Zygotic activity of the nullo locus is required to stabilize the actin-myosin network during cellularization in Drosophila

Cellularization of the Drosophila embryo requires the establishment of a hexagonal network of actin and myosin filaments that are interconnected around the nuclei in the cortex of the syncytial blastoderm. This cytoskeletal network provides the framework and possibly the contractile force for the membrane invaginations that synchronously subdivide the syncytial embryo into individual cells. Zygotic expression of the nullo locus is essential for the preservation of an intact actin-myosin network. Embryos deleted for the nullo locus have a disrupted network, resulting in the formation of many multinucleate cells. We show that nullo is not required for the initial formation of the actin-myosin network, but is necessary for the maintenance of its hexagonal shape during cellularization. The phenotype of embryonic mosaics is nonautonomous, indicating that nullo does not have to be expressed in every nucleus for proper cellularization. Examination of nullo mutant clones in adults reveals that nullo activity is not required for cell division in imaginal discs. Furthermore, germline clone experiments suggest that maternal expression of the nullo locus is not essential for either germline proliferation or the cellularization of progeny. We propose a model in which nullo functions specifically at cellularization to stabilize the actin-myosin network during contraction.

Schizodeme analysis of Trypanosoma cruzi stocks from South and Central America by analysis of PCR-amplified minicircle variable region sequences

Kinetoplast DNA (kDNA) was isolated from 56 stocks of Trypanosoma cruzi isolated from human patients, animals and insects from Brazil, Venezuela, Colombia and Costa Rica. Comparison of the patterns of digested kDNA on acrylamide gels led to the grouping of several stocks into two schizodemes. Schizodeme analysis was also performed using a set of 330-bp fragments representing all the variable regions of the minicircle DNA molecules, which were obtained by PCR amplification of the kDNA using conserved region primers. The results of this analysis were consistent with the analysis using total kDNA, but the more informative restriction profiles allowed the construction of additional schizodemes. In addition, two oligomers were generated from variable region sequences of cloned minicircles from a Y and a Cl strain, and these were used as schizodeme-specific probes to detect homologous sequences in the amplified minicircle DNAs. The results indicate that a combination of restriction enzyme fingerprinting and hybridization of amplified variable region minicircle DNA with schizodeme-specific probes can be used for both sensitive detection and classification of T. cruzi.

Guide RNAs in kinetoplastid mitochondria have a nonencoded 3' oligo(U) tail involved in recognition of the preedited region

Maxicircle-encoded guide RNAs (gRNAs) for cytochrome b and maxicircle unidentified reading frames 2 and 3 (MURF2 and MURF3) were isolated by hybrid selection and sequenced. All three gRNAs contained nonencoded 3' oligo(U) tails 5-24 nucleotides in length, with a mean length of approximately 15 nucleotides. Secondary structure calculations indicate a functional role of the 3' oligo(U) tail in stabilizing the initial hybrid formed between the gRNA and the preedited mRNA, and allowed the identification of potential mRNA recognition sites for an editing complex. In addition, isolated MURF2 gRNA-II could be 5' capped with [alpha-32P]-GTP and guanylyltransferase, suggesting that at least some gRNAs represent primary transcripts.

Kinetoplast DNA minicircles encode guide RNAs for editing of cytochrome oxidase subunit III mRNA

Guide RNAs (gRNAs) for the editing of sites 1-8 of COIII mRNA and an "unexpected" partially edited COIII mRNA are encoded in the variable regions of specific kinetoplast DNA minicircles. The gRNAs can form 37 and 44 nucleotide perfect hybrids (allowing for G-U base pairs) with edited mRNAs. The gRNAs were detected on Northern blots and shown to have unique 5' ends situated close to the beginning of the potential base pairing with the edited mRNAs. We suggest that kinetoplast DNA minicircle molecules in general may encode gRNAs for editing of cryptogene mRNAs by a mechanism similar to that previously proposed for editing by maxicircle-encoded gRNAs.

Partially edited mRNAs for cytochrome b and subunit III of cytochrome oxidase from Leishmania tarentolae mitochondria: RNA editing intermediates

Partially edited mRNAs were selected by the polymerase chain reaction and sequenced. In the case of cytochrome b, 102 out of 106 clones displayed patterns of editing that were consistent with a strictly progressive 3' to 5' editing process, as predicted by the guide RNA model of RNA editing. In the case of cytochrome oxidase subunit III (COIII), 177 out of 304 clones displayed strictly progressive 3' to 5' patterns of editing. However, the remaining 127 COIII clones displayed unexpected patterns in which upstream editing preceded downstream editing, uridines were inserted at sites not normally edited, and purine residues were deleted. We suggest that many of these RNAs are produced by normal 3' to 5' editing of the COIII mRNA with incorrect guide RNA molecules.

A model for RNA editing in kinetoplastid mitochondria: "guide" RNA molecules transcribed from maxicircle DNA provide the edited information

A class of small RNA molecules possibly involved in RNA editing is present in the mitochondrion of Leishmania tarentolae. These "guide" RNA (gRNA) molecules are encoded in intergenic regions of the mitochondrial maxicircle DNA and contain sequences that represent precise complementary versions of the mature mRNAs within the edited regions. In addition, the 5' portions of several gRNAs can form hybrids with mRNAs just 3' of the preedited region. A model is presented in which a partial hybrid formed between the gRNA and preedited mRNA is substrate for multiple cycles of cleavage, addition or deletion of uridylates, and religation, eventually resulting in a complete hybrid between the gRNA and the mature edited mRNA.

Genomic organisation of nuclear tRNAGly and tRNALeu genes in Trypanosoma brucei

We have isolated a 0.3-kb HaeIII restriction fragment from Trypanosoma brucei which contains two tRNA genes. Secondary structure models predict that the two genes identified encode tRNA molecules which specify glycine (anticodon UCC) and leucine (anticodon CAG). The two genes are separated by 86 nucleotides, transcribed in the same direction and contain features of conventional RNA polymerase III transcription units. Southern blot analysis indicates the presence of multicopy tRNa gene families in T. brucei.

The Leishmania kinetoplast-mitochondrion contains terminal uridylyltransferase and RNA ligase activities

Purified mitochondria of Leishmania tarentolae contain 3'-terminal uridylyltransferase and RNA ligase activities which can be solubilized by detergent lysis of the organelle. Run-off transcription of maxicircle and minicircle DNA also occurs in intact and Triton-lysed mitochondria, using [32P]GTP as the labeled precursor. Heparin inhibits the solubilized terminal uridylyltransferase activity but does not affect the labeling of endogenous RNAs in intact mitochondria with [32P]UTP. Clarification of the mitochondrial Triton lysate causes an increase in terminal uridylyltransferase activity with exogenous substrates. These two activities are candidates for involvement in a post-transcriptional RNA editing process of mitochondrial transcripts.

Internal frameshifts within the mitochondrial genes for cytochrome oxidase subunit II and maxicircle unidentified reading frame 3 of Leishmania tarentolae are corrected by RNA editing: evidence for translation of the edited cytochrome oxidase subunit II mRNA

The Leishmania tarentolae cytochrome oxidase (EC 1.9.3.1) subunit II (COII) and maxicircle unidentified reading frame 3 (MURF3) mRNAs are edited internally by the addition of four and five uridine residues, respectively, which eliminate -1 and +1 reading frameshifts in the gene sequences. The editing events in COII are conserved in three kinetoplastid species, and those in MURF3 are conserved in two species. A primer extension assay showed that the ratio of edited to unedited RNA differed for each gene: 89% of the COII and 36% of the MURF3 transcripts are edited. Preliminary evidence was obtained for translation of the edited COII transcript into protein: antibodies generated against a synthetic peptide with the predicted carboxyl-terminal amino acid sequence reacted with a polypeptide of the correct molecular weight in immunoblots of a mitochondrial lysate.

Kinetoplastid mitochondria contain functional tRNAs which are encoded in nuclear DNA and also contain small minicircle and maxicircle transcripts of unknown function

The mitochondrion of Leishmania tarentolae contains approximately 35-40 tRNAs many of which comigrate with cytoplasmic tRNAs. Both mitochondrial (KtRNA) and cytoplasmic (CtRNA) tRNAs are functional, as they could be acylated either by mitochondrial or cytoplasmic synthetase extracts. There are two methionyl tRNA species in the cytoplasmic and mitochondrial fractions, one of which is unique to each fraction, indicating that the KtRNA fraction is free of CtRNA contamination. Leucyl and glycyl tRNAs were identified by hybridization with a genomic clone from Trypanosoma brucei. KtRNA hybridizes with nuclear chromosomes, but not with minicircle or maxicircle DNA. KtRNA isolated by DEAE chromatography or agarose gel electrophoresis contains additional small RNAs which hybridize with both minicircle and maxicircle DNA. These transcripts do not migrate like tRNAs in acrylamide gels and their functions is unknown. We suggest that most if not all mitochondrial tRNAs in L. tarentolae are nuclear-encoded and imported into the mitochondrion.

A central role for adenosine in the hypotension elicited by hypoxia in anesthetized rats

Brief inhalation of an oxygen-deficient (5%) gas mixture evoked a rapidly developing, profound hypotension in anesthetized rats. Recovery upon reoxygenation was also rapid. A potential involvement of adenosine in the genesis of this hypotension was evaluated with various peripherally administered adenosine antagonists. Caffeine (10 mg/kg), which readily crosses the blood-brain barrier, significantly attenuated the hypoxia-evoked hypotension. 8-p-Sulphophenyltheophylline and xanthine amine congener, which do not readily penetrate the blood-brain barrier, had little effect on the magnitude of the hypotension. The data suggests that hypoxia-elicited hypotension in anesthetized rats results from the activation of central adenosine receptors.

Detection and characterization of a B cell stimulatory factor (BSF-TC) derived from a bone marrow stromal cell line

Stromal cell lines derived from murine bone marrow support the growth of immature pre-B cells and produce cytokines that affect the growth and differentiation of other hematopoietic precursors. Conditioned medium (CM) from one such line (TC-1) stimulated marked proliferation of B cells previously activated by anti-Ig (anti-Ig blasts). Proliferation of anti-Ig blasts was not induced by purified cytokines known to be produced by TC-1 (CSF-1, GM-CSF, or G-CSF) or by IL-1, IL-2, IL-3, IL-4, IL-5, or IL-6. Furthermore, IL-2, IL-4, and IL-5, alone or in combination, failed to support proliferation or differentiation of anti-Ig blasts. TC-1 CM enhanced proliferation of B cells that were co-cultured with LPS, anti-Ig, or dextran sulfate; co-stimulation with anti-Ig was unaffected by the presence of monoclonal anti-IL-4. Proliferation of low, but not high, density B cells isolated from spleen was directly stimulated by TC-1 CM. These results suggest that bone marrow stromal cells produce a novel B cell stimulatory factor (BSF-TC) that induces proliferation of activated B cells.

Detection and characterization of a B cell stimulatory factor (BSF-TC) derived from a bone marrow stromal cell line

Stromal cell lines derived from murine bone marrow support the growth of immature pre-B cells and produce cytokines that affect the growth and differentiation of other hematopoietic precursors. Conditioned medium (CM) from one such line (TC-1) stimulated marked proliferation of B cells previously activated by anti-Ig (anti-Ig blasts). Proliferation of anti-Ig blasts was not induced by purified cytokines known to be produced by TC-1 (CSF-1, GM-CSF, or G-CSF) or by IL-1, IL-2, IL-3, IL-4, IL-5, or IL-6. Furthermore, IL-2, IL-4, and IL-5, alone or in combination, failed to support proliferation or differentiation of anti-Ig blasts. TC-1 CM enhanced proliferation of B cells that were co-cultured with LPS, anti-Ig, or dextran sulfate; co-stimulation with anti-Ig was unaffected by the presence of monoclonal anti-IL-4. Proliferation of low, but not high, density B cells isolated from spleen was directly stimulated by TC-1 CM. These results suggest that bone marrow stromal cells produce a novel B cell stimulatory factor (BSF-TC) that induces proliferation of activated B cells.

Characterization of a protein fraction containing cytochromes b and c1 from mitochondria of Leishmania tarentolae

A soluble red band fraction was obtained from Leishmania tarentolae cells by sucrose gradient sedimentation of a Triton X-100 lysate. Spectral analysis indicated that cytochrome b was present in the red band: the reduced minus oxidized difference spectra revealed absorption maxima at 562,527, and 431 nm at room temperature and 562, 530, and 422 nm at 77K. In addition, a 28-kDa protein was identified in this fraction which retained heme-associated peroxidase activity even after denaturation on SDS-polyacrylamide gels. The amino acid composition of this protein showed a strong similarity to cytochrome c1 of both bovine and yeast.

Structure, genomic organization and transcription of the bifunctional dihydrofolate reductase-thymidylate synthase gene from Crithidia fasciculata

The bifunctional dihydrofolate reductase-thymidylate synthase (DHFR-TS) gene from the monogenetic kinetoplastid protozoan, Crithidia fasciculata, was isolated and characterized. The gene is located on a single chromosome of approximately one megabase, and shows significant sequence similarity to other eukaryotic and prokaryotic DHFR and TS genes. There is a single low-abundance polyadenylated DHFR-TS transcript of approximately 3100 nt. One major miniexon splice site was identified by primer extension analysis. The 5' flanking region of the gene is divergently transcribed and shows strong similarities to a consensus DHFR promoter as well as to other eukaryotic 'housekeeping' gene promoter regions. A sequence downstream of the DHFR promoter consensus region is complementary to the 3' end of the C. fasciculata miniexon-derived RNA. This suggests a means by which the two separately transcribed RNAs may be juxtaposed for trans-splicing. In the 3' flanking region of the DHFR-TS gene, there is a sequence that is present in all of the chromosomes from this species and also from Leishmania tarentolae.

Sensitive detection and schizodeme classification of Trypanosoma cruzi cells by amplification of kinetoplast minicircle DNA sequences: use in diagnosis of Chagas' disease

Amplification of DNA sequences from the kinetoplast minicircle DNA was employed as a method for the detection and classification of small numbers of Trypanosoma cruzi cells. Two overlapping fragments from the conserved 120 bp minirepeat regions of the minicircle DNA and one fragment covering the adjacent variable regions were amplified. The minimal amount of minicircle DNA required to detect a product by hybridization with an oligonucleotide probe was 0.015 fg, which represents approximately 10 molecules or 0.1% of the minicircle DNA component of a single cell. The amplification worked equally well with kDNA from several strains of T. cruzi and did not occur with kDNA from several other kinetoplastids. kDNA recovered from less than 10 trypanosomes in whole blood could be used as a template for amplification; the presence of a several billion fold excess of human DNA had no effect on the amplification process. Schizodeme analysis by hybridization with specific oligonucleotides or by direct restriction enzyme digestion could be performed on the amplified fragments representing the minicircle conserved region or variable regions. This method should prove useful as a rapid, specific and sensitive assay for Chagas' disease in chronic patients as well as for epidemiological studies of infected animals and insects.

Similar-sequence and similar-structure in retarded and non-retarded children's development

Three questions important in relation to the developmental-difference controversy were addressed. The first, to what extent do retarded and non-retarded children show a similar sequence in their development of concepts, was answered using scalogram analyses which supported a common order of acquisition of conservation concepts when intermediate as well as conservation and non-conservation categories were used. There was a high degree of similarity in sequence within as well as between attributes. The second question, how far does the similar-structure hypothesis hold, was answered in the terms set by the developmental theorists. Multiple regression analyses and comparisons of mean mental ages for each of the conservation subgroups supported the similar-structure hypothesis. Non-retarded and retarded children with no known organic condition revealed similar structures. The third question concerned findings of volume conservation in retarded children and how these might be interpreted. It is argued that recognition of conservation in displacement volume tasks need not imply a generalised stage of formal operations nor be interpreted in terms of ceiling in development. Overall the findings have implications for ordering and providing appropriate levels of experiences for retarded children without assuming fixed limits in their development.

Evolution of parasitism: kinetoplastid protozoan history reconstructed from mitochondrial rRNA gene sequences

A phylogenetic tree for the evolution of five representative species from four genera of kinetoplastid protozoa was constructed from comparison of the mitochondrial 9S and 12S rRNA gene sequences and application of both parsimony and evolutionary parsimony algorithms. In the rooted version of the tree, the monogenetic species Crithidia fasciculata is the most deeply rooted, followed by another monogenetic species, Leptomonas sp. The three digenetic species Trypanosoma cruzi, Trypanosoma brucei, and Leishmania tarentolae branch from the Leptomonas line. The substitution rates for the T. brucei and T. cruzi sequences were 3-4 times greater than that of the L. tarentolae sequences. This phylogenetic tree is consistent with our cladistic analysis of the biological evidence including life cycles for these five species. A tentative time scale can be assigned to the nodes of this tree by assuming that the common ancestor of the digenetic parasites predated the separation of South America and Africa and postdated the first fossil appearance of its host (inferred by parsimony analysis). This time scale predicts that the deepest node occurred at 264 +/- 51 million years ago, at a time commensurate with the fossil origins of the Hemiptera insect host. This implies that the ancestral kinetoplastid and its insect host appeared at approximately the same time. The molecular data suggest that these eukaryotic parasites have an evolutionary history that extends back to the origin of their insect host.

Editing of kinetoplastid mitochondrial mRNAs by uridine addition and deletion generates conserved amino acid sequences and AUG initiation codons

RNA editing is a novel type of mRNA processing in the kinetoplastid mitochondrion that involves the co- or posttranscriptional addition of uridine residues within transcripts. The result is an mRNA nucleotide sequence which differs from that of the corresponding gene. We have found that RNA editing may also occur through the deletion of genome-encoded uridines from the RNA sequence. Uridine additions and deletions in the 5' ends of the COIII, MURF2, and MURF3 transcripts create new N-terminal amino acid sequences that are conserved between species, and new AUG initiation codons in several cases. These results suggest that the creation of new amino acid sequences and methionine initiation codons may be important functions of RNA editing in the kinetoplastid mitochondrion.

The status of Leishmania tarentolae/Trypanosoma platydactyli

Taxonomic studies and classification of Leishmania species have developed rapidly in recent years, but controversy still surrounds the relationships between those species infecting lizards and those infecting mammals. Some authorities maintain that the leishmanias o f lizards form a sufficiently distinct group to be ranked as a separate genus - Sauroleishmania(1,2) - while Wallbanks et al. have gone further to suggest that such species might be classified within the genus Trypanosoma(3). This suggestion followed from work showing that promostigote forms of Trypanosoma platydactyli from a gecko, had similar isoenzyme profiles to Leishmania tarentolae, a well-known species from lizards. In this article however, Larry Simpson and George Holz Jr discuss conflicting evidence, concluding from recent studies of DNA and lipid composition that the lizard leishmanias are more closely related to mammalian leishmanias than to trypanosomes.0.

Comparison of several lizard Leishmania species and strains in terms of kinetoplast minicircle and maxicircle DNA sequences, nuclear chromosomes, and membrane lipids

Eight strains of a lizard Leishmania species, L. tarentolae, were compared with four other saurian species [L. hoogstrali, L. adleri, L. agamae and Leishmania sp. LizS], with L. major from man and with Trypanosoma platydactyli, a putative lizard trypanosome, in terms of kinetoplast DNA minicircle and maxicircle sequences and in terms of nuclear chromosome patterns on orthogonal gel electrophoresis. The L. tarentolae strains fell into two major groups, one (group A) consisting of the L. tarentolae strains, UC, Krassner and Trager, derived from an Algerian gecko isolate and the other (group B) consisting of five L. tarentolae LEM strains isolated from geckos in southern France. T. platydactyli TPCL2, which was postulated by Wallbanks et al. to represent the lizard form of a French L. tarentolae strain, was closely related to the UC strain and not to the LEM strains, in all respects analyzed. Leishmania sp. LizS from a Mongolian gecko and L. hoogstrali from a Sudanese gecko showed some sequence similarities to the L. tarentolae strains, but the leishmanias said to be L. adleri from a Kenyan lacertid and L. agamae from an Israeli agamid showed no minicircle sequence similarities with lizard Leishmania and in fact were probably the same species. The maxicircle divergent region was larger in the group B strains than in the group A strains, but there were sequences in common with both groups, and not with L. hoogstrali and L. major. Four strains of L. tarentolae, the four other supposed saurian Leishmania species, three mammalian leishmanias, T. platydactyli and four other trypanosomes, T. cyclops (Malaysian macaque), T. conorrhini (Hawaiian reduviid bug), T. cruzi (man) and T. lewisi (feral rat) were analyzed for their contents of sterols and phosphoglyceride fatty acyl groups. T. platydactyli TPCL2 contained a sterol (5-dehydroepisterol), a phosphatidylcholine fatty acyl group (alpha-linolenic acid) and a phosphatidylethanolamine fatty acyl group (dihydrosterculic acid) characteristic of members of the genus Leishmania and not the genus Trypanosoma. The proportions of those lipids in the free sterol and phosphoglyceride fractions of T. platydactyli TPCL2 most closely resembled those seen in the Leishmania strains from Algerian, French, Mongolian and Sudanese geckos.

Creation of AUG initiation codons by addition of uridines within cytochrome b transcripts of kinetoplastids

The cytochrome b gene of Trypanosoma brucei has an ATG codon near its 5' end but the cytochrome b genes of the related kinetoplastids Leishmania tarentolae and Crithidia fasciculata lack an ATG. Recent results have shown that 34 uridines that are not encoded in the genome are added within the 5' end of T. brucei cytochrome b transcripts during or after transcription. These additions create an AUG in the transcript that is 20 amino acids upstream of the AUG predicted from the genomic sequence. We report here that the cytochrome b transcripts of L. tarentolae and C. fasciculata also contain added uridines within their 5' ends. The additions occur in similar numbers and positions and an in frame AUG is created at a similar site in all three species. These data strongly suggest that the created AUG functions as the initiation codon for cytochrome b in these species. Since some other kinetoplastid mitochondrial genes also lack conventional initiation codons, creation of initiation codons may be an important function of uridine addition.

Peculiar sequence organization of kinetoplast DNA minicircles from Trypanosoma cruzi

The sequences of two minicircles from the kinetoplast DNA of the CL strain and one of the Y strain of Trypanosoma cruzi are reported. These 1.4 kb molecules have a peculiar sequence organization, the most distinctive feature being the occurrence of a 120 bp sequence repeated four times, located at 0, 90, 180 and 270 degrees along each circle. We have termed these conserved regions in this species 'minirepeats'. Minirepeats have a 3-fold higher concentration of cytosine residues in comparison with the variable regions and contain the universal 12-mer motif GGGGTTGGTGTA present in all sequenced minicircles and which was shown to be involved in DNA replication. A consensus sequence of T. cruzi minirepeats was determined using the 20 minirepeats present in five known T. cruzi minicircle sequences. This consensus sequence contains regions which have been remarkably well preserved in strains which show great biological diversity. In addition a low level of intraminicircle sequence similarity was also observed within the variable region, but this similarity did not extend between strains. The abundance of conserved minirepeat sequences containing invariant restriction sites in T. cruzi cells may prove valuable for the development of new direct diagnostic methods for Chagas' disease based on DNA probe technology.

T-independent and T-dependent steps in the murine B cell response to antiimmunoglobulin

Sepharose-anti-Ig and purified populations of small, high-density B cells have been used to study the formation and function of B lymphoblasts. Sepharose-anti-Ig converts small, Ia-poor B cells with a high-buoyant density to large, Ia-rich, B blasts with a low-buoyant density. We find that this response proceeds efficiently in the absence of IL-4 (BSF-1) as well as most T cells, macrophages, and dendritic cells. Further development of the blasts requires an additional stimulus, such as LPS or the conditioned medium of stimulated EL-4 thymoma cells. Within 6 h, blasts begin to enter S phase and within 24 h most divide. At later times (48-72 h) most of the blasts are actively secreting IgM. Recombinant IL-1, -2, -3, and -4 have little or no effect on the B blasts, and a neutralizing mAb to IL-4 does not block the response to EL-4 Sn. We conclude that Sepharose-anti-Ig induces B cell blastogenesis in a T-independent fashion and that these blasts represent a highly enriched population of cells that respond to distinct, T cell-derived lymphokines.

Comparison of the maxicircle (mitochondrial) genomes of Leishmania tarentolae and Trypanosoma brucei at the level of nucleotide sequence

The entire 16.7-kilobase (kb) transcribed region of the Leishmania tarentolae maxicircle was compared to the entire 15-kb transcribed region of the Trypanosoma brucei maxicircle at the nucleotide sequence level by dot matrix analysis and by alignments of individual genes. The L. tarentolae NADH dehydrogenase subunit 1 (ND1) gene was identified in a newly obtained 2.9-kb sequence. All but two regions which flank the cytochrome b gene are highly conserved in both species. One 3.1-kb region in L. tarentolae that contains the cytochrome oxidase subunit III (COIII) gene and several open reading frames corresponds to a 2-kb sequence in T. brucei with limited sequence homology that lacks the COIII gene. Another 0.6-kb region that comprises an unidentified open reading frame (open reading frame 12) in L. tarentolae is substituted by a nonhomologous 0.4-kb open reading frame in T. brucei. A short intergenic region between the ND1 gene and the maxicircle unidentified reading frame 1 gene shows limited sequence homology, and the regions between the ND4 and ND5 genes and between the COI and ND4 genes are not conserved. All of the intergenic regions share G + C richness and a similar pattern of G versus C strand bias. 1.8 kb of the L. tarentolae divergent region (DV) and around 3 kb of the T. brucei DV were also obtained. The T. brucei DV sequences were not homologous to the L. tarentolae DV sequence but were organized in a similar fashion with tandem repeats of varying complexity.

The monogenetic kinetoplastid protozoan, Crithidia fasciculata, contains a transcriptionally active, multicopy mini-exon sequence

A repeated sequence from the Crithidia fasciculata nuclear genome has been isolated which is homologous to the mini-exon genes of other kinetoplastid protozoa. Sequence analysis of the 417 bp monomeric unit confirmed the presence of a 35 nt sequence within the repeat that is 77% homologous with the Trypanosoma brucei 35-mer mini-exon or spliced leader sequence. The repeat is present at approximately 250 copies per cell and is organized into one, or a few, large head to tail tandem clusters predominantly on a single chromosome. The mini-exon repeat unit hybridizes to a major 84 nt and a minor 87 nt poly (A)- steady state transcript, the first 35 nts of which comprise the mini-exon sequence found at the 5' end of mRNAs in several other kinetoplastid species. The 3'-termini of the transcripts map to positions on the DNA sense strand directly preceeding a stretch of 8 thymidine residues. Crithidia represents the most primitive kinetoplastid species which apparently possesses a discontinuous type of mRNA processing, implying that this represents a conserved feature in possibly all genera of kinetoplastid protozoa.

Introduction of plasmid DNA into the trypanosomatid protozoan Crithidia fasciculata

Crithidia fasciculata cells were treated with a plasmid (pDK96) containing pBR322 sequences, a Leishmania tarentolae maxicircle autonomously replicating sequence, and the bacterial gene for aminoglycoside 3' phosphotransferase I inserted between the yeast alcohol dehydrogenase 1 promotor and terminator sequences. Resistant colonies were selected on agar plates containing paromomycin and screened for vector DNA by hybridization. Approximately 1% of the resistant colonies contained detectable vector DNA, which was present as extrachromosomal closed circular molecules ranging in copy number from 1 to 160 per cell. The plasmids could be recovered from Escherichia coli transformed to ampicillin resistance with Crithidia total cell DNA. Most of the recovered plasmids were a deleted product of pDK96, which lacked the maxicircle autonomously replicating sequence and contained a unique fragment of Crithidia nuclear DNA present at a low copy number in the wild-type genome. The plasmid DNA in resistant Crithidia was unstable even under selective conditions and was lost within 30 cell divisions.

Specific cleavage of kinetoplast minicircle DNA from Leishmania tarentolae by mung bean nuclease and identification of several additional minicircle sequence classes

Multiple sequence classes of kinetoplast minicircle DNA from Leishmania tarentolae were cleaved by mung bean nuclease in the presence of formamide, yielding unit length linear molecules which retained the anomalous electrophoretic mobility in acrylamide characteristic of minicircle DNA. No specific cleavage site sequence common to all minicircle sequence classes was apparent, although the main region of nuclease cleavage was localized approximately 350 bp from the unique SmaI restriction site of the conserved region found in all minicircle sequence classes. Covalent closure of the minicircle substrate was not a requirement for cleavage, as linearized network-derived or cloned minicircles were also cleaved by mung bean nuclease at similar locations. The partial sequences of several new minicircle sequence classes released from the network by mung bean nuclease are also reported.

Impaired drug uptake in methotrexate resistant Crithidia fasciculata without changes in dihydrofolate reductase activity or gene amplification

Crithidia fasciculata cells grown in defined medium are sensitive to methotrexate (MTX), an inhibitor of dihydrofolate reductase (DHFR). When cells are challenged with 2-5 microM MTX, cell division ceases after 3-4 divisions and the cells become rounded and immotile for approximately 60 h, with a 40% decrease in cell viability occurring during this period. The cells then recover normal morphology and cell division resumes. Cells which undergo this treatment can be transferred directly into high levels of the drug (1-2 mM). The resistance phenotype is stable in the absence of the drug. Resistance correlates with impaired uptake of [3H]MTX, which in wild-type cells is taken up by a carrier-mediated process. There is no indication of gene amplification at the DNA level or at the level of DHFR activity, as occurs in the case of MTX-resistant Leishmania major. Several lines of MTX-resistant L. major which show gene amplification also exhibit impaired uptake of [3H]MTX.

Trypanosoma brucei: differentiation of in vitro-grown bloodstream trypomastigotes into procyclic forms

Trypanosoma brucei strain 366D trypomastigotes grown at 37 degrees C in the presence of a human fibroblast cell line formed foci underneath the feeder cells whereas trypanosomes grown in the presence of a human epithelial cell line grew only in the culture supernatant. A culture system was developed to study the differentiation of bloodstream trypomastigotes grown in the epithelial cell system into procyclic trypomastigotes at 27 degrees C. The morphological differentiation into the procyclic form was complete by 48 h. Cell division did not occur until 30-40 h after transfer to 27 degrees C. Various characteristics of this system were examined, including the effect of the feeder layer, the type of medium, the presence of the metabolites cis-aconitate and citrate, the preadaptation period, and the trypanosome cell concentration. The respiration of the recently differentiated procyclic cells was less sensitive to inhibition by CN- than that of established procyclic forms, implying a delayed appearance of complete mitochondrial oxidative pathways. This trypanosome differentiation system has the advantage that the animal host is not needed and the entire process is carried out in in vitro culture.

Mapping and 5' end determination of kinetoplast maxicircle gene transcripts from Leishmania tarentolae

Transcripts for six Leishmania tarentolae maxicircle structural genes (cytochrome oxidase subunits I, II and III, cytochrome b, human mitochondrial unidentified reading frames 4 and 5) and several unidentified open reading frames were mapped, and the locations of the 5' ends determined by primer runoff analysis. All genes studied here are transcribed from the same strand as the 12S and 9S ribosomal RNAs except for the cytochrome oxidase subunit I gene. In two cases (ORF3 and ORF4, ORF5 and ORF6), a single transcript covers two contiguous overlapping reading frames. The 5' ends of the RNAs are located 20-64 nt from the putative translation initiation codons. Primary transcripts from a mitochondrial RNA preparation were 5' end-labeled with guanylyltransferase and alpha -32P-GTP; the major labeled species comigrated with the 12S and 9S mitochondrial rRNAs, and in addition there were at least four higher molecular weight labeled species.

Effect of tryptophan derivatives on the phase properties of bilayers

Binding of several tryptophan derivatives and tryptophan-containing peptides to bilayers is examined by monitoring fluorescence enhancement as a function of lipid concentration. The thermodynamic and spectral parameters of the solutes in the bilayers of vesicles and liposomes do not exhibit any anomalous dependence upon the gel or the liquid-crystalline phase state of the bilayer. Effects of these solutes on the phase-transition profiles of the bilayers of liposomes and vesicles are examined, and the lowering of the phase-transition temperature is correlated with the mole fraction of the solute in the bilayer. The partition coefficients do not change at the main phase-transition temperature. These observations contradict the thermodynamic explanation of the solute-induced lowering of the phase-transition temperature which is based on the Van't Hoff relationship for distribution of the solute in the two coexisting phases at the phase-transition temperature. It is postulated that solute molecules bound to defect sites in bilayers modulate the phase properties of bilayers. These defect sites are induced in the gel phase of bilayers of liposomes above the subtransition temperature.

The divergent region of the Leishmania tarentolae kinetoplast maxicircle DNA contains a diverse set of repetitive sequences

A 2.76 kb segment of the 12 kb divergent region of the Leishmania tarentolae kinetoplast maxicircle DNA consists almost entirely of repeated sequences. The repeats can be grouped into six families, some of which are present throughout the remainder of the divergent region. The repeats are oriented in a head-to-tail fashion with the three simplest repeats clustered into large arrays. A 47 bp palindrome and two copies of a "supercluster" of three different types of repeats are also present in the sequenced region. A sequence change in the divergent region is described for a clonal strain of L. tarentolae which was passaged continuously for several years. The repetitive sequences found in the divergent region appear to be appropriate substrates for the presumed deletion/insertion/recombination events occurring in this rapidly evolving portion of the maxicircle.

Primary sequence and partial secondary structure of the 12S kinetoplast (mitochondrial) ribosomal RNA from Leishmania tarentolae: conservation of peptidyl-transferase structural elements

The sequence of the 1173 nt 12S kinetoplast ribosomal RNA from Leishmania tarentolae was determined from the maxicircle DNA sequence, and the 5' and 3' ends localized by primer runoff and S1 nuclease protection experiments. The gene was shown to be free of introns by S1 nuclease analysis. A partial secondary structure model of the 12S RNA molecule is presented which is equivalent in certain respects to the corresponding portions of the Escherichia coli 23S ribosomal RNA model. Domain II of the E. coli model is completely missing in the kinetoplast model with the exception of several phylogenetically conserved stems and one loop. There is a striking conservation of the functionally important peptidyl-transferase region except for the deletion of a few stems and loops. The 12S RNA is the smallest large subunit ribosomal RNA described to date.

A minimal ribosomal RNA: sequence and secondary structure of the 9S kinetoplast ribosomal RNA from Leishmania tarentolae

The portion of the Leishmania tarentolae kinetoplast maxicircle DNA encoding the 9S RNA gene was sequenced, and the 5' and 3' ends of the transcript were determined. A secondary structure for the 9S RNA was determined based on the Escherichia coli 16S model. The 610-nucleotide 9S RNA exhibits a minimal secondary structure in which all four domains of the E. coli 16S structure are preserved. Within domains, however, some stems and loops have been greatly reduced or eliminated entirely. It is presumed that these reduced domains represent the minimal essential small ribosomal RNA secondary structures necessary for a functional ribosome. Alignment of the L. tarentolae 9S rRNA sequence with the published Trypanosoma brucei 9S rRNA sequence shows a nucleotide similarity of 84% and a transversion/transition ratio of 1.66.

Central nervous regulation of body temperature in vertebrates: comparative aspects

Thermal fluctuations affect, and are responded to by, nearly all forms of life. The basic vertebrate template has guided and shaped the ways that animals in this subphylum cope with thermal challenges. This has led to a situation where there are major similarities in the neuronal mechanisms which sense temperature and control the responses to temperature change in all vertebrates, from fish to mammals. The PO/AH is the most important single integration site for temperature regulation and (except for birds) is also important in the sensing of core temperature. Other portions of the brainstem as well as the spinal cord are also involved in thermal control and can sense, integrate, and produce appropriate efferent signals to varying degrees. Peripheral thermal input to the hypothalamic areas is via the brainstem reticular areas. A number of studies has related the thermal response characteristics of CNS single neurons to the thermoregulatory output of intact animals. These studies have been performed on neurons in whole animal, brain slice, and tissue culture preparation. These neurophysiological studies of central neurons are informative, but are sometimes difficult to interpret because of the chronic lack of definite criteria to differentiate generalized thermal sensitivity from thermal sensitivity utilized for regulating body temperature. Recent neuroanatomical work has illustrated that many areas previously implicated in the thermoregulatory network (such as the septum, various hypothalamic nuclei, the midbrain reticular formation, and the midbrain raphé nuclei) receive direct projections from PO/AH neurons. When compared, the neurophysiological and neuroanatomical characteristics of the preoptic nucleus and anterior hypothalamic area are similar, but not identical. The broad differences in the responses that vertebrates utilize to deal with thermal change is largely determined by the respiratory medium (water or air) and whether metabolic energy (endothermy) or ambient temperature (ectothermy) is of primary importance in the determination of internal temperature. A number of physiological systems are perturbed in water breathing ectotherms when the ambient temperature is altered. In these vertebrates long-term acclimation is very important and has a major effect on temperature selection. Air breathing ectotherms are less adversely affected by temperature change; long-term thermal acclimation is less important and has little effect upon temperature selection; large thermal changes are often initiated by these animals. Endotherms rely on insulation and a high, variable metabolic rate to maintain a constant internal temperature.(ABSTRACT TRUNCATED AT 400 WORDS)

Sequences of six genes and several open reading frames in the kinetoplast maxicircle DNA of Leishmania tarentolae

The DNA sequence of approximately 80% of the transcribed region of the kinetoplast maxicircle DNA of Leishmania tarentolae was obtained, and structural genes were localized by comparison of the translated amino acid sequences with those of known mitochondrial genes from other organisms. By this method, the genes for cytochrome oxidase subunits I, II, and III, cytochrome b, and human mitochondrial unidentified reading frames 4 and 5 were identified. By comparing the amino acid sequences of the putative L. tarentolae genes with those of known genes, we conclude that TGA codes for tryptophan, as in most other mitochondrial systems. This is the only apparent change from the universal genetic code. The six identified structural genes show various degrees of divergence from the homologous genes in other species, with cytochrome oxidase subunit I being the most conserved and cytochrome oxidase subunit III being the least conserved. A comparison of the cytochrome b genes from L. tarentolae and Trypanosoma brucei showed that the ratio of transversions to transitions is 1:1, suggesting that these species diverged from each other more than 80 X 10(6) years ago. Several as yet unidentified open reading frames were also present in the maxicircle sequence. These data confirm that maxicircle DNA has a coding potential which typifies other mitochondrial systems.