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G Childs

Publications and source records attributed to G Childs.

At least 19 recordsLinked to original sources
PubMed1990

Identification of a Caenorhabditis elegans histone H1 gene family. Characterization of a family member containing an intron and encoding a poly(A)+ mRNA.

The isolation and properties of a gene encoding a histone H1 protein of Caenorhabditis elegans, his-24, are described. The predicted protein sequence is similar to histone H1 proteins of other eukaryotes. However, the gene structure of his-24 is atypical for a histone H1 gene; it contains an intron and encodes a polyadenylated mRNA. A family of approximately five histone H1 genes is defined by cross-hybridization to his-24. All appear to encode polyadenylated mRNAs. One gene is expressed specifically in male germ cells. These histone H1 genes are dispersed individually in the genome, apart from the previously described clusters of core histone genes (H2A, H2B, H3 and H4), which probably all encode non-polyadenylated mRNAs. This histone gene organization, with clustered core histone genes, encoding non-polyadenylated transcripts, and dispersed, histone H1 genes from which it appears only polyadenylated messages arise, suggests that C. elegans is at a stage of evolution of the histone gene family intermediate between lower eukaryotes (e.g. yeast) and the most advanced forms.

Amino Acid Sequence↗
PubMed1989

Nucleotide sequences of Caenorhabditis elegans core histone genes. Genes for different histone classes share common flanking sequence elements.

We have determined the nucleotide sequence of core histone genes and flanking regions from two of approximately 11 different genomic histone clusters of the nematode Caenorhabditis elegans. Four histone genes from one cluster (H3, H4, H2B, H2A) and two histone genes from another (H4 and H2A) were analyzed. The predicted amino acid sequences of the two H4 and H2A proteins from the two clusters are identical, whereas the nucleotide sequences of the genes have diverged 9% (H2A) and 12% (H4). Flanking sequences, which are mostly not similar, were compared to identify putative regulatory elements. A conserved sequence of 34 base-pairs is present 19 to 42 nucleotides 3' of the termination codon of all the genes. Within the conserved sequence is a 16-base dyad sequence homologous to the one typically found at the 3' end of histone genes from higher eukaryotes. The C. elegans core histone genes are organized as divergently transcribed pairs of H3-H4 and H2A-H2B and contain 5' conserved sequence elements in the shared spacer regions. One of the sequence elements, 5' CTCCNCCTNCCCACCNCANA 3', is located immediately upstream from the canonical TATA homology of each gene. Another sequence element, 5' CTGCGGGGACACATNT 3', is present in the spacer of each heterotypic pair. These two 5' conserved sequences are not present in the promoter region of histone genes from other organisms, where 5' conserved sequences are usually different for each histone class. They are also not found in non-histone genes of C. elegans. These putative regulatory sequences of C. elegans core histone genes are similar to the regulatory elements of both higher and lower eukaryotes. The coding regions of the genes and the 3' regulatory sequences are similar to those of higher eukaryotes, whereas the presence of common 5' sequence elements upstream from genes of different histone classes is similar to histone promoter elements in yeast.

Animals↗
PubMed1989

Attack ferrets?

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Animals↗
PubMed1989

Histone gene expression during sea urchin spermatogenesis: an in situ hybridization study.

The expression of testis-specific and adult somatic histone genes in sea urchin testis was investigated by in situ hybridization. The testis-specific histone genes (Sp H2B-1 of Strongylocentrotus purpuratus and Sp H2B-2 of Lytechinus pictus) were expressed exclusively in a subset of male germ line cells. These cells are morphologically identical to replicating cells pulse-labelled with 3H-thymidine. Genes coding for histones expressed in adult somatic and late embryo cells (H2A-beta for S. purpuratus and H3-1 for L. pictus) were expressed in the same germ line cells, as well as in the supportive cells (nutritive phagocytes) of the gonad. All histone mRNAs detected in the male germ lineage declined precipitously by the early spermatid stage, before cytoplasmic reduction. The data suggest that both testis-specific and adult somatic histone genes are expressed in proliferating male germ line cells. Testis-specific gene expression is restricted to spermatogonia and premeiotic spermatids, but somatic histone expression is not. The decline of histone mRNA in nondividing spermatids is not merely a consequence of cytoplasmic shedding, but probably reflects mRNA turnover.

Animals↗
PubMed1989

Developmental control of promoter-specific factors responsible for the embryonic activation and inactivation of the sea urchin early histone H3 gene.

We have begun an investigation of the molecular basis for the temporal embryonic expression of the early histone H3 gene of the sea urchin Strongylocentrotus purpuratus. Cloned constructs exhibit the proper temporal regulation following microinjection into one-cell zygotes of the related sea urchin species, Lytechinus pictus. Deletion analysis of the upstream promoter region of the H3 gene revealed several regions that are involved in both positive and negative control. DNase I footprinting, mobility shift, and methylation interference experiments reveal multiple sequence-specific DNA-binding proteins that interact with at least five distinct regions within 200 bp upstream of the RNA initiation site. Extracts prepared from staged embryos revealed that the ability of the factors to bind their target sequences was regulated. Proteins bound at four different sites were detected only at stages when the H3 gene was active transcriptionally. In addition, three different forms of a CCAAT-binding protein also are regulated temporally. The activity of these protein(s), however, correlates inversely with the transcriptional activity of the gene. The TATA box and CCAAT sequences are all that is required for expression of low levels of H3 transcripts with the proper temporal pattern. This approach should be useful in understanding the mechanisms used to regulate temporal patterns of gene expression during early embryogenesis.

Animals↗
PubMed1989

Absence of mouse mammary tumor virus proviral amplification in chemically induced lymphomas of RF/J mice.

RF/J mice are susceptible to the induction of thymic lymphomas by the carcinogens 3-methylcholanthrene and N-methyl-N-nitrosourea. Given the association of mouse mammary tumor virus (MMTV) with certain thymomas, we examined genomic DNA from chemically induced lymphomas of RF/J mice for new MMTV proviruses. Of 13 tissue culture lines derived from 3-methylcholanthrene-induced tumors, 5 had acquired new proviruses. MMTV amplification coincided with the appearance of viral mRNAs and proteins. However, no primary tumors or animal-passaged tumors contained new proviruses. These observations indicate that MMTV does not have a role in the tumor induction process, although it may become activated and amplified in tissue culture lines derived from tumors.

Animals↗
PubMed1989

An embryonic enhancer determines the temporal activation of a sea urchin late H1 gene.

Normal development requires that individual genes be expressed in their correct temporal patterns, but the mechanisms regulating this process during early embryogenesis are poorly understood. We have studied the early and late sea urchin histone genes during embryogenesis to address the molecular mechanisms controlling temporal gene expression. By measuring the changes in expression of cloned H1-beta DNA constructs after microinjection into fertilized one-cell zygotes, we demonstrated that a highly conserved 30-base-pair segment of DNA between positions -288 and -317 (USE IV) is responsible for the transcriptional activation of this late histone gene at the late blastula stage. In this report, we demonstrate that an oligonucleotide corresponding to USE IV acts as an embryonic enhancer element capable of activating the simian virus 40 early promoter in a stage-specific manner. Using an in vivo competition assay and in vitro DNase I footprinting and mobility shift assays, we also identified a protein(s) that interacts with this enhancer. Results of the competition assay suggested that this factor acts to stimulate transcription of the H1-beta gene. The factor was found to be stored in mature eggs as well as in all embryonic stages examined. The mobility of the factor found in eggs, however, differed from that of the embryonic form, which suggested that posttranslational modification occurs after fertilization.

Animals↗
PubMed1988

A histone H1 protein in sea urchins is encoded by a poly(A)+ mRNA.

Typical histone genes lack intervening sequences and encode small mRNAs (400-800 nucleotides) with short leader and trailer regions. Most histone mRNAs are not polyadenylylated but rather terminate in a highly conserved stem and loop structure. The early, late, and testis-specific histone genes of sea urchins, described to date, have this typical histone gene structure. We have identified an unusual H1 gene, H1-delta, in sea urchins that encodes a poly(A)+ mRNA. This mRNA is one of a group of polyadenylylated transcripts homologous with H1 gene probes. The sequence of H1-delta had been determined. H1-delta encodes a different H1 protein. Although the temporal expression of H1-delta mRNA is similar to that of other late H1 (beta and gamma) mRNAs, its spatial distribution at the time of maximal accumulation is distinct and confirms that H1-delta is regulated differently than other H1 genes.

Amino Acid Sequence↗
PubMed1988

Both basal and ontogenic promoter elements affect the timing and level of expression of a sea urchin H1 gene during early embryogenesis.

Late histone H1-beta mRNA accumulates with the correct ontogenic pattern following microinjection of the cloned gene into fertilized sea urchin eggs. Sequences upstream of the gene encoding the sea urchin H1-beta protein contain both basal and developmentally regulated elements. One late H1-specific activator sequence (USE IV) is required for the accumulation of mRNA following the blastula stage of development. All late H1 genes also contain a highly conserved GC-rich sequence resembling a low-affinity binding site for the mammalian transcription factor Sp1 that is required for basal expression of the H1-beta gene at all stages of embryogenesis. When this GC-rich sequence (GGGCTG) is converted to a perfect core Sp1 sequence (GGGCGG), the H1-beta transcripts accumulate to much greater levels and their peak accumulation is shifted to the early blastula stage rather than late blastula and gastrula stages of development. Coincidently, early H1 genes, whose peak expression is also at the early blastula stage, all contain the same core consensus sequence (GGGCGG). Thus, both gene-specific activator sequences, as well as sequences that resemble sites for general transcription factors, may play a major role in determining the temporal patterns of gene expression during early embryogenesis.

Animals↗
PubMed1988

Characterization of the structure and transcriptional patterns of the gene encoding the late histone subtype H1-beta of the sea urchin Strongylocentrotus purpuratus.

We have cloned and characterized the gene encoding the late histone H1-beta subtype from the sea urchin Strongylocentrotus purpuratus. The gene contains all of the upstream sequence homologies previously seen in late H1-gamma genes. The expression of H1-beta mRNA is coordinated with that of H1-gamma mRNA, and like H1-gamma it is expressed in all adult somatic tissues tested.

Amino Acid Sequence↗
PubMed1987

Molecular characterization of the histone gene family of Caenorhabditis elegans.

The core histone genes (H2A, H2B, H3 and H4) of Caenorhabditis elegans are arranged in approximately 11 dispersed clusters and are not tandemly arrayed in the genome. Three well-characterized genomic clones, which contain histone genes, have one copy of each core histone gene per cluster. One of the clones (lambda Ceh-1) carries one histone cluster surrounded by several thousand base-pairs of non-histone DNA, and another clone (lambda Ceh-3) contains a histone cluster duplication surrounded by non-histone DNA. A third clone (lambda Ceh-2) carries a cluster of core histone genes flanked on one side (12,000 base-pairs away) by a single H2B gene and on the other by non-histone DNA. A fourth cluster (clone BE9) has one copy each of H3 and H4 and two copies each of H2A and H2B. This cluster is also flanked by non-histone DNA. Analysis of cosmid clones which overlap three of the clusters shows that no other histone clusters are closer than 8000 to 60,000 base-pairs, although unidentified non-histone transcription units are present on the flanking regions. Gene order within the histone clusters varies, and histone mRNAs are transcribed from both DNA strands. No H1 sequences are found on these core histone clones. Restriction fragment length polymorphisms between two related nematode strains (Bristol and Bergerac) were used as phenotypic markers in genetic crosses to map one histone cluster to linkage group V and another to linkage group IV. Hybridization of gene-specific probes from sea urchin to C. elegans RNA identifies C. elegans core histone messenger RNAs of sizes similar to sea urchin early stage histone mRNAs (H2A, H2B, H3 and H4). The organization of histone genes in C. elegans resembles the clustering found in most vertebrate organisms and does not resemble the tandem patterns of the early stage histone gene family of sea urchins or the major histone locus of Drosophila.

Animals↗
PubMed1986

Isolation and characterization of the gene encoding the testis specific histone protein H2B-2 from the sea urchin Lytechinus pictus.

We have cloned and characterized the gene encoding a sperm specific H2B-2 histone subtype from the sea urchin L. pictus. The gene is not clustered with any other histone genes. However, it resembles other histone genes in many respects. The gene contains no intervening sequences or polyadenylation signals. Like other histone genes it contains the conserved 3' hairpin loop sequence and CAAGAAAGA box necessary for the processing of the 3' end of the histone transcript. Upstream of the gene in addition to the TATA box, and two copies of inverted CCAAT Boxes is a conserved sequence element found in many H2B genes. Unlike most histone genes, the H2B-2 gene is expressed in a sex and tissue specific manner only in testis. The sperm H2B-2 subtype encoded by this gene is 142 amino acids in length. The larger size of this H2B protein is accounted for by residues in the N-terminus of the protein consisting of a series of pentapeptide repeats typical of this histone subtype.

Animals↗
PubMed1986

Analysis of histone gene expression in adult tissues of the sea urchins Strongylocentrotus purpuratus and Lytechinus pictus: tissue-specific expression of sperm histone genes.

We analyzed the histone mRNA population found in several adult tissues of the sea urchin Strongylocentrotus purpuratus and in testis of Lytechinus pictus. Unique species of H1 and H2b mRNAs encoding the sperm-specific histone subtypes can be found exclusively in testis RNA. S. purpuratus contains two distinct testis-specific H1 transcripts, while L. pictus contains one such transcript. Each of these mRNAs is larger than either early or late embryonic H1 mRNAs. Other somatic adult tissues contain transcripts derived from members of the late embryonic H1 histone gene family. S. purpuratus contains one H2b transcript found exclusively in testis, while L. pictus contains two such H2b mRNAs. Similarly, in tissues other than testis, late H2b transcripts were found. While there is no sperm-specific H2a protein, a limited set of late histone H2a genes encoding primarily the H2a-beta subtype is expressed in testis. The majority of the H2a protein found in diploid adult tissues is also the H2a-beta subtype; however, the size of the H2a transcripts differs between testis and other tissues. We conclude that different members of the late H2a gene family are differentially expressed in embryos and adult tissues. We prepared and characterized cDNA clones encoding the sperm-specific H2b protein as well as the H2a-beta protein found in testis.

Amino Acid Sequence↗
PubMed1985

Comparison of chemically induced and spontaneous murine thymic lymphomas in RF and AKR mice: differential expression of c-myc and c-myb.

Expression of 11 cellular oncogenes was determined in normal vs. lymphomatous thymic tissues of RF and AKR mice; only c-myc and c-myb transcripts were detected in an age-inappropriate pattern in thymomas. Normal thymocytes from young RF mice contained RNA transcripts of both genes, but the transcripts were no longer detected at 9 or more weeks of age. More than 90% of RF thymomas, occurring at 20-28 weeks of age after skin painting with 3-methylcholanthrene at 12 weeks, contained c-myc transcripts, and 70% of the tumors contained c-myb transcripts. Seven cell lines derived from these 3-methylcholanthrene thymomas expressed both cellular genes, as did 2 rare spontaneous thymomas of 12-month-old RF mice. No indication of rearrangement or amplification of either gene was seen in any of the RF tumors or cell lines. In AKR mice, transcripts of the 2 genes persisted longer in the normal thymus than in RF mice, but they were no longer detected at 26 weeks of age. Of 3 thymomas in 6-month-old 3-methylcholanthrene-treated AKR mice, all expressed c-myb and 2 expressed c-myc. Among 11 spontaneous AKR thymomas, however, only 2 showed detectable levels of both genes, and 2 more expressed c-myc or c-myb but not both.

Animals↗
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↗
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↗