Human myometrial chorionic gonadotropin/luteinizing hormone receptors in preterm and term deliveries

Nonpregnant human myometrium contains functional hCG/LH receptors. The present study investigated whether pregnant human myometrium also contains these receptors and whether they vary as a function of delivery in preterm or term pregnancies. Northern blotting revealed that pregnant human myometrium contains 4.3- and 2.2-kilobase receptor messenger ribonucleic acid transcripts. Immunoblotting with a specific hCG/LH receptor antibody showed that myometrium contains 70- and 50-kilodalton immunoreactive proteins. Ligand blotting demonstrated that only the 50-kilodalton protein could bind [125I]hCG, and this binding was inhibited by excess unlabeled hCG. In situ hybridization and immunocytochemistry revealed that the receptor messenger ribonucleic acid and receptor protein are present in myometrial and vascular smooth muscle. The myometrial smooth muscle receptor levels were lower during labor compared to those before labor at preterm and term pregnancy. In summary, our study demonstrates that pregnant human myometrium express hCG/LH receptor gene. The receptor levels were lower during labor compared to those before labor in preterm or term pregnancy. These data suggest that hCG, via its receptors, may contribute to myometrial quiescence until labor begins at the end of pregnancy.

Differential cyclooxygenase-1 and -2 gene expression in human myometria from preterm and term deliveries

The expression of cyclooxygenase-1 (COX-1) and COX-2 genes in myometria from preterm and term pregnancies was investigated by in situ hybridization, immunoblotting, and immunocytochemistry. In situ hybridization revealed that myometrial smooth muscle contained both COX-1 and COX-2 messenger ribonucleic acid transcripts. Immunoblotting revealed that myometria contained 55- and 67-kilodalton COX-1 proteins as well as 72- and 56-kilodalton COX-2 proteins. Immunocytochemistry showed that COX-1 and COX-2 proteins are present in the myometrial smooth muscle. The expression of COX-1 and COX-2 genes differed in myometria. For example, although COX-1 expression was lower, COX-2 expression was higher at term compared to preterm pregnancy not in labor. In addition, although COX-1 expression was not dependent on labor, COX-2 expression was lower with labor compared to not in labor for both preterm and term pregnancy. The myometrial smooth muscle also immunostained for prostaglandin E2 (PGE2) and PGF2 alpha, suggesting that the cyclooxygenases are catalytically active. The changes in PGE2 and PGF2 alpha paralleled the changes in COX-1 enzyme in terms of being lower at term compared to preterm pregnancy and the changes in COX-2 enzyme in terms of being lower during labor at preterm and term pregnancy. In summary, our results demonstrate that pregnant human myometria express both COX-1 and COX-2 genes. The expression of these genes differed in preterm or term pregnancy myometria from in labor and not in labor.

Lack of self-regulation of human chorionic gonadotropin biosynthesis in human choriocarcinoma cells

Human gestational trophoblastic neoplasms overexpress hCG/LH receptors. Whether this overexpression is a reflection of a loss of self-regulation of hCG biosynthesis was investigated using JAR human choriocarcinoma cells. The results show that exogenous hCG did not affect steady state hCG alpha and hCG beta mRNA or dimer hCG protein levels in JAR cells. The JAR cells, however, responded to 8-bromo-cAMP with an increase in hCG alpha mRNA levels, suggesting that cAMP-mediated regulation of the hCG subunit genes was intact in the cells. Disruption of receptor function by a receptor antibody, which resulted in an increase in hCG alpha mRNA levels and hCG secretion in normal trophoblasts, had no effect on JAR cells. Unlike normal trophoblasts, which contain a predominant receptor transcript of 1.8 kilobases (kb), with minor higher molecular size (7.5 and 5.4 kb) transcripts occasionally seen, JAR cells contain a higher abundance of multiple transcripts (7.5, 5.4, 3.5, and 1.8 kb), with the predominant transcript being 5.4 kb. In addition, although normal trophoblasts contain an 80-kilodalton receptor protein, JAR cells contain only a 50-kilodalton hCG/LH receptor isoform. In contrast to the effects of exogenous hCG on normal placental tissue in vitro, it was unable to down-regulate receptor transcripts or receptor protein in JAR cells. In summary, JAR cells lack the ability to self-regulate hCG biosynthesis. This loss could explain how hCG can reach very high levels in gestational trophoblastic disease compared to those in normal pregnancy.

Molecular mutagenesis induced by glycidyl methacrylate

Glycidyl methacrylate (GMA) is a recently recognized mutagen. In order to explore the mutagenicity and mechanism of GMA, plasmid pBR322 was used for in vitro binding, mutant screening, restriction enzyme mapping, and DNA sequencing. To explore the mechanism by which an initial premutational event is converted into a stable heritable mutation, pBR322 and GMA-bound pBR322 were transformed into E. coli HB101, and the following results were obtained: 1) GMA-bound pBR322 induced phenotype changes in competent cells. Two stable and heritable mutants were isolated (ApRTcS and ApSTcR). 2) When restriction enzyme mapping was used to analyze the mutant ApRTcS, four of seven maps showed changes, but no large DNA insertion or deletion were observed. 3) The frequency of deletion and insertion forms counted about 10%. Sequence specificity and hot spot regions were evident in the sequence analysis of mutated plasmid. The above results indicate that the premutagenic lesions of plasmid induced by GMA can be converted into point mutations in vivo.

Spectrum of glycidyl methacrylate-induced mutation in plasmid-Escherichia coli system

In order to characterize the spectrum of mutation induced by glycidyl methacrylate (GMA), the plasmid pBR322 was modified with this mutagen in vitro, transfected into appropriate Escherichia coli host HB101. The mutants were then screened and defined by DNA sequencing. Sequence analysis reveals that GMA induces two classes of mutations: deletion of the mono-, di- or tetra-base or the insertion of mono- or di-base. Both types of mutations, with about 10% frequency, occur predominantly at C-G runs and at 5'-CNCCN-3' sequence, which are hotspots for GMA damage and may cause frameshift mutation.

Construction of cosmid contigs and high-resolution restriction mapping of the Huntington disease region of human chromosome 4

The gene responsible for Huntington disease (HD) has been localized to a 2.2 million base pair (Mbp) region between the loci D4S10 and D4S98 on the short arm of human chromosome 4. As part of a strategy originally designed to clone the gene based on its chromosomal location, we and others previously identified overlapping yeast artificial chromosome (YAC) clones covering most of this region. While these YAC clones were useful for initially obtaining long-range clone continuity, a number of features of the YACs indicated that smaller clones are generally more useful in the subsequent steps of the positional cloning strategy. In this paper, we use these YAC clones to generate sets of overlapping cosmid clones covering most of the HD region. We isolated a large number of cosmids by screening a chromosome 4-specific cosmid library with labeled DNA from a minimal overlapping set of YAC clones. These cosmid clones were further analyzed by restriction mapping and hybridization experiments, leading to the assembly of 185 cosmids into eleven contigs covering more than 1.65 Mbp and to a fine-structure restriction map of the region. Nine of these contigs cover 90 percent of the 1.7 Mbp subregion between loci D4S125 and D4S98 where the HD gene is now known to lie. The detailed restriction map and the cosmid clones should facilitate the identification and localization of cDNAs and polymorphic markers, and they provide reagents for large scale DNA sequencing of this region of the human genome. Our results suggest that this strategy should be generally useful for converting YAC clones into cosmid contigs and generating high-resolution restriction maps of genomic regions of interest.

Synergistic activation of transcription is mediated by the N-terminal domain of Drosophila fushi tarazu homeoprotein and can occur without DNA binding by the protein

Synergistic activation of transcription by Drosophila segmentation genes in tissue culture cells provides a model with which to study combinatorial regulation. We examined the synergistic activation of an engrailed-derived promoter by the pair-rule proteins paired (PRD) and fushi tarazu (FTZ). Synergistic activation by PRD requires regions of the homeodomain or adjacent sequences, and that by FTZ requires the first 171 residues. Surprisingly, deletion of the FTZ homeodomain does not reduce the capacity of the protein for synergistic activation, although this mutation abolishes any detectable DNA-binding activity. This finding suggests that FTZ can function through protein-protein interactions with PRD or other components of the homeoprotein transcription complex, adding a new layer of mechanisms that could underlie the functional specificities and combinatorial regulation of homeoproteins.

Cloning of the Huntington disease region in yeast artificial chromosomes

The gene responsible for Huntington disease has been localized to a 2.5 million base pair (Mb) region between the loci D4S10 and D4S168 on the short arm of chromosome 4. As part of a strategy to clone the HD gene on the basis of its chromosomal location, we isolated genomic DNA from the HD region as a set of overlapping yeast artificial chromosome (YAC) clones. Twenty-eight YAC clones were identified by screening human YAC libraries with twelve PCR-based sequence-tagged sites (STSs) from the region. We assembled the YAC clones into overlapping sets by hybridizing them to a large number of DNA probes from the HD region, including the STSs. In addition, we isolated the ends of the human DNA inserts of most of the YAC clones to assist in the construction of the contig. Although almost half of the YACs appear to contain chimeric inserts and several contain internal deletions or other rearrangements, we were able to obtain over 2.2 Mb of the HD region in YACs, including one continuous segment of 2.0 Mb covering the region that most likely contains the HD gene. Ten of the twenty eight YAC clones comprise a minimal set spanning the 2.2 Mb. These clones provide reagents for the complete characterization of this region of the genome and for the eventual isolation of the HD gene.

Recombination of 4p16 DNA markers in an unusual family with Huntington disease

The Huntington disease (HD) mutation has been localized to human chromosome 4p16, in a 6-Mb region between the D4S10 locus and the 4p telomere. In a report by Robbins et al., a family was identified in which an affected individual failed to inherit three alleles within the 6-Mb region originating from the parental HD chromosome. To explain these results, it was suggested that the HD locus (HD) lies close to the telomere and that a recombination event took place between HD and the most telomeric marker examined, D4S90. As a test of this telomere hypothesis, we examined six members of this family, five of whom are affected with HD, for the segregation of 12 polymorphic markers from 4p16, including D4S169, which lies within 80 kb of the 4p telomere. We separated, in somatic cell hybrids, the chromosomes 4 from each family member, to determine the phase of marker alleles on each chromosome. We excluded nonpaternity by performing DNA fingerprint analyses on all six family members, and we found no evidence for chromosomal rearrangements when we used high-resolution karyotype analysis. We found that two affected siblings, including one of the patients originally described by Robbins et al., inherited alleles from the non-HD chromosome 4 of their affected parents, throughout the 6-Mb region. We found that a third affected sibling, also studied by Robbins et al., inherited alleles from the HD chromosome 4 of the affected parent, throughout the 6-Mb region. Finally, we found that a fourth sibling, who is likely affected with HD, has both a recombination event within the 6-Mb region and an additional recombination event in a more centromeric region of the short arm of chromosome 4. Our results argue against a telomeric location for HD and suggest that the HD mutation in this family is either associated with DNA predisposed to double recombination and/or gene conversion within the 6-Mb region or is in a gene that is outside this region and that is different from that mutated in most other families with HD.

[New mutagen, glycidyl methacrylate (GMA) changed restriction enzyme map of plasmid]

Our present work showed that the mutant TcS ApR of plasmid pBR322 induced by GMA changed restriction enzyme map in the single and double enzyme digestions. Results indicated that the mutant plasmid has lots of mutated sites which are disappeared on some sites and appeared on others in resistance gene region, for example, sites of Bg I, EcoRI, HindIII and HincII, and occurred a new recognition site for HincII (252). The relationship between gene mutation and genotoxicity of GMA was discussed.