone gene family. Heteroduplex analysis and restriction endonuclease mapping experiments indicate that the LpE family is more closely related to the B-C than the A-D family of early histone genes. Examination of several individual sperm DNA samples has revealed considerable polymorphism in each of the three tandem repeat families. Within an individual, however, each family is remarkably homogeneous. Thus, our results indicate that rapid fixation of variants acts to homogenize the members of a single tandem array at a considerably faster rate within a family than between families. However, at least some exchange of sequences between families is evident based on the conservation of many restriction endonuclease recognition sites and from analysis of a a cosmid clone in which the A-D and E tandem repeats are found adjacent to one another. These differences in the rate of fixation of variants within and between these families are likely to be responsible for the maintenance of diversity between the different families.

Animals↗
PubMed1984

Sequence comparisons of non-allelic late histone genes and their early stage counterparts. Evidence for gene conversion within the sea urchin late stage gene family.

We have determined the nucleotide sequence of sea urchin (Lytechinus pictus) late stage H3 and H4 histone genes contained on the clone pLpH3H4 -21 and of the early stage H3 gene contained on the plasmid pLpA . Comparison of these differentially regulated histone genes with each other and with other L. pictus late and early stage histone H3 and H4 genes previously sequenced confirms that members of each histone gene family (early and late) are more homologous to each other than they are to members of other histone gene families. The spacer regions between two late H3-H4 gene pairs on the clones pLpH3H4 -19 and pLpH3H4 -21 have diverged to the point where they are no longer homologous. However, comparative analysis of the 5' flanking DNA has identified a sequence 5'C-T-C-A-T-G-T-A-T-T3' upstream of both late H4 genes and another, 5'A-G-A-T-T-C-A3', upstream of both H3 genes. Except for a short conserved sequence near the initiation codon, the transcribed 5' leaders of the late mRNAs differ in length and sequence in the two non-allelic late histone gene pairs. This divergence contrasts with the 95 to 96% conservation found between late histone gene coding sequences. The results suggest that there is intergenic exchange in the germline among members of the late histone gene family and that the unit of exchange is the individual gene rather than the heterotypic dimer which includes the common spacer DNA.

Animals↗
PubMed1983

Distinct organizations and patterns of expression of early and late histone gene sets in the sea urchin.

The set of histone genes that are active late in embryogenesis of the sea urchin (Strongylocentrotus purpuratus) are present in 5-12 copies per genome and, unlike the clustered, tandemly arrayed early histone genes, are dispersed and irregularly arranged. Late H2B gene expression is activated by events accompanying fertilization and its mRNAs a, first detectable by as early as 6 h of development (16 cells) and increase only slightly in amount during the period of rapid cleavage between 6 and 14 h. However, during the short interval between 14 and 16 h, while the amount of early histone mRNA is declining, there is a greater than 15-fold burst in the rate of late H2B mRNA accumulation.

Animals↗
PubMed1982

Sea urchin (lytechinus pictus) late-stage histone H3 and H4 genes: characterization and mapping of a clustered but nontandemly linked multigene family.

We have cloned and characterized members of a small multigene family that encodes late-stage histone H3 and H4 mRNAs from the sea urchin Lytechinus pictus. Unlike their highly repetitive histone gene counterparts, which are expressed at an earlier developmental stage, late H3 and H4 histone genes are not present in tandem repeats. In addition, the late stage H3 and H4 genes are not always tightly clustered together with the H1, H2A and H2B genes as they are in early histone genes. The spacer DNA that separates adjoining H3 and H4 coding regions is not conserved between nonallelic members of the late histone gene family. We have determined the nucleotide sequence of a continuous 2100 bp segment of DNA including both H3 and H4 coding sequences, the entire spacer DNA separating the genes and surrounding nonhistone DNA. The late histone H3 and H4 genes encode proteins identical to their early gene counterparts; however, the 5' leader sequence is shorter in late genes and the codon usage is different.

Animals↗
PubMed1982

Application of the avidin-biotin-peroxidase complex (ABC) method to the light microscopic localization of pituitary hormones.

The avidin-biotin-peroxidase complex (ABC) method was applied to semithin (0.5-1 micron) plastic-embedded sections of intact male rat pituitaries with the use of techniques previously developed for the peroxidase-antiperoxidase complex (PAP) method. Stains for adrenocorticotropin (ACTH), thyroid stimulating hormone (TSH), luteinizing hormone (LH), and follicle stimulating hormone (FSH) were cleaner, more reliable, and more efficient. The ABC method allowed the use of the same high dilutions of primary antisera used with the PAP method. Incubation time was cut to a third of the time used for the PAP stain. Furthermore, if the incubation time matched that used with the PAP method, (24-48 hr), the antisera could be diluted 2- to 4-fold further. This enhanced specific staining and allowed the use of dilutions similar to those used in the radioimmunoassay. In agreement with Hsu and Raine (J Histochem Cytochem 29:1349, 1981), the ABC method produced staining after only a 1-4 hr incubation in primary antibody that was diluted optimally for the PAP complex method. The stain was weak, however, and cell counts showed that it was restricted to the fraction of the specific cell population which stored the most hormone. Our tests showed that the most convenient incubation times for optimal staining were 12-16 hr. Furthermore, the ABC method appeared to stabilize greatly the reaction for FSH and thus improved its precision and reliability.

Adrenocorticotropic Hormone↗
PubMed1981

Orphons: dispersed genetic elements derived from tandem repetitive genes of eucaryotes.

We have discovered in animal cells a novel class of dispersed, solitary genetic elements derived from tandem multigene families. We refer to such displaced elements as orphons. Orphons arise from both protein-coding and non-protein-coding structural gene families, including those of histone and ribosomal genes. Southern transfer hybridization experiments, on DNA digested with enzymes that do not cut the major repeat unit of the family of genes of interest, reveal histone gene orphons in the sea urchin (Lytechinus pictus), ribosomal gene orphons in yeast (Saccharomyces cerevisiae) and ribosomal and H3 histone gene orphons in Drosophila melanogaster. There are more than 50 histone gene orphons in each sea urchin genome. Each of the five histone-coding regions has a number of orphons (5--20), in addition to the several hundred copies in the clusters that are not cut by Bam HI. Most such orphons appear to contain only one coding region. Nearly all sea urchin histone gene orphon loci are polymorphic in the population; no two individuals have the same sets of histone orphons for any coding region. An H3-coding orphon, pLpH30-1, was isolated from the genome of L. pictus. The H3 region homologous to the histone gene clusters is 1200 bases long and includes the complete early H3 gene and some surrounding histone DNA. THe orphon is flanked by at least 1.7 kb of 5' and 3 kb of 3' nonhistone DNA. These flanking sequences are each moderately repetitive in the genome and are not homologous to each other. The orphon differs less than 2% in base sequence from the analogous region of pLpC and only slightly more from pLpA (the major histone gene clones). DNA sequence analysis of the junctions between the H3 region and the immediate flanking nonhistone DNA reveals no evidence of repetitive or palindromic sequences.

Animals↗
PubMed1981

Monocistronic transcription is the physiological mechanism of sea urchin embryonic histone gene expression.

We have examined histone gene expression during the early stages of sea urchin embryogenesis. The five histone genes expressed at that time are contained in tandem repetitive segments. It has been suggested that adjacent coding regions and their intervening spacer sequences are transcribed into large polycistronic messenger ribonucleic acid (RNA) precursors. We have subcloned into pBR322 deoxyribonucleic acid (DNA) sequences mapping either in the coding region, the 5' spacer, or the 3' spacer of the H2B histone gene. These clones were used to produce radioiodinated hybridization probes. We measured the steady-state quantity of H2B messenger RNA as well as spacer-specific RNA in the total RNA from embryos taken at various stages of development from fertilization to hatching of blastulae (0 to 22 h post-fertilization). Small amounts of RNA hybridizing to both spacer probes could be found. However, we show that these RNAs form mismatched hybrids with the spacer DNA and therefore cannot originate from the spacers present in the histone genes. We conclude that there is no detectable transcription of the spacer regions on either side of the H2B histone gene. The detection limit for RNA complementary to the 5' spacer sequence corresponds to a maximum of about three RNA molecules per cell, an amount shown to be far less than the projected steady-state pool size of a putative polycistronic transcript, if such a precursor were to be the obligatory transcript of the histone genes. (This conclusion was derived by using the known rates of production of H2B mRNA throughout early development [R. E. Maxson and F. H. Wilt, Dev. Biol., in press].) The physiologically relevant transcript of the histone genes in early development is therefore monocistronic and probably identical to the messenger RNA itself.

Animals↗
PubMed1981

Postnatal maturation of gonadotropes in the male rat pituitary.

The postnatal maturation of gonadotropes was studied with the use of electron microscopic-immunocytochemical strains for the beta-chains of LH and FSH on serially sectioned fields. A third serially sectioned field was stained with antiserum to ACTH-(17-39). Morphometric studies on semithin and ultrathin plastic sections stained for LH and FSH showed a 200-300% increase in the percentages of LH and FSH cells during the first week of postnatal life. In the 1- to 2-week-old rats, the percentage of gonadotropes in the population was greater than that in the adult. Analysis of the hormone content of serially sectioned gonadotropes showed that storage patterns similar to those in the adult were reached by the seventh day of life. In the neonatal group, 66% of the serially sectioned cells contained both FSH and LH, 20% contained only LH, and 14% contained only FSH. In the 7- to 15-day-old rats, the percentages of gonadotropes containing both hormones increased to 79% while 10-11% of the cells contained only LH or FSH. This is similar to the findings in the adult rat population (75% LH and FSH cells, 14.2% LH cells, and 11% FSH cells). The fields stained for ACTH showed that 35-80% of the gonadotropes contained ACTH-like immunoreactivity during neonatal development, with the highest values seen in the 7- to 15-day-old rats. In the normal adult rats, 2-10% of the gonadotropes contain ACTH activity. Cells containing only ACTH were also seen in all age groups examined. The morphological analysis showed that immature gonadotropic cells contained scattered storage granules, arranged either at the cell periphery or concentrated near the nucleus. They were small, irregularly shaped, and often exhibited a high nucleo-cytoplasmic ratio. They were difficult to distinguish from corticotropes. More mature cell types were found after 1 week of age. These were ovoid and contained numerous large and small granules, features similar to the adult type I cell. The granules, however, were more irregularly shaped (pleomorphic). Immature forms were observed in the gonadotrope population as late as 15 days of age. Most gonadotropes from the 20- to 25-day-old rats resembled those in the adult population. Our findings support the physiological studies which show that the first week of life is an important time for functional and morphological maturation of the gonadotrope population. They also support the finding that immature gonadotropes are larger, more numerous, and more heterogeneous than those in the adult male rat population. Finally, we propose that a subpopulation of gonadotropes may serve as a stem cell or may be involved in the development of adrenal-gonadal interactions.

Adrenocorticotropic Hormone↗
PubMed1979

Rapid purification of biologically active individual histone messenger RNAs by hybridization to cloned DNA linked to cellulose.

We describe a rapid and simple method for the purification of biologically active messenger RNAs. The method allows the isolation in a few hours of specific mRNAs from either whole cell or polysomal RNA even if the RNA represents less than 1% of the starting molecules. We used, as a model, cloned sea urchin (Strongylocentrotus purpuratus) histone gene fragments linked to cellulose by the method of B. E. Noyes & G. R. Stark (1975) Cell 5, 301--310) as hybridization probes to isolate specific histone mRNAs from whole cell and polysomal RNA extracts. RNAs isolated in this manner maintain their biological activity, serving as templates for histone proteins in a wheat-germ, cell-free protein translation system. In addition, radiolabeled histone-specific RNA purified from cleavage stage sea urchin embryos, pulse labeled for short periods of time and analyzed on denaturing polyacrylamide gels, was the same size as mature histone mRNA's.

Animals↗
PubMed1978

Sea urchin nuclei use RNA polymerase II to transcribe discrete histone RNAs larger than messengers.

RNA transcribed in isolated sea urchin nuclei and assayed by hybridization to histone genes cloned in E. coli contains sequences homologous to each of the five histone genes. Histone RNA is synthesized exclusively from the same DNA strand which is the template in vivo. Synthesis of the histone gene transcripts is sensitive to alpha-amanitin concentrations which inhibit RNA polymerase II activity. The fraction of histone RNA synthesized in vitro is comparable at two developmental stages to the fraction synthesized in vivo. The nuclear histone transcripts contain sequences homologous to spacer DNA regions present between the coding regions of the 6500 base pair (bp) histone gene repeat unit. The transcription of spacer sequences was demonstrated by hybridization of the nuclear transcripts to subcloned spacer DNA. Although the bulk of the RNA transcripts are greater than 2000 bases long, the histone-specific transcripts are of discrete sizes ranging from 100 bases to about 1100 bases long. Each histone gene hybridizes with at least one of the larger transcripts and with a different subset of smaller RNAs. We do not detect any giant polycistronic transcript spanning the entire histone repeat unit.

Amanitins↗
PubMed1977

Detection of messenger RNA from the isoleucine--valine operons of Salmonella typhimurium by heterologous DNA-RNA hybridization: involvement of transfer RNA in transcriptional repression.

A hybridization assay using Escherichia coli K-12 DNA isolated from the specialized transducing bacteriophage gammaCI857St68h80 dilv was used to examine the rate of synthesis of the messenger RNA's (mRNA) derived from the isoleucine-valine (ilv) gene cluster of Salmonella typhimurium. In all cases examined, changes in ilv enzyme levels could be correlated with changes in the rate of synthesis of ilv mRNA. Several well characterized regulatory mutants of S. typhimurium had rates of synthesis of ilv mRNA 3 to 8-fold higher than the repressed wild-type strain. The increased rates of ilv mRNA synthesis found in a hisT strain as well as in isoleucyl-and leucyl-tRNA SYNTHETASE MUTANTS, STRONGLY SUGGESTS A ROLE FOR BRANCHED-CHAIN AMINOACYL-TRNA's in transcriptional control.

Coliphages↗
PubMedDate not supplied

Rapamycin blocks IL-2-driven T cell cycle progression while preserving T cell survival.

Effective cellular immune responses require increases in antigen-specific T lymphocytes; IL-2 drives antigen-stimulated T cell proliferation and is largely responsible for the increases observed. We used microarrays containing approximately 9000 mouse cDNAs to study IL-2-induced gene expression. IL-2 induces the expression of genes that regulate cell cycle progression, control cell survival, and increase synthetic and metabolic processes during proliferation. IL-2 also suppresses expression of genes that block cell cycle progression and promote cell death. Rapamycin inhibits IL-2-driven proliferation by downregulating the expression of genes required for key processes required for cell cycle progression. Rapamycin also preserves cell survival by keeping intact the IL-2-induced cell survival programs. These complex multifaceted programs of gene expression permit a dynamic regulation of cellular proliferation and cellular survival.

Animals↗