The extraction, characterization and in vitro translation of RNA from adult Schistosoma mansoni

CRISPR-Cas13: A new technology for the rapid detection of pathogenic microorganisms

Pathogenic microorganisms have major impacts on human lives. Rapid and sensitive diagnostic tools are urgently needed to facilitate the early treatment of microbial infections and the effective control of microbial transmission. CRISPR-Cas13 employs programmable RNA to produce a sensitive and specific method with high base resolution and thus to provide a novel tool for the rapid detection of microorganisms. The review aims to provide insights to spur further development by summarizing the characteristics of effectors of the CRISPR-Cas13 system and by describing the latest research into its application in the rapid detection of pathogenic microorganisms in combination with nucleic acid extraction, isothermal amplification, and product detection.

Inhibition of histone methyltransferase EZH2 in Schistosoma mansoni in vitro by GSK343 reduces egg laying and decreases the expression of genes implicated in DNA replication and noncoding RNA metabolism

Background

The possibility of emergence of praziquantel-resistant Schistosoma parasites and the lack of other effective drugs demand the discovery of new schistosomicidal agents. In this context the study of compounds that target histone-modifying enzymes is extremely promising. Our aim was to investigate the effect of inhibition of EZH2, a histone methyltransferase that is involved in chromatin remodeling processes and gene expression control; we tested different developmental forms of Schistosoma mansoni using GKS343, a selective inhibitor of EZH2 in human cells.

Methodology/Principal findings

Adult male and female worms and schistosomula were treated with different concentrations of GSK343 for up to two days in vitro. Western blotting showed a decrease in the H3K27me3 histone mark in all three developmental forms. Motility, mortality, pairing and egg laying were employed as schistosomicidal parameters for adult worms. Schistosomula viability was evaluated with propidium iodide staining and ATP quantification. Adult worms showed decreased motility when exposed to GSK343. Also, an approximate 40% reduction of egg laying by GSK343-treated females was observed when compared with controls (0.1% DMSO). Scanning electron microscopy showed the formation of bulges and bubbles throughout the dorsal region of GSK343-treated adult worms. In schistosomula the body was extremely contracted with the presence of numerous folds, and growth was markedly slowed. RNA-seq was applied to identify the metabolic pathways affected by GSK343 sublethal doses. GSK343-treated adult worms showed significantly altered expression of genes related to transmembrane transport, cellular homeostasis and egg development. In females, genes related to DNA replication and noncoding RNA metabolism processes were downregulated. Schistosomula showed altered expression of genes related to cell adhesion and membrane synthesis pathways.

Conclusions/Significance

The results indicated that GSK343 presents in vitro activities against S. mansoni, and the characterization of EZH2 as a new potential molecular target establishes EZH2 inhibitors as part of a promising new group of compounds that could be used for the development of schistosomicidal agents.

Schistosomiasis is a chronic and debilitating disease caused by a trematode of the genus Schistosoma. The current strategy for the control of the disease involves treatment with praziquantel, the only available drug. The development of new drugs is therefore a top priority. Drugs that inhibit histone modifying enzymes have been used in cancer, altering gene expression, replication, repair and DNA recombination. Schistosoma parasites have some characteristics similar to malignant tumors, such as intense cell division and high levels of metabolic activity. Here we evaluate in Schistosoma mansoni the effect of GSK343, an inhibitor of the histone methyltransferase EZH2 that had been shown to arrest or reduce the growth of human cancer cells. We show that GSK343 causes damage to the parasite tegument and reduces egg laying in vitro, concomitant with a decrease in levels of H3K27me3, the histone mark put in place by EZH2. RNA-seq and proteomic analyses of treated parasites showed changes in the expression of hundreds of genes involved in important metabolic processes. In females, a marked decrease was observed in the expression of genes related to processes such as DNA replication and noncoding RNA metabolism. In conclusion, the histone methyltransferase EZH2 seems to be a promising novel drug target against schistosomiasis.

Identification and characterization of novel microRNAs from Schistosoma japonicum

BACKGROUND

Schistosomiasis japonica remains a major public health problem in China. Its pathogen, Schistosoma japonicum has a complex life cycle and a unique repertoire of genes expressed at different life cycle stages. Exploring schistosome gene regulation will yield the best prospects for new drug targets and vaccine candidates. MicroRNAs (miRNAs) are a highly conserved class of noncoding RNA that control many biological processes by sequence-specific inhibition of gene expression. Although a large number of miRNAs have been identified from plants to mammals, it remains no experimental proof whether schistosome exist miRNAs.

METHODOLOGY AND RESULTS

We have identified novel miRNAs from Schistosoma japonicum by cloning and sequencing a small (18-26 nt) RNA cDNA library from the adult worms. Five novel miRNAs were identified from 227 cloned RNA sequences and verified by Northern blot. Alignments of the miRNAs with corresponding family members indicated that four of them belong to a metazoan miRNA family: let-7, miR-71, bantam and miR-125. The fifth potentially new (non conserved) miRNA appears to belong to a previously undescribed family in the genus Schistosome. The novel miRNAs were designated as sja-let-7, sja-miR-71, sja-bantam, sja-miR-125 and sja-miR-new1, respectively. Expression of sja-let-7, sja-miR-71 and sja-bantam were analyzed in six stages of the life cycle, i.e. egg, miracidium, sporocyst, cercaria, schistosomulum, and adult worm, by a modified stem-loop reverse transcribed polymerase chain reaction (RT-PCR) method developed in our laboratory. The expression patterns of these miRNAs were highly stage-specific. In particular, sja-miR-71 and sja-bantam expression reach their peaks in the cercaria stage and then drop quickly to the nadirs in the schistosomulum stage, following penetration of cercaria into a mammalian host.

CONCLUSIONS

Authentic miRNAs were identified for the first time in S. japonicum, including a new schistosome family member. The different expression patterns of the novel miRNAs over the life stages of S. japonicum suggest that they may mediate important roles in Schistosome growth and development.

Identification of Schistosoma mansoni gender-associated gene transcripts by cDNA microarray profiling

BACKGROUND

Parasitic helminths of the genus Schistosoma mate, achieve sexual maturity and produce eggs in the bloodstream of their definitive hosts, and the most important pathological consequences of the infection are associated with this process. We have used cDNA microarray technology to initiate genome-wide gene-expression studies of sex and sexual development in mature Schistosoma mansoni parasites.

RESULTS

An S. mansoni-specific cDNA microarray was fabricated using 576 expressed sequence tags selected from three cDNA libraries and originating from two different parasite developmental stages. Five independent cDNA microarray hybridizations were analyzed using stringent filtering criteria and careful quality control, leading to the identification of 12 new female-associated and 4 new male-associated gene transcripts in the mature adult schistosome. Statistical analysis of variation demonstrated high levels of agreement within a cDNA microarray (correlation coefficient 0.91; median coefficient of variation 11.1%) and between cDNA microarrays (correlation coefficient 0.90; median coefficient of variation 14.4%). RT-PCR analysis confirmed the cDNA microarray results, thereby supporting the reliability of the system.

CONCLUSIONS

Our study expands the list of S. mansoni gender-associated gene transcripts from all previous studies by a factor of two. Among the new associations identified, a tyrosinase ortholog was preferentially expressed in the adult female, and a dynein light-chain ortholog was highly induced in the adult male. cDNA microarrays offer the potential for exponential leaps in the understanding of parasite biology and this study shows how molecules involved in sexual biology can be rapidly identified.

A hidden break in the 28.0S rRNA from Diphyllobothrium dendriticum

Nondenatured and denatured total RNA from the tapeworm Diphyllobothrium dendriticum (Cestoda) was analysed by agarose gel electrophoresis. It was found that the large subunit ribosomal RNA (lrRNA) is 28.0S and the small subunit ribosomal RNA (srRNA) is 19.5S. Following denaturation the 28.0S rRNA was disrupted into a 19.5S subfragment and a 20.7S subfragment due to the presence of a centrally located hidden break. By hybridization of Northern blot membranes with oligonucleotide probes specific for the 5'- and 3'-ends of the lrRNA respectively, we have shown that the 19.5S subfragment is from the 5'-end (the alpha-subfragment) and the 20.7S subfragment from the 3'-end (the beta-subfragment) of the 28.0S rRNA of D. dendriticum.

Identification and analysis of the gap region in the 23S ribosomal RNA from Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans is a Gram-negative coccobacillus which can cause certain severe extra-oral infections as well as forms of human periodontal disease such as localized juvenile periodontitis. In contrast to many prokaryotic and eukaryotic species which exhibit an intact 23S ribosomal RNA (rRNA) molecule, examination of six A. actinomycetemcomitans strains--including three serogroup representative strains and two strains from non-human primates--revealed that this micro-organism does not produce an intact 23S ribosomal RNA (rRNA) molecule but, rather, two smaller forms of 1.8 kb and 1.2 kb designated as 23S alpha and 23S beta fragments. On the other hand, 14 other strains of Actinobacillus, Haemophilus, and Pasteurella species demonstrated intact 23S rRNA. The sequence of the region of the 23S rRNA gene in A. actinomycetemcomitans strain ATCC 43718 containing the cleavage site was determined by dideoxynucleotide sequencing, while the location of the 3' and 5' termini of the 23S alpha and 23S beta fragments was resolved by S1 nuclease mapping and cDNA primer-extension. A deletion of 112 bases was noted in comparisons of base sequences from A. actinomycetemcomitans rRNA and rDNA. The DNA intervening sequence was localized to nucleotide 1180 of the Escherichia coli 23S rRNA map. While the primary structure of the gap region showed little homology with the gap regions described in other organisms, the secondary structure was similar to that previously described in the parasitic helminth Schistosoma japonicum. Restriction enzyme and nucleotide sequence analysis of the gap region in eight other A. actinomycetemcomitans strains showed it to be highly conserved.

Comparison of in vitro translation products of Sarcocystis gigantea and Sarcocystis tenella

Poly(A)+ RNA was purified from cystozoites of Sarcocystis gigantea and Sarcocystis tenella and used to in vitro translate polypeptides in a wheat germ and a rabbit reticulocyte translation system. The in vitro translated polypeptides were compared by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The S. tenella mRNA translated at least two polypeptides (mol. wt about 80,000 and 21,500) in both translation systems that were not translated by the S. gigantea mRNA. To study co-translational and initial post-translational processing in Sarcocystis, the poly(A)+ RNA preparations were in vitro translated in the rabbit reticulocyte translation system in the presence or absence of canine microsomal membranes. Based on electrophoresis, there appeared to be modification of at least some Sarcocystis polypeptides in the mol. wt range 17,000-30,000. In addition, the translation products were immunoprecipitated with a homologous and a heterologous antiserum. The immunoprecipitated polypeptides were compared by electrophoresis and the S. tenella translation products contained at least one unique antigenic polypeptide with a mol. wt of about 34,700 that was not processed by the microsomal membranes. These results suggest that there is at least one polypeptide that is a candidate for use as an antigen for the differentiation of S. gigantea and S. tenella infections in sheep.

Antibody responses to in vitro translation products following albendazole therapy for Echinococcus granulosus

Immunoprecipitation of antigens translated in vitro from Echinococcus granulosus RNA revealed that albendazole treatment of human hydatidosis induced antibodies to previously undetectable antigens and that the response to most antigens was specific, although cross-reactivity was observed between Schistosoma mansoni and E. granulosus antisera for two proteins.

Schistosoma haematobium and S. japonicum: analysis of the ribosomal RNA genes and determination of the "gap" boundaries and sequences

We have determined the intragenic organization of the rRNA genes of Schistosoma haematobium and S. japonicum and found them to be similar to that of S. mansoni and other eukaryotes. An entire ribosomal repeat approximately 10 kbp in size from each species was isolated as a SalI fragment from a genomic library constructed in bacteriophage lambda. The segments encoding both the small and large rRNAs have been identified using three cloned EcoRI fragments of S. mansoni as probes. There were three EcoRI fragments (4.2, 3.0, 1.6 kbp) from S. haematobium and four EcoRI fragments (4.6, 2.3, 1.7, 1.0 kbp) from S. japonicum. As in a wide variety of organisms within the protostome phyla, the 28S rRNA in schistosomes contains a "gap" which separates it into two fragments. The length of the gap sequence in S. haematobium is 54 bases and it is identical to that in S. mansoni in both length and sequence. However, in S. japonicum the sequence is between 64-67 bases long. In each case, irrespective of the species, the gap is located at the same position within the 28S rRNA. Secondary structures of the gap sequence derived by computer analysis predict a conformation with the minimum free energy that has an UAAU tract in a hairpin loop for S. haematobium and an UAUU tract for S. japonicum.

Characterization of a 54-nucleotide gap region in the 28S rRNA gene of Schistosoma mansoni

We have analyzed 572 bp in the 28S rDNA of the human blood fluke Schistosoma mansoni which correspond to expansion segment 5 of domain IV as defined by Clark et al. for the Xenopus laevis 28S rRNA. S1 nuclease mapping and primer extension analysis comparing this region with the mature 28S rRNA indicate that there are 54 nucleotides present in the 28S rDNA which are absent from the mature rRNA. This defines a gap that creates two 28S rRNA subunits (28S alpha and 28S beta). Comparison of the S. mansoni sequence with rDNAs of other organisms which contain gaps in their 28S rRNA shows that the overall features are conserved except that the S. mansoni gap is less A + T-rich. The conserved features include: (1) the location of the gap within the 28S rRNA; (2) the predicted secondary structure of the gap, containing a stem-loop with a UAAU sequence within the loop; and (3) a conserved CGAAAGGG on the 3' side of the gap.

Cloning and characterization of the ribosomal RNA gene repeat from Ostertagia ostertagi

Clones of the rRNA genes of Ostertagia ostertagi were selected from a library prepared from the genomic DNA of adult worms of strain LA-2. A 13.4-kb insert in a clone, lambda OOR78, is comprised of one complete 7.5-kb rDNA unit and portions of two adjacent units. The rDNA unit is directly repeated in a head-to-tail fashion and represents approximately 0.9% of the total genomic DNA. This repeating unit appears to be the only long tandemly repeated sequence in the genome. Restriction enzyme recognition sites in the rDNAs of four strains of O. ostertagi were fully conserved with the exception of one PstI site present in the large rRNA gene which was absent from a proportion of the genes of the LA-2 strain. The rDNA of O. ostertagi is more similar to that of Caenorhabditis elegans in unit length and arrangement than to parasitic helminths previously examined.

Use of the polymerase chain reaction for the differential cross screening of libraries cloned into phage-lambda-based vectors

We describe a simple and rapid method that can be used to identify sequences present in any two DNA libraries (either genomic or cDNA), provided only that the libraries are in different vectors with different cloning sites. This procedure makes use of the polymerase chain reaction (PCR) to amplify the inserts of one library. The product of the PCR reaction is then used to screen a second library to identify sequences which are common to both. We illustrate the use of this method for the systematic isolation of human X-chromosome-linked genomic clones that harbor sequences expressed in human chorioretinal tissue.

Vitellogenin gene expression in male rainbow trout (Salmo gairdneri)

Estrogen has a marked effect on the expression of vitellogenin, the egg yolk precursor protein in the liver of egg-laying vertebrates. cDNA clones specific for trout vitellogenin mRNA have been used to study the expression of the vitellogenin genes in rainbow trout (Salmo gairdneri). The steady-state levels of vitellogenin mRNA in the liver of male rainbow trout were measured during primary and secondary stimulation with estradiol. The kinetics of induction in trout appear to be very similar to those seen in Xenopus and chicken in that a lag of approximately 2 days is observed in the accumulation of serum vitellogenin during primary induction. This lag is not observed during the secondary stimulation. The primary induction of vitellogenin mRNA in trout liver, using a single injection of estradiol (3 mg/kg body wt) results in a short-lived rise, reaching a maximum level of 260 ppm total RNA on Day 2. Using silastic implants of estradiol to induce a primary response produces a large increase in the steady-state level of vitellogenin mRNA which reaches a maximum of 2750 ppm total RNA on Day 10. During secondary stimulation, using silastic tubing the maximum level reached was 1200 ppm of the total RNA on Day 7, approximately half the level seen in the primary induction using the silastic implants. The difference in these two levels is due to an increase in the steady-state levels of rRNA, which appear to increase between Days 10 and 21 after the primary stimulation. These results demonstrate that the induction of vitellogenesis in the trout by estradiol involves changes in the steady-state levels of a number of different mRNA and rRNA sequences and resembles that seen in Xenopus and chicken.

Comparison of the in vitro translation capacity of Taenia crassiceps metacestode mRNA prepared by the phenol and cesium chloride method

Total RNA of T. crassiceps metacestodes harvested from male and female NMRI mice was prepared by both the phenol extraction technique and cesium chloride (CsCl) gradient centrifugation. mRNA was selected by oligo (dT)-cellulose affinity chromatography and used as the template for the in vitro translation of parasite polypeptides in a cell-free rabbit reticulocyte lysate. The template activity of the mRNA obtained after CsCl preparation was clearly higher, as shown by the amount of 35S-methionine incorporated into the translation products and by fluorographed SDS-PAGE of the synthesized labelled polypeptides. SDS-PAGE fluorographs of antigens encoded by the mRNA prepared by CsCl centrifugation and selected by immunoprecipitation using purified IgG antibodies of T. crassiceps-infected mice (day 80 postinfection) exhibited seven labelled polypeptides of about 65, 46, 45, 42, 34, 29 kDa and a predominant 20-kDa antigen. The latter polypeptide was the only one recognized by the antibodies amongst the in vitro translation products directed by mRNA prepared by the phenol method.

Treatment with antiandrogens induces an androgen-repressed gene in the rat ventral prostate

We have recently described an androgen-repressed gene in the rat ventral prostate, termed TRPM-2, that appears to be involved in the processes of cell regression and programmed cell death. We have analyzed the effect of two antiandrogens currently used in the treatment of prostatic carcinoma on the induction of this gene. Cyproterone acetate (10 mg/day) and flutamide (15 mg/day), when administered to castrated rats receiving a maintenance dose of 5 alpha-dihydrotestosterone proprionate (250 micrograms/day), induce the expression of TRPM-2. Northern hybridization and dot blot analysis demonstrate that TRPM-2 steady-state levels reach a maximum on day 4 of treatment with cyproterone acetate (520 ppm) and on day 6 of treatment with flutamide (190 ppm). During this time the steady-state levels of the androgen-dependent prostate steroid-binding protein mRNA are reduced dramatically (from approximately 75,000 to 10,000 ppm), but are not eliminated even after extended treatment. Treatment with the two antiandrogens produces a substantial reduction in the organ weight/body weight ratio and RNA content of the prostate when compared to rats receiving the maintenance dose alone. These results suggest that while neither cyproterone acetate nor flutamide fully repress the androgen-dependent functions of the prostate, they do induce some of the androgen-repressed sequences in the prostate that have been implicated in the process of cell death.

Isolation of cDNA clones for differentially expressed genes of the human parasite Schistosoma mansoni

Little is known about the mechanisms that control transformations during the life cycle of Schistosoma mansoni. To enable isolation of DNA sequences encoding developmentally regulated antigens a cDNA expression library in the vector lambda gt11 amp3 was constructed from adult mRNA and immunologically screened with sera from infected individuals. We report here on the properties of three recombinant clones that derive from developmentally regulated genes. Clone 10-3 encoded a beta-galactosidase fusion protein present in high abundance in infected Escherichia coli. Clones 7-2 and 8-2 also produced immunologically recognized proteins; however, the peptides did not appear to be beta-galactosidase fusion proteins. The expression of mRNAs hybridizing to these cDNAs was examined in the different stages of the parasite life cycle. Messenger RNA corresponding to clone 10-3, approximately equal to 1000 bases in length, was present in higher abundance in male worms than in females but was not detected in schistosome eggs. A 900-base mRNA hybridizing to clone 7-2 was observed in adult worms and eggs. Both clone 10-3 and clone 7-2 hybridized to smaller mRNAs in cercariae and freshly transformed schistosomula than in adult worms. Clone 8-2 contained tandem cDNA inserts. One cDNA hybridized to a 1700-base mRNA present in all stages, while the second hybridized to an 800-base mRNA specific to adult female worms.

Immunoprecipitation of in vitro translation products of Fasciola hepatica RNA

Incubation of in vitro translation products of RNA isolated from Fasciola hepatica with immune rat serum and sera from infected sheep resulted in the immunoprecipitation of a number of polypeptides, most of which had similar electrophoretic mobilities. Although only one of these (a 30 kDa species) correlated precisely in mobility with that of biosynthetically labelled excretory-secretory (ES) antigens, this polypeptide (along with several others) was also immunoprecipitated by sheep sera raised against authentic ES antigens. This verified that the isolated RNA contained mRNA species encoding ES antigens of the parasite. In addition, immune rat serum immunoprecipitated a 64 kDa polypeptide which was not immunoprecipitated by infected sheep serum or anti-ES antigen sheep serum. The possible significance of this finding in terms of the ability of rats to develop resistance to fascioliasis in contrast to sheep which apparently cannot is discussed.

Androgen-repressed messages in the rat ventral prostate

Poly (A)+ RNA from the prostates of both intact and castrated rats was translated in a message-dependent reticulocyte lysate, and the translation products were electrophoresed on SDS/polyacrylamide gels. Fluorography of these gels showed the expected disappearance, after castration, of the prostate steroid-binding proteins as well as a number of other androgen-dependent proteins. Two major (Mr 40,000 and 45,000) and several minor proteins appeared in the translation products of the castrated rat prostate RNA. Criss-cross liquid hybridization analysis between prostate poly (A+) RNA from intact and castrated rats also showed the disappearance of the abundant prostate steroid-binding protein sequences after castration and the synthesis of several new low to medium abundance sequences. Northern hybridization experiments demonstrated the presence of at least two, and possibly four androgen-repressed poly (A)+ RNA sequences. The most prominent of these, an RNA of 2,000 nucleotides, appeared within 2 days of castration, reaching a maximum on day 4 at a level approximately 400 times greater than the normal level. The other major sequence (a sequence of 1,000 nucleotides) appears after 4 days, reaching a peak between days 8 and 11. Sequences similar to these new RNAs could play an important role in the long-term resistance of prostatic cancer to hormone therapy in humans.

Isolation and characterisation of nucleic acids from the hydatid organisms, Echinococcus spp. (Cestoda)

DNA and RNA in combination have been prepared and characterised from the hydatid disease organisms, Echinococcus granulosus and Echinococcus multilocularis. The DNA obtained is of high molecular weight, pure and can be cleaved by restriction enzymes, thereby facilitating future production of genomic DNA probes for studies of Echinococcus gene expression. Moreover, cloned DNA segments from Schistosoma mansoni hybridise strongly to Echinococcus DNA following restriction and Southern blot analysis. The extracted RNA is functional and has been translated in vitro. The major translated polypeptides and antigens have been identified, and the technique can now be used to analyse differential gene expression during development and differentiation of the hydatid organisms and to identify specific polypeptide antigens which may have potential as immunodiagnostic reagents.

Translation of Schistosoma mansoni antigens in Xenopus oocytes microinjected with mRNA from adult worms

Oocytes from Xenopus laevis microinjected with RNA isolated from Schistosoma mansoni adult worms translated antigens recognized by sera from infected rats, humans, and from immunized rabbits. The pattern of immunoprecipitated proteins analysed by SDS-polyacrylamide gel electrophoresis was species specific in rats. Serum from infected Fischer rats recognized antigens of 20, 27 and several bands in the 50-60 kDa range whereas serum from infected Brown Norway rats also immunoprecipitated major bands at 29, 43 and 100 kDa. Human infection sera gave a very variable pattern of immunoprecipitation not apparently dependent on the patients' age. At least 20 different antigenic species could be identified ranging from 14 to 150 kDa. Some S. mansoni antigenic proteins could be isolated from the membrane fraction of the oocytes whereas notably the 29 kDa band was present mainly in the soluble fraction. N-Glycosylation of S. mansoni antigens occurred as evidenced by the effects of tunicamycin treatment and concanavalin A binding. A multiple series of bands between 50 and 60 kDa, present in the membrane fraction, were glycosylated and secreted from the oocytes. Monoclonal antibodies to larval stage surface antigens failed to immunoprecipitate oocyte translation products, but sera absorbed with live schistosomula identified at least three putative surface antigens of 100, 43 and 29 kDa. However, the 29 kDa molecule was neither synthesized into membranes, nor secreted from oocytes.

Organization of the ribosomal RNA genes in Schistosoma mansoni

The organization of the rRNA genes of Schistosoma mansoni has been determined by Southern blot analysis of genomic DNA digested with restriction enzymes, by isolation of the entire repeat on a single fragment of about 11 kilobase pairs from a genomic DNA library constructed in bacteriophage lambda and by characterization of three cloned EcoRI fragments which span the entire repeat. The segments encoding both the large and small rRNA subunits have been identified using specific cloned yeast rDNA fragments as probes and EcoRI, HindIII and BamHI restriction enzyme maps of the rRNA genes were constructed. The ends of the RNAs have been precisely mapped on the genomic DNA by S1 protection experiments. Our data indicate that the rRNA genes are present as a tight cluster. The total length of the rDNA repeat is about 10 kilobase pairs. There appears to be no variation in the size of transcribed and non-transcribed spacer DNA. At the RNA level we have characterized and mapped a small gap in the 28S RNA molecule. The interruption causes the RNA to dissociate into two equal sized fragments when analyzed under denaturing conditions.

The arrangement of ribosomal RNA genes in Schistosoma mansoni. Identification of polymorphic structural variants

The two large ribsomal RNA subunits of Schistosoma mansoni are encoded within a 10 000-base sequence, which is tandemly repeated in the schistosome genome. Restriction endonuclease digestion with Bam HI cuts the rRNA gene into three fragments, which have been clones separately in pBR322 and used to constract a physical map of the gene. The sequence encoding the smaller rRNA subunit is about 2000 bases in length and is situated on the 5' sie of the sequence encoding the larger subunit, which is about 4000 bases. Approximately 4000 bases of the rRNA gene are spacer and do not code for mature rRNA. There are approximately 100 copies of the rRNA gene per haploid genome of which about 10% exhibit length heterogeneity, as judged by the hybridization of the rDNA plasmids to restriction endonuclease digests of genomic DNA. These structural variants appear to contain additional DNA sequences at more than one site within the gene and are polymorphic within the species S. mansoni.

Cloning and characterization of a ribosomal RNA gene from Plasmodium berghei

The ribosomal RNA (rRNA) of Plasmodium berghei strain NYU2 was characterized with respect to size and used to identify molecular clones of ribosomal RNA genes (rDNA) from this organism. The intact large rRNA species (Mr 1.40 X 10(6] is intermediate in size between prokaryotic and eukaryotic large rRNAs. It is specifically cleaved in vivo near the 5'-end yielding one large component (Mr 1.10 X 10(6] and one small component (Mr 0.30 X 10(6]. The small rRNA species (Mr 0.75 X 10(6] is larger than in higher eukaryotic organisms, but is similar in size to some other protozoa. Using 5'-end labeled rRNA as a probe, clones of rDNA were selected from genomic DNA libraries prepared in lambda phage Charon 4A and plasmid pBR322. The clones prepared in lambda were prone to recombination. The 14.7 kilobase (kb) insert in phage lambda PbR27 contains the complete coding sequences for both the small and larger rRNA species. A complete set of small plasmid clones were isolated which hybridize to the different segments of the rRNA transcription unit. A restriction map of the genes cloned in lambda PbR27 with the approximate position of the coding region is presented. The polarity of transcription of the rDNA was determined by hybridizing 3'-OH end labeled rRNA to Southern blots of genomic and cloned rDNA. The results indicate that a transcription unit of P. berghei rDNA is arranged as in other organisms with the small rRNA at the 5' end and the large rRNA at the 3' end.

Messenger RNA extracted from Schistosoma mansoni larval forms codes for parasite antigens when translated in vitro

Intact messenger RNA was extracted from three stages of development of the parasite Schistosoma mansoni, cercariae, 3 h (mechanically prepared) schistosomula and adults. Some of the in vitro translation products are precipitable with immune rat and human serum showing that these sera recognize protein determinants. Whereas the patterns of the total translation products show major proteins expressed at all three developmental stages, immunoprecipitation delineates patterns unique to each stage. Serum from chronically infected patients is likely to preferentially recognize proteins expressed by the adult parasite yet precipitates more products of translation of cercarial RNA than of adult RNA, suggesting that many of the same epitopes are already coded by cercarial messenger RNA. It seems, however, that antigens appear on lower molecular weight species in the adult. The experiments described here open the way to cloning the genes of antigens from S. mansoni.